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The CORRECT choice is (d) Endoplasmic RETICULUM

Explanation: The endoplasmic reticulum is not responsible for the formation of chromosomes. Chromosomes are made up of proteins, DNA, and RNA. The loss or gain of a segment of DNA often CAUSES the alternation of chromosomes.

The correct answer is (a) Deletion

Explanation: The removal of ONE or more bases from the NUCLEOTIDE CHAIN is also known as deletion. Deletion is a TYPE of frame-shift mutation. If we ADD one or more bases in a nucleotide chain, then it is called insertion.

The correct option is (b) Sickle cell ANAEMIA

The best explanation: Sickle cell anaemia is a CLASSIC example of point MUTATION. Point mutation generally means that when a SINGLE base pair of DNA changes, a gene mutation occurs that CAUSES the alternation of DNA.

The correct choice is (d) Colourful mutations

To explain I would SAY: Mutations are of three different TYPES DEPENDING upon their CAUSE and environment. The three types are:

i. Gene mutation

ii. Chromosomal aberrations

iii. Genomatic mutations

The CORRECT option is (b) Continuous

Explanation: Mutations are not continuous. Instead, mutations are discontinuous VARIATIONS in the genotype and phenotype of an organism. This is DUE to the changes in chromosomes and DNA. Mutations are sudden and they are a cause of the VARIATION in DNA.

Right answer is (a) Haplodiploid

The explanation: Honey BEES EXHIBIT a haplodiploid type of sex-determination system. This type of system has SPECIAL characteristic features LIKE the males produce sperms by mitosis. The male individuals do not have a father and thus cannot have sons, but can have a grandfather and a grandson.

Right OPTION is (c) HONEY bees

For explanation I WOULD say: The female PROGENY of a honey bee DEVELOPS from the union of a sperm and an egg whereas a male progeny develops from an unfertilised egg by the means of parthenogenesis. This means that the males have half the number of chromosomes than that of a female.

The correct OPTION is (b) Grasshopper

The explanation: Grasshoppers do not show FEMALE heterogametic conditions. BUTTERFLIES, moths, and birds show female heterogametic conditions where female individuals PRODUCE two different kinds of gametes.

Right option is (d) Grasshoppers

The best I can explain: Grasshoppers do not show XY TYPE of male heterogametic condition. XY type of male heterogametic condition is SHOWN by a number of insects like Drosophila and MAMMALS including human beings and elephants, the males in this type bear two types of SEX CHROMOSOMES- X and Y type.

Correct answer is (a) Testis determining FACTOR

For explanation I would say: TDF stands for testis determining factor. TDF is essential for the DEVELOPMENT of male sex organs and if it is not PRODUCED in the body then it LEADS to the formation of the female sex organ.

Right answer is (b) 50%

The best EXPLANATION: The probability of having a GIRL child in the sixth pregnancy, where the first five progenies were MALE is 50%. As humans SHOW XY type of male heterogamety, where 50% sperms carry 22+ X chromosomes and the other 50% carry 22+Y chromosomes, therefore in each pregnancy there is 50% probability of either a male or a female child.

Right choice is (c) Grasshopper

To explain: In a grasshopper, MALE and female individuals have a different number of chromosomes because grasshoppers exhibit XO type of male heterogamety where 2 kinds of SPERMS are formed- ONE with X-chromosome and the other with no SEX chromosome.

Right option is (B) Sperm

To elaborate: When the condition of male heterogamety is present, then sperm determines the sex of the offspring because two KINDS of sperms are present, one with X-chromosome and the other with Y-chromosome. EGGS of an individual are the same as both of them CONTAIN 22+ X CHROMOSOMES.

Right option is (d) Birds

Best explanation: Birds do not SHOW MALE heterogametic conditions. Instead, they show the female heterogametic condition. Male heterogametic condition is characterised by male individuals producing TWO DIFFERENT types of gametes.

The correct choice is (a) False

The best I can explain: Henking was studying SPERMATOGENESIS in insects where he OBSERVED that only 50% of the sperms received a structure which he later termed as ‘X body’. But he could not explain the SIGNIFICANCE of this body.

The correct option is (a) STEVENS

Explanation: Stevens was the scientist who first discovered Y-chromosome. Many scientists concluded that the ‘X body’ which was discovered by HENKING was a chromosome. Therefore, in 1905, X and Y chromosomes were named as SEX chromosomes by Stevens and WILSON.

Right OPTION is (c) Henking

Easiest explanation: The foundation of the chromosomal basis of SEX determination was laid down by Henking in 1891. He STUDIED a specific nuclear structure THOUGH SPERMATOGENESIS in a few insects.

The correct choice is (c) PATTERN baldness

To elaborate: Pattern baldness is not an example of a holandric TRAIT. Holandric traits are the Y-linked traits that are inherited from MALE parent to male progeny only. These include porcupine skin, HYPERTRICHOSIS, Testes determining factor, ETC.

Right answer is (d) PATTERN baldness

The explanation is: Pattern baldness is an EXAMPLE of a sex-INFLUENCED trait. These traits are controlled by those genes which are influenced by the sex of the bearer. These genes are known as autosomal genes.

Right option is (a) Grasshopper

To explain: Grasshopper does not SHOW and environmental MECHANISM of sex DETERMINATION. It shows the CHROMOSOMAL basis of sex determination. The environmental mechanism of sex determination is SHOWN by Bonnelia, Crepidula, and Ophryotrocha.

The CORRECT ANSWER is (b) Silk MOTH

Explanation: Gynandromorphism is seen in Silk moth and Drosophila. It gets developed due to the accidental loss of the X-chromosome from a 2A + XX type of CELL during the process of mitosis.

The correct OPTION is (c) Gynander has PATCHES of tissues of other sex on it

The BEST I can explain: A gynander DIFFERS from a gynandromorph in the fact that a gynander maybe a male or female with patches of tissues of other sex on it while gynandromorph is an individual with the one-HALF body as male and the other half as a female.

The correct ANSWER is (c) 1.5

The BEST I can explain: The X/A ratio is the ratio of the number of X-chromosomes and the set of autosomes. The X/A ratio of SUPER FEMALES of Drosophila is 1.5. The X/A ratio of normal females, intersex, and super males of Drosophila is 1, 0.67, and 0.33 respectively.

Correct answer is (b) False

The best I can EXPLAIN: The Y-chromosome does not PLAY any role in the sex DETERMINATION of Drosophila. According to C.B. BRIDGES, the ratio between the number of X-chromosome and the SET of autosomes determines the sex of Drosophila.

Right answer is (d) Phenylalanine

Best explanation: PHENYLKETONURIA is caused DUE to the ACCUMULATION of phenylalanine in the brain of the AFFECTED individuals. Phenylalanine and its derivative are also excreted through the urine because they are POORLY absorbed by the kidneys.

Correct answer is (C) Phenylalanine hydroxylase

For explanation: The individual which is affected by phenylketonuria lacks a liver enzyme CALLED phenylalanine hydroxylase which is responsible for converting phenylalanine, an AMINO ACID into tyrosine, another amino acid.

Right choice is (b) False

Explanation: Phenylketonuria is not a sex-linked trait. INSTEAD, it is an INBORN error of metabolism which is also inherited as an autosomal RECESSIVE trait which MEANS this disease will only OCCUR in a progeny if it carries both the recessive genes from the parents.

The correct answer is (c) White URINE

For explanation: White urine is not a symptom of PHENYLKETONURIA. Phenylketonuria is a disease that is CAUSED by a single gene mutation and is characterised by mental retardation, reduction in hair, BLACK urine, and skin pigmentation.

The correct option is (C) PHENYLKETONURIA

The BEST I can explain: PKU stands for phenylketonuria. This disease is caused by a pleiotropic gene where a single gene mutation takes place. The gene which CODES for PHENYLALANINE hydroxylase gets mutated.

The correct answer is (b) Effect of a gene on METABOLIC pathways

The EXPLANATION is: Pleiotropy is the phenomenon by which a SINGLE gene affects different metabolic pathways and these different metabolic pathways result in different PHENOTYPES.

The correct answer is (a) A single gene can exhibit multiple expressions

To explain I WOULD say: Pleiotropy is different from polygenic INHERITANCE due to the FACT that a single gene can exhibit multiple phenotypic expressions whereas in polygenic inheritance multiple GENES control a single CHARACTER.

The correct choice is (d) Blood groups in humans

The best EXPLANATION: Cob LENGTH in maize, HEIGHT in humans, human intelligence, milk and meat production, height in humans and size, shape and NUMBER of seeds and fruits in plants are some of the common examples of quantitative traits.

The CORRECT answer is (b) Intermediate phenotypes are more frequent

Explanation: We can draw two conclusions by STUDYING a histogram. These are that in a polygenic INHERITANCE, the EXTREME phenotypes are rare and the intermediate ones are more frequent.

Right choice is (c) HISTOGRAM

For explanation I would say: We can study the frequency distribution of skin COLOUR in the form of a bell-shaped NORMAL distribution curve which is also REPRESENTED by a Histogram.

Right CHOICE is (b) False

Explanation: Davenport was a scientist who demonstrated that six genes are involved in CONTROLLING the skin COLOUR in human beings. He also showed that skin colour can only be STUDIED in a POPULATION.

Right OPTION is (c) Number of dominant GENES

Best explanation: The amount of MELANIN produced in the skin of HUMANS is always proportional to the number of dominant genes. The effect of all the genes that are responsible for the skin colour is additive.

The correct option is (a) Number of dominant alleles

The BEST EXPLANATION: When we CROSSED a red and WHITE kernelled VARIETY of wheat, we saw that all the red kernels do not exhibit the same shade of redness. The degree of redness was found to depend upon the number of dominant alleles.

The correct CHOICE is (B) Red and white kernelled VARIETY

Easiest explanation: In order to study the KERNEL colour of wheat, H. Nilsson crossed red kernelled variety with a white kernelled variety of wheat. He found out that the kernel colour in wheat is determined by AA and BB genes.

Right answer is (c) Black

Easy explanation: The five PHENOTYPIC classes OBTAINED while crossing red and WHITE kernelled wheat variety are: the EXTREME red, deep red, intermediate red, LIGHT red and white.

Right OPTION is (c) 1: 4: 6: 4: 1

The EXPLANATION: The ratio of F2 generation when red and white kernelled wheat VARIETIES were crossed was obtained as-1: 4: 6: 4: 1. Also, five DIFFERENT phenotypic classes were obtained.

The correct answer is (b) H. Nilsson-Ehle

The best I can explain: H. Nilsson-Ehle in 1908 and East in 1910 DEMONSTRATED the SEGREGATION and ASSORTMENT of genes that controlled the QUANTITATIVE traits, e.g., Kernel colour in wheat and corolla LENGTH in tobacco.

Correct answer is (a) Skin colour in humans

Explanation: Skin colour in humans is a CLASSIC example of polygenic INHERITANCE as this trait is controlled by three or more genes and we can SEE that this trait is not so distinct amongst the HUMAN population and is spread across a gradient.

Right option is (B) False

Explanation: HEIGHT of humans is a polygenic trait and is THEREFORE not limited to only TALL and short people. Instead of two distinct ALTERNATIVE traits, a range of all the possible heights is present in a human population.