Ch. 4 - Modification of Mendelian Ratios

Klug - Essentials of Genetics 10th Edition

Klug10th EditionEssentials of GeneticsISBN: 9780135588789Not the one you use?Change textbook

Klug 10th Edition

Ch. 4 - Modification of Mendelian Ratios

Problem 13a

Chapter 4, Problem 13a

In cats, orange coat color is determined by the b allele, and black coat color is determined by the B allele. The heterozygous condition results in a coat pattern known as tortoiseshell. These genes are X-linked. What kinds of offspring would be expected from a cross of a black male and a tortoiseshell female? What are the chances of getting a tortoiseshell male?

Verified step by step guidance

Identify the genotypes of the parents based on the information given: The black male has genotype X\^B Y (since males have one X and one Y chromosome), and the tortoiseshell female has genotype X\^B X\^b (heterozygous for black and orange alleles).

Determine the possible gametes each parent can produce: The male can produce sperm carrying either X\^B or Y, and the female can produce eggs carrying either X\^B or X\^b.

Set up a Punnett square to combine the male and female gametes, showing all possible combinations of offspring genotypes: cross X\^B and Y from the male with X\^B and X\^b from the female.

Analyze the genotypes of the offspring: Female offspring will be either X\^B X\^B (black) or X\^B X\^b (tortoiseshell), and male offspring will be either X\^B Y (black) or X\^b Y (orange).

Calculate the probability of each offspring type by counting the number of each genotype combination and dividing by the total number of possible offspring; specifically, note that tortoiseshell males (X\^B X\^b Y) are not possible because males have only one X chromosome.

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. Males have one X and one Y chromosome, so they express the allele present on their single X chromosome. Females have two X chromosomes, allowing for heterozygous combinations that can produce unique phenotypes, such as tortoiseshell coat color in cats.

Alleles and Phenotypes in Coat Color

The B allele codes for black coat color, while the b allele codes for orange. In heterozygous females (Bb), both alleles are expressed in different cells due to X-chromosome inactivation, resulting in the tortoiseshell pattern. Males, having only one X chromosome, show either black or orange but not tortoiseshell.

Punnett Square and Probability in Genetic Crosses

A Punnett square helps predict offspring genotypes and phenotypes by combining parental alleles. For X-linked traits, it is important to consider the sex chromosomes separately. Calculating the chances of specific phenotypes, like tortoiseshell males, involves analyzing possible allele combinations and their associated probabilities.

Recommended video:

Guided course

07:41

Probability

Related Practice

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?

1181

views

Textbook Question

In goats, the development of the beard is due to a recessive gene. The following cross involving true-breeding goats was made and carried to the F₂ generation:

Offer an explanation for the inheritance and expression of this trait, diagramming the cross. Propose one or more crosses to test your hypothesis.

738

views

Textbook Question

In Drosophila, an X-linked recessive mutation, scalloped (sd), causes irregular wing margins. Diagram the F₁ and F₂ 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 with those that would be obtained if the scalloped gene were autosomal.

1656

views

Textbook Question

Another recessive mutation in Drosophila, ebony (e), is on an autosome (chromosome 3) and causes darkening of the body compared with wild-type flies. What phenotypic F₁ and F₂ male and female ratios will result if a scalloped-winged female with normal body color is crossed with a normal-winged ebony male?

Work out this problem by both the Punnett square method and the forked-line method.

884

views

Textbook Question

While vermilion is X-linked in Drosophila and causes the eye color to be bright red, brown is an autosomal recessive mutation that causes the eye to be brown. Flies carrying both mutations lose all pigmentation and are white-eyed. Predict the F₁ and F₂ results of the following crosses:

vermilion females x brown males

470

views