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Chapter 4: Problem 8

Two different genes, located on two different chromosomes, are responsible for color production in the aleurone layer of com kernels. For color production (either purple or red), the dominant alleles of these two genes \((C \text { and } R\) ) must come together. Furthermore, a third gene, located on a third chromosome, interacts with the \(C\) and \(R\) alleles to determine whether the aleurone will be red or purple. While the dominant allele ( \(P\) ) ensures purple color, the homozygous recessive condition (pp) makes the aleurone red. Determine the \(\mathrm{P}_{1}\) phenotypic ratio of the following crosses: (a) \(C C r r P P \times \operatorname{ccRRp} p\) (b) \(C c R R p p \times C C R r p p\) (c) \(\operatorname{CcRrPp} \times\) CcRrpp.

Short Answer

Expert verified
Answer: The phenotypic ratios of the offspring for each cross are as follows: (a) 100% Purple, (b) 100% Purple, and (c) 2:1 Purple:Red.

Step by step solution

01

Cross (a): CCrrPP x ccRRpp

In this cross, we will first determine the gametes produced by each parent and then find the possible genotypic combinations for the offspring. Since C and R are dominant and required for color production, we will need the presence of at least one C and R allele for the color to be expressed: Parent 1: CCrrPP - gametes: CRP and CRp Parent 2: ccRRpp - gametes: cRp Offspring genotypes: CcRRPp Since the offspring has at least one C and R allele, color will be produced. The presence of the dominant P allele ensures a purple color. Therefore, the P1 phenotypic ratio for this cross is: 100% Purple
02

Cross (b): CcRRpp x CCRRpp

In this cross, we will follow the same procedure as before to determine the possible genotypic combinations: Parent 1: CcRRpp - gametes: CRp and cRp Parent 2: CCRRpp - gametes: CRp Offspring genotypes: CCRRpPp and CcRRPp Both genotypes have at least one C and one R allele, so color will be produced. However, both genotypes are heterozygous for the P gene (Pp), which results in a purple color. The P1 phenotypic ratio for this cross is: 100% Purple
03

Cross (c): CcRrPp x CcRrpp

This cross involves all heterozygous parents with respect to the three genes. To find the gametes produced by each parent, we need to consider the possible allele combinations for each gene. Parent 1: CcRrPp - gametes: CRP, CRp, cRP, cRp Parent 2: CcRrpp - gametes: CRp, cRp Now, let's find the possible genotypic combinations for the offspring and the corresponding phenotypes by considering the presence of the required alleles: Offspring genotypes and phenotypes: 1. CCRrPp (Purple) 2. CcRRPp (Purple) 3. CCRrpP (Purple) 4. CcRrpP (Purple) 5. CcRRpp (Red) 6. CcRrpp (Red) The P1 phenotypic ratio for this cross is: 4:2 or 2:1 Purple:Red

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Most popular questions from this chapter

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 \(\mathrm{F}_{1}\) and \(\mathrm{F}_{2}\) results of the following crosses: (a) vermilion females \(\times \quad\) brown males (b) brown females \(\times\) vermilion males (c) white females \(\times\) wild males

In cattle, coats may be solid white, solid black, or black-andwhite spotted. When true-breeding solid whites are mated with true-breeding solid blacks, the \(\mathrm{F}_{1}\), generation consists of all solid white individuals. After many \(\mathrm{F}_{1} \times \mathrm{F}_{1}\) matings, the following ratio was observed in the \(\mathrm{F}_{2}\) generation: \(12 / 16\) solid white \(3 / 16\) black-and-white spotted \(1 / 16\) solid black Rxplain the mode of inheritance governing coat color by determining how many gene pairs are involved and which genotypes yield which phenotypes. Is it possible to isolate a true-breeding strain of black-and-white spotted cattle? If so, what genotype would they have? If not, explain why not.

A geneticist from an alien planet that prohibits genetic research brought with him two true-breeding lines of frogs. One frog line croaks by uttering "rib-it rib-it" and has purple eyes. The other frog line croaks by muttering "knee- deep knee-deep" and has green eyes. He mated the two frog lines, producing \(\mathrm{P}_{1}\) frogs that were all utterers with blue eyes. A large \(\mathrm{F}_{2}\) generation then yielded the following ratios: \(27 / 64\) blue, utterer \(12 / 64\) green, utterer \(9 / 64\) blue, mutterer \(9 / 64\) purple, utterer \(4 / 64\) green, mutterer \(3 / 64\) purple, mutterer (a) How many total gene pairs are involved in the inheritance of both eye color and croaking? (b) Of these, how many control eye color, and how many control croaking? (c) Assign gene symbols for all phenotypes, and indicate the genotypes of the \(P_{1}, F_{1},\) and \(F_{2}\) frogs. (d) After many years, the frog geneticist isolated true-breeding lines of all six \(\mathrm{F}_{2}\) phenotypes. Indicate the \(\mathrm{F}_{1}\) and \(\mathrm{P}_{2}\) phenotypic ratios of a cross between a blue, mutterer and a purple, utterer.

The trait of medium-sized leaves in iris is determined by the genetic condition \(P P^{\prime}\). Plants with large leaves are \(P P\), whereas plants with small leaves are \(P^{\prime} P^{\prime} .\) A cross is made between two plants each with medium-sized leaves. If they produce 80 seedlings, what would be the expected phenotypes, and in what numbers would they be expected? What is the term for this allelic relationship?

What genetic criteria distinguish a case of extranuclear inheritance from (a) a case of Mendelian autosomal inheritance; (b) a case of \(\mathrm{X}\) -linked inheritance?
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