NEET Practice Questions (MCQs) with Answers & Solutions

One of Mendel's key conclusions from his experiments with pea plants was the concept of inheritance in discrete units or genes, rather than a 'blending' of traits. He observed that traits are passed down from parents to offspring as distinct, indivisible units.

An organism with two copies of the same allele for a particular gene is said to be homozygous for that trait. Homozygous individuals have identical alleles, either dominant or recessive, for the gene in question.

Complete dominance occurs when the heterozygote phenotype is indistinguishable from that of the homozygous parent. The heterozygote phenotype differs from the phenotypes of both homozygote parents is a demonstration of partial or incomplete dominance. Codominance occurs when the phenotypes of both parents are simultaneously expressed in the same offspring organism.

Given n alleles at a locus, the number genotypes possible is the sum of the integers between 1 and n: With 2 alleles, the number of genotypes is 1 + 2 = 3. 3 alleles there are 1 + 2 + 3 = 6 genotypes. 4 alleles there are 1 + 2 + 3 + 4 = 10 genotypes.

For 7 alleles = 1+2+3+4+5+6+7 =28.

Diseases caused by the malfunction of a pleiotropic gene, which affects multiple traits, are often called syndromes. Pleiotropic genes have widespread effects on various aspects of the organism's development and function. When these genes malfunction, it can lead to a constellation of symptoms and phenotypic effects, collectively referred to as a syndrome.

In incomplete or reduced penetrance, some individuals will not express the trait even though they carry the allele.

NCERT Page No. 83

NCERT Page No. 84