Heredity And Variation 4 - From Past 28 Years Questions Free MCQ Practice

Parents : AB/ab × ab/ab

Aneuploidy is numerical change in the chromosome number in the genome. Euploidy is the phenomenon of having multiple or more than twice the number of genome.

One bar body is present in each somatic cell of female (XX).

Sickle cell anaemia is a genetic disorder caused by a defective allele on chromosome 11. Hemophilia is a sex linked recessive disorder. Down's syndrome is caused by trisomy of the 21^st chromosome.

AIDS is a viral disease. Syphilis and gonorrhoea are both sexually transmitted diseases. Colour blindness is a sex linked disease.

A dominant gene would lead to the expression of its phenotype irrespective of the fact whether its allelic gene is dominant or recessive.

Sex linked disorders follow criss-cross inheritance pattern that affected father passes it on to their daughters. The daughters receive one of their X - chromosome from their fathers.

a − b = 20 %, b − c = 28 %, a − c = 8%

Percent crossing over between two genes is proportional to the distance between them. 

Calvin Bridges demonstrated that in Drosophila, the sex is determined by ratio of the number of X chromosomes to the sets of autosomes.

Male sterility in plants can be controlled by nuclear genes or cytoplasm or by both. Three different mechanisms for control of male sterility in plants are :
(i) Genetic male sterility;
(ii) Cytoplasmic male sterility;
(iii) Cytoplasmic genetic male sterility. In Maize the genes for cytoplasmic control of male sterility are located in cytoplasm.

Correct option is

C

They cannot interbreed in nature.

The term species evolves from word specific means only those group of plants or animals come under one species which can interbreed and produce fertile offsprings naturally. N. tobacum and N. sylvestris cannot produce flowers naturally have different photoperiods, hence they cannot belong to the same species. Thus the correct answer is 'They can not interbreed in nature.'

Yellow seed colour is dominant over green seed colour.

The seventraits are now know to be present on 4 chromosome. But they do not show linkage, because of large distances between them on the chromosome.

Dihybrid cross is made between individuals having contrasting traits in order to study the inheritance of two pairs of alleles. Test cross is a back cross between individual with a dominant trait and its recessive parent to know whether the individual is homozygous or heterozygous for the trait.

Mapping of genes on chromosomes is based on the assumption that genes are arranged on the chromosome and that the percentage of crossing over (recombination frequency) between two genes is an index of their distance apart. Distances between genes is expressed as map units, where, one map unit 

  Traits or characters which develop only in one sex are called sex-limited characters. They are produced and controlled by the genes which may be located on autosomes in only one sex, eg. Moustaches and beards in human males, breast in human females, milk secretion in human females.

50% of ova will have (n + 1) chromosome which would, on fertilisation, yield abnormal zygotes (n + 1) + (n) = 2n + 1.

The lack of inde pendent assor tment in sweet pea and Drosophila is due to linkage. 

Males have only one X - chromosome. Hence any gene present on the lone X - chromosome expresses itself  in males. Females have two X- chromosomes . The mutant  allele must be present on both the X-Chromosomes  to express itself phenotypically. If only one copy of allele present, then the female only becomes a carrier showing no external manifestation of the gene. Sublethal condition can never arise in males.

Chance of getting a = 1/2
Chance of getting b = 1/2
Chance of getting h = 1/2
Chance of getting sperms with 

Normal woman with colour blind father would be a carrier

50% of the sons would be colour blind.

Mitochondria is an organelle present in the cytoplasm. A zygote receives its cytoplasm from the female parent gamete. Hence in the given question, the F₂ progenies do not receive the mitochondrial genome from the male parent and mutation is not passed to progenies.