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Mendelian Inheritance

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1.) Fur color in rabbits is determined by a single gene locus for which there are four alleles. Four phenotypes are possible: black, Chinchilla (gray color causes by white hairs with black tips), Himalayan (white with black patches on extremities), and white. The black allele (C) is dominant over all other alleles, the Chinchilla allele (C^ch) is dominant over Himalayan (C^h), and the white allele (c) is recessive to all others.

a.) A black rabbit is crossed with a Himalayan, and F1 consists of a ratio of 2 black to 2 Chinchilla. Can you determine the genotypes of the parents?

b.) A second cross was done between a black rabbit and a Chincilla. The F1 contained a ratio of 2 black to 1 Chinchilla to 1 Himalayan. Can you determine the genotypes of the parents of this cross?

2.) In Labrador retriever dogs, the dominant gene B determines black coat color and bb produces brown. A separate gene E, however, shows dominant epistasis over the B and b alleles, resulting in a "golden" coat color. The recessive e allows expression of B and b. A breeder wants to know the genotypes of her three dogs, so she breeds them and makes note of the offspring of several litters. Determine the genotypes of the three dogs.

a.) golden female (Dog 1) x golden male (Dog 2)
offspring: 7 golden, 1 black, 1 brown

b.) black female (Dog 3) x golden male (Dog 2)
offspring: 8 golden, 5 black, 2 brown

3.) You cross true-breeding red-flowered plants with true-breeding white-flowered plants, and the F1 are all red-flowered plants. The F2, however, occur in a ratio of 9 red: 6 pale purple: 1 white.

How many genes are involved in the inheritance of this color character?

Explain why the F1 are all red and how the 9:6:1 ratio of the phenotypes in the F2 occurred.

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1.) Fur color in rabbits is determined by a single gene locus for which there are four alleles. Four phenotypes are possible: black, Chinchilla (gray color causes by white hairs with black tips), Himalayan (white with black patches on extremities), and white. The black allele (C) is dominant over all other alleles, the Chinchilla allele (C^ch) is dominant over Himalayan (C^h), and the white allele (c) is recessive to all others.

a.) A black rabbit is crossed with a Himalayan, and F1 consists of a ratio of 2 black to 2 Chinchilla. Can you determine the genotypes of the parents?

To summarize, there are 4 alleles: C, Cch, Ch, and c. They are dominant to each other in that order.

The parents in this problem are black and Himalayan, which means that their genotypes are C_ and Ch_ . Set up a Punnett square for this cross:

C ?
Ch CCh Ch?
? C? ??

Currently, there are two black offspring (CCh and C?), one that is black, Himalayan or Chinchilla (Ch?: it will be black if the missing allele is C, Chinchilla if the mystery allele is Cch, and Himalayan if it is Ch or c).

Because the F1 generation consists of only black and Chinchilla offspring, the Ch? offspring must be Chinchilla, which means that the missing allele from the C? parent is Cch. Adding that information to the Punnett square, we have:

C Cch
Ch CCh ChCch
? C? Cch?

Now, we have 2 black offspring (CCh and C?), one Chinchilla (ChCch), and one that can be either black or Chinchilla (Cch?). We know that this last one has to be Chinchilla, in order to get the correct ratio for the F1 generation. However, this could happen if the missing allele is Ch, or ...

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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

A

B

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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