Sex determination Questions in English

(A) In birds,the female is heterogametic $(ZW)$ and the male is homogametic $(ZZ)$.
In humans,males are heterogametic $(XY)$ and females are homogametic $(XX)$.
In Drosophila,males are heterogametic $(XY)$ and females are homogametic $(XX)$.
In honey bees,sex determination is based on the number of sets of chromosomes (haplodiploidy),where males are haploid and females are diploid.
Therefore,the heterogametic male condition ($XY$ or $XO$) does not occur in birds.

(C) According to Bridges' genic balance theory of sex determination in Drosophila,the sex of an individual is determined by the ratio of the number of $X$-chromosomes to the number of sets of autosomes $(A)$.
If the ratio $(X/A)$ is $1.0$,the individual is a female.
If the ratio $(X/A)$ is $0.5$,the individual is a male.
If the ratio is between $0.5$ and $1.0$,it is an intersex.
If the ratio is greater than $1.0$,it is a superfemale.
If the ratio is less than $0.5$,it is a supermale.
Therefore,for a ratio of $0.5$,the individual will be male.

(D) In birds,sex determination follows the $ZW-ZZ$ system.
In this system,the female is heterogametic,meaning she possesses two different sex chromosomes,represented as $ZW$.
The male is homogametic,possessing two similar sex chromosomes,represented as $ZZ$.

(B) In mammals,if there is more than one $X$-chromosome,one $X$-chromosome remains active,while the other becomes inactive and highly condensed to form a structure known as the Barr body.
Barr body is a type of sex chromatin particle.
It serves as a sex marker and its number is always one less than the total number of $X$-chromosomes present in the cell (i.e.,$n-1$ rule,where $n$ is the number of $X$-chromosomes).

(A) Sex-linked traits are those traits whose determining genes are located on the sex chromosomes (also known as allosomes).
$(i)$ Sex-linked traits: These are traits determined by genes present on sex chromosomes. They exhibit criss-cross inheritance,a phenomenon first studied by $T.H. Morgan$ in $1910$.
$(ii)$ Sex-limited traits: These are autosomal traits expressed in only one sex due to the influence of sex hormones,such as milk production in females.
$(iii)$ Sex-influenced traits: These are traits whose expression is influenced by sex hormones,such as pattern baldness in males.
Since the question specifically asks for 'sex-linked traits',the correct answer is sex chromosomes (allosomes). Note that in many contexts,'sex chromosomes' and 'allosomes' are synonymous.

(D) In the somatic cells of a normal female $(XX)$,one of the two $X$-chromosomes undergoes heterochromatinization and becomes inactive during interphase. This inactive,condensed $X$-chromosome is known as the Barr body (or sex chromatin). It is typically located at the periphery of the nucleus,adjacent to the nuclear membrane. The number of Barr bodies is calculated as $(n - 1)$,where $n$ is the total number of $X$-chromosomes present. Thus,a normal female $(XX)$ has $2 - 1 = 1$ Barr body.

(C) The determination of the sex of each child is an independent and mutually exclusive event.
In humans,the sex of the child is determined by the sex chromosomes of the father $(XY)$ and the mother $(XX)$.
During fertilization,there is a $50\, \%$ chance that the sperm carrying the $X$ chromosome will fertilize the egg,resulting in a girl,and a $50\, \%$ chance that the sperm carrying the $Y$ chromosome will fertilize the egg,resulting in a boy.
Therefore,regardless of the gender of the previous children,the probability of having a girl in the next pregnancy remains $50\, \%$.

(B) The Barr body,often appearing as a 'drumstick' appendage,is a condensed form of the inactive $X$ chromosome.
It is found in the neutrophils (polymorphonuclear leukocytes) of females.
Approximately $3$ to $5 \%$ of neutrophils in females exhibit this structure,whereas it is absent in males.

(D) Environmental determination of sex refers to the process where environmental factors like temperature or chemical signals influence the sex of an organism.
In $Bonellia$ (a marine worm),the sex of the larva is determined by its environment. If a larva settles alone,it develops into a large $(2.5 \ cm)$ female. If it lands on or near an existing female,chemical substances secreted by the female cause the larva to develop into a tiny $(1.3 \ cm)$ male.
In many reptiles like turtles and alligators,the incubation temperature of the eggs determines the sex of the offspring. Generally,a temperature below $28^{\circ}C$ produces more males,a temperature above $33^{\circ}C$ produces more females,and a temperature between $28^{\circ}C$ and $33^{\circ}C$ produces both males and females in equal proportions.
Therefore,all the given examples exhibit environmental sex determination.

(C) In $Drosophila$,sex determination follows the genic balance theory proposed by $C.B. Bridges$.
According to this theory,the sex of an individual is determined by the ratio of the number of $X$-chromosomes to the number of sets of autosomes (represented as $A$).
If the ratio $(X/A)$ is $1.0$,the individual is a female.
If the ratio is $0.5$,the individual is a male.
If the ratio is between $0.5$ and $1.0$,it results in an intersex individual.

(C) The mechanisms of sex determination that involve dissimilar sex chromosomes are as follows:
$(i)$ $XY$ type (e.g.,humans,where males are $XY$ and females are $XX$)
$(ii)$ $XO$ type (e.g.,grasshoppers,where males are $XO$ and females are $XX$)
$(iii)$ $ZW$ type (e.g.,birds,where females are $ZW$ and males are $ZZ$)
$(iv)$ $ZO$ type (e.g.,some butterflies and moths,where females are $ZO$ and males are $ZZ$)
Thus,there are $4$ such conditions where dissimilar sex chromosomes are involved in sex determination.

(A) In bugs and cockroaches,sex determination occurs via the $XX-XO$ type mechanism.
In this system,females possess two $X$ chromosomes $(XX)$,while males possess only one $X$ chromosome and lack the homologous partner,denoted as $XO$.
During gametogenesis,the female produces gametes that all contain an $X$ chromosome $(A+X)$. The male produces two types of gametes: half containing an $X$ chromosome $(A+X)$ and half lacking a sex chromosome $(A+O)$.
When these gametes fuse,the resulting offspring are either $AA+XX$ (female) or $AA+XO$ (male),maintaining a $1:1$ sex ratio.

(A) male has one $X$-chromosome and one $Y$-chromosome $(XY)$.
He passes his $X$-chromosome to all his daughters and his $Y$-chromosome to all his sons.
Therefore,an $X$-linked recessive or dominant trait present on the father's $X$-chromosome will be inherited by his daughters,but never by his sons,because the son receives the $Y$-chromosome from the father.

(A) In humans,a male has $XY$ sex chromosomes.
He inherits his $Y$-chromosome from his father and his $X$-chromosome from his mother.
The mother,in turn,inherits one $X$-chromosome from her father (maternal grandfather) and one $X$-chromosome from her mother (maternal grandmother).
Therefore,the $X$-chromosome that a man receives from his mother could have originally come from either his maternal grandmother or his maternal grandfather.
Thus,the correct option is $A$.

(C) The initial clues regarding the genetic or chromosomal basis of sex determination were provided by the experiments conducted on insects. In $1891$,Henking observed a specific nuclear structure during spermatogenesis in a few insects,which he termed the $X$-body. Later,it was discovered that this $X$-body was actually a chromosome,now known as the $X$-chromosome.

(A) In the $XY$ type of sex determination,both males and females possess the same total number of chromosomes.
For example,in humans,the female genotype is $44 + XX$ ($46$ chromosomes) and the male genotype is $44 + XY$ ($46$ chromosomes).
In contrast,in $XO$ and $ZO$ types,the heterogametic sex has one chromosome less than the homogametic sex.

(D) In birds,sex determination follows the $ZW-ZZ$ type,where the female is heterogametic $(ZW)$ and the male is homogametic $(ZZ)$.
Because the female is heterogametic,she produces two different types of gametes: one containing the $Z$ chromosome and the other containing the $W$ chromosome.
Therefore,female birds produce two different types of gametes in terms of sex chromosomes.

(B) Individuals with homomorphic sex chromosomes (e.g.,$XX$ in females) possess identical sex chromosomes.
During gametogenesis,they produce only one type of gamete containing the same sex chromosome.
For example,an individual with genotype $AA+XX$ will produce gametes of the type $(A+X)$ only.
Therefore,they produce one type of gametes.

(B) In many insects,the mechanism of sex determination is of the $XO$ type.
In this type,females have two $X$-chromosomes $(XX)$,while males have only one $X$-chromosome $(XO)$.
During gametogenesis in females,all eggs produced contain an autosome $(A)$ and one $X$-chromosome $(A + X)$.
During spermatogenesis in males,two types of sperms are produced: $50$% of the sperms contain an autosome and an $X$-chromosome $(A + X)$,while the other $50$% contain only an autosome $(A + O)$.
Therefore,it is observed that some of the sperms bear the $X$-chromosome.

(B) Hypertrichosis is a $Y$-linked trait,meaning the gene is located on the $Y$ chromosome.
In humans,males have $XY$ chromosomes and females have $XX$ chromosomes.
$A$ father passes his $Y$ chromosome only to his sons,while he passes his $X$ chromosome to his daughters.
Since the daughter receives an $X$ chromosome from her father and an $X$ chromosome from her mother,she does not inherit the $Y$ chromosome.
Therefore,$0\;\%$ of the daughters will have hairy ears.

(A) Holandric traits are controlled by genes present on the non-homologous region of the $Y$ chromosome.
Since these genes are located on the $Y$ chromosome,they are passed directly from father to son.
Because they are $Y$-linked,they appear exclusively in males and are not found in females,which satisfies the condition of appearing more frequently in one sex than the other.
Therefore,both the Assertion and the Reason are correct,and the Reason correctly explains why these traits are sex-specific.

(C) In bacteria,sex determination is not based on sex chromosomes (allosomes) but is controlled by specific genetic elements known as the $F$-plasmid (fertility factor) or sex factor.
Bacteria do not exhibit sex determination based on environmental factors; rather,it is a genetically regulated process involving the transfer of genetic material through conjugation.
Therefore,the Assertion is correct as it refers to non-allosomic genic determination,but the Reason is incorrect because sex in prokaryotes is not determined by environmental factors.

(A) The drumstick is a small,club-shaped appendage attached to the nucleus of neutrophils in females.
It represents the inactivated $X$ chromosome,also known as the $Barr$ body.
Since females have two $X$ chromosomes $(XX)$,one is inactivated to form the $Barr$ body,which appears as a drumstick in neutrophils.
Males have only one $X$ chromosome $(XY)$,which remains active for transcription,so they do not possess a $Barr$ body or a drumstick appendage in their neutrophils.
Therefore,both the Assertion and the Reason are correct,and the Reason correctly explains why the drumstick is present in females and absent in males.

(A) In the $XO$ type of sex determination,males have only one $X$-chromosome and some other autosomes,while females have a pair of $X$-chromosomes.
During spermatogenesis,males produce two types of gametes: $50\%$ of the sperms carry the $X$-chromosome,and $50\%$ do not carry any sex chromosome.
This mechanism is observed in many insects,such as grasshoppers.
Therefore,both the Assertion and the Reason are correct,and the Reason provides the correct explanation for the Assertion.

(B) In the $XO$ type of sex determination,the male has only one $X$ chromosome,while the female has two $X$ chromosomes $(XX)$.
This mechanism is observed in many insects,including grasshoppers.
In grasshoppers,males produce two types of gametes: $50\%$ with an $X$ chromosome and $50\%$ without an $X$ chromosome.
Birds exhibit $ZW-ZZ$ type sex determination,while $Drosophila$ and humans exhibit $XY$ type sex determination.

(C) In humans,the sex determination is based on the $XY$ chromosome system.
Females are homogametic,meaning they possess two $X$ chromosomes $(XX)$. During oogenesis,all ova produced contain only one type of sex chromosome,which is the $X$ chromosome.
Therefore,females produce only one type of ovum $(22 + X)$.
Males are heterogametic,meaning they possess $XY$ chromosomes. During spermatogenesis,two types of sperms are produced: $50\%$ of sperms contain the $X$ chromosome $(22 + X)$ and $50\%$ of sperms contain the $Y$ chromosome $(22 + Y)$.
Thus,males produce two types of sperms.

(B) In humans,the sex of an individual is determined by the sex chromosomes.
An individual with $XX$ chromosomes is genetically female.
An individual with $XY$ chromosomes is genetically male.
Therefore,an infant with $XX$ chromosomes results in a female,and an infant with $XY$ chromosomes results in a male.

(A) The image shows the sexual dimorphism in Drosophila melanogaster (fruit fly).
In fruit flies,the female is generally larger in size with a pointed abdomen,while the male is smaller in size with a rounded,darker posterior end of the abdomen.
Based on the provided image,organism $P$ is smaller with a rounded abdomen,representing the male fruit fly.
Organism $Q$ is larger with a pointed abdomen,representing the female fruit fly.
Therefore,$P$ is the male fruit fly and $Q$ is the female fruit fly.

(C) In grasshoppers,sex determination follows the $XO$ type mechanism.
In this mechanism,the male has one $X$ chromosome and lacks the other homologous chromosome,resulting in a total of $23$ chromosomes $(22 + XO)$.
The female has a pair of $X$ chromosomes,resulting in a total of $24$ chromosomes $(22 + XX)$.
Therefore,the male has $23$ chromosomes and the female has $24$ chromosomes.

(C) In humans,sex determination is based on the $XY$ chromosome system.
During fertilization,the male gamete (sperm) can carry either an $X$ chromosome or a $Y$ chromosome,while the female gamete (ovum) always carries an $X$ chromosome.
When an $X$-carrying sperm fertilizes an $X$-carrying ovum,a daughter $(XX)$ is produced.
When a $Y$-carrying sperm fertilizes an $X$-carrying ovum,a son $(XY)$ is produced.
Since the chance of a sperm carrying an $X$ or $Y$ chromosome is equal,the probability of having a son or a daughter in any given pregnancy is always $50 \,\%$.
Previous births do not influence the genetic outcome of future pregnancies.

(D) The haplo-diploid sex-determination system is a mechanism where sex is determined by the number of sets of chromosomes an individual receives.
In honeybees $(Apis \text{ } mellifera)$, the queen produces eggs by meiosis, and drones produce sperm by mitosis.
Females (queens and workers) are diploid $(2n = 32)$ and develop from fertilized eggs.
Males (drones) are haploid $(n = 16)$ and develop from unfertilized eggs through a process called parthenogenesis.
Therefore, the correct answer is $D$ (Honeybee).

(C) In $1891$,Henking observed a specific nuclear structure during spermatogenesis in a few insects. He observed that $50 \%$ of the sperms received this specific structure after meiosis,whereas the other $50 \%$ did not. He named this structure the $X-$body. Later,it was discovered that this $X-$body was actually a chromosome,which is now known as the $X-$chromosome.

(B) The initial experiments regarding the genetic basis of sex determination were conducted by $Hermann \text{ } Henking$ in $1891$ on insects. He observed a specific nuclear structure in all sperms of a few insects and named it the $X$-body. Later, it was discovered that this $X$-body was actually a chromosome, which is now known as the $X$-chromosome. This discovery laid the foundation for understanding sex determination in organisms.

(B) The correct matches are as follows:
$1$. $P$. $XO$ type: This mechanism is observed in insects like grasshoppers,where males have one $X$ chromosome and females have two $(XX)$. Thus,$P-I$.
$2$. $Q$. Haplo-diploid mechanism: This is a unique sex determination system found in honey bees,where females are diploid $(2n)$ and males are haploid $(n)$. Thus,$Q-III$.
$3$. $R$. $XY$ type: This is the common sex determination mechanism found in Drosophila (fruit flies) and humans,where males are $XY$ and females are $XX$. Thus,$R-II$.
Therefore,the correct sequence is $(P-I), (Q-III), (R-II)$.

(D) Male heterogamety refers to a condition where the male produces two different types of gametes (e.g.,$XY$ or $XO$ types).
In insects (like grasshoppers and Drosophila),male heterogamety is present ($XO$ or $XY$ type).
In honey bees,sex determination is based on the number of sets of chromosomes (haplodiploidy),where males are haploid and females are diploid; thus,they do not exhibit male heterogamety.
In birds,female heterogamety is observed ($ZW$ type for females and $ZZ$ type for males),meaning males are homogametic.
Therefore,both honey bees and birds lack male heterogamety.

(B) Female heterogamety is a mechanism of sex determination where the female produces two different types of gametes.
In birds,sex determination is of the $ZW-ZZ$ type,where females are $ZW$ (heterogametic) and males are $ZZ$ (homogametic).
In honey bees,sex determination is based on the number of sets of chromosomes (haplo-diploidy). Females are diploid $(2n = 32)$ and males are haploid $(n = 16)$. This is not considered female heterogamety in the traditional sense of sex chromosomes.
Therefore,birds exhibit female heterogamety. The correct option is $B$.

(A) In honeybees,sex determination is based on the number of sets of chromosomes an individual receives. Females are diploid $(2n = 32)$ and males are haploid $(n = 16)$.
$1$. The female (queen) produces eggs through meiosis,so each egg has $n = 16$ chromosomes.
$2$. The male (drone) produces sperms through mitosis,so each sperm has $n = 16$ chromosomes.
$3$. $Q$ represents the sperm produced by the male through mitosis,so $Q = 16$.
$4$. $P$ is a male produced from an unfertilized egg (parthenogenesis),so it retains the haploid number,$P = 16$.
$5$. $R$ is a female produced from the fertilization of an egg $(16)$ by a sperm $(16)$,resulting in a diploid zygote,so $R = 16 + 16 = 32$.
Therefore,$P = 16, Q = 16, R = 32$.

(A) In humans,the sex of the child is determined by the sex chromosomes inherited from the parents.
Human males have $XY$ sex chromosomes,while human females have $XX$ sex chromosomes.
During gametogenesis,males produce two types of sperms: $50\%$ carrying the $X$ chromosome and $50\%$ carrying the $Y$ chromosome.
Females produce only one type of ovum,which always carries the $X$ chromosome.
If a sperm carrying the $X$ chromosome fertilizes the ovum,the zygote develops into a female $(XX)$.
If a sperm carrying the $Y$ chromosome fertilizes the ovum,the zygote develops into a male $(XY)$.
Therefore,the sex of the offspring is determined by the male gamete (sperm) that fertilizes the egg.

(C) In the given image,$P$ and $Q$ represent male and female Drosophila (fruit flies),while $R$ and $S$ represent a rooster and a hen.
In Drosophila,sex determination is of the $XX-XY$ type. The male $(P)$ is heterogametic,producing two types of gametes ($X$ and $Y$),while the female $(Q)$ is homogametic.
In birds,sex determination is of the $ZW-ZZ$ type. The female $(S)$ is heterogametic,producing two types of gametes ($Z$ and $W$),while the male $(R)$ is homogametic.
Therefore,the organisms that produce two types of gametes are the male Drosophila $(P)$ and the female bird $(S)$.

(C) Male heterogamety occurs when the male produces two different types of gametes (e.g.,$XY$ or $XO$ type). This is seen in humans $(I)$,Drosophila $(III)$,and grasshoppers $(IV)$.
Female heterogamety occurs when the female produces two different types of gametes (e.g.,$ZW$ type). This is seen in birds $(II)$.
Therefore,$P = I, III, IV$ and $Q = II$.
The correct option is $C$.

(C) In $1891$,German biologist $Hermann \ Henking$ observed a specific nuclear structure during spermatogenesis in some insects. He noted that this structure was present in only $50\%$ of the sperm cells. He named this structure the $x-$body. Later,it was discovered that this $x-$body is actually the $X$ chromosome,which plays a crucial role in sex determination.

(B) Henking $(1891)$ was the first to trace a specific nuclear structure during spermatogenesis in a few insects.
He observed that $50 \%$ of the sperms received this specific nuclear structure,which he named the $X$-body,while the other $50 \%$ did not.
Later,it was discovered that the $X$-body was actually a chromosome,now called the $X$-chromosome.
This type of sex determination,where males have one $X$-chromosome and one missing chromosome (denoted as $O$),is known as the $XX - XO$ type of sex determination.
In this system,females are homogametic $(XX)$,and males are heterogametic $(XO)$.

(C) Allosomes,also known as sex chromosomes,are chromosomes that differ in size,form,and behavior from autosomes. In humans,the $X$ and $Y$ chromosomes are allosomes. Their primary function is the determination of the sex of an individual. Autosomes are responsible for the determination of body characters (somatic traits),whereas allosomes specifically carry genes that dictate sexual development.

(A) In $ZW-ZZ$ type of sex determination,the female is heterogametic $(ZW)$ and the male is homogametic $(ZZ)$. This mechanism is characteristic of birds and some reptiles.

Organism	Type of sex determination
Birds	$ZW-ZZ$
Honeybees	Haplo-diploid
Human beings	$XX-XY$
Bonellia	Environmental factor dependent

(C) Statement $I$ is correct: The $X$ chromosome is genetically active and contains a large amount of euchromatin,which is loosely packed and transcriptionally active,and a small amount of heterochromatin.
Statement $II$ is incorrect: The homologous region of the $X$ chromosome is significantly larger and contains a much higher number of genes compared to the homologous region of the $Y$ chromosome. The $Y$ chromosome is largely heterochromatic and gene-poor.

(D) In honeybees,the sex-determination system is haplodiploid.
$1.$ The queen $(2n)$ produces eggs by meiosis.
$2.$ The drone $(n)$ is produced from unfertilized eggs via parthenogenesis.
$3.$ Since the drone is already haploid $(n)$,it produces sperms by mitosis,not meiosis,because it cannot undergo further reduction division.
$4.$ Therefore,in the drone bee,gametogenesis occurs only by mitosis.

(A) Incomplete sex linkage is exhibited by genes located on the homologous regions of $X$ and $Y$ chromosomes.
These genes undergo crossing over during meiosis,which leads to the exchange of genetic material between the $X$ and $Y$ chromosomes.
Because they are present on the homologous segments,they do not show complete linkage,hence the term 'incomplete sex linkage'.

(C) In humans,males have one $X$ chromosome and one $Y$ chromosome $(XY)$,while females have two $X$ chromosomes $(XX)$.
If a recessive gene is present on the non-homologous part of the $X$ chromosome,it will be expressed in males because they possess only one $X$ chromosome and lack a corresponding allele on the $Y$ chromosome to mask its effect.
In contrast,females have two $X$ chromosomes; if they carry a recessive gene on one $X$ chromosome,the presence of a dominant allele on the other $X$ chromosome can suppress its expression,making them carriers rather than showing the trait.

(B) In $1891$,German biologist Hermann Henking was studying spermatogenesis in the insect $Anasa$ $tristis$ (the squash bug).
He observed a specific nuclear structure that segregated to only half of the sperm cells during meiosis.
He named this structure the '$X$' body.
Later,it was discovered that this '$X$' body was actually the $X$ chromosome,which plays a crucial role in sex determination.

(C) In honey bees,sex determination is based on the number of sets of chromosomes.
Statement $I$ is incorrect because the queen honey bee is a fertile diploid female that develops from a fertilized egg (zygote),not by parthenogenesis.
Statement $II$ is incorrect because,in honey bees,all diploid zygotes develop into females (either queens or workers),while haploid eggs develop into males (drones) via parthenogenesis.
Therefore,both statements are incorrect.