Two linked genes are 24 map units apart…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
Two linked genes are map units apart. A plant that is AB over ab is crossed with a plant that is aabb. The cross gives offspring.
- How many offspring are parental?
- How many offspring are recombinant?
- How many offspring are Aabb?
Need a reminder? The key ideaShow
Linked genes lie on the same chromosome. In a test cross of a double heterozygote with a double recessive, the recombinant offspring are the small classes. The recombination frequency is the number of recombinants divided by all the offspring, in per cent, and one per cent is one map unit. Of three linked genes, the two that are farthest apart are the end genes.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. map units, so a recombination frequency of . Total .
Plan. Find the recombinants first. The rest are parental. Then split each group into its two equal kinds.
Step 1. (b) Recombinants: offspring.
Step 2. (a) Parental: offspring.
Step 3. (c) The two recombinant kinds, Aabb and aaBb, are equal, so Aabb is offspring. Each parental kind (AaBb and aabb) is .
Answer: parental; recombinant; Aabb.
Check. .
Watch out. The two parental kinds are not each equal to the recombinant kinds. With linked genes the four classes are not equal.
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