Test: Pedigree Analysis (NCERT) - NEET MCQ

• In the given cross, passing of disease is from carrier female to male progeny (criss-cross inheritance). Any trait that shows criss-cross inheritance is located on the sex chromosome.
• Presence of a single recessive gene i.e. Xc in carrier individuals (XXC) does not cause the disease, thus the trait is recessive.

Mendelian disorders are mainly determined by alterations or mutations in a single gene and are transmitted to the offspring based on the principles of inheritance, which can be traced using pedigree analysis.

Genotypes of different individuals in the given pedigree chart can be illustrated as:

In pedigree analysis, solid symbol shows affected individuals.

The assertion is true because a man affected by hemophilia will pass his affected X chromosome to all of his daughters, making them carriers of the disease. The reason is also true and provides the correct explanation because hemophilia is indeed a sex-linked recessive disorder carried on the X chromosome, and males pass their single X chromosome to all their daughters.

Given pedigree chart for fused ear lobes (autosomal recessive trait) can be explained as follows:

The given trait cannot be sex-linked as sex-linked traits follow criss-cross inheritance and in the given pedigree, no criss-cross inheritance is being followed. The trait exhibited in pedigree chart is autosomal recessive. An autosomal recessive trait appears in case of marriage between two heterozygous individuals (Aa x Aa=3Aa+1aa), a recessive individual with hybrid (Aa x aa=2Aa+2aa) and two recessives (aa x aa= all aa). It expresses its effect only in pure or homozygous state.

If the trait had been controlled by dominant gene, then one of the parent must have possessed the dominant gene and hence the disease.

Given pedigree can be illustrated as follows:

Autosomal domionant trait can express its effect in homozygpous as well as heterzygous condition.

Albinism is hereditary lack of pigmentation in an organism. It is an autosomal recessive disorder. Albino humans lack dark pigment melanin in their skin, hair or eyes. The allele responsible is recessive to allele for normal pigmentation. Father's and mother's genotype should be Aa. They both are carriers of the disease.

The chances of this couple's fifth child being an albino are 1 in 4.