# Best answer: When two heterozygous parents are crossed in a dihybrid cross what fraction of offspring will be homozygous recessive?

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## How many heterozygous are in a dihybrid cross?

A dihybrid cross describes a mating experiment between two organisms that are identically hybrid for two traits. A hybrid organism is one that is heterozygous, which means that is carries two different alleles at a particular genetic position, or locus.

## When crossing two parents that are both heterozygous at a single locus what is the expected genotypic ratio of the offspring?

The expected genotype ratio when two heterozygotes are crossed is 1 (homozygous dominant) : 2 (heterozygous) : 1 (homozygous recessive). When a phenotypic ratio of 2 : 1 is observed, there is probably a lethal allele.

## What type of cross produces a 1 1 1 1 phenotypic ratio?

In the monohybrid cross, a testcross of a heterozygous individual resulted in a 1:1 ratio. With the dihybrid cross, you should expect a 1:1:1:1 ratio!

## What fraction of offspring from the cross AaBb AaBb will be heterozygous for both traits?

In a dihybrid cross, AaBb x AaBb, what fraction of the offspring will be homozygous for both recessive traits? 1/4 of the gametes of each parent will be ab. The fraction of the offspring homozygous for both recessive traits will be 1/4 times 1/4, or 1/16.

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## When you cross 2 heterozygous individuals in a dihybrid cross what fraction of the offspring will be dominant for both traits?

Explanation: When crossing organisms that are heterozygous for two traits, the result is a dihybrid cross. The phenotypic ratio of a heterozygous dihybrid cross for autosomal (none-sex-linked) traits is always 9:3:3:1. Nine offspring will show both dominant traits (AABB, AaBB, AABb, AaBb).

## What fraction of the cross will be recessive for both traits?

The correct answer is 1/16. A dihybrid cross results in a phenotypic ratio of 9:3:3:1. The 1 in the ratio is indicative of the double recessive phenotype, with a homozygous recessive genotype for both traits. Thus, only 1/16 of the offspring will display both recessive phenotypes.

## What are the heterozygous genotypes?

(HEH-teh-roh-ZY-gus JEE-noh-tipe) The presence of two different alleles at a particular gene locus. A heterozygous genotype may include one normal allele and one mutated allele or two different mutated alleles (compound heterozygote).