Question

1. Differentiate the phenotypic patterns of sex-limited and sex-influenced traits by filling in the tables below. You may want to refer to the information in chapter 5 of the text. Sex-influenced: beardedness in goats Phenotype P generation Parent Genotype Male BB Female BB +F1 generation Genotype Male phenotype Female phenotype F2 generation Genotype Male phenotype Female phenotype Sex-limited: hen feathering in chickens Phenotype P generation Parent Genotype Male Female HH hh F1 generation Genotype Male phenotype Female phenotype F2 generation Genotype Male phenotype Female phenotype

^^^ 2. How would you tell whether a novel trait is sex-influenced or sex-limited? Compare the F2 generation tables and write a sentence describing the difference between sex-limited and sex-influenced.

In males : B+B+ beardless, B+b^b is bearded, B^b B^b is bearded.

In females: B+B+ is beardless, B+b^b is beardless and B^bB ^b is bearded.

HH is hen feathering in both males and females; Hh is hen feathering in both males and females; and hh in males- cock feathering and hh in females in hen feathering.

Hope this is enough information ! Thanks.

Answer 1

Answer :-

P generation Parent Genotype Male Female BP Bb Phenotype beardless bearded #F1 generation Genotype Male phenotype Female phenotype B+BAbbearded beardless F2 generation Genotype Male phenotype Female phenotype B+B+ beadedless beardless B+BAb bearded beardless BAB^b bearded | bearded Sex-limited: hen feathering in chickens P generation Parent Genotype Male hh Female HH Phenotype | cock feathering hen feathering Fi generation Genotype Male phenotype Female phenotype Hh hen feathering hen feathering F2 generation Genotype Male phenotype Female phenotype HH Then feathering hen feathering Hh hen feathering hen feathering hh cock feathering hen feathering

Sex influenced trait :- determined by autosomal gene.

Traits are influenced by sex i.e alleles are dominant in one sex and Recessive in apposite sex.

Here heterozygous phenomenon is present i.e men heterozygous for gene shows the trait whereas heterozygous females don't.

Sex limited trait:- this are mainly autosomal.

Traits are expressed only in one gender i.e trait has zero penetrance in apposite sex.

On comparing f2 offspring of both the examples we came to the conclusion that

In second example cock feathering is only present in male therefore it is a sex limited trait.

And in first example ,only male follows the heterozygous phenomenon i.e heterozygous male showing the trait (bearded) therefore it is sex influenced trait.