Genetics and Evolution
14 multiple choice
no constructed response question
no constructed response question
a. Explain the inheritance of traits which are determined by one or more genes, including dominance, recessiveness, sex linkage, phenotypes, genotypes, and incomplete dominance
There are sets of coded instruction which make up the DNA molecules of a chromosome. Each gene is connected to a series of 250 “rungs” on the DNA “ladder”. Since the order of the rungs vary, each gene has a different code relating to one specific trait. The paired genes control the same characteristics and may give identical or different instructions.
Dominance- instructions given from one gene that overrides the recessive gene's. Example: a person with both genes for brown and green eyes will have brown eyes since the brown eye gene is dominant. If the dominant gene, D, for dark hair, then a person is heterozygous, Dd, for hair color (instructions from two genes are different).
Recessive Gene- failure of one gene (allele) to express itself in an observable manner. Even though the gene is present in the genotype, it is not observable in it's phenotype (organisms physical physical or biochemical characteristic). Example: Curly hair (dominant-C) and straight hair (recessive-c) both are present in a person's genotype. However, the person has straight hair. Recessive genes are always written in lower case.
Incomplete Dominance- one allele for a specific trait is not completely dominant of the other allele. The result is a combined phenotype. Example: Camelia flowers that have both red (dominant-A) and white (recessive-a) genes will produce a flower with pink petals.(heterozygot-Aa)
Codominance- pair of genes controlling the same characteristics give different instructions. Neither genes are dominant and both are represented in the result. Example: Human blood AB
Linked Genes- alleles inherited together. Genes physically close to one another on the same chromosome. Stay together during meiosis= genetically linked.
Sex-linked Genes- Genes located on one of the sex chromosomes. Since the x chromosome is longer, it contains genes not found on the Y chromosome. Therefore, most sex-linked genes are x-linked genes. Sex-linked genes do not have an allelic counterpart on the Y chromosome.
Purebred- produces offsprings with the same traits. The alleles are homozygous. .
Dominance- instructions given from one gene that overrides the recessive gene's. Example: a person with both genes for brown and green eyes will have brown eyes since the brown eye gene is dominant. If the dominant gene, D, for dark hair, then a person is heterozygous, Dd, for hair color (instructions from two genes are different).
Recessive Gene- failure of one gene (allele) to express itself in an observable manner. Even though the gene is present in the genotype, it is not observable in it's phenotype (organisms physical physical or biochemical characteristic). Example: Curly hair (dominant-C) and straight hair (recessive-c) both are present in a person's genotype. However, the person has straight hair. Recessive genes are always written in lower case.
Incomplete Dominance- one allele for a specific trait is not completely dominant of the other allele. The result is a combined phenotype. Example: Camelia flowers that have both red (dominant-A) and white (recessive-a) genes will produce a flower with pink petals.(heterozygot-Aa)
Codominance- pair of genes controlling the same characteristics give different instructions. Neither genes are dominant and both are represented in the result. Example: Human blood AB
Linked Genes- alleles inherited together. Genes physically close to one another on the same chromosome. Stay together during meiosis= genetically linked.
Sex-linked Genes- Genes located on one of the sex chromosomes. Since the x chromosome is longer, it contains genes not found on the Y chromosome. Therefore, most sex-linked genes are x-linked genes. Sex-linked genes do not have an allelic counterpart on the Y chromosome.
Purebred- produces offsprings with the same traits. The alleles are homozygous. .
b. Solve problems that illustrate monohybrid and dihybrid crosses
Reginald Punnett created this tool, Punnett square, to predict the likelihood of inheriting particular traits. Setting up and using a Punnett square:
1. You begin by drawing a grid of perpendicular lines (think tic tac toe)
2. Next step is to put the genotype of one parent across the top and the other down the left side (it does not matter which parent is on the side and which is on the top). For example, if a parent pea plant genotypes were TT and BB, then the setup would look like:
S S
T
T
3. Next step is to fill in the boxes by copying the row and column letters into each square. Doing this will give us a prediction of all potential genotypes each time reproduction occurs.
S S
T TS TS
T TS TS
In the above example, 100% of the offspring will likely be heterozygous- TS. Let's say the T allele is dominant for tall and S allele is recessive for short, then 100% of the offspring will have a tall phenotype.
Another example:
Let's say both plants are heterozygous (TS) genotypes.
T S
T TT TS
S TS SS
The result will be:
25% SS- Homozygous, short
25% TT- Homozygous, tall
50% TS- heterozygous, tall
Link to a quiz: http://biology.clc.uc.edu/courses/bio105/geneprob.htm
1. You begin by drawing a grid of perpendicular lines (think tic tac toe)
2. Next step is to put the genotype of one parent across the top and the other down the left side (it does not matter which parent is on the side and which is on the top). For example, if a parent pea plant genotypes were TT and BB, then the setup would look like:
S S
T
T
3. Next step is to fill in the boxes by copying the row and column letters into each square. Doing this will give us a prediction of all potential genotypes each time reproduction occurs.
S S
T TS TS
T TS TS
In the above example, 100% of the offspring will likely be heterozygous- TS. Let's say the T allele is dominant for tall and S allele is recessive for short, then 100% of the offspring will have a tall phenotype.
Another example:
Let's say both plants are heterozygous (TS) genotypes.
T S
T TT TS
S TS SS
The result will be:
25% SS- Homozygous, short
25% TT- Homozygous, tall
50% TS- heterozygous, tall
Link to a quiz: http://biology.clc.uc.edu/courses/bio105/geneprob.htm
c. Compare sexual and asexual reproduction
Sexual Reproduction- this is the type of reproduction that we see in flowering plants and animals. The process involves the union of two gametes (sex cells), one female (ova) and one male (spermatozoa), that join together called fertilization to produce a fertilized egg called a zygote. The zygote undergoes cell division, called cleavage. It produces a ball of cells called morula, which continues to divide forming a blastocyst, which implants onto the wall of the uterus. As it grows, the cells become differentiated into one kind of cell (nerve, muscle, skin, etc).
Gametes only have half the number of chromosomes called the haploid number. Gametes are achieved through special cell division called meiosis. There are two separate divisions called the first and second meiotic division. The first meiotic division ensures that each daughter cell receives half the number of chromosomes.
FIRST:
Prophase (early phase): threads of chromatin in the nucleus coil up to form chromosomes. Paired chromosomes line up side by side forming pairs called bivalents. Duplicates becomes a pair of chromatids (group of four called tetrad). Centrioles move to opposite sides of poles. Chromatids of each tetrads cross over each other (at the chiasma). A piece of chromatid centrioles pieces breaks off and trade. This mixes genes to ensure that it will not be identical to parents.
Prophase (late stage): homologous chromosomes move to equator of cell.
Metaphase: nuclear membrane disappear, two centrioles form spindle. Chromosomes become attached to spindle by centromeres.
Anaphase: the homologous chromosomes (still pairs of chromatids) separate, dragged apart by fibers of spindle, towards opposite poles of the cell
Telephase: spindle disappears, centrioles duplicate, cytokineses occurs (division of cytoplasm). Two new cells formed with half the original number of chromosomes (each two chromatids). Interphase follows where the nuclear membranes form and chromosomes uncoil again to form chromatin.
SECOND: The cells from the first meiotic cell division divides with the same phases as mitosis, just with haploid number of chromosomes. Process differs whether male or female, plant or animal.
Prophase 2: DNA does not duplicates
Metaphase 2: Chromosomes align at the equatorial plate
Anaphase 2: Centromeres divide and sister chromatids migrate separately toward opposite poles
Telephase 2: Cell division is completed
Four halploid daughters are obtained.
Asexual reproduction is a from of reproduction occurring in many simple plants and animals. The resulting offspring often have the exact same genetic information as the parent. There are a number of different types of asexual reproduction:
Before a cell divides, it's nucleus undergoes division. Each chromosome is copied and each nucleus receives the same genetic material. As each cell divides, the two resulting daughter cells are exact copies of one another.
Gametes only have half the number of chromosomes called the haploid number. Gametes are achieved through special cell division called meiosis. There are two separate divisions called the first and second meiotic division. The first meiotic division ensures that each daughter cell receives half the number of chromosomes.
FIRST:
Prophase (early phase): threads of chromatin in the nucleus coil up to form chromosomes. Paired chromosomes line up side by side forming pairs called bivalents. Duplicates becomes a pair of chromatids (group of four called tetrad). Centrioles move to opposite sides of poles. Chromatids of each tetrads cross over each other (at the chiasma). A piece of chromatid centrioles pieces breaks off and trade. This mixes genes to ensure that it will not be identical to parents.
Prophase (late stage): homologous chromosomes move to equator of cell.
Metaphase: nuclear membrane disappear, two centrioles form spindle. Chromosomes become attached to spindle by centromeres.
Anaphase: the homologous chromosomes (still pairs of chromatids) separate, dragged apart by fibers of spindle, towards opposite poles of the cell
Telephase: spindle disappears, centrioles duplicate, cytokineses occurs (division of cytoplasm). Two new cells formed with half the original number of chromosomes (each two chromatids). Interphase follows where the nuclear membranes form and chromosomes uncoil again to form chromatin.
SECOND: The cells from the first meiotic cell division divides with the same phases as mitosis, just with haploid number of chromosomes. Process differs whether male or female, plant or animal.
Prophase 2: DNA does not duplicates
Metaphase 2: Chromosomes align at the equatorial plate
Anaphase 2: Centromeres divide and sister chromatids migrate separately toward opposite poles
Telephase 2: Cell division is completed
Four halploid daughters are obtained.
Asexual reproduction is a from of reproduction occurring in many simple plants and animals. The resulting offspring often have the exact same genetic information as the parent. There are a number of different types of asexual reproduction:
- binary fission- process of simple organism dividing into two identical ones.
- vegetative reproduction- multicellular structure becomes detached and develops into new individuals.
- Fragmentation- Most likely occurs in mold, yeast, and mushrooms. These organisms produce tiny filaments called hyphae. The hyphae obtains nutrients from the bodies of other organisms. When a piece of the hyphae breaks off, it grows into a new individual.
- germation- form of fission where the parent cell forms a bud-like cell that separates and forms an independent existence.
- sporulation- this is the production of bodies called spores. This can occur in two ways:
1) develops in complex fungi, mosses, and ferns by a special cell division. New plants are not the same at s the parent plants.
2) produced in simple plants which are identical to the parents. True asexual preproduction occurs with this type. - Regeneration- this process takes place with invertebrates of the animal kingdom. This process produces offspring that is identical to the parents. Planaria, for example, is able to reproduce by dividing in two and then regenerating the missing parts.
Before a cell divides, it's nucleus undergoes division. Each chromosome is copied and each nucleus receives the same genetic material. As each cell divides, the two resulting daughter cells are exact copies of one another.
d. Explain how the coding of DNA (deoxyribonucleic acid) controls the expression of traits by genes
DNA- Found in the nuclei of cells. Each molecule is very large and is composed of many individual units called nucleotides that are twisted around each other forming a shape called double helix.
N= nitrogen base (linked nitrogen, carbon, hydrogen, and oxygen atoms). There are five types:
A= adenine T-thymine (Always paired in DNA)
G= guanine C= cytosine (always paired in DNA)
U= uracil (this is only found in RNA and replaces thymine of DNA)
Each DNA molecule contains around 1,000 genes. Genes are the sets of coded instruction. Since the order of the connected genes vary, each gene has a different code that relates to one specific characteristic of an organism. Except for sex chromosomes, paired genes are carried on paired homologous chromosomes and run down the chromosome in the same order. The paired genes control the same characteristic and may have the same instructions. If the instructions are different, then the dominant gene will "mask out" the recessive gene. Otherwise different sets of instruction may be found in incomplete dominance or codominance.
Incomplete dominance is where a pair of genes have different instructions, but neither one is dominant. A blending occurs. For example, a white flower + red flower= pink flower.
Codominance is where pair of genes have different sets of instruction, but neither is dominant and both genes are visible in the phenotype. For example, the human blood type AB is the result of equal dominance between a gene for group A and group B.
N= nitrogen base (linked nitrogen, carbon, hydrogen, and oxygen atoms). There are five types:
A= adenine T-thymine (Always paired in DNA)
G= guanine C= cytosine (always paired in DNA)
U= uracil (this is only found in RNA and replaces thymine of DNA)
Each DNA molecule contains around 1,000 genes. Genes are the sets of coded instruction. Since the order of the connected genes vary, each gene has a different code that relates to one specific characteristic of an organism. Except for sex chromosomes, paired genes are carried on paired homologous chromosomes and run down the chromosome in the same order. The paired genes control the same characteristic and may have the same instructions. If the instructions are different, then the dominant gene will "mask out" the recessive gene. Otherwise different sets of instruction may be found in incomplete dominance or codominance.
Incomplete dominance is where a pair of genes have different instructions, but neither one is dominant. A blending occurs. For example, a white flower + red flower= pink flower.
Codominance is where pair of genes have different sets of instruction, but neither is dominant and both genes are visible in the phenotype. For example, the human blood type AB is the result of equal dominance between a gene for group A and group B.
e. Define mutations and explain their causes
Mutation-a permanent change in the DNA sequence of a gene.
How does it happen?
DNA sequence is interpreted in groups of three nucleotide basis called codons. Each codon specifies a single amino acid in a protein. Some times there is a simple copying error that are introduced when DNA replicates itself. A mutation in the DNA alters the genotype, however is may not affect the phenotype.
Environmental agents such as sunlight, certain chemicals, ultraviolet radiations or other external factors may cause a mutation to occur. Our cells have the ability to repair the changes that occur during DNA replication or from environmental damage. However, as we age, our DNA repair does not work as effectively and we begin to accumulate more changes.
Some are not passed on to our children (such as changes that occur due to sun exposure(, but other errors can occur in the DNA of cells that produce the eggs and sperm, called germline mutations and can be passed down.
If a child inherits a germ-line mutation, then every cell in their body will have this error in their DNA. This is responsible for hereditary diseases.
A gene is kind of a sentence that is made up of the bases A,T, G, and C that explains how to make a protein. There are various way to change this “sentence”:
1. Point Mutations- Changes in one base pair of a cell's DNA sequence. There are a few different types of point mutations.
a) Silent- no effect on the functioning of the protein. This is the least harmful.
b) Nonsense- Change in one DNA base pair. The altered DNA sequence interrupts the building of a protein. The result may cause a shortened protein that may or may not be functional.
c) Missense- changes a codon so that a different protein is created
Example:
Before: Max and Nan hit the can. (Each three letter “word” represents a codon)
After: Max and Fan hit the can.
2. Frame shift mutation- this occurs when one or more bases are inserted or deleted. Since our cells read in three letter “words”, adding or removing one “letter” changes each subsequent word, shifting the “letters” over. For example if we remove the x in the word Max, then all of the bases would shift over. The result would be a shortened protein, most likely non-functional.(Insertions, deletions, and duplications can all be frameshift mutations).
Before: Max and Nan hit the can.
After: Maa ndN anh itt hec an.
3. Deletion- a removal can be something small, such as removing 1 “word”, or longer deletions that affects large numbers of genes on the chromosome. Deletion can also cause frame shift mutation. The deleted DNA may alter the function a protein.
Before: Max and Nan hit the can.
After: Max and hit the can.
4. Insertion- this is an addition of one or more types of nucleotide base pairs in the DNA. Can cause frame shift mutation. This may result in a nonfunctional protein.
Before: Max and Nan hit the can.
After: Max and hub Nan hit the can.
5. Inversion- an entire section of the DNA is reversed. May be a few bases or a large region of the chromosome.
Before: Max and Nan hit the can.
After: Max and nac eht tih naN.
6. Duplication- A piece of DNA that is abnormally copied or more time times. This may affect the function of a protein.
DNA expression- this affects where and how much of a protein is made. Protein can be made at the wrong time or in the wrong cell types. This results in either too much or too little protein being made.
How does it happen?
DNA sequence is interpreted in groups of three nucleotide basis called codons. Each codon specifies a single amino acid in a protein. Some times there is a simple copying error that are introduced when DNA replicates itself. A mutation in the DNA alters the genotype, however is may not affect the phenotype.
Environmental agents such as sunlight, certain chemicals, ultraviolet radiations or other external factors may cause a mutation to occur. Our cells have the ability to repair the changes that occur during DNA replication or from environmental damage. However, as we age, our DNA repair does not work as effectively and we begin to accumulate more changes.
Some are not passed on to our children (such as changes that occur due to sun exposure(, but other errors can occur in the DNA of cells that produce the eggs and sperm, called germline mutations and can be passed down.
If a child inherits a germ-line mutation, then every cell in their body will have this error in their DNA. This is responsible for hereditary diseases.
A gene is kind of a sentence that is made up of the bases A,T, G, and C that explains how to make a protein. There are various way to change this “sentence”:
1. Point Mutations- Changes in one base pair of a cell's DNA sequence. There are a few different types of point mutations.
a) Silent- no effect on the functioning of the protein. This is the least harmful.
b) Nonsense- Change in one DNA base pair. The altered DNA sequence interrupts the building of a protein. The result may cause a shortened protein that may or may not be functional.
c) Missense- changes a codon so that a different protein is created
Example:
Before: Max and Nan hit the can. (Each three letter “word” represents a codon)
After: Max and Fan hit the can.
2. Frame shift mutation- this occurs when one or more bases are inserted or deleted. Since our cells read in three letter “words”, adding or removing one “letter” changes each subsequent word, shifting the “letters” over. For example if we remove the x in the word Max, then all of the bases would shift over. The result would be a shortened protein, most likely non-functional.(Insertions, deletions, and duplications can all be frameshift mutations).
Before: Max and Nan hit the can.
After: Maa ndN anh itt hec an.
3. Deletion- a removal can be something small, such as removing 1 “word”, or longer deletions that affects large numbers of genes on the chromosome. Deletion can also cause frame shift mutation. The deleted DNA may alter the function a protein.
Before: Max and Nan hit the can.
After: Max and hit the can.
4. Insertion- this is an addition of one or more types of nucleotide base pairs in the DNA. Can cause frame shift mutation. This may result in a nonfunctional protein.
Before: Max and Nan hit the can.
After: Max and hub Nan hit the can.
5. Inversion- an entire section of the DNA is reversed. May be a few bases or a large region of the chromosome.
Before: Max and Nan hit the can.
After: Max and nac eht tih naN.
6. Duplication- A piece of DNA that is abnormally copied or more time times. This may affect the function of a protein.
DNA expression- this affects where and how much of a protein is made. Protein can be made at the wrong time or in the wrong cell types. This results in either too much or too little protein being made.
f. Explain the process of DNA replication
Step 1: Unwinding- This is an extremely difficult task to do- at least one of the strands must be broken in order to relieve the thermodynamic strain and allow the two halves to be pulled apart. Special unwinding proteins attach to the DNA. The hydrogen bonds are weakened until the base pairs break between the two anti-parallel strands. The region where the unwinding of the two strands begins is called the starting point. The splitting happens in places of the chain that are rich in A-T (Adenine-Thymine) bases because there are only two bonds between them. There are 3 bonds between the C-G (Cytosine-Guanine) bases. Helicase is the enzyme that splits the two strands apart. The initiation point where the splitting starts is called the “origin of replication”. The structure creates a "Y" shape and is known as “replication fork”. Single stranded DNA binding proteins prevent the two strands from annealing.
Step 2: Binding of the RNA primase. Each DNA strand now has exposed bases that are unpaired. The RNA primase begins binding at the initiation points of the 3'-5' parent chain. RNA primase can attract RNA nucleotides which binds to the DNA nucleotides of the 3'-5' strand due to the hydrogen bonds between the bases. RNA nucleotides are the primers for the biding of DNA nucleotides.
Step 3: The elongation process. The elongation process is different for the 5'-3' and 3'-5'.
The 3'-5' proceeding daughter strand, that uses a 5'-3' template, is called leading strand because DNA polymerase can read the template and adds nucleotides (complimentary to the nucleotides of the template, for ex. Adenine opposite to thymine).
5'-3' Template cannot be read by DNA polymerase. The replication of this template is complicated and the new strand is called lagging strand. In the lagging strand, the RNA primase adds more RNA primers. DNA polymerase reads the template and lengthens the burst. The gap between the two NRA priers is called the “Ozaki Fragments”. The RNA primers are necessary for NDA polymerase to bind nucleotides to the 3' end of them. The daughter strand is elongated with the binding of more DNA nucleotides.
Step 4: In the lagging strand, the DNA polymerase 1, exonuclease, reads the fragments and removes the RNA primers. The gaps are closed with the action of the DNA polymerase (adds complimentary nucleotides to the gaps) and DNA ligase (adds phosphates in the remaining gaps of the phosphate-sugar backbone). Each new double helix is consisted of one old and one new chain, called semi-conservative replication.
Step 5: Last step is called Termination. This process happens when the DNA polymerase reaches to the end of the strands. Since the RNA primer is removed, it is not possible for the DNA polymerase to seal the gap. So, the end of the parental strand where the last primer isn't replicated. These ends of the linear DNA consists of non-coding DNA that contains repeat sequences and are called telomeres. As a result, a part of the telomere is removed in every cycle of the DNA replication.
Step 6: Fixing up to do. The DNA is not completed before a mechanisms of repair fixes possible errors caused during the replication. Enzymes like nuclease remove the wrong nucleotides and the DNA polymerase fills the gaps.
Quick Quiz Time!
What is the function of the RNA?
a) to code for carbohydrates
b) to code for proteins
c) to code for minerals
d) to code for proteins
Correct Answer: B
Step 2: Binding of the RNA primase. Each DNA strand now has exposed bases that are unpaired. The RNA primase begins binding at the initiation points of the 3'-5' parent chain. RNA primase can attract RNA nucleotides which binds to the DNA nucleotides of the 3'-5' strand due to the hydrogen bonds between the bases. RNA nucleotides are the primers for the biding of DNA nucleotides.
Step 3: The elongation process. The elongation process is different for the 5'-3' and 3'-5'.
The 3'-5' proceeding daughter strand, that uses a 5'-3' template, is called leading strand because DNA polymerase can read the template and adds nucleotides (complimentary to the nucleotides of the template, for ex. Adenine opposite to thymine).
5'-3' Template cannot be read by DNA polymerase. The replication of this template is complicated and the new strand is called lagging strand. In the lagging strand, the RNA primase adds more RNA primers. DNA polymerase reads the template and lengthens the burst. The gap between the two NRA priers is called the “Ozaki Fragments”. The RNA primers are necessary for NDA polymerase to bind nucleotides to the 3' end of them. The daughter strand is elongated with the binding of more DNA nucleotides.
Step 4: In the lagging strand, the DNA polymerase 1, exonuclease, reads the fragments and removes the RNA primers. The gaps are closed with the action of the DNA polymerase (adds complimentary nucleotides to the gaps) and DNA ligase (adds phosphates in the remaining gaps of the phosphate-sugar backbone). Each new double helix is consisted of one old and one new chain, called semi-conservative replication.
Step 5: Last step is called Termination. This process happens when the DNA polymerase reaches to the end of the strands. Since the RNA primer is removed, it is not possible for the DNA polymerase to seal the gap. So, the end of the parental strand where the last primer isn't replicated. These ends of the linear DNA consists of non-coding DNA that contains repeat sequences and are called telomeres. As a result, a part of the telomere is removed in every cycle of the DNA replication.
Step 6: Fixing up to do. The DNA is not completed before a mechanisms of repair fixes possible errors caused during the replication. Enzymes like nuclease remove the wrong nucleotides and the DNA polymerase fills the gaps.
Quick Quiz Time!
What is the function of the RNA?
a) to code for carbohydrates
b) to code for proteins
c) to code for minerals
d) to code for proteins
Correct Answer: B
G. Describe evidence, past and present, that supports the theory of evolution, including diagramming relationships that demonstrate shared characteristics of fossil and living organisms
Evolution in organisms refers to changes over time. At the smallest scale, individuals go through changes during their lifetimes. These changes are called ontogentic changes. Microevolution are changes that occur within species or population from one generation to the next. Parents pass on their traits (morhpoogy behavior) on to their offspring. Macroevolution is evolution at the species level and includes speciation, changes in the tree of life, and extinction.
Jean-Baptiste Lamarck and Georges-Luis Buffon demonstrated that species descended from other species an were not morphologically fixed (plants and animals remained unchanged from their first appearance on Earth). Natural section, the driving force that drives biological evolution, explained that organisms best suited to their environment are expected to survive in their reproductive age and produce offspring. Whereas individuals less suited their their environment will be eliminated.
Evidence for this theory:
Jean-Baptiste Lamarck and Georges-Luis Buffon demonstrated that species descended from other species an were not morphologically fixed (plants and animals remained unchanged from their first appearance on Earth). Natural section, the driving force that drives biological evolution, explained that organisms best suited to their environment are expected to survive in their reproductive age and produce offspring. Whereas individuals less suited their their environment will be eliminated.
Evidence for this theory:
- Embryology- this is the study of embryos. Scientists observed that in the early stages of embryo development, vertebrates, such as fish, reptiles, birds, and mammals, are nearly indistinguishable. The similarities is the result of shared common ancestry. As they progress, they develop characteristics that differentiates them from other species. The development of different characteristics mirrors the macroevolution ancestry of each animal. This also shows in microcosmic view of how species have evolved in different ways.
- Homologous structure-these are morpho9lci features in organisms that have similar positions and evolutionary origin. They do not necessarily have identical structure or function because the structures have evolved as a result of adaption to differing environmental influences and ways of life. For example, the forelimbs of vertebrate animals have the save evolutionary origin but have developed differently in response to differing uses for the appendages. Amphibians have legs adapted to walking/crawling; Birds have wings that were adapted to flight, especially with the addition of feathers; bats have elongated finger bones and a thin membrane of skin stretched between the fingers to form a wing; whales have shortened, thickened bones for propulsion as they swim; horses have toes that were reduced to one enlarged two.
- Vestigial Structure- a vestigial structure in an organism is one that is in the process of disappearing. They are typically reduced in size or function compared to species in earlier evolutionary lineage. These structures were once function in an ancestral species. In humans, we have a coccyx at the base of the vertebrae even through we have no use for a tail. In whales, they still have their pelvic bones even though they lost their rear legs.
- Breeding Experiments-focus is to accelerate change in a population and concentrating on desirable characteristics. In selective breeding, humans decide which traits are desirable (whereas in natural selection, nature decides which ones are the best). For example, dogs originally were domesticated from while gray wolves. Today, thousands of breeds with desirable traits have been bred.
- Fossil record- According to Darwin, the fossil-record is a long-term documentation of evolution. Natural selection was proposed as the mechanism to explain how descent with modification or evolution happened. Natural selection is based on the observation that populations are usually composed of more individuals than the environment can support. Because more offspring are produced that can possibly survive, individuals in a population must engage in a struggle for existence. They compete for food, shelter, survival (avoid falling to preys) and reproductive mates. Individuals show variations in their traits and those that survive to reproductive age are able to contribute their traits to the next generation. The differences in individuals with traits that make them more superior may be slight and over a long period of time, those advantages to variations in traits will accumulate in a population. Reproductive isolation may lead to the evolution of new species.
- Genetics and the molecular record- another evidence of evolution is the common genetic and molecular make up. All organisms have the basic hereditary units for all life made up of the same four nucleotides and proteins that are arranged in different arrangements.
h. Explain the theory of natural selection, including adaptation, speciation, and extinction
Natural Selection- Evolution by natural selection is responsible for the tremendous diversity of species found in fossils and living organism. Natural selection is the mechanism that influences which varieties are more likely to survive and pass their genes onto the next generation. Natural selection states that organisms that are best applied to their environment are more likely to survive and transmit their genetic characteristics to successive generation than less adapted organisms.
The specific traits that favor an organism depend on the environmental conditions that affect the survival of some organisms with certain traits more than others.
Speciation- this is a macroevolutionary process in development of new species from existing ones. There are three types of speciation:
Adaptation-involves the modification of an organism or its parts so that it is better fitted of survival in the condition of its environment.
Extinction- The death of the last individual of that species. Typically, species become extinct after 10 million years of its first appearance.
The specific traits that favor an organism depend on the environmental conditions that affect the survival of some organisms with certain traits more than others.
Speciation- this is a macroevolutionary process in development of new species from existing ones. There are three types of speciation:
- allopatric speciation- occurs when there is a disruption of gene flow between population due to physical barrier. The population then diverges genetically. Isolation can occur by dispersal movement of vicariance.
a) Dispersal- this may occur if there are a chain of islands. One island is inhabited by a certain type of species. A group migrtes to another island and the small population diverges genetically from the parent population.
b) Vicariance- a region, populated by a species, is split and breaks apart into two. Species on both regions diverge genetically. - Sympatric speciation- two diverging species within a region have overlapping ranges. Genetic isolation follows a change in ecologic strategy, such as a change in feeding preference, among some individuals of the parent population.
- Parapatric speciation- two species may diverge from a single species following hybridization of a population that have limited gene flow. When partially isolated population established contact, a zone of hybridization can develop. Divergence of nonhybridized stock would result in speciation.
Adaptation-involves the modification of an organism or its parts so that it is better fitted of survival in the condition of its environment.
Extinction- The death of the last individual of that species. Typically, species become extinct after 10 million years of its first appearance.
I. List major events that affected the evolution of life on Earth (e.g., climate changes, asteroid impacts)
Asteroid impacts- impacts from asteroids sends dust and debris into the atmosphere. Enough dust and debris may cause the sunlight to be blocked from the surface of the Earth. This limits photosynthesis from taking place. Earth may also become darkened from the dust covering Earth and plunge it into a cold, winter-like condition. This may have also produced sulfuric acid-tainted rain which may have poisoned life forms. After the dust settled from the atmosphere, the greenhouse gases may have stimulated rapid warming of Earth. For example, the asteroid that hit the Earth during the Cretaceous-Tertiary time caused 16% of marine and 18% of vertebrate families to become extinct.
Volcanic activity- similar to the effects of an asteroid impact in that ash and debris fills up the atmosphere, blocking Earth from sunlight. Oceans also fills with volcanic ash, which affects the chemical makeup of the ocean affecting marine life. Volcanic activity during the end of the Triassic Period may have triggered a deadly global warming resulting in 22% of marine families to become extinct.
Climatic change- often linked to biotic changes. During the carboniferous period, the Earth was going through a greenhouse stage. The second half of the carboniferous period was followed by rapid glacial cycles. These changes affected life on Earth. During warm periods, sea level rose, flooding continental shelves with marine water. When Earth switched to an icehouse world, the polar caps expanded, covering many areas with a blanked of ice sheet. For example, during the Ordovician-Silurian time period, a drop in sea level when glacials formed then the rise in sea level when glacials melted resulted in the destruction of habitats and has changed in a way that it is unfavorable to a group of species. 25% of marine families became extinct.
Continental Drift- movement of continents altered global distribution of species called alloptatric speciation.
© Science CSET: Free Prep Guides, 2008. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Science CSET: Free Prep Guides with appropriate and specific direction to the original content.
Volcanic activity- similar to the effects of an asteroid impact in that ash and debris fills up the atmosphere, blocking Earth from sunlight. Oceans also fills with volcanic ash, which affects the chemical makeup of the ocean affecting marine life. Volcanic activity during the end of the Triassic Period may have triggered a deadly global warming resulting in 22% of marine families to become extinct.
Climatic change- often linked to biotic changes. During the carboniferous period, the Earth was going through a greenhouse stage. The second half of the carboniferous period was followed by rapid glacial cycles. These changes affected life on Earth. During warm periods, sea level rose, flooding continental shelves with marine water. When Earth switched to an icehouse world, the polar caps expanded, covering many areas with a blanked of ice sheet. For example, during the Ordovician-Silurian time period, a drop in sea level when glacials formed then the rise in sea level when glacials melted resulted in the destruction of habitats and has changed in a way that it is unfavorable to a group of species. 25% of marine families became extinct.
Continental Drift- movement of continents altered global distribution of species called alloptatric speciation.
© Science CSET: Free Prep Guides, 2008. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Science CSET: Free Prep Guides with appropriate and specific direction to the original content.