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Ch. 3 - Mendelian Genetics
Klug - Concepts of Genetics 12th Edition
Klug12th EditionConcepts of GeneticsISBN: 9780135564776Non è quello che usi tu?Cambia libro di testo
Tutti i libri di testoKlug 12th EditionCh. 3 - Mendelian GeneticsProblema 12a
Capitolo 3, Problema 12a

In Drosophila, gray body color is dominant to ebony body color, while long wings are dominant to vestigial wings. Assuming that the P₁ individuals are homozygous, work the following crosses through the F₂ generation, and determine the genotypic and phenotypic ratios for each generation.
gray, long x ebony, vestigial

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Identify the alleles and their dominance relationships: gray body color (G) is dominant to ebony (g), and long wings (L) are dominant to vestigial wings (l). Since the P₁ individuals are homozygous, the gray, long parent is GGLL and the ebony, vestigial parent is ggll.
Set up the P₁ cross: GGLL (gray, long) × ggll (ebony, vestigial). Since both parents are homozygous, all F₁ offspring will be heterozygous for both traits (GgLl), showing the dominant phenotypes gray body and long wings.
Determine the F₁ genotype and phenotype: All F₁ individuals have the genotype GgLl and display gray body color and long wings because of dominance.
Set up the F₁ cross to produce the F₂ generation: Cross GgLl × GgLl. Use a dihybrid Punnett square to find all possible genotype combinations for the two traits.
Calculate the genotypic and phenotypic ratios in the F₂ generation by analyzing the Punnett square results. The phenotypic ratio will reflect the dominant and recessive traits' combinations, typically following a 9:3:3:1 ratio for two independently assorting traits.

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Mendelian Inheritance and Dominance

Mendelian inheritance describes how traits are passed from parents to offspring through dominant and recessive alleles. A dominant allele masks the expression of a recessive allele in heterozygotes, resulting in the dominant phenotype. In this question, gray body and long wings are dominant traits, while ebony body and vestigial wings are recessive.
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Variations on Dominance

Dihybrid Cross and Independent Assortment

A dihybrid cross involves two traits, each with two alleles, to study how they are inherited together. According to Mendel’s law of independent assortment, alleles of different genes segregate independently during gamete formation, producing a variety of genotype combinations in offspring. This principle helps predict phenotypic and genotypic ratios in the F2 generation.
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Gamete Genetics and Independent Assortment

Genotypic and Phenotypic Ratios

Genotypic ratios describe the frequency of different allele combinations in offspring, while phenotypic ratios describe the frequency of observable traits. Calculating these ratios involves determining all possible allele combinations from the parents and predicting the resulting traits, which is essential for understanding inheritance patterns in the F1 and F2 generations.
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Gamete Genotypes
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In Drosophila, gray body color is dominant to ebony body color, while long wings are dominant to vestigial wings. Assuming that the P₁ individuals are homozygous, work the following crosses through the F₂ generation, and determine the genotypic and phenotypic ratios for each generation.

gray, vestigial x ebony, long

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Domanda del libro di testo

In Drosophila, gray body color is dominant to ebony body color, while long wings are dominant to vestigial wings. Assuming that the P₁ individuals are homozygous, work the following crosses through the F₂ generation, and determine the genotypic and phenotypic ratios for each generation.

gray, long x gray, vestigial.

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What is the basis for homology among chromosomes?

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In a cross between a black and a white guinea pig, all members of the F₁ generation are black. The F₂ generation is made up of approximately 3/4 black and 1/4 white guinea pigs. What will the offspring be like if two F₂ white guinea pigs are mated?

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How many different types of gametes can be formed by individuals of the following genotypes:

(a) AaBb

(b) AaBB

(c) AaBbCc

(d) AaBBcc

(e) AaBbcc

(f) AaBbCcDdEe

What are the gametes in each case?

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In a cross between a black and a white guinea pig, all members of the F₁ generation are black. The F₂ generation is made up of approximately 3/4 black and 1/4 white guinea pigs. Two different matings were made between black members of the F₂ generation, with the following results. Diagram each of the crosses.

Cross Offspring

Cross 1 All black

Cross 2 3/4 black, 1/4 white

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