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Chapter 4: Problem 33

In four o'clock plants, many flower colors are observed. In a cross involving two true-breeding strains, one crimson and the other white, all of the \(P_{1}\) generation were rose color. In the \(F_{2}\), four new phenotypes appeared along with the \(P_{1}\) and \(F_{1}\) parental colors. The following ratio was obtaincd: \(1 / 16\) erimson \(2 / 16\) orange \(1 / 16\) yellow \(2 / 16\) magenta \(4 / 16\) rose \(2 / 16\) pale yellow \(4 / 16\) white Propose an explanation for the inheritance of these flower colors.

Short Answer

Expert verified
Answer: The inheritance pattern responsible for the flower colors in this cross is a dihybrid inheritance pattern with incomplete dominance. Two separate genes with incomplete dominance, one for crimson pigment (C) and one for yellow pigment (Y), control the inheritance of the flower colors.

Step by step solution

01

Understanding the initial cross

The two parental strains with crimson and white flowers were true-breeding, meaning they were homozygous for their respective flower color genes. When crossed, the \(P_{1}\) generation showed an intermediate rose color, suggesting incomplete dominance.
02

Identifying the pattern in the \(F_{2}\) generation

Examine the ratio of flower colors in the \(F_{2}\) generation: \(1 / 16\) crimson \(2 / 16\) orange \(1 / 16\) yellow \(2 / 16\) magenta \(4 / 16\) rose \(2 / 16\) pale yellow \(4 / 16\) white The pattern follows a \(1:2:1:2:4:2:4\) ratio, which is derived from the product of two \(1:2:1\) ratios, suggesting that two separate gene interactions are responsible for the flower color inheritance.
03

Assigning alleles for flower colors

Assign two pairs of alleles, \(C\) and \(Y\), which control the crimson and yellow pigments in the flowers, respectively. The homozygous recessive genotype for both pairs of alleles will be white (e.g., \(ccyy\)).
04

Combining the genotypes with phenotypes

Now, combine the genotypes of alleles \(C\) and \(Y\) with the observed phenotypes: \(1 / 16\) crimson: \(CCYY\) \(2 / 16\) orange: \(CCYy\) \(1 / 16\) yellow: \(CCyy\) \(2 / 16\) magenta: \(CcYY\) \(4 / 16\) rose: \(CcYy\) \(2 / 16\) pale yellow: \(Ccyy\) \(4 / 16\) white: \(ccyy\)
05

Proposing an explanation for the inheritance of flower colors

The inheritance of flower colors in this case appears to be controlled by two separate genes with incomplete dominance, one responsible for crimson pigment (\(C\)) and the other for yellow pigment (\(Y\)). The \(C\) allele determines the degree of crimson pigmentation, with \(CC\) being fully crimson, \(Cc\) being partially crimson, and \(cc\) having no crimson pigment. The \(Y\) allele determines the degree of yellow pigmentation, with \(YY\) being fully yellow, \(Yy\) being partially yellow, and \(yy\) having no yellow pigment. The ratio of flower colors in the \(F_{2}\) generation can be explained by the interactions between these two genes and their alleles, revealing the \(1:2:1:2:4:2:4\) ratio. This suggests a dihybrid inheritance pattern with incomplete dominance at play.

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Most popular questions from this chapter

Students taking a genetics exam were expected to answer the following question by converting data to a "meaningful ratio" and then solving the problem. The instructor assumed that the final ratio would reflect two gene pairs, and most correct answers did. Here is the exam question: "Flowers may be white, orange, or brown. When plants with white flowers are crossed with plants with brown flowers, all the \(\mathrm{F}_{1}\) flow ers are white. For \(\mathrm{F}_{2}\) flowers, the following data were obtained: 48 white 12 orange 4 brown Convert the \(\mathrm{F}_{2}\) data to a meaningful ratio that allows you to explain the inheritance of color. Determine the number of genes involved and the genotypes that yield each phenotype." (a) Solve the problem for two gene pairs. What is the final \(\mathrm{F}_{2}\) ratio? (b) A number of students failed to reduce the ratio for two gene pairs as described above and solved the problem using three gene pairs. When examined carefully, their solution was deemed a valid response by the instructor, Solve the problem using three gene pairs.

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.

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.

Two mothers give birth to sons at the same time at a busy urban hospital. The son of mother 1 has hemophilia, a disease caused by an X-linked recessive allele. Neither parent has the disease. Mother 2 has a son without hemophilia, despite the fact that the father has hemophilia. Several years later, couple 1 sues the hospital, claiming that these two newborns were swapped in the nursery following their birth. As a genetic counselor, you are called to testify. What information can you provide the jury concerning the allegation?

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.
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