If A / A ·B / B is crossed with a / a ·b / b and the F1 is testcrossed, what percentage of the t

step 1 Let us talk about the first case, that is when the two genes are unlinked, the ratio in the prog

If A / A ·B / B is crossed with a / a ·b / b and the F1 is...

If $A / A \cdot B / B$ is crossed with $a / a \cdot b / b$ and the $F_{1}$ is testcrossed, what percentage of the testcross progeny will be $a / a \cdot b / b$ if the two genes are (a) unlinked; (b) completely linked (no crossing over at all); (c) $10 \mathrm{m}$.u. apart; (d) $24 \mathrm{m} .$ u. apart?

If $A / A \cdot B / B$ is crossed with $a / a \cdot b / b$ and the $F_{1}$ is testcrossed, what percentage of the testcross progeny will be $a / a \cdot b / b$ if the two genes are (a) unlinked;
(b) completely linked (no crossing over at all); (c) $10 \mathrm{m}$.u. apart;
(d) $24 \mathrm{m} .$ u. apart?

Key Concepts

Testcross

A testcross is a genetic cross between an individual showing the dominant phenotype (but with an unknown genotype) and a homozygous recessive individual. This cross is used to determine the genotype of the dominant phenotype carrier by analyzing the traits in the progeny, where the appearance of recessive traits reveals heterozygosity.

Gene Linkage

Gene linkage occurs when two or more genes are located close together on the same chromosome and tend to be inherited together. Because recombination between linked genes occurs less frequently, their segregation patterns deviate from those predicted by independent assortment.

Recombination Frequency

Recombination frequency is the measure of how often crossing over occurs between two genes during meiosis and is used to infer the genetic distance between them. It is expressed as a percentage or in map units (centiMorgans), with higher frequencies indicating greater distances.

Independent Assortment

Independent assortment is a principle that describes how genes located on different chromosomes segregate into gametes independently of one another. This results in predictable, often equal, ratios in the offspring when no linkage exists between the genes.

Crossing Over

Crossing over is the process during meiosis where homologous chromosomes exchange genetic material, creating new combinations of alleles. This is the underlying mechanism responsible for recombination, which affects the distribution of traits in the progeny, particularly for linked genes.

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