In Drosophila, yellow body color is due to an X-linked gene...

In Drosophila, yellow body color is due to an X-linked gene that is recessive to the gene for gray body color, (FIGURE CAN'T COPY)a. A homozygous gray female is crossed with a yellow male. The $\mathrm{F}_{1}$ are intercrossed to produce the $\mathrm{F}_{2} .$ Give the genotypes and phenotypes, along with the expected proportions, of the $\mathrm{F}_{1}$ and $\mathrm{F}_{2}$ progeny. b. A yellow female is crossed with a gray male. The $\mathrm{F}_{1}$ are intercrossed to produce the $\mathrm{F}_{2}$. Give the genotypes and phenotypes, along with the expected proportions, of the $\mathrm{F}_{1}$ and $\mathrm{F}_{2}$ progeny. c. A yellow female is crossed with a gray male. The $\mathrm{F}_{1}$ females are backcrossed with gray males. Give the genotypes and phenotypes, along with the expected proportions, of the $\mathrm{F}_{2}$ progeny. d. If the $\mathrm{F}_{2}$ flies in part $b$ mate randomly, what are the expected phenotypes and proportions of flies in the $\mathrm{F}_{3} ?$

In Drosophila, yellow body color is due to an X-linked gene that is recessive to the gene for gray body color,
(FIGURE CAN'T COPY)a. A homozygous gray female is crossed with a yellow male. The $\mathrm{F}_{1}$ are intercrossed to produce the $\mathrm{F}_{2} .$ Give the genotypes and phenotypes, along with the expected proportions, of the $\mathrm{F}_{1}$ and $\mathrm{F}_{2}$ progeny.
b. A yellow female is crossed with a gray male. The $\mathrm{F}_{1}$ are intercrossed to produce the $\mathrm{F}_{2}$. Give the genotypes and phenotypes, along with the expected proportions, of the $\mathrm{F}_{1}$ and $\mathrm{F}_{2}$ progeny.
c. A yellow female is crossed with a gray male. The $\mathrm{F}_{1}$ females are backcrossed with gray males. Give the genotypes and phenotypes, along with the expected proportions, of the $\mathrm{F}_{2}$ progeny.
d. If the $\mathrm{F}_{2}$ flies in part $b$ mate randomly, what are the expected phenotypes and proportions of flies in the $\mathrm{F}_{3} ?$

Key Concepts

Backcross and Random Mating

Backcrossing involves mating an offspring with one of its parents or a genetically similar individual to analyze the expression of specific alleles, while random mating refers to a population breeding without selection, reflecting natural genetic mixing. These breeding strategies are pivotal in genetics to study inheritance patterns over multiple generations and understand how alleles distribute in a population.

Punnett Square Analysis

Punnett squares are conceptual tools used to predict the outcomes of a cross by showing all possible allele combinations from the parental genotypes. They allow for the calculation of expected genotypic and phenotypic ratios in the offspring, making them essential for solving problems involving Mendelian genetics, including those with sex-linked traits.

Cross Design and Breeding Strategies

This concept involves setting up various types of genetic crosses—such as intercrosses, backcrosses, and crosses that involve random mating—to analyze inheritance patterns. Each design helps isolate and understand different genetic factors and interactions by controlling breeding pairs and observing the resulting offspring's genetic distribution.

Dominance and Recessivity

This concept explains how one allele can mask or hide the expression of another allele at the same locus. A dominant allele will determine the phenotype even when only one copy is present, while a recessive allele's effect is only observed in the absence of a dominant allele. Understanding these relationships is crucial for predicting the outcomes of genetic crosses and interpreting patterns of inheritance.

X-Linked Inheritance

X-linked inheritance refers to genes that are located on the X chromosome. In organisms with sex chromosomes, like Drosophila, the pattern of inheritance for X-linked genes is different between males and females because males have only one X chromosome while females have two. This concept is critical for predicting the distribution of traits that are linked to the X chromosome, as males will express whatever allele is present on their single X, even if it is recessive.

Genotype and Phenotype

The genotype refers to the genetic constitution of an organism, the specific alleles it carries, while the phenotype is the observable expression of these genes. In the context of genetic crosses, it is important to distinguish between the genetic makeup and the physical traits manifested, as crossing different genotypes results in various phenotypic ratios, which can be predicted using genetic principles.

Transcript

00:01 This question asks in josophilia, yellow body color is due to an x -linked gene that is recessive to the gene for gray body color.

00:08 For part a, a homozygous gray female is crossed with the yellow male.

00:13 The f -1 are intercrossed to produce the f -2, give the phenotypes and the genotypes, along with the expected proportions of the f -1 and f -2 progeny.

00:22 So if we look at the f -1s, we find that they are going to be half -gray.

00:32 Female with the genotype x plus y x y um x y and then half will be gray male which will have the genotype x plus y for the f2 generation we are going to have one fourth of our offspring be gray females with the genotype x plus x plus, another fourth will be gray female with the genotype x plus xy.

01:37 We will produce another fourth that is gray male with the genotype x plus y and also one fourth yellow male in this case.

01:57 So that will be yellow male with the genotype xyy.

02:05 For part b, we are going to take a look at yellow female, cross with the gray male.

02:15 What will be the progeny for their genotypes and the phenotypes? well, for our f1, we are going to have one half of the progeny be gray females.

02:32 With an x plus and an xy for their genotype.

02:37 And the other half will be yellow males with an xy -y -y genotype.

02:48 And then for f -2, we are going to have one -fourth gray females with the genotype with the genotype x plus y, x plus x, x, y, y, one -fourth yellow females with the genotype xy xy, x, y...

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