21. Consider the trait used in class. \"Tongue rolling\" is determined by a sing

Question

21. Consider the trait used in class. "Tongue rolling" is determined by a single gene with two alleles "T" allele - the ability to roll tongue, dominant, allele frequency 0.447 "t" allelecannot roll tongue, recessive, allele frequency 0.553 If this gene were not autosomal, but was instead located on the X chromosome please answer the questions below. a) Frequency of males who can roll their tongues? b) Frequency of females who cannot roll their tongues? c) If there were 100 individuals (50 males and 50 females) in our class how many would be able to roll their tongues? Please show your work.

Explanation / Answer

Since females have 2 X chromosomes normal Hardy weinberg equation applies to them.

According to Hardy weinberg equilibrium, the allele frequencies p (for dominant allele) and q (for recessive allele) will give the value of genotype frequencies by the equation

(p+q)2 = p2+2pq+q2 Now here the genotypes can be calculated as

(allele T) p=0.447

(allele t) q=0.553

genotype frequency of homozygous dominant TT = p2 = 0.447X 0.447

genotype frequency of heterozygous individuals Tt = 2pq= 2X0.447X0.553

genotype frequency of homozygous recessive individuals tt = q2 = 0.553X0.553

Since males have only one X chromosome, genotype frequencies among males will be same as the allelic frequencies

So T= p= 0.447

and t=q= 0.553

so frequency of males who can role their tongues is same as the frequency of the allele that enables this trait (T)that is 0.447

Frequency of females who cannot role their tongue will be those who are homozygous recessive genotype for this trait, that is tt

Frequency of tt individuals among females is (0.553)2 = 0.305

Frequency of femalew who can role their tongues= 1- frequency of females who cannot (1-.3058)or frequency of homozygous TT plus frequency of heterozygous TT(.199 + .4943) which is around 0.694

So in a class of 50 females 50 X 0.69 females can role their tongue= 34.5 or 35 females.

and in a class of 50 males 50 X 0.447 males can role their tongue= 22.35 or 22 males

so in a class of 100 , 57 can role their tongue

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