Question

You cross true breeding adults for traits that are controlled by the a and b loci (the wild type alleles for both loci are dominant) and then perform a test cross against their offspring. The results you obtain from this test cross are below.

Baby Phenotype	Observed # of babies
a+b+	965
ab	944
a+b	206
ab+	185
	Total = 2300 babies

a) Are a and b linked? How can you tell? Use a chi-squared test show that the observations deviate significantly from expectations based on Mendelian rules of inheritance.

b) Were the alleles in cis or trans configuration in the P generation? How can you tell?

c) What is the map distance between a and b?

d) Which one comes first?

Answer 1

D. We cannot tell which gene comes first. We can only tell about the distance between them.

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