In humans, the allele N causes an abnormal shape of the patella in the knee (n i
ID: 52875 • Letter: I
Question
In humans, the allele N causes an abnormal shape of the patella in the knee (n is the normal allele). A separate gene is concerned with finger length the allele B causes abnormally short fingers, whereas b gives normal length. A study focused on people who have abnormal patellae and short fingers (N/n.B/b in genotype), having inherited the N allele from one parent and the B allele from the other parent. These N/n.B/b people mated with normal spouses producing 40 progeny, classified as follows:
Normal 3
Abnormal knees and fingers 2
Abnormal knees only 17
Abnormal fingers only 18
What ratios of parental and recombinant phenotypes would you expect if these genes are linked? Unlinked?
Use a Chi-square test to check if the genes are linked. If they are, provide a map distance for these two genes.
Explanation / Answer
Parental Genotypes- Nn Bb * nn bb
Expected Ratio
Expected ratio = 1:1:1:1
Now table for Chi square-
By using the table we get that probability is 1%. Since its less than 5%, hypothesis is rejected i.e. genes are not linked.
Parental Nn Bb nn bb Gametes NB nb Nb nB nb F1 Generation NB Nb nB nb nb Nn Bb Nn bb nn BB nn bb Abnormal knees and fingers Abnormal knees Abnormal fingers Normal