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Ch. 4 - Modification of Mendelian Ratios
Klug - Essentials of Genetics 10th Edition
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Tutti i libri di testoKlug 10th EditionCh. 4 - Modification of Mendelian RatiosProblema 7
Capitolo 4, Problema 7

Flower color may be red, white, or pink, and flower shape may be personate or peloric. For the following crosses, determine the P₁ and F₁ genotypes:
Crosses showing flower color and shape combinations with resulting F1 genotypes and phenotypic ratios for given crosses.

Guida verificata passo dopo passo
1
Step 1: Define the alleles and their dominance relationships for both traits. For flower color, red (R) and white (W) show incomplete dominance, resulting in pink (RW) in heterozygotes. For flower shape, personate (P) and peloric (p) are determined by a simple dominant-recessive relationship, where personate (P) is dominant over peloric (p).
Step 2: Assign genotypes to the P₁ parents in crosses (a) and (b) based on the phenotypes and the F₁ results. For example, in (a), since crossing red peloric with white personate yields all pink personate F₁, deduce the genotypes of the parents considering incomplete dominance for color and dominance for shape.
Step 3: Determine the F₁ genotypes for crosses (a) and (b) by combining the alleles from the P₁ parents. Use the rules of inheritance: incomplete dominance for color (heterozygotes are pink) and dominance for shape (presence of P allele results in personate).
Step 4: For part (c), cross the F₁ genotypes from (a) and (b). Set up a Punnett square for both traits separately (color and shape), then combine the results to find the phenotypic ratios. Remember to consider the independent assortment of the two traits.
Step 5: Calculate the phenotypic ratios by multiplying the probabilities of each color genotype with each shape genotype from the Punnett squares. This will give the expected proportions of each phenotype in the offspring.

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Incomplete Dominance

Incomplete dominance occurs when the heterozygous phenotype is intermediate between the two homozygous phenotypes, such as red and white flower colors producing pink flowers. This concept explains why crossing red and white flowers results in all pink offspring in the F1 generation.
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Percorso guidato
04:37
Variations on Dominance

Independent Assortment

Independent assortment refers to the principle that alleles of different genes segregate independently during gamete formation. This explains the variety of phenotypic combinations (color and shape) seen in the offspring, as flower color and shape genes assort independently.
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Percorso guidato
04:58
Gamete Genetics and Independent Assortment

Genotype and Phenotype Ratios

Genotype ratios describe the genetic makeup of offspring, while phenotype ratios describe observable traits. Understanding how to deduce genotypes from phenotypes and predict offspring ratios is essential for solving crosses and interpreting the results shown in the problem.
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07:52
Gamete Genotypes
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With regard to the ABO blood types in humans, determine the genotype of the male parent and female parent shown here:

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Female parent: Blood type A; father type B

Predict the blood types of the offspring that this couple may have and the expected proportion of each.

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In rats, the following genotypes of two independently assorting autosomal genes determine coat color:

A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. Determine the F₁ phenotypic ratio of the following crosses:

AAbbCC×aaBBcc

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

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Given the inheritance pattern of coat color in rats described in Problem 17, predict the genotype and phenotype of the parents who produced the following offspring:

9/16 gray: 3/16 yellow: 3/16 black: 1/16 cream

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In rats, the following genotypes of two independently assorting autosomal genes determine coat color:

A third gene pair on a separate autosome determines whether or not any color will be produced. The CC and Cc genotypes allow color according to the expression of the A and B alleles. However, the cc genotype results in albino rats regardless of the A and B alleles present. Determine the F₁ phenotypic ratio of the following crosses:

AaBbCc×AaBbcc

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