Botany MCQs for NEET — Practice Questions with Answers

The physical distance between two genes determines both the strength of the linkage and the frequency of the crossing over between two genes.The strength of the linkage increases with the closeness of the two genes. On the other hand the frequency of crossing over increases with the increase in the physical distance between the two genes.

Turner's syndrome is caused due to the absence of one of the X chromosomes i.e., 45 chromosomes total with sex chromosomes as XO. Such females are sterile as ovaries are rudimentary. Besides this, other features include lack of other secondary sexual characters, etc. 

In normal females, number of Barr bodies is one less than the number of X chromosomes. One Barr body means the female has two X chromosomes. Turner's syndrome (44 + X0) is a genetic disorder that affects only females. In this condition, cells of the affected female possess only one X chromosome, instead of two.Due to the presence of only one X chromosome, no Barr body is present in females suffering from Turner's syndrome.

Barr body is also known as sex chromatin or X chromatin. Barr body is partially inactivated and development of this facultative heterochromatin occurs in one of the two X chromosomes in interphase nuclei of human female. Any of the two X-chromosomes can become heterochromatin.

When a heterozygous individual (Aa) is crossed with a homozygous recessive individual (aa), the F1 progeny will show a 1:1 ratio of dominant and recessive phenotypes. This follows the Mendelian law of segregation, where the two alleles separate during gamete formation.

If a pea plant with violet-colored flowers (heterozygous, Vv) is crossed with a plant having white-colored flowers (vv), the progeny will show a 1:1 ratio of violet and white flowers. Since 50% of the progeny had white flowers, the parent with violet flowers must be heterozygous (Vv).

E. coli contain single chromosome. So, the number of linkage groups in E. coli is 1.

 Holandric genes  are the Y-linked genes. The Y-linked type sex-linked inheritance is performed by those genes which are localised in the non-homologous sections of Y-chromosome and that have no alleles in X-chromosome. 

Cystic fibrosis - Produciton of thick mucous that cloge airways

Sickle cell anaemia - Defective haemoglobin in RBCs, effect on oxygen transport, tendency to form clots in vessels

Achondroplasia - Dwarfism

Huntingon's disease - Progressive deterioration of brain cells.