Question

5. Certain people are able to taste the chemical phenylthiocarbamide (PTC) when it is present in wet filter paper. These people are called 'tasters'. Others are unable to detect PTC and have the 'nontaster' phenotype. PTC tasting is an example of variation in sensory perception, and the genetic basis is thought to be rather simple. The ability to taste PTC is attributed to a dominant allele, denoted T, located on chromosome 7. The recessive allele is designated t. From analysis of pedigrees, 259 taster children and 278 non taster progeny were observed where one parent was heterozygous and could 'taste' PTC and the other parent was a 'nontaster'. Does this data set support the suggestion that his variation is due to a simple Mendelian pattern?

Answer 1

Parents: Tt ( taster) × tt ( nom taster)

Punnet square:

Gametes	t
T	Tt ( taster)
t	tt ( non taster)

The phenotypic ratio should be 1: 1

Taster number =(1/2)×537=268.5

Non taster =(1/2)×537=268.5

Chi square test:

Phenotype	Observed (O)	Expected (E)	(O-E)^2/E
Taster	259	268.5	(259-268.5)^2/268.5=0.336
Non taster	278	268.5	(278-268.5)^2/268.5=0.336
Total	537	537	0.672

Chi square vale from table at degree of freedom n-1=2-1=1 and at p=0.05 is 3.841

As our chi square experimental is less than chi square feom table. That's why therethis variation is due to simple mendelian genetics. There is not found significant difference between observed and expected value.

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