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Punnett Squares and Genetics

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1) Assume the gene for dimples, d, is recessive. Then assume that two individuals with the genotypes Dd and dd mate. Create a Punnett square for this mating and state the probability that their offspring will have dimples.

2) Briefly explain epistasis.

3) List the steps of mitosis and briefly describe what happens in each.

4) What is the role of mRNA in the synthesis of proteins?

5) What is an intron?

6) In the process of protein synthesis, what is the difference between transcription and translation?

7) For animals, what is the advantage of internal fertilization and what type of species utilize it?

8) What is the reproductive purpose of fruits?

9) What is the genetic advantage of sexual reproduction?

Assignment Expectations:

Provide a short but thorough answer to each question. In doing so, you will demonstrate your understanding of the principles of inheritance, the molecular basis of genetics, and the structure of reproduction.

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1) Assume the gene for dimples, d, is recessive. Then assume that two individuals with the genotypes Dd and dd mate. Create a Punnett square for this mating and state the probability that their offspring will have dimples.

D d
d Dd dd
d Dd dd

After the Punnett square showing that Dd X dd, the resulting offsprings have 50% Dd and 50% dd indicating that 50% of the population will have the recessive alleles for dimples. So the probability that the offspring will have dimples is 50%.

2) Briefly explain epistasis.


The scientific definition of epistasis is a "situation in which the differential phenotypic expression of genotypes at one locus depends upon the genotype at another locus. " (1)
Similar, an "epistatic gene allele of one gene eliminates expression of the alternative phenotypes of another gene, and inserts its own phenotype instead. " (1)
For example, let look at color inheritance in dogs.

Two alleles of gene B and b determines black and brown furs, respectively.

B = Black fur
B= brown fur

A separate gene E encode for color deposition in the coat, and ee genotype prevents color deposition in the coat resulting in golden phenotype.
Thus, dogs with genotype BBEE have black coat fur, dogs with bbEE have brown coat with color deposition. Dogs with BBee or bbee have golden coat because the ee genotype prevents color deposition. Thus, the ee is a recessive epistasis.

3) List the steps of mitosis and briefly ...

Solution Summary

The expert creates a Punnett square for the mating. The probability of their offspring will have dimples is determined.

See Also This Related BrainMass Solution

Genetics (DNA, Mutations, Cell Division, Protein Synthesis): Punnet squares, mendelian genetics, blood types, and mitosis.

Part 1: Genetics Problem- Human Blood Types

Mendel is the father of modern genetics, but there are some genetic characteristics that cannot be explained by simple Mendelian genetics. Such is the case with the human blood types in which there are 3 alleles for the same gene, A B, and o. A parent can pass allele A, B, or o to the offspring based on the parent's genotype.

From these 3 alleles, there are 4 blood types (phenotypes): A, B, AB, and O, and there are six genotypes: AA, Ao, BB, Bo, AB, or oo. This is an example of codominance in which both A and B alleles are codominant to each other.

Blood types can be used in forensics to determine if blood is from the victim or criminal. Blood types can be used to determine parental source in situation where the father is unknown; however, blood types can only eliminate certain blood types. DNA fingerprinting is a better method that is used often in criminal and parental determination cases.

A o



Punnett squares such as the one shown above are used to determine the probabilities (percentages) for genotypes of offspring given specific genotypes for the parents.

A) In the example above, the Punnett Square represents a cross (mating) between a male (on the left side) with blood type AB, and a female, (top of square), with blood type A, genotype Ao.

Answer the following for the cross represented above.

1) What are the possible blood types for the offspring?

2) What are the ratios or percentages for each possible blood type from this cross?

3) What blood type is not possible from this cross?

B) Fill out two Punnett squares for a cross between a male with blood type B and a female with blood type AB. (Note that we do not know if the father is genotype BB or Bo from the information given. Thus there are two solutions to the possible cross.)

Set up two Punnett squares and answer the following questions about them.

1) What are the possible blood types for the cross between the type B (BB or Bo?) male and AB female?

2) What are the percentages (%) or probabilities for each blood type in the offspring?

3) What blood type(s) would not be possible in a cross between these two parents?

Hint: There are two answers for questions 1 & 2 above and only one for 3.

Turn in the Punnett Squares and your answers to the questions.

Part 2 : Cell division, mutations and genetic variability.

Eukaryotic cells can divide by mitosis or meiosis. In humans, mitosis produces new cells for growth and repair. And, meiosis produces sex cells (gametes), called sperm and eggs. Changes or mutations in genes in sex cells can be inherited by human offspring. Genetic variation in a population of organisms is good; however, sometimes mutations can be harmful or cause genetic disorders.

Briefly, answer the following questions:

How do meiosis and sexual reproduction (fertilization) produce offspring that differ genetically from the parents?

Describe one example of a human disorder that is inherited and also describe the specific inheritance pattern. For this example, pick disorders that result from mutations in DNA or chromosome number rather than examples such as a genetic tendency for a disorder such as cancer.

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