Biology End-of-Course ReviewConstructed Review

1. In 1859, twenty-four European rabbits were brought to Australia for sport hunting. The rabbits had no natural predators, resulting in an exponential growth pattern for the rabbits. They ate crops and became a serious, destructive pest within a relatively short period of time. In an attempt to control the rabbit population, the myxoma virus was introduced into the rabbit population in 1950. Initially, the virus was highly effective, reducing the rabbit population in 1950 by 99%. Currently, the myxoma mortality rate is less than 50%.

A. Describe one scientifically probable change in the rabbit population of Australia that resulted in the reduced effectiveness of the myxoma virus in controlling the number of wild rabbits.

ANSWER:• Some rabbits had a genetic immunity.• Some rabbits had a genetic mutation that made them immune to the

virus.• Natural selection selected for the rabbits that were able to survive the

virus and then pass that immunity to their offspring.• Any other plausible reason for the change in the immunity of the

rabbit population.

B. Describe one scientifically probable change in the myxoma virus that resulted in the reduced effectiveness of the virus in controlling the number of wild rabbits.

ANSWER:• One of the less deadly strains of the virus were able to survive and

reproduce within the rabbit population.• The virus mutated to a less deadly strain.• Natural selection selected for only the less deadly strains of the virus.• Any other plausible reason for the change in the myxoma virus.

2. List TWO significant contributions made by Gregor Mendel to the field of biology.

Answer:• An inherited characteristic (trait) is determined by the combination of a pair of hereditary factors

(genes).

• For each trait, offspring receive one version of the gene (allele) from each of the parents’ reproductive cells.

• Different offspring of the same parents receive different sets of alleles.

• During fertilization, gametes randomly pair to produce four combinations of alleles.

• Inherited traits are dominant or recessive.

• Hybrids do not breed true.

• Many traits are inherited in pairs.

• The law of independent assortment (the emergence of one trait will not affect the emergence of another).

• The law of segregation.

• Keeping meticulous records.

• The study of only one trait at a time.

3. After looking at the following bird beak drawings, indicate which of the following beak-diet combinations is most probable.A. 1: nectar; 2: nuts & seeds; 3:

aquatic organisms; 4; meatB. 1: nectar; 2: meat; 3: nuts &

seeds; 4: aquatic organismsC. 1: aquatic organisms; 2: nuts &

seeds; 3: nectar; 4: meatD. 1: aquatic organisms; 2: nuts &

seeds; 3: meat; 4: nectar

Answer to Multiple Choice is Letter “B”Open-Ended Response …Give a detailed explanation of your answer. Explain why you chose each beak-diet combination.Answer: (4 pt answer)The long and narrow beak (#1) looks like it would be ideal for, and efficient at, getting the nectar out of flowers. It also looks like the beak of a hummingbird. Beak (#2) is not as long, but is thicker, curved, and has a sharp end that could be used in shredding/cutting meat. It also looks like the beak of a hawk. Beak (#3) is short and curved, shaped similar to a nut-cracker. This resembles the beak of a parrot that eats nuts & seeds. The last beak resembles a duck’s beak, which is an aquatic organism.

4. Some climatologists dismiss the current evidence of global warming and instead claim the phenomenon is the result of natural variation in temperature. Others believe global warming is caused by human activity. Based on your understanding of the evidence, which conclusion do you think is most likely? Why or Why not? What other types of information would you want to see?

Answer:

• Must respond with a yes or no! • Answer must be supported by at least 2 reasons…• If you say “yes” that Global warming is caused by human activity…An increase in combustion of fossil fuels (in automobiles, heavy industry,

aircraft, etc…) produces more carbon dioxide and thus may increase the global temperatures

An increase in combustion from heavy industry, automobiles, etc… producing toxins and poisons, killing plants which photosynthesize, leaving more carbon dioxide in the atmosphere.

Clear-cutting for agriculture or other human development reduces plants which photosynthesize, thus increasing carbon dioxide levels in the atmosphere.

Phytoplankton at the ocean’s surface are dying from increasing ultraviolet rays from the Sun; certain types of plankton are responsible for some photosynthesis

Answer to #4 continued…

• If you say “no”…Global warming is actually the result of a natural variation in temperatures…

Other factors are involved in maintaining a proper atmosphere balance, such as the ocean absorbing carbon dioxide. Although average surface air temperature appears to be going up along with human activity, cause and effect still need to be verified.

The increase in average global temperatures is actually a normal trend in a cycle of increasing and decreasing surface temperatures over many, many years.

5. Give two examples of personal lifestyle decisions that can increase or decrease the amount of greenhouse gases. Be specific as to why each example would increase or decrease the amount of greenhouse gases.

Personal decisions affecting the amount of greenhouse gases could include things such as: (increasing or decreasing CO2)Deciding to bicycle, carpool or use public transportationInsulating the home for more efficient heating and coolingPlanting treesBuying rain forest acreage for preservation, etc…Burning yard waste, such as tree limbs, etc…

Answer to #5 Continued…

Explanations of why the above examples increase or decrease the amount of greenhouse gases could include the following:Decrease use of automobiles would decrease the amount of greenhouse gases in the air because

carbon dioxide (CO2) is released in automobile exhaust.Insulating the home for more efficient heating and cooling would decrease the amount of

greenhouse gases because chlorofluorocarbons were prevalent in air conditioners (before recent restrictions) and the burning of fossil fuels releases CO2 into the air.

Planting trees would decrease the amount of greenhouse gases because plants remove CO2 from the air during photosynthesis.

Buying rain forest acreage for preservation would decrease the amount of greenhouse gases. The preservation of the rain forest acreage would prohibit the burning of the trees, which releases CO2 into the air, and it would maintain those trees, which remove CO2 during photosynthesis.

Burning yard waste, such as tree limbs would increase greenhouse gases because burning wood and other materials releases CO2 into the air.

6. Background information… You have recently been hired as a genetic counselor for Bates Hospital because of your expertise in genetic and molecular biology. Your first clients are the parents of a child with Phenylketonuria, PKU. Individuals with PKU are missing an enzyme needed for metabolism and can develop severe mental retardation if untreated. The parents do NOT have PKU and neither do their other two children. The parents have many questions about how their child inherited this disorder and how it affects their child’s well being. The PKU gene is located on chromosome #12.

Your task: Fill in the answers that you, as the genetic counselor, would give to the parent’s following questions. Be sure to provide answers that are detailed. You need to answer the parent’s questions fully and show how well you understand the process of genetic inheritance.

A. Parents: How did our child get the genes for PKU since neither one of us has PKU?

What is the probability of our next child getting the disease? (Include a Punnett Square or other type of illustration to help with your explanation. Clearly indicate the affected child in your diagram.)

Answer to “A”Genetic Counselor: Both of you carry a dominant and recessive allele of the locus controlling the PKU enzyme. Only one allele of a pair was passed on to the sperm and egg that fused and became your child. Each parent has a 50% probability of passing to the offspring either a dominant allele (P) or a recessive allele (p). You both passed on your recessive allele to this child. The probability of a child having PKU (pp) when both parents are Pp is 25%. This can be represented using a Punnett Square or other illustration that illustrates a monohybrid (single locus) cross.

Affected Child: There is a 25% chance for each birth that offspring will have both recessive alleles.

Answer “A” continued…

Could also draw a pedigree…

#6 Part B:

Parents: We read in a science article that PKU is caused by a missing protein needed for normal metabolism. The article also said proteins are synthesized according to the directions contained in genes. How does this happen? Please give us an overview of the process of protein synthesis by answering the following two questions. Us a diagram if you think it will be helpful.

B. What is synthesized during transcription and where does transcription occur in the cell?

Describe the process of translation and where it occurs in the cell.

Answer to #6 Letter B:

Genetic Counselor: The process of making proteins begins in the nucleus with transcription. The DNA sequence on one strand of the molecule is transcribed into a molecule called messenger RNA, or mRNA. The mRNA moves out of the nucleus into the cytoplasm of the cell where ribosomes associate with it. In the second phase of protein synthesis, the mRNA code is translated into the appropriate amino acid sequence. Amino acids are brought to ribosomes by tRNA molecules. As tRNA molecules align themselves along the mRNA molecule, amino acids attached to the tRNA are arranged side-by-side in the proper sequence and form peptide bonds. The amino acids bond together to form a protein.

Helpful Diagram:

Transcription Translation

7. Ectothermic animals are unable to regulate their body temperature internally and their temperature reflects the temperature of their surroundings. Endothermic animals are able to regulate a constant body temperature internally. Discuss one advantage and one disadvantage of being an ectothermic animal.

Answer: Advantage…Do not use a great amount of energy to heat the

body OR more energy available for other uses.

Disadvantage…Limited environment in which to live OR activity is limited to times and locations of external sources

of heat.

8. Scientists making weather observations forecast a severe winter and cold summer. Discuss how both ectothermic and endothermic animals would respond to an unusually cool year and how they would respond if the climate continues to cool over a period of 1,000 years.

Ectothermic AnimalsAnswer: Short-Term…• Animals might be more sluggish.

• Animals might move to a warmer area that still provides conditions optimal for their survival.

• Animals might expose themselves to sunlight for longer period of time.

• Any other reasonable response.

Long-Term…• Animals might move to a warmer habitat.

• There might be natural selection of those animals able to survive in the cooler climate.

• Any other reasonable response

Endothermic AnimalsAnswer: Short-Term…• Animals would maintain their normal temperature (basal

metabolism would be maintained) but they would require more energy (food) to do so. (Only if the temperature changed dramatically—above or below the thermoneutral zone– would their metabolisms need to change).

• Animals might eat more food.

• Any other reasonable response

Long-Term…• There might be natural selection of those animals able to survive

in the cooler climate. Might increase in size to retain more heat The amount of hair or feathers they have might increase for

better insulation Metabolism rates might change

• Animals might migrate to a warmer climate.

9. List and describe three processes used by cells to control the movement of substances across the cell membrane.Answer: Key Elements• Selective permeability is used by the cell membrane to allow certain substances to move across.

• Passive transport occurs when substances move from an area of higher concentration to an area of lower concentration.

• Osmosis is the diffusion of water across the cell membrane.

• Facilitated diffusion when the membrane controls the pathway for a particle to enter or leave a cell.

• Active transport occurs when a cell uses energy to move a substance across the cell membrane, and/or a substance moves from an area of low to high concentration, or against the concentration gradient.

• Pumps are used to move charged particles like sodium and potassium ions through membranes using energy and carrier proteins.

• Membrane-assisted transport occurs when the membrane of the vesicle fuses with the cell membrane as in endocytosis.

• Membrane-assisted transport occurs when vesicles are formed around large molecules as phagocytosis.

• Membrane-assisted transport occurs when vesicles are formed around liquid droplets as in pinocytosis.

• Protein channels or channel proteins allow for the movement of specific molecules or substances into or out of the cell.

#9 continued…

Answer awarded maximum points…• Osmosis is a process in which water travels along a selectively

permeable membrane. • Diffusion is the process a cell uses in which particles move from and

area of high concentration to an area of low concentration.• Active transport is a process in which the cell uses energy to move

something from one part of the cell to another.

10. Define the term homeostasis.

Answer:• The maintaining of a constant internal environment.• The maintenance of a body’s internal environment.

11. Describe a change inside or outside the human body that could affect homeostasis of the human body and describe how the body might respond involuntarily to that change.Answer: • An increase in heat or physical activity would cause sweat, the body’s attempt of

maintaining a constant internal temperature.Key Elements that can be used:• The body responds by having counter reactions such as sweating when hot.• The body responds by not sweating, blood vessels constricting.• Introduction of infection, fever.• Cold environment, shivering.• Glucose level rises above a set point, pancreas secretes insulin, glucose level drops.• Glucose level drops below a set point, pancreas secretes glucagon, glucose level rise.

12. A population of fish lives in a pond near an industrial park. Many of the fish develop abnormal growths on their gills, but the growths do not affect their survival.

Describe a potential cause of this growth and what happens within the cells.• The fish were probably exposed to high levels of a substance that can cause genetic

mutations found in the water.Is it likely that this trait will be inherited by the next generation? Explain why or why not.• It is not likely that this trait will be inherited by the next generation, because it is not

typically an inheritable trait.• If mutation is not occurring in its gametes, then the affects will not be seen in

offspring.• Mutations in gametes can cause the gamete cell to not produce viable offspring.• The trait will not be inherited, if the growth prevents them from reproducing.

13. Current knowledge of alleles helps to explain what Charles Darwin did not understand when he was trying to explain inheritance.

List two statements that describes how alleles affect inherited traits.Answer: (any of the two)• Organisms can have different alleles for (some) single traits.• Alleles are independently assorted during reproduction.• Alleles are segregated during reproduction.• Alleles are passed on to offspring.• Alleles can be dominant/co-dominant or recessive.• Alleles determine individual’s genotype and phenotype.• Similar phenotypes can have different genotypes (homozygous and

heterozygous).

#13 continued…

Describe how variation in alleles affects natural selection within a species.• Assortment of and changes in alleles can lead to variation within a

species, which may lead to better survival and reproduction (evolution).• Assortment of and changes in alleles can lead to variation within a

species, which may lead to differential survival and reproduction.

#13 Correct Response:

Alleles are either dominant or recessive, usually the dominant trait is shown. Alleles come from both parents. The necessary traits are passed on and the organisms without the necessary traits die.

14. A. Explain how the fossil record provides evidence for evolution.Answer:• By looking at younger to older rock layers, the fossil record supports the

idea that a variety of different extinct organisms are related to one another and to living organisms.• Similar structures and features of organisms that are located in different

layers (younger and older) of the fossil record.OR….• The fossil record shows that organisms have evolved from simpler

organisms into more complex organisms over time.• The fossil record shows evidence of extinction events/extinction of species.

#14 continued…Part B: Give two reasons why the fossil record is not representative of all evolution on Earth.

Answer:• Not all species are represented in the fossil record because they were

not preserved.• Fossils can be destroyed by geologic processes.• Some species have left no fossils in the fossil record.

#14 Correct Response:

Fossils can show how the skeletal shape of an organism has changed over million of years.

Not everything has been fossilized. It does not show how the animals have changed when it comes to skin, or internal organs.

15. Sickle-cell disease occurs when a child is born with two recessive copies of defective gene.

A. If neither biological parent has the disease, what are the possible genotypes of the biological parents of a child that has sickle-cell disease?

Answer:• Both parents must be carriers of a recessive allele for Sickle-cell

disease.• Both parents are heterozygous.

# 15 Part “B”:

Explain the mechanism for inheritance of this disorder.Answer:• During meiosis, each gamete will receive one allele for each gene. If

the allele is dominant, it will be apparent in the offspring. If the allele is recessive, it will only be expressed in offspring that received a like allele (recessive) from the other biological parent.

#15 Correct Response:

Both parents would have to be heterozygous for the disease. Both parents contribute one allele to the child and if both had contributed the recessive allele then the child would be homozygous recessive causing him to have the disease.

16. A. Identify the elements that make up a molecule of water.Answer:• Water—hydrogen and oxygen• Hydrogen and oxygen make up water.• H2O—2 parts hydrogen and 1 part oxygen make up water.

16. B. Identify the elements that make up a molecule of glucose.Answer:• Glucose—carbon, hydrogen, and oxygen• Glucose is made up of carbon, hydrogen and oxygen.• C6H12O6—6 parts carbon, 12 parts hydrogen, 6 parts oxygen make up

glucose

16. C. Identify which of these molecules, water or glucose, provides energy for an organism and briefly explain what happens to the molecule that enables an organism to obtain energy.

Answer:• Organisms obtain energy from glucose as the chemical bonds are

broken.• Glucose is converted to ATP/chemical energy.Correct Response should look like…• Glucose provides energy for an organism. When the bonds of the

glucose molecule break energy is released.

17. Mendel crossed a pea plant with green pods (GG) and a pea plant with yellow pods (gg).

A. Explain why only plants with green pods appeared in the F1 generation.

Answer:• Every plant in the F1 generation inherited a dominant allele for green.• Green pods only appeared in the F1 generation because they were

dominant and all of the allele possibilities were heterozygous, which means the green pod allele would be covering up the recessive yellow pod allele.

#17. Continued…Part “B”:Mendel crossed offspring of this cross (F1) with each other and found that both plants with green pods and plants with yellow pods were produced.

B. Explain why both colors of pea pods appeared in the F2 generation.Answer:• Every cross in the F1 generation involved two heterozygous parents.

Therefore, some of the F2 plants were homozygous recessive.• Both colors of pea pods appeared in the F2 generation because not

every allele possibility was heterozygous. Some were just recessive, gg, and some were heterozygous, Gg. With the recessive gg, the pods would be yellow and with the heterozygous Gg, the pods would be green.

18. Describe two pieces of evidence to support the claim that chimpanzees are a close living relative of humans.

A. Describe two pieces of evidence.Answer:• The DNA between chimpanzees and humans is about 98% the same.• Chimpanzees have similar bone structures as we do.• Chimpanzees and humans share similar physical characteristics (give

example).• Chimpanzees and humans share similar behaviors (give example).• Chimpanzees and humans have a high degree of amino acid similarity.

19. The stomach contains enzymes that aid in digestion and that are active within a small pH range.A. Describe what would happen to the enzyme’s FUNCTION if the pH was outside this range.B. Describe what would happen to the enzyme’s STRUCTURE if the pH was outside the range.Answer:• The enzyme would stop functioning.• The enzyme would decrease in activity.• The enzyme would have no activity.• The shape of the enzyme would fall apart.• The enzyme would denature.Example…• The enzyme would lose most of it’s function and not be able to do it’s job of aiding in

digestion. The enzymes shape would change and it would not be able to grab a hold of the chemical it needs to speed up.

20. Predict whether you would expect muscle cells or fat cells to contain more mitochondria and explain why.

Answer:• Identification that muscle cells would have more mitochondria that

fat cells.• Mitochondria transform energy in the cell, and muscle cells require

more energy to function that fat cells do.• Muscle cells require more energy to function that fat cells, and

mitochondria convert food energy to ATP for the cell, so the muscle cells would have greater mitochondria that fat cells.• Muscle cells contain more mitochondria because they require a great

deal of energy to do cellular work.

21. The work performed in cells is carried out by proteins, lipids, carbohydrates and nucleic acids.

Choose three of these molecules and describe one function that each of them carries out within the cell.• Proteins—function as enzymes, hormones, connective and supportive

tissue• Lipids—store energy, structural support, and specific reactants in

metabolic reactions, cell membrane component• Carbohydrates—store and transport energy• Nucleic acids—store genetic information

22. Explain how the multiplication of individual cells in a multi-cellular organism is similar to reproduction in a single-celled organism.Answer:• Individual cells and single-celled organisms reproduce through

division.

23. Explain why a male with a recessive X-linked trait usually produces no female offspring with the trait.

Answer: • Because even though the male (father) may pass on the recessive

allele for the disease attached to his X, the daughter will have another X from mother. Females are XX. As long as one X is not affected, the daughter will not have the disease because she is a heterozygote.

24. If a male with a recessive X-linked trait does produce a female offspring with the trait, what are possible genotypes of the mother?Answer: • The only way that a female offspring can have the recessive trait is if

she has received an affected X from both parents. Whereas with males, they only have to have one affected X to show the trait.• Possible genotypes of the mother are XaX and the daughter received

the Xa, or the mother is XaXa, but she would have to have the disorder.

25. Below is a diagram of the structure found in a typical animal cell. A. List the names of any three structures shown in the diagram.

B. Describe the function of each of the structures listed.

Answer:

• Cell membrane—form the outer covering of the cell; and is semi-permeable

• Cytoplasm—is a gel-like matrix, where all the other cell organelles are suspended inside the cell

• Nucleus—contain the hereditary material DNA and directs the activities of the cell

• Centrioles—organize the microtubules assembly during cell division

• Endoplasmic Reticulum—are a network of membranes composed of rough and smooth endoplasmic reticulum

• Golgi Apparatus—is responsible for storing, packaging of cellular products

• Ribosome—are made up of RNA and proteins, and are sites of protein synthesis

• Lysosome—are enzymes sacs, that digest cellular wastes

• Microtubules—are hollow rods, function primarily as support and shape to the cell

• Mitochondrion--is the site for cellular respiration, and the producers of energy (ATP); the power-house of the cell

• Nucleolus—is the structure within the nucleus and helps in the synthesis of ribosomes

• Nuclear Pores—is the tiny hole in the nuclear membrane, allows the movement of nucleic acids and proteins in/out of cell

• Vacuole/vesicle—is for storage, intracellular digestion and waste removal

• Cytoskeleton—helps maintain cell shape

26. The diagram below, called a cladogram, shows a proposed evolutionary relationship among animals.According to this cladogram, what four characteristics separate a trout from a rat?

Answer:

• Lungs

• Claws or nails

• Fur

• Mammary Glands

27. Below is a sequence of bases that make up a segment of DNA. A A C T A C A G T C T A C C A T A CA. When this segment of DNA is translated into mRNA, how many codons

would be represented in this segment?Answer: 6 codonsB. How are codons used in the process of protein synthesis?Answer: The ribosome proceeds to the elongation phase of protein synthesis. During this stage, complexes, composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA. Each codon codes for a specific amino acid. Codons determine the sequence of amino acids.

28. Use the chart to answer the question.

Below is an RNA sequence consisting of three amino acids and a stop codon. Above each amino acid and the stop codon is the list of bases that code for that amino acid.

#28 Continued…

A. What will be the fourth codon in the new sequence?Answer: The fourth codon in the new sequence will be UUG (resulting from the insertion of a single adenine (A) nucleotide into position 3 of the sequence)B. What amino acid will be coded for by the fourth codon in the new sequence?Answer: Leu will be coded for by this codon.C. What name is given to this type of mutation?Answer: This type of mutation can be referred to as one of the following…• Frameshift mutation• Insertion• Point Mutation

29. A. Identify two structures or molecules in cells that participate in the process of making proteins.

Answer: • Nucleus or DNA• Nucleolus• Ribosomes• RNA• ATP • Rough ER• Amino acids• Enzymes• mRNA• tRNA• Golgi apparatus

#29 Continued…B. Explain how each structure plays a role in this process.Answer: • Nucleus/DNA: Provides template for transcription, production of mRNA• Nucleolus: rRNA is synthesized here with proteins from the cytoplasm to form ribosomal subunits

(components of ribosomes)• Ribosomes: structure/base for translation of mRNA into tRNA and formation of the polypeptide chain• ATP: provides energy in the process of making proteins• RNA: Plays integral role in transcribing and translating DNA into polypeptides (via mRNA and tRNA)• Rough ER: Site for ribosomes to synthesize proteins• Amino acids: Building blocks of proteins• Enzymes: Play various important roles in protein synthesis, including assisting DNA replication and formation

of amino acids, among others• mRNA: carries genetic message from the DNA to the protein synthesizing part of the cell• tRNA: transfers amino acids from cytoplasm to ribosomes• Golgi apparatus: processes and packages proteins

#29 Example:

Ribosomes and mRNA (messenger RiboNucleic Acid) participate in protein synthesis, the process of making proteins.

mRNA plays a role in protein synthesis by taking the information from the DNA in the nucleus to the ribosome. This information is a section of the cell’s DNA strand and tells the ribosome which protein(s) to make. Ribosomes play a part by building amino acids (brought to the ribosome by tRNA) into protein chains, which the cell can use.

30. Describe the function of the cell membrane.A. Explain how a cell could be affected if the cell membrane does not function properly.Answer: • The cell membrane regulates which substances enter and leave the cell.OR• The cell membrane separates the interior of the cell from the exterior, and holds the contents of the

cell intact (under normal conditions).• The cell membrane creates and electrochemical gradient.• The cell membrane is responsible for movement in pseudopods.AND• If the cell membrane does not function properly, the substances that need to cross the membrane

inside the cell will not be delivered (or the substances that need to be released from the cell will not be released) and the cell will not be able to conduct normal cellular activities needed for the cell to survive.

• If the cell membrane does not function properly, communication between cells is limited.

30.B. Explain why plant cells require cell walls in addition to the cell membrane.Answer:• Cell walls in plants provide strength and protection against physical pressure

and pressure caused by the contents of the cell, in particular the central vacuole.

OR• Cell walls in plants provide structural integrity to the plant so it remains

upright and intact in order to conduct photosynthesis and grow.Example: The cell membrane keeps things out of the cell, while letting molecules that the cell needs in. If that cell membrane would fail to function, it could either starve the cell of what it needs, or it could let anything that’s on the outside rush into the cell. Plant cells need cell walls to support both itself and the plant because the plant has no structure besides the cells themselves.

31. Rabbits may have a coat of black fur or a coat of brown fur. Black fur is completely dominant over brown fur.

A rabbit homozygous for black fur is crossed with a rabbit homozygous for brown fur.

A. What are the possible genotypes of the parents in this cross?Answer:• The parents are BB (homozygous dominant) and bb (homozygous recessive).

B. What phenotype(s) of the offspring are possible in this cross?Answer: All offspring have a phenotype of a black coat. (100%)

• The parents are Bb (heterozygous dominant) and bb (homozygous recessive).• Half of the offspring have a phenotype of a black coat; half of the offspring have

a phenotype of a brown coat.

#31. Continued… A rabbit homozygous for brown fur is crossed with a rabbit heterozygous for black fur.

A. What are the possible genotypes of the parents in this cross?Answer: The parents are Bb (heterozygous dominant) and bb (homozygous recessive).

B. What phenotype(s) of the offspring are possible in this cross?Answer: Half of the offspring have a phenotype of a black coat; half of the offspring have a phenotype of a brown coat.

32. Mitosis is the process by which cells divide into two daughter cells. Mitosis can be divided into four stages—prophase, metaphase, anaphase, and telophase.A. Select one of the stages of mitosis and describe what happens during that stage.Answer:• Prophase—The chromosomes begin condensing, the nuclear envelope begins breaking down, and the

network of spindle fibers form.• Metaphase—Chromosomes move to the center of the cell and line up along the middle. Each

chromosome is held in place by the microtubules attached to the kinetochore.• Anaphase—The two chromatids separate when the centromere divides. The chromatids (now called

chromosomes) are pulled to the opposite sides of the cell by the attached fibers.• Telophase—The chromosomes uncoil and a new nuclear envelope forms. The spindle fibers break down

and disappear.B. Explain why DNA replication is essential before beginning mitosis.Answer: • The cell must have two sets of chromosomes present so that each daughter cell receives a copy of each

chromosome. This is essential in maintaining the correct number of chromosomes in each daughter cell.

#32 Example Response:

In metaphase the chromosomes are lining up in the middle of the cell to get ready for the cell to divide. DNA replication (which happens during the S phase or Interphase) is important because each of the daughter cells of mitosis have to have 46 chromosomes.

33. Round seeds (R) are the dominant seed shape for pea plants; wrinkled (r) is the recessive seed shape for pea plants. A pea plant with round seeds is crossed with a pea plant with wrinkled seeds and all of the offspring have round seeds.

A. What are the genotypes of the two parent plants in this cross?Answer: RR and rr or RR and RrOR• Homozygous dominant or homozygous recessive or homozygous dominant

and heterozygousB. What is the expected phenotypic ratio of seed shape in offspring if a heterozygous plant is crossed with a homozygous recessive plant?Answer:• The phenotypic ratio for offspring is 2 round and 2 wrinkled. Fifty percent

of the seeds will be round and fifty percent of the seeds will be wrinkled.