In cattle, an autosomal mutation called Dexter produces calves with short stature and short limbs. Embryos that are homozygous for the Dexter mutation have severely stunted development and either spontaneously abort or are stillborn. What progeny phenotypes do you expect from the cross of two Dexter cows? What are the expected proportions of the expected phenotypes?

Verified step by step guidance

1. Step 1: Understand the genetic basis of the Dexter mutation. The mutation is autosomal and exhibits incomplete dominance. Heterozygous individuals (Dd) display the Dexter phenotype, while homozygous dominant individuals (DD) are non-viable and homozygous recessive individuals (dd) are normal.
2. Step 2: Set up a Punnett square for the cross between two Dexter cows, both of which are heterozygous (Dd). The possible gametes from each parent are D and d.
3. Step 3: Fill in the Punnett square by combining the gametes from each parent. The resulting genotypes will be: DD, Dd, Dd, and dd.
4. Step 4: Analyze the phenotypes associated with each genotype. DD embryos are non-viable and will not survive. Dd individuals will have the Dexter phenotype, and dd individuals will have the normal phenotype.
5. Step 5: Calculate the expected proportions of the phenotypes. From the Punnett square, the ratio of genotypes is 1 DD : 2 Dd : 1 dd. Since DD individuals are non-viable, the surviving progeny will consist of 2 Dexter (Dd) : 1 normal (dd), or 2/3 Dexter and 1/3 normal.

Key Concepts

Autosomal Mutation

An autosomal mutation occurs in genes located on the autosomes, which are the non-sex chromosomes. In the case of the Dexter mutation in cattle, it affects growth and development, leading to phenotypes such as short stature. Understanding how these mutations are inherited is crucial for predicting the outcomes of genetic crosses.

Homozygosity and Phenotypic Expression

Homozygosity refers to having two identical alleles for a particular gene. In the context of the Dexter mutation, homozygous individuals exhibit severe developmental issues, leading to spontaneous abortion or stillbirth. This concept is essential for predicting the phenotypic ratios in offspring when crossing two Dexter cows, as it influences the viability of the progeny.

Punnett Square and Expected Ratios

A Punnett square is a tool used to predict the genotypic and phenotypic ratios of offspring from a genetic cross. By using the genotypes of the parent cows (e.g., homozygous Dexter vs. heterozygous), one can determine the expected proportions of phenotypes in the progeny. This method is fundamental for understanding inheritance patterns and calculating the likelihood of specific traits appearing in the offspring.