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Chapter 4: Problem 8

The following genotypes of two independently assorting autosomal genes determine coat color in rats: \(A-B-(\text { gray }) ; A-b b\) (yellow) \(; a a B-\) (black); \(a a b b\) (cream) A third gene pair on a separate autosome determines whether any color will be produced. The \(C C\) and \(C c\) genotypes allow color according to the expression of the \(A\) and \(B\) alleles. However, the ce genotype results in allbino rats regardless of the \(A\) and \(B\) alleles present. Determine the \(F_{1}\) phenotypic ratio of the following crosses: (a)AAbbCC \(\times\) aaBBcc; (b) \(A a B B c c \times A A B b c c\) (c) \(A a B b C c \times A a B b c c\)

Short Answer

Expert verified
What is the F1 phenotypic ratio for the following crosses for a three-gene system determining coat color in rats: (a) AAbbCC x aaBBcc: 100% gray (b) AaBBcc x AABBcc: 100% albino (c) AaBbCc x AaBbcc: 3:3:1:1:4 (gray:black:yellow:cream:albino)

Step by step solution

01

Analyze the given genotypes

Start by writing down the parent genotypes: AAbbCC and aaBBcc. Note that gene A is heterozygous in one parent and homozygous recessive in the other parent, gene B is homozygous in both parents but with different alleles, and gene C is homozygous in both parents but with different alleles.
02

Determine the genotype probabilities for the offspring

Using the rules of probability, determine the offspring's genotype probabilities for each gene: - For gene A: (Aa) - For gene B: (AB or Ba) - For gene C: (Cc)
03

Combine the probability to determine the F1 phenotypes

The combined genotype of the offspring will be AaBbCc. According to the provided information on the genotype and phenotype relationship, this genotype will result in gray coat color because the dominant alleles A and B are both present and the genotype Cc allows color according to the gene A and B alleles being present. Therefore, the \(F_{1}\) phenotypic ratio for this cross is 100% gray. ##Cross (b): AaBBcc \(\times\) AABBcc##
04

Analyze the given genotypes

Start by writing down the parent genotypes: AaBBcc and AABBcc. Note that gene A is heterozygous in one parent and homozygous dominant in the other parent, gene B is homozygous dominant for both parents, and gene C is homozygous recessive for both parents.
05

Determine the genotype probabilities for the offspring

Using the rules of probability, determine the offspring's genotype probabilities for each gene: - For gene A: (AA or Aa) - For gene B: (BB) - For gene C: (cc)
06

Combine the probability to determine the F1 phenotypes

The possible genotypes of the offspring are AABBcc and AaBBcc. However, since the genotype cc is homozygous recessive for gene C, it results in albino rats regardless of the A and B alleles present. Therefore, the \(F_{1}\) phenotypic ratio for this cross is 100% albino. ##Cross (c): AaBbCc \(\times\) AaBbcc##
07

Analyze the given genotypes

Start by writing down the parent genotypes: AaBbCc and AaBbcc. Note that gene A is heterozygous in both parents, gene B is heterozygous in one parent and homozygous recessive in the other parent, and gene C is heterozygous in one parent and homozygous recessive in the other parent.
08

Determine the genotype probabilities for the offspring

Using the rules of probability, determine the offspring's genotype probabilities for each gene: - For gene A: (AA, Aa, aA, or aa) - For gene B: (BB, Bb, bB, or bb) - For gene C: (CC, Cc, or cc)
09

Combine the probability to determine the F1 phenotypes

There are multiple possible genotypes for the offspring, so the phenotypic outcome will vary based on the final combination. However, knowing the relationship between the genotypes and phenotypes, we can do a weighted calculation by the number of each phenotype: - 3 gray:[\((AA,B_,C_)\), \((Aa,B_,C_)\) or \((Aa,B_,Cc)\)] - 3 black:[\((aa,B_,C_)\), \((aa,B_,C_)\) or \((aA,B_,Cc)\)] - 1 yellow:[\((A_,bb,C_)\)] - 1 cream:[\((a a b b C_)\)] - 4 albino:[\((_,_,cc)\)] Therefore, the \(F_{1}\) phenotypic ratio for this cross is \(3:3:1:1:4\) (gray:black:yellow:cream:albino).

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Most popular questions from this chapter

In goats, development of the beard is due to a recessive gene. The following cross involving true-breeding goats was made and carried to the \(\mathrm{F}_{2}\) generation: \(P_{1}:\) bearded female \(\times\) beardless male \(\mathrm{F}_{1}:\) all bearded males and beardless females \\[ \mathrm{P}_{1} \times \mathrm{F}_{1} \longrightarrow\left\\{\begin{array}{l} 1 / 8 \text { beardless males } \\ 3 / 8 \text { bearded males } \\ 3 / 8 \text { beardless females } \\ 1 / 8 \text { bearded females }\end{array}\right.\\] Offer an explanation for the inheritance and expression of this trait, diagramming the cross. Propose one or more crosses to test your hypothesis.

While vermilion is X-linked in Drosophila and causes eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the \(F_{1}\) and \(F_{2}\) results of the following crosses: (a) vermilion females \(\times\) brown males (b) brown females \(\times\) vermilion males (c) white females \(\times\) wild males

In Drosophila, an \(\mathrm{X}\) -linked recessive mutation, scalloped (sd), causes irregular wing margins. Diagram the \(F_{1}\) and \(F_{2}\) results if (a) a scalloped female is crossed with a normal male; (b) a scalloped male is crossed with a normal female. Compare these results to those that would be obtained if the scalloped gene were autosomal.

Horses can be cremello (a light cream color), chestnut (a reddish brown color), or palomino (a golden color with white in the horse's tail and mane). Of these phenotypes, only palominos never breed true. The following results have been observed: cremello \(\times\) palomino \(\longrightarrow 1 / 2\) cremello \(1 / 2\) palomino chestnut \(\times\) palomino \(\longrightarrow 1 / 2\) chestnut \(1 / 2\) palomino palomino \(\times\) palomino \(\longrightarrow 1 / 4\) chestnut \(1 / 2\) palomino \(1 / 4\) cremello (a) From these results, determine the mode of inheritance by assigning sene symbols and indicating which genotypes yield which phenotypes. (b) Predict the \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) results of many initial matings between cremello and chestnut horses.

In foxes, two alleles of a single gene, \(P\) and \(p,\) may result in lethality \((P P),\) platinum coat \((P p),\) or silver coat \((p p) .\) What ratio is obtained when platinum foxes are interbred? Is the \(P\) allele behaving dominantly or recessively in causing (a) lethality; platinum coat color?
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