Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

2. Mendel's Laws of Inheritance

Sex-Linked Genes

Genetics

2. Mendel's Laws of Inheritance

Sex-Linked Genes

Previous problemNext problem

3:52 minutes

Problem 23

Textbook Question

In fruit flies, yellow body (y) is recessive to gray body , and the trait of body color is inherited on the X chromosome. Vestigial wing (v) is recessive to full-sized wing (v⁺), and the trait has autosomal inheritance. A cross of a male with yellow body and full wings to a female with gray body and full wings is made. Based on an analysis of the progeny of the cross shown below, determine the genotypes of parental and progeny flies.
[Table below appears at this point containing crosses and results]

Verified step by step guidance

Step 1: Identify the inheritance patterns and alleles involved. The yellow body (y) is recessive and located on the X chromosome, while gray body (Y⁺) is dominant. Vestigial wing (v) is recessive and autosomal, with full wing (v⁺) being dominant.

Step 2: Determine the genotypes of the parental flies based on the problem statement. The male has yellow body and full wings, so his genotype for body color is X^yY (since males have one X chromosome) and for wings is v⁺v⁺ or v⁺v (we will confirm this later). The female has gray body and full wings, so her genotype for body color is X^Y⁺X^Y⁺ or X^Y⁺X^y (to be determined) and for wings is v⁺v⁺ or v⁺v.

Step 3: Analyze the progeny phenotypes and numbers from the table. Notice that the numbers of males and females with each phenotype are roughly equal, suggesting autosomal inheritance for wings and X-linked inheritance for body color. The presence of vestigial wings in both sexes indicates that the vestigial allele is segregating in the parents.

Step 4: Use the phenotypic ratios to deduce the genotypes of the parents. For the X-linked body color, since the male parent is yellow (X^yY) and the female is gray, the female must be heterozygous (X^Y⁺X^y) to produce both yellow and gray offspring. For the autosomal wing trait, the presence of vestigial wings in offspring suggests both parents are heterozygous (v⁺v).

Step 5: Assign genotypes to the progeny based on the parental genotypes and inheritance patterns. Males inherit their X chromosome from the mother and Y from the father, so their body color depends on the mother's alleles. Females inherit one X from each parent. Wings follow Mendelian autosomal inheritance, so use a Punnett square to determine the expected genotypes and phenotypes of the progeny.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

X-linked Inheritance

X-linked inheritance refers to genes located on the X chromosome, which affects males and females differently due to their sex chromosome composition (XY in males, XX in females). In this case, the yellow body trait is X-linked recessive, meaning males express the trait if they inherit the recessive allele, while females require two copies. Understanding this helps predict phenotypic ratios in progeny.

Autosomal Inheritance

Autosomal inheritance involves genes located on non-sex chromosomes, inherited equally by males and females. The vestigial wing trait is autosomal recessive, so individuals must inherit two recessive alleles to express the trait. This concept is crucial for analyzing the segregation of wing phenotypes independent of sex.

Dihybrid Cross and Phenotypic Ratios

A dihybrid cross examines the inheritance of two traits simultaneously, predicting offspring phenotypes based on parental genotypes. The table shows four phenotypic classes with roughly equal numbers, indicating independent assortment of the X-linked and autosomal traits. Understanding how to interpret these ratios is key to deducing parental and progeny genotypes.

Watch next

Master Sex-Linked Genes with a bite sized video explanation from Kylia

Start learning

Related Videos

Related Practice

Textbook Question

For each pedigree shown,

Identify which simple pattern of hereditary transmission (autosomal dominant, autosomal recessive, X-linked dominant, or X-linked recessive) is most likely to have occurred. Give genotypes for individuals involved in transmitting the trait.

392

views

Textbook Question

The genes encoding the red- and green-color-detecting proteins of the human eye are located next to one another on the X chromosome and probably evolved from a common ancestral pigment gene. The two proteins demonstrate 76 percent homology in their amino acid sequences. A normal-visioned woman (with both genes present on each of her two X chromosomes) has a red-color-blind son who was shown to have one copy of the green-detecting gene and no copies of the red-detecting gene. Devise an explanation for these observations at the chromosomal level (involving meiosis).

509

views

Textbook Question

The following figure illustrates reciprocal crosses involving chickens with sex-linked dominant barred mutation. For Cross A and for Cross B, cross the F₁ roosters and hens and predict the feather patterns of roosters and hens in the F₂.

426

views

Textbook Question

A husband and wife have normal vision, although both of their fathers are red–green color-blind, an inherited X-linked recessive condition. What is the probability that their first child will be (a) a normal son, (b) a normal daughter, (c) a color-blind son, (d) a color-blind daughter?

749

views

Textbook Question

In a species of fish, a black spot on the dorsal fin is observed in males and females. A fish breeder carries out a pair of reciprocal crosses and observes the following results.

Identify which sex is heterogametic. Give genotypes for the parents in each cross, and explain the progeny proportions in each cross.

413

views

Textbook Question

In a species of fish, a black spot on the dorsal fin is observed in males and females. A fish breeder carries out a pair of reciprocal crosses and observes the following results.

Why does this evidence support the hypothesis that a black spot is sex linked?

422

views

Textbook Question

In humans, the ABO blood type is under the control of autosomal multiple alleles. Color blindness is a recessive X-linked trait. If two parents who are both type A and have normal vision produce a son who is color-blind and is type O, what is the probability that their next child will be a female who has normal vision and is type O?

1090

views

Textbook Question

Lesch–Nyhan syndrome (OMIM 300322) is a rare X-linked recessive disorder that produces severe mental retardation, spastic cerebral palsy, and self-mutilation.

What is the probability that the first son of a man whose brother has Lesch–Nyhan syndrome will be affected?

589

views

Show more practices

Download the Mobile app

Privacy

Do not sell my personal information

Accessibility

Patent notice

Sitemap