Sex determination Questions in English

(C) In honey bees,the sex determination is based on the number of sets of chromosomes an individual receives. Females (queen and workers) are diploid $(2n = 32)$,while males (drones) are haploid $(n = 16)$. Therefore,the statement that queen and worker bees have a haploid number of chromosomes is incorrect,as they are diploid.

(D) Holandric genes are those genes that are located exclusively on the non-homologous part of the $Y$ chromosome.
These genes are inherited directly from father to son and are never expressed in females.
Since they are present only on the $Y$ chromosome,they are also known as $Y$-linked genes.
Therefore,the correct option is $D$.

(D) In higher unisexual organisms,the chromosomes are categorized into two types: autosomes and sex chromosomes.
Autosomes are identical in both sexes and determine somatic traits.
Sex chromosomes are the pair of chromosomes that differ between the two sexes and are responsible for sex determination.
For example,in humans,females have a pair of $X$ chromosomes $(XX)$,while males have one $X$ and one $Y$ chromosome $(XY)$.
Since the $X$ and $Y$ chromosomes are not identical,they are referred to as sex chromosomes or allosomes.

(C) Sex-linked traits appear more frequently in males because they have only one '$X$' chromosome,so the recessive gene gets a chance to express itself.
Colour blindness is caused due to a defect in the gene that prevents the proper formation of colour-sensitive cells in the retina.
Drone bees are haploid and produce sperms by mitosis,not meiosis.
Human females have two '$X$' chromosomes,which is referred to as a double dose of the '$X$' chromosome.

(B) In the given cross,the male parent has the genotype $X^h Y$ and the female parent has the genotype $X^H X^H$.
The gametes produced by the male parent are $X^h$ and $Y$.
The gametes produced by the female parent are $X^H$ and $X^H$.
By performing the cross:
$(1)$ $X^h$ from male combines with $X^H$ from female to form $X^H X^h$.
$(2)$ $X^h$ from male combines with $X^H$ from female to form $X^H X^h$.
$(3)$ $Y$ from male combines with $X^H$ from female to form $X^H Y$.
$(4)$ $Y$ from male combines with $X^H$ from female to form $X^H Y$.
Thus,the correct sequence is $(1)$ - $X^H X^h$,$(2)$ - $X^H X^h$,$(3)$ - $X^H Y$,$(4)$ - $X^H Y$.

(B) In humans,sex determination is governed by the presence of specific sex chromosomes ($XX$ in females and $XY$ in males). These chromosomes are present in the germ cells (gametes) which determine the sex of the offspring upon fertilization. While somatic cells also contain these chromosomes,the fundamental mechanism of sex determination is defined by the chromosomal constitution of the germ cells (sperm and egg) that fuse to form the zygote.

(B) The given figure represents the sex determination mechanism in honeybees (haplodiploidy).
$1$. In the female (diploid,$32$ chromosomes),the formation of gametes (haploid,$16$ chromosomes) occurs via 'Meiosis' $(Z)$.
$2$. In the male (haploid,$16$ chromosomes),the formation of gametes (haploid,$16$ chromosomes) occurs via 'Isosomal division' or 'Mitosis' $(Y)$.
$3$. The development of an unfertilized egg into a male (drone) is a form of 'Asexual reproduction' or 'Parthenogenesis' $(X)$.
Therefore,$X$ = Asexual reproduction,$Y$ = Isosomal division,$Z$ = Meiosis.

$(A)$ The provided chart illustrates the sex determination mechanism in honeybees $(Apis \text{ } mellifera)$.
$1$. In honeybees, the female is diploid $(2n = 32)$ and the male is haploid $(n = 16)$.
$2$. The female produces gametes (eggs) by meiosis. Thus, $Z$ represents Meiosis $(32 \rightarrow 16)$.
$3$. The male produces sperms by mitosis because it is already haploid. Thus, $Y$ represents Mitosis $(16 \rightarrow 16)$.
$4$. The union of an egg and a sperm forms a diploid zygote $(32)$, which develops into a female. An unfertilized egg develops into a male by parthenogenesis. Thus, $X$ represents Parthenogenesis.
Therefore, the correct sequence is $X = \text{Parthenogenesis}$, $Y = \text{Mitosis}$, $Z = \text{Meiosis}$.

(D) The correct answer is $D$.
In the male heterogametic type of sex determination,the male individual produces two different types of gametes (e.g.,$X$ and $Y$ in humans or $X$ and $O$ in some insects),which is why they are called heterogametic. The female,in this case,is homogametic,meaning she produces only one type of gamete $(X)$.

(D) In the $ZZ-ZW$ type of sex determination,the male is homogametic $(ZZ)$ and the female is heterogametic $(ZW)$.
This system is commonly observed in birds and some reptiles.
In contrast,$XX-XO$ and $XX-XY$ systems represent male heterogamety,where the male produces two different types of gametes.

(B) The correct answer is $B$ (male heterogamety).
In both $XO$ type and $XY$ type of sex determination,the male individual produces two different types of gametes (heterogametes).
In $XO$ type,males produce gametes with an $X$ chromosome and gametes without an $X$ chromosome.
In $XY$ type,males produce gametes with an $X$ chromosome and gametes with a $Y$ chromosome.
Since the male produces two different types of gametes,this mechanism is known as male heterogamety.

(A) The correct answer is $A$.
In honey bees,sex determination is based on the number of sets of chromosomes an individual receives.
This mechanism is known as $Haplo-diploidy$.
In this system,females (queens and workers) are diploid $(2n = 32)$ and are produced from fertilized eggs.
Males (drones) are haploid $(n = 16)$ and are produced from unfertilized eggs via parthenogenesis.

(B) is the correct answer: $XO$ type of sex determines male sex in grasshopper.
In $Drosophila$,the $XX$ condition (homozygous) results in a female,while $XY$ results in a male.
In birds,the $ZZ$ condition (homozygous) results in a male,while $ZW$ results in a female.
In humans,Klinefelter's syndrome is characterized by an $XXY$ genotype ($47$ chromosomes),not $XO$.

(A) In honeybees,the sex-determination system is known as haplodiploidy.
Females are diploid $(2n)$,produced from the union of a sperm and an egg (fertilized eggs).
Males are haploid $(n)$,produced from unfertilized eggs through a process called parthenogenesis.
Since males are haploid,they cannot undergo meiosis to produce gametes; instead,they produce sperms by mitosis.
Therefore,statements $A, B, C,$ and $E$ are correct,while statement $D$ is incorrect.

(B) Grasshoppers exhibit $XO$ type of sex determination.
Females are homogametic $(XX)$ and males are heterogametic $(XO)$.
Therefore,males have one chromosome less than females.
If females have $24$ chromosomes $(22+XX)$,males have $23$ chromosomes $(22+XO)$.