Botany MCQs for NEET — Practice Questions with Answers

The more maternal influence can be expected in the cytoplasmic inheritance (i.e., the inheritance of genes contained in the cytoplasm of a cell, rather than the nucleus). The resason is that the female reproductive cell or the egg has a large amount of cytoplasm containing many such organelles which ciontain their own genes and can reproduce independently (e.g., mitochondra and chloroplast) and whcih are consequently incorporated into the cytoplasm of all the cells of the embryo. The male reproductive cells (sperm or pollen) consist almost solely of a nucleus. Cytoplasmic organelles are thus, not inherited from the male parent. 

This is why, the cytoplasmic inheritance is also called as maternal inheritance.

Genes located on Y-chromosome are called Y-genes and their inheritance is called Y-linked inheritance. This carries the paternal influences.

A gene located in the X-chromosome is said to be X-linked and its inheritance is called X-linked inheritance. In this, a male transmits his X-chromosome only to his daughters while a female transmits one of her X-chromosomes to the offspring of both sexes. 

The types of gametes produced by a plant depend upon the number of heterozygous pair.

Number of types f gametes = Zⁿ

n = nymber of heterozygous pair

2¹ = 2

The gametes are — ABC and AbC.

Polygenic inheretance  involves the determination of a particular phenotypic characteristic by many genes, called polygenes (i.e., the group of genes influencing a quantitative characteristic), each having a small effect individually. 

The characteristics controlled in this way show continuous variation and are called polygenic characters e.g., height and skin color in humans.

The polygenic inheritance is called multifactorial inheritance or quantitative inheritance. 

the pink flower colour in Mirabilis jalapa is an example of incomplete dominance which production of male honey bee is an example of parthenogenesis.

The test cross involves the crossing of F₁ hybrid with a double recessive genotypic parent. By test cross, the heterozygocity and homozygocity of the organism can be tested. 

Thus, the offispring will be 100% dominant, if the individual which crossed with recessive parent, i.e., (tt) was homozygous dominant and ratio will be 50% dominant and 50% recessive if the individual was heterozygous dominant. in dihybrid test cross, ratio will be 1:1:1:1.

Trait is any detectable phenotypic variation of a particular inherited character.

Cri du chat is a rare syndrome (1 in 50, 000 live births) caused by a deletion on the short arm of chromosome 5, is a rare genetic disorder due to a missing portion of chromosome 5. It was first described by Lejeune in 1963. The name of this syndrome is French for "cry of the cat," referring to the distictive cry of children with this disorder. The cry is caused by abnormal larynx development, which becomes normal within larynx development, which becomes normal within a few weeks of birth. Infants with cri du chat have low birth weight and may have respioratory problems. 

Recombination is the natural process of breaking and rejoining DNA strands to produce new combination of genes and, thus, generate genetic variation. This is the phenomenon which occurs during meiosis I.

Polygenic inheritance is the inheritance pattern of a trait controlled by two or more genes. Genes may be on the same or different chromosomes and each gene may have two or more alleles. The gene expression is influenced by a variety of factors including gender, nutrition, breed, rate of growth, and amount of exercise. These traits are quantitative traits - that is, there is a wide range within the population. Such traits include height, weight, character, working abilities, and some genetic defects.

One example is height in humans - there are a larger number of phenotypes, each differing slightly from the next and forming a graduated series. Some variation in height in humans is due to environmental factors such as diet, exercise and disease. However, if the environmental factors were constant, there would still be continuous variation in height due to such things as formation and hormone levels. Themore genes that control a characteristic, the more possible gene combinations exist and the more phenotypes.

Other examples of polygenic inheritance include : skin colour in humans, colour in wheat kemels, egg weight in poultry, fleece wieght in sheep. Kemal colour in wheat is determined by two gene pairs, so called polygenes that produce a range of colors from white to dark red depending on the combination of alleles. Dark red plants are homozygous AABB and white plants are homozygous aabb. When these homozygotes are crossed the F₁ offspring are all double heterozygotes AaBb. Thus crossing individuals with the phenotype extremes yeild offspring that are a 'blend' of the two parents.

Test cross is across made to identify hidden recessive alleles in an individual of unknown genotye. This individual is crossed with one that is homozygous for the allele being investigated (i.e., a homozygous recessive). The homozygous recessive individual may be the parent of the individual being investigated.

Turner's syndrome is characterised by the monosomy of XO type. It is characterized by a lack of ovaries an menstrual cycle. Affected women are sterile and lack secondary sexual characteristics, although the exrternal genitalia are present. The syndrome is named after the US endocrinologist H.H. Turner (1892-1970), who first described it. 

Down's Syndrome is a congential form of mental retardation due to a chromosome defect in which there are three copies of chromosome no. 21 instead of the usual two. The affected individual has a short broad face and slanted eyes (as in the MOngolian races), short fingers, and weak muscles. Down's syndrome can be detected before birth by aminocentesis. It is name after the British physician John Down (1828-96), who first studied the incidence of the disorder. Klinefelter's syndrome is characterised by trisomy (XXY). These are male individuals, who are phenotypically fairly normal but have a fairly low sperm count and therefore sterile.