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Right choice is (c) X chromosomes are inactivated

To explain: Due to dosage COMPENSATION only ONE X CHROMOSOME in XXY says active. So the EFFECT of excess X chromosome is somewhat mitigated. In autosome there is no such inactivation and excess of GENE products leads to lethality.

The correct answer is (a) XIST

The best I can EXPLAIN: The X inactive SPECIFIC transcript (XIST in humans/ Xist in mice) gene, is located in the XIC, it’s expressed exclusively from the inactive X chromosome, PRODUCING a 17 kb non-coding RNA that is not translated. Ribosome GENES are in nucleolus.

The correct option is (d) 1^st meiotic division of father

For EXPLANATION I would say: The non DISJUNCTION must be in the male parent as the child was not COLOR blind. This is possible only if one X chromosome was normal which here came from father. ALSO as the disjunction produced XY and not two copies of same chromosome it must have been in 1^st division.

The correct answer is (b) False

Easiest EXPLANATION: Both 1^st and 2^nd MEIOTIC non-disjunction in female can give AA+ XXX combination. Also 2^nd meiotic non-disjunction in male gamete where two X chromosome moves to same pole can also give this result.

Right option is (b) Female

To elaborate: In CALICO cats there is development of black and orange and white patches. This is POSSIBLE only when the dominant O allele is turned off in some X chromosome DUE to DOSAGE compensation. As males have only one X chromosome they are never turned off. THUS, only females show this trait.

Correct option is (a) Complete colorblindness

To explain I would say: While red green colorblindness is an X linked recessive TRAIT. Complete colorblindness HOWEVER is a PARTIALLY sex linked GENE in man.

Right choice is (b) Male, 2ND

The explanation is: A female can never have Y chromosome to start with so the non-disjunction is in a male. If the non-disjunction was in 1st DIVISION improper segregation of X and Y will produce XY gamete. Here there is an improper 2nd division where 2Y generated in meiosis 2 moves to same POLE giving YY gamete.

The correct ANSWER is (b) False

The explanation is: In HUMAN beings unlike drosophila there is dosage compensation for the extra X chromosome. DUE to this reason this person will be a viable female.

Right CHOICE is (d) All GENES present on Y chromosome are unique to it

The explanation: There is a homologous region between the X and Y chromosome, and genes in Y chromosome in that area is not unique to it. TDF is another NAME used for SRC gene that is also located on Y chromosome.

Right choice is (C) Mitosis but no fertilization

For EXPLANATION: Bees have XO system of sex determination. In it the MALES are produced by parthenogenesis i.e. here is mitosis occurring in the mother that GIVES the zygote for male offspring.

The CORRECT option is (b) Female

To explain I would say: Females being heterozygous will lack the compensating functional copy from other Z chromosomes will EXPRESS it with greater probability. This is SIMILAR to the fact that X linked recessive DISORDER in mammals is expressed more in males.

Right option is (b) Father

Easy explanation: The MALES are produced by parthenogenesis, i.e. by mitosis. While fertilization only takes place in case of a FEMALE child, only the two X chromosomes COME TOGETHER. Thus, the male has a mother but no father; they do however have a grandfather.

Right option is (B) 15^th day after fertilization

For explanation I would SAY: Lysonization process takes place in the 15^th day after fertilization when the EMBRYO is 500-1000 CELL STAGE. This inactivated one X chromosome in each cell.

The correct OPTION is (d) Faulty tooth ENAMEL

For explanation I would say: While the first three diseases are X linked recessive diseases, the last i.e. faulty tooth enamel and decolonization is a dominant TRAIT.

Right answer is (c) MAT

To EXPLAIN: In yeast, the GENES at the MAT locus are responsible for determining the SEX. Sex is mainly determined as mating FACTOR and it alternates with every generation.

Correct OPTION is (b) No female will express the gene

The best EXPLANATION: If the sex influenced trait is more expressed in MEN then it ACTS as a dominant trait in men. And at the same time, it acts as a recessive trait in female. The female with homozygous form of this trait will thus express it, and men LACKING any copy of it in case of recessive homozygote will not express it.

The correct option is (a) Autosome

Easy explanation: Sex INFLUENCED TRAITS are present in the autosomes. They are not present in the sex CHROMOSOME; ALTHOUGH their expression is DEPENDENT on the sex of the individual.

Right answer is (c) Hypertrichosis

Easy explanation: Among the following options only hypertrichosis is a Y linked gene. It is the presence of HAIR in the ear. It FOLLOWS the Y linked RULE of INHERITANCE.

The correct answer is (c) The cell DEVELOP male character

Easiest explanation: The SHORT arm of the Y CHROMOSOME is carrying the SRY gene which DETERMINES the sex of the organism. Thus introduction of Y chromosome will promote the development of male characters.

Right OPTION is (b) SXL- Tra- SR- Dsx- MALE gene repression

For explanation: Functional Sxl PROTEINS, controls the splicing of tra gene and produces functional Tra protein. Tra INTERACTS with SR proteins controlling splicing of Dsx giving female specific DsxF which ultimately represses male specific characters.

Correct choice is (C) Male

Explanation: In this combination the X: A ratio is o.5 which will PRODUCE a male. ALTHOUGH there will be some PROBLEM in disjunction and male gamete PRODUCTION, otherwise the male is perfectly viable.