GENETICS Compulsive channel switching (i.e. channel surfing) is found to be caus
ID: 54490 • Letter: G
Question
GENETICS
Compulsive channel switching (i.e. channel surfing) is found to be caused by a recessive (but highly prevalent) gene on the X chromosome (cs). Also located on the X chromosome are two other recessive genes - one that causes an addiction to watching football on TV (fba), and one that causes excessive burping in public (bp). The location of these genes on the X chromosome are 25 (cs/ cs+), 43 (fba/fba+) and 76 (bp/bp+) map units. The level of interference over this linkage group (i.e. the Coefficient of Interference) is 0.15. A normal female has the genotype cs+fba bp+ /cs fba+bp. What is the probability that she will produce a gamete that contains all three recessive alleles?
Explanation / Answer
cs+fba bp+ / cs fba+bp = 8 possible genotypes
Genotypes Crossovers Number Total
cs+fba bp+ None, the parental genotypes 479 952
cs fba+bp None, the parental genotypes 473
cs+fba+bp Single, between locus cs+ and the others 15 28
cs fba bp+ Single, between locus cs+ and the others 13
cs+fba bp Single, between locus bp+ and the others 9 18
cs fba+bp+ Single, between locus bp+ and the others 9
cs+fba+bp+ Double recombinants 1 2
cs fba bp Double recombinants 1
Totals 1000
The probability that she will produce a gamete that contains all three recessive alleles is cs fba bp = 2
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