Two genes, A and B, are located on the same chromosome. In a testcross between an individual with the genotype AaBb and one with aabb, the following offspring were produced:

380 AaBb

370 aabb

120 Aabb

130 aaBb

Based on these results, what can be concluded about the relationship between genes A and B?

Question

Two genes, A and B, are located on the same chromosome. In a testcross between an individual with the genotype AaBb and one with aabb, the following offspring were produced:

380 AaBb

370 aabb

120 Aabb

130 aaBb

Based on these results, what can be concluded about the relationship between genes A and B?

BlackTom AI · Accepted Answer

The problem presents a testcross between AaBb and aabb, with the following offspring counts: 380 AaBb, 370 aabb, 120 Aabb, and 130 aaBb.

First, examine the parental (non-recombinant) phenotypes. In a testcross, the parental phenotypes are the most frequent classes, since they result from no or very little recombination between linked genes. Here, the two most frequent classes are AaBb (380) and aabb (370). These align with the parental chromosome combinations AaB- and a-b- in the coupling phase.

Next, look at the recombinant phenotypes. The less frequent classes are Aabb (120) and aaBb (130). These arise from a crossover event between the two genes during meiosis, producing new allele combinations not present in the parental genotype.

To quantify linkage, compute the recombination frequency (RF):
- Total offspring = 380 + 370 + 120 + 130 = 1000
- Recombinants = 120 + 130 = 250
- RF = (recombinants / total) × 100 = (250 / 1000) × 100 = 25%

An RF of 25% is significantly less than 50%, which indicates that the genes are not assorting independently. In other words, A and B are on the same chromosome and are linked, with crossing over between them occurring at a measurable frequency.

Interpreting the data, you can infer that there is linkage between A and B (they are on the same chromosome), and the observed recombinant classes confirm that crossing over takes place between them, albeit at a moderate rate given the 25% RF. If the genes were unlinked, you would expect roughly equal frequencies among all four classes, around 25% each, which is not what the data show here.

In summary, the pattern of parental dominance (AaBb and aabb being most frequent) together with the presence of recombinants (Aabb and aaBb) demonstrates that A and B are linked but that crossing over between them occurs, producing the recombinant offspring observed.

AGRI10051_2025_SM2 Revision Questions Weeks 1-4 UNMARKED

查看解析

登录即可查看完整答案

类似问题

A testcross is performed on an individual who is heterozygous for three linked traits. What phenotypes concerning the three genes will be found most often among the progeny?

What is the likely inheritance of alleles of two linked genes?

Which of the following statements regarding gene linkage is correct?

What is the likely inheritance of alleles of two linked genes?

Why are linked genes often inherited together?

更多留学生实用工具

考试浏览器助手

风格化写作助手

论文查重助手

文献引用助手

课堂转译助手

课堂笔记助手

Quiz搜索助手

学校历年真题

智能刷题助手

智能匹配练习

希望你的学习变得更简单