What is a genetic test cross used for?

What is a genetic test cross used for?

• A. To determine haplotype blocks
• B. To determine homozygosity or heterozygosity for a dominant phenotype
• C. To create new alleles
• D. To measure mutation rate

Answer: (B)

A genetic test cross is used to reveal the zygosity of a trait expressed in a dominant phenotype. By crossing the individual with a tester that is homozygous recessive for the trait, you can see how the offspring appear and infer the parent's genotype. If the parent with the dominant phenotype is homozygous dominant, all offspring will display the dominant trait when crossed with the recessive tester. If the parent is heterozygous, you'll get a mix of offspring—some show the dominant trait and some show the recessive trait—indicating the presence of a single recessive allele. This pattern lets you distinguish between homozygous dominant and heterozygous genotypes for that trait. It’s not used to determine haplotype blocks, create new alleles, or measure mutation rates, which are different genetic questions and require other approaches.

A genetic test cross is used to reveal the zygosity of a trait expressed in a dominant phenotype. By crossing the individual with a tester that is homozygous recessive for the trait, you can see how the offspring appear and infer the parent's genotype.

If the parent with the dominant phenotype is homozygous dominant, all offspring will display the dominant trait when crossed with the recessive tester. If the parent is heterozygous, you'll get a mix of offspring—some show the dominant trait and some show the recessive trait—indicating the presence of a single recessive allele. This pattern lets you distinguish between homozygous dominant and heterozygous genotypes for that trait.

It’s not used to determine haplotype blocks, create new alleles, or measure mutation rates, which are different genetic questions and require other approaches.