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Correct answer is (b) SKIP generations

To explain: Sex LINKED GENES especially the sex linked recessive gene skips generations before EXPRESSION. It is expressed more in males than female and is not necessarily lethal.

The correct OPTION is (d) Can’t be SPECIFIED

The EXPLANATION: Milking factor is a sex influenced trait that is only EXPRESSED in females i.e. cows. Bulls will never express these genes irrespective of their phenotype. Hence, their GENOTYPE can’t be specified.

The correct option is (c) Female with H h^+

Easy EXPLANATION: This SEX INFLUENCED trait is dominant for male and recessive for female. Out of the given OPTIONS only heterozygous female will not express this trait making it the off one.

Right answer is (d) The male X chromosome is hyper active

The best EXPLANATION: In Drosophila, DOSAGE compensation is achieved in a different way. The male’s X chromosome appears to be hyperactivated, ALLOWING it to be transcribed at twice the rate of either X chromosome in the female.

Right CHOICE is (a) ALWAYS be activated

The best explanation: XIC is X inactivation centre, only one X with XIC stays ACTIVE in a cell. Now is a chromosome loses is XIC that will not be counted as X chromosome and will stay active.

Correct option is (b) Father

For explanation I would say: The only POSSIBILITY here is that the MOTHER was a carrier. The EGG received this defective X chromosome from mother and no sex chromosome from the father. Thus, there was non disjunction in the father. The RESULTANT child was AA+ X’O. (X’=mutant).

Right option is (d) 1

To explain: Baldness is a sex influenced trait, so the mother is certainly B/b and the father is b+,b+. So, the son will get at least one baldness allele from the mother. Heterozygous male EXPRESSES the sex influenced trait; hence the son will DEFINITELY be BALD.

Right option is (B) False

The explanation: Sex INFLUENCED TRAIT effects both males and females. They can be more EXPRESSED in male or FEMALE depending on the nature of the trait.

Correct answer is (b) Heterozygous

Easy explanation: The O GENE is responsible for orange color DEVELOPMENT. Only dominant O can express it over the mutant B gene that causes black color. O gene is located in X CHROMOSOME. Thus in heterozygous condition if O CARRYING X chromosome is inactivated it leads to black patch as SEEN here.

Correct ANSWER is (c) INACTIVATION of chromosome 3

The explanation: As XIC translocated to chromosome 3 now it can be counted as an X chromosome. In some cells randomly this chromosome 3 is condensed and inactivated which prevents the important AUTOSOMAL gene product from being formed. THUS the INDIVIDUAL dies.

The correct ANSWER is (b) In the nuclei of female

For EXPLANATION I would say: The inactivated X chromosome in female forms a highly condensed structure called the BARR body which is found in the nuclei. As male have only one X chromosome is no INACTIVATION and no Barr body.

Correct choice is (a) MAMMALS

Explanation: Only in case of mammals dosage compensation mechanism is by inactivation of one X CHROMOSOME. In DROSOPHILA there is a different mechanism.

The correct answer is (d) Non-disjunction in any of the gametes

To explain: Klinefelter syndrome results from a GENETIC combination AA+ XXY; this can RESULT from non-disjunction in either male or FEMALE gamete.

Right CHOICE is (a) XX/ XY

Best explanation: Like Drosophila MAMMALS also have XX/ XY mode of SEX determination. HOWEVER, the mechanism of sex determination in this CASE is much different.

Right choice is (c) LOSS of Y chromosomes from some cells

The best I can explain: Intersex has the combination AA+ XO/XY. PRESENCE of Y chromosomes develops male CHARACTER so AA+XY cells are male. ABSENCE of Y gives female characters so AA+XO gives female, this is due to loss of Y chromosome from these cells. Overall it results in intersex.

The CORRECT answer is (d) AA+ XO

The BEST explanation: AA+ XO will be a TURNER. This CONDITION the female characters are underdeveloped due to the ABSENCE of one X chromosome. AA+ XO/XY on the other hand is intersex.

Correct option is (a) Insects

Explanation: Insects have this XO system of sex DETERMINATION. THUS it can be seen in Grasshopper, COCKROACHES, bees etc. Other options here have different MODES of sex determination other than XO.

The correct answer is (B) AA + XXY

Best explanation: In the following case the X: A ratio is 1 which is REQUIRED for DEVELOPING female CHARACTERS. In all the other cases viable female is not produced.

Right option is (d) EXPRESSED only in MEN

Easy explanation: A Y linked gene is expressed only in men and never in females as females lack a Y chromosome. It is not expressed in homozygous, rather in hemizygous for as its present only in a SINGLE copy. The REGION near that telomere is common for both sex chromosomes, so it is not sex linked.

The correct choice is (a) Cock feathering

Easy explanation: Cock feathering is a SEX limited trait which is expressed only on ONE sex DEPENDING. Even if the other sex is homozygous for it, the phenotype will not be expressed unless there is SERIOUS hormonal change.

Right choice is (a) 0

The best I can explain: Sons get the Y chromosome from FATHER and the X from mother. So UNLESS the mother is also a carrier, there is no probability of the son being COLORBLIND.

The correct answer is (c) SHORT arm of human Y chromosome

The EXPLANATION: Short arm of human Y chromosome is not homologous to X chromosome. Thus, GENES there will show Y linkage. SEX INFLUENCED genes don’t show linkage and are not exclusive to X or Y chromosomes, so it will not be present there.

The correct choice is (a) True

The EXPLANATION is: During X inactivation the X CHROMOSOME is converted to heterochromatin by histone remodeling. This is a heritable character that is not present in the DNA SEQUENCE but histone code. THUS it is an epigenetic phenomenon.

Right answer is (a) The mother

The explanation is: Males have only one X chromosome, so if the father or NORMAL son CARRIED the defective X gene they would show the PHENOTYPIC effect. Since the female has two copies of X chromosome, only in homozygous form the recessive gene like COLORBLINDNESS is EXPRESSED. So mother here is a carrier.

Correct OPTION is (b) Straight

Easiest explanation: The inheritance pattern of Y linked GENE is straight as it MOVES from FATHER to son. Only males can inherit these TRAITS.

The correct option is (c) Females have ZW constitution

The explanation is: ZZ/ZW SEX determination SYSTEM is much LIKE XX/XY system. However, in this case MALE is homozygous ZZ and female is heterozygous ZW. In this case to avoid confusion different notation is used and not because of the shape.

The correct ANSWER is (a) True

Explanation: As FEMALES have TWO copies of X gene, if only ONE of them is mutant there is a 50% chance of the mutant X gene being turned off in a cell due to dosage COMPENSATION. Thus, the effect of the mutant gene product is diluted.

Right choice is (c) Deacetylase and specific methylase

To EXPLAIN: Histone deacetylases lead to the removal of acetyl group from specific histone RESIDUES. This leads to EXPOSURE of positive charges on then and CAUSES stronger binding. Specific methylase also plays similar role. Together they help in HETEROCHROMATIN formation.

Correct choice is (C) Tra

To elaborate: Sxl directly affects the splicing of tra pre-mRNA and PRODUCES a functional gene when Sxl is TURNED on. DOWNSTREAM of this the female characters are produced. Xce is present in human and not in DROSOPHILA.

The correct option is (B) XCE

To explain I would SAY: XCE or X controlling element that is PRESENT in the XIC REGION determines which X CHROMOSOME will be inactivated.

The correct ANSWER is (c) Two X chromosome will always produce a female

The best EXPLANATION: In DROSOPHILA the sex is determined by the sex chromosome: set of autosome ratio. If X:A is 1 as in case of XX then it’s a female, ratio of 0.5 in case of XY gives a male. The presence or even absence of Y chromosome makes little difference.

Correct ANSWER is (d) Osteoporosis

For explanation I would say: All the mentioned options are sex influenced TRAITS. Cleft palate, CLUB FOOT and Gout are dominant for males while osteoporosis is dominant for females.

The CORRECT option is (C) Klinefelter

For explanation: IN mammals unlike drosophila the presence of Y chromosome determines MALENESS, thus XXY will have male CHARACTERS. Again the presence of additional X chromosome will give rise to some female characters resulting in klinefelter.

Right CHOICE is (a) Yeast

Best explanation: Yeast and other EUKARYOTIC microorganism have this GENIC system of sex determination. In this case there is no SPECIAL sex CHROMOSOME.

Right answer is (b) False

To EXPLAIN I would say: Although INTRIGUING but parthenogenesis is not POSSIBLE for HUMAN beings. This is because of imprinting where some genes from a particular parent are turned off in offspring depending on its GENDER.

The correct option is (a) Development of MALE characters

The explanation: Development of male characters is LIKE a DEFAULT PATHWAY in Drosophila which is turned off by female specific GENES.

The correct CHOICE is (c) b/b+ non-bald

To elaborate: BALDNESS is a dominant gene for a male. A bald mother is thus homozygous for the allele; at least one baldness gene will thus pass to offspring from her. The father is normal so he must LACK any baldness allele and a normal gene will pass from him. HENCE daughter is a heterozygote and normal.

Correct choice is (c) PARTIALLY sex linked

The explanation is: Genes present in the homologous region of X and Y chromosomes are known as partially sex linked. Although they are present on sex chromosome their INHERITANCE pattern is LIKE NORMAL genes.

Correct option is (B) GENE locus determines gender

The best explanation: GENIC mode of sex determination is seen in eukaryotic microorganisms. In this case, there is no SEPARATE CHROMOSOME but allele at the gene locus determines sex.

Right OPTION is (d) Sxl

The explanation: Sxl or sex lethal GENE is responsible for the development of male or female characters in DROSOPHILA. Other genes mentioned work in HUMAN beings.

Right choice is (B) False

The EXPLANATION: It is true that the sex influenced trait is expressed in FEMALES in homozygous condition, but the expression is not the same as that in male. In females the expression is much DELAYED under the influence of hormones.

The correct CHOICE is (C) Y LINKED gene like haemophilia passes from father to SON

Easy explanation: It is true that Y linked genes pass from father to son, but Haemophilia is not a Y linked gene. It is a recessive X linked gene.

The correct choice is (B) OFF, 0.5

Explanation: The Sxl GENE is TURNED ON only when the RATIO of X:A is 1, other times it is OFF. An OFF state PRODUCES a male while on state produces a female.

Correct choice is (b) False

The best explanation: There is a homologous region in the SEX chromosome X and Y. Thus GENES PRESENT there shows normal inheritance pattern.

Right OPTION is (b) False

The best I can explain: EVEN though Human and drosophila both have XY system it is named so just DEPENDING on the structural constitution of chromosomes of normal male and FEMALE. However, the mechanism of maleness and femaleness development in both cases in very different.