Multiple Choice Questions (MCQs): Inheritance & Variation - NEET MCQ

If a plant with RRTt genotype is crossed with a plant that is rrtt 50% of the offspring will be tall with red fruit.

AB blood group of mother have two alleles IA and IB. The heterozygous B blood group of father has alleles IB and i. The possible outcome are IA IB,IAi,IBIB and IBi. That form AB, A, B and B blood group respectively.

Two genes p and q showing 1.3% of recombination while other two genes x and y show 37.2 percent of recombination. p and q genes are present close to each other as they show less recombination percentage.

An organism with lethal mutation may not even develop beyond zygote stage due to change in gene but all kinds of mutations are not lethal. Mutation is main source of variation essential for evolution.

Monohybrid cross with incomplete dominance shows both genotypic and phenotypic ratio as same (1 : 2 : 1).

Genotypic ratio - 1(AA):2(Aa):1(aa)
Phenotypic ratio - 1(Red):2(Pink):1(White)

The expected Phenotypes in the F2 generation of the cross RRYY x rryy is Round-yellow; wrinkled-yellow; round-green and wrinkled-green in 9:3:3:1 similar to dihybrid results.

In birds male contain a pair of Z chromosome as sex chromosome besides autosomes while female contain one Z and one W chromosome.

Crossing over occurs at four strand stage of panchytene of meiosis-I. Each homologous chromosome has two stands. Exchange of gene occurs during this period.

Deviation from Medelism’s occurs due to co-dominance, multiple alleles, incomplete dominance in which single gene is not completely dominant over the other to produce dominant trait.

Thalassemia can be classified according to which chain of the haemoglobin molecule is affected. In α Thalassemia, production of α globin chain is affected while in β Thalassemia, production of β globin chain is affected. α Thalassemia is controlled by two closely linked genes HBA1 and HBA2 on chromosome 16 of each parent and it is observed due to mutation or deletion of one or more of the four genes. The more genes affected, the less alpha globin molecules produced. While β Thalassemia is controlled by a single gene HBB on chromosome 11 of each parent and occurs due to mutation of one or both the genes.

Chromosome theory of XY sex determination was proposed by Wilson and Stevens.

The crossing of F1 to any one of the parents is called back cross. It is used to check the purity of individual. When F1 is crossed with recessive parent, it is called test cross.

A patient with Down’s syndrome (karyotype 47,XX,+21) might exhibit features such as many loops on fingertips, congenital heart disease, and a big and wrinkled tongue. Mucus clogging of airways is not typically associated with Down’s syndrome.

In human beings, 23 pairs of chromosomes are present in diploid cells.
Twenty two pairs of chromosomes are equal in male and female but a pair sex chromosome is different in them. Male contain XY and female contain XX sex chromosome.

Linkage is the physical association of two genes present on same chromosome. Genes located close to each other have high linkage percentage.

When two pea plants having red (dominant)c coloured flowers with unknown genotype are crossed, the 75% red and 25% white flowered plants will be produced by following the law of Mendel. This is possible only if the parents are heterozygotes. 

Independent Assortment describes how different genes independently separate from one another when reproductive cells develop. Independent assortment of genes and their corresponding traits was first observed by Gregor Mendel. Recombination occurs during meiosis and is a process that breaks and recombines pieces of DNA to produce new  combinations of genes. Recombination scrambles pieces of maternal and paternal genes, which ensures that genes assort independently from one another.

Male birds bears ZZ sex chromosome as sex determination is ZO type, in which ZZ is male and ZO is female.

According to question, tallness (T) is dominant over dwarfism (t) and red colour (R) is dominant over white (r) fruit colour.

Parent Generation; P₁ : RRTt  x  rrtt

F₁ generation :

Phenotypic ratio = 1  (tall plant, red fruit)         
: 1 (dwarf plant, red fruit)
; thus, percent of tall plant with red fruit is 50%.