Assume that a probe can hybridize to alleles of two, unlinked minisatellite orva

Question

Assume that a probe can hybridize to alleles of two, unlinked minisatellite orvariable number of tandem repeats (VNTR) loci in humans. A woman has alleles of 9 kband 13 kb at one locus and is homozygous for an allele of 7 kb at the second locus. Herhusband has alleles of 8 kb and 10 kb at one locus and is homozygous for a 6 kb allele atthe second locus. They have a child whose DNA is fingerprinted for these two loci bySouthern blotting and subsequent hybridization with the probe specific for these two loci.What is the probability that the child’s DNA will show bands of 7 kb, 9 kb, 6 kb, and 10kb? (Assume no new mutations are produced by either parent.)

answer should be =1/4

not sure how to solve this...

Explanation / Answer

This can be solved simply by using a punnet square.

The possible combination of gametes produced by Male parent:

alleles

9

13

7

7/9

7/13

7

7/9

7/13

The probability of gametes with 7/9 kb STR is 0.5 (2 out of four - 1/2 or 0.5)

Similarly, the possible combinations of gametes produced by Female parent are:

alleles

8

10

6

6/8

6/10

6

6/8

6/10

The probability of gametes with allele combination 6/10 is 0.5 or 1/2

From the product rule, the probability of the child inheriting the alleles 7/9 and 6/10 is 1/2 x 1/2 = 1/4

or the probability is 0.25

alleles

9

13

7

7/9

7/13

7

7/9

7/13

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