Sex determination Questions in English

(C) heterosome is a chromosome that differs from the ordinary autosomes in form,size,or behavior. In most organisms,these are the chromosomes involved in sex determination,commonly known as sex chromosomes (e.g.,$X$ and $Y$ chromosomes in humans). Therefore,the term heterosome is synonymous with sex chromosome.

(C) An autosome is any chromosome that is not a sex chromosome. In humans,there are $22$ pairs of autosomes and $1$ pair of sex chromosomes. Autosomes contain genes that determine somatic characteristics of the body and are not involved in sex determination.

(B) Sex determination is classified based on the time at which it occurs:
$1$. $Progamic$: Sex is determined before fertilization (e.g.,in some rotifers).
$2$. $Syngamic$: Sex is determined at the time of fertilization due to the fusion of gametes (e.g.,in humans,where the $X$ or $Y$ chromosome from the sperm determines the sex).
$3$. $Epigamic$: Sex is determined after fertilization,influenced by environmental factors (e.g.,in some reptiles like crocodiles).
Therefore,when sex is determined at the time of fertilization,it is known as $Syngamic$.

(B) In humans,females are homogametic,meaning they produce only one type of gamete (ovum) containing $22 + X$ chromosomes. Therefore,all eggs are alike. Males are heterogametic,producing two types of sperms: $22 + X$ and $22 + Y$. Thus,statement $(b)$ is incorrect.

(C) In humans,males are $XY$ and females are $XX$.
Since males have only one $X$ chromosome,any recessive gene present on the $X$ chromosome will be expressed because there is no corresponding allele on the $Y$ chromosome to mask its effect.
This condition is known as hemizygous.
Therefore,a single recessive gene on the $X$ chromosome of a male is sufficient to express the trait.

(C) According to the British geneticist Mary Lyon $(1961)$,one of the two $X$-chromosomes of a normal female becomes heterochromatic and appears as a Barr body. This phenomenon is known as Lyonization or $X$-inactivation. Therefore,Barr bodies are associated with the female sex chromosome.

(B) The chromosomes that are responsible for the determination of sex in an organism are known as sex chromosomes or allosomes.
Autosomes are the chromosomes that do not play a direct role in sex determination.
Multiple alleles refer to the presence of more than two alleles for a single gene locus.
Heterosis refers to the phenomenon where the progeny of two genetically different parents show superior traits compared to the parents.
Therefore, the correct option is $B$.

(D) In humans,sex determination is of the $XY$ type. 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 egg,carrying the $X$ chromosome. When a sperm carrying the $X$ chromosome fertilizes an egg,a female $(XX)$ is produced. When a sperm carrying the $Y$ chromosome fertilizes an egg,a male $(XY)$ is produced. Since the probability of either type of sperm fertilizing the egg is equal ($50\%$ each),the theoretical ratio of male to female offspring is $1:1$.

(B) The sex determination system in honeybees is known as $Haplodiploidy$.
In this system, the sex of the offspring is determined by the number of sets of chromosomes it receives.
Females ($queens$ and $workers$) are $diploid$ $(2n = 32)$, developing from fertilized eggs.
Males ($drones$) are $haploid$ $(n = 16)$, developing from unfertilized eggs through a process called $parthenogenesis$.

(C) In humans,the sex of the child is determined by the sex chromosomes present in the sperm.
Females have $XX$ chromosomes and produce gametes with only the $X$ chromosome.
Males have $XY$ chromosomes and produce two types of sperm: $50\%$ containing the $X$ chromosome and $50\%$ containing the $Y$ chromosome.
If a sperm carrying the $X$ chromosome fertilizes the egg,the zygote develops into a female $(XX)$.
If a sperm carrying the $Y$ chromosome fertilizes the egg,the zygote develops into a male $(XY)$.
Therefore,the father's contribution determines the sex of the child.

(D) The Lyon hypothesis,proposed by Mary Lyon,states that in female mammals,one of the two $X$ chromosomes in each somatic cell is randomly inactivated during early embryonic development.
This inactivated $X$ chromosome becomes highly condensed and is visible as a dense,dark-staining body in the nucleus,known as a Barr body.
Therefore,the Lyon hypothesis explains the mechanism of dosage compensation in mammals by relating the number of $X$ chromosomes to the number of Barr bodies present in the cell.

(C) In $Drosophila$,sex determination is based on the ratio of $X$ chromosomes to sets of autosomes $(A)$.
Meta-females (or super-females) are individuals with an $X:A$ ratio greater than $1.0$.
Typically,these individuals possess $3X$ chromosomes and $2$ sets of autosomes $(3X:2A)$,resulting in a ratio of $1.5$.
Therefore,the correct chromosome complement for a meta-female is $XXX$.

(A) In humans,the sex of a child is determined by the sex chromosomes.
Females are homogametic,producing eggs that always contain an $X$ chromosome.
Males are heterogametic,producing two types of sperm: those carrying an $X$ chromosome and those carrying a $Y$ chromosome.
If a sperm carrying an $X$ chromosome fertilizes the egg,the resulting zygote will be $XX$ (female).
If a sperm carrying a $Y$ chromosome fertilizes the egg,the resulting zygote will be $XY$ (male).
Therefore,the sex of the child depends on the nature of the sperm that fertilizes the egg.

(B) The determination of sex at the cellular level is often done by identifying the $Barr$ body,which is an inactivated $X$ chromosome in females. $Barr$ bodies can be demonstrated in various somatic cells,including skin cells,nerve cells,cells of the buccal epithelium,hair roots,and cells lining the vagina and urethra. Therefore,both buccal epithelium and hair roots are suitable sources for this analysis.

(C) The sex of a human child is determined at the time of fertilization.
In humans, the female produces only one type of gamete (ovum) containing the $22 + X$ chromosome constitution.
The male produces two types of sperms: $50\%$ containing $22 + X$ and $50\%$ containing $22 + Y$.
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 genetic sex is established at the moment of fertilization.

(D) In $Drosophila \text{ } melanogaster$, sex determination is based on the ratio of the number of $X$ chromosomes to the number of sets of autosomes $(A)$.
This is known as the Genic Balance Theory, proposed by $C.B. Bridges$.
If the ratio of $X/A$ is $1.0$, the individual is female.
If the ratio of $X/A$ is $0.5$, the individual is male.
Therefore, both $X$ chromosomes and autosomes play a crucial role in determining the sex of the fruit fly.

(B) In humans,the sex of the child is determined by the father's sperm.
Females produce eggs that contain only the $X$ chromosome.
Males produce two types of sperms: those carrying the $X$ chromosome and those carrying the $Y$ chromosome.
If a sperm carrying the $Y$ chromosome fertilizes the egg,the resulting zygote will have $XY$ chromosomes,which develops into a male child.
If a sperm carrying the $X$ chromosome fertilizes the egg,the resulting zygote will have $XX$ chromosomes,which develops into a female child.

(B) The Barr body is a condensed,inactive $X$ chromosome found in the somatic cells of female mammals. According to the Lyon hypothesis,one of the two $X$ chromosomes in female somatic cells undergoes heterochromatinization during early embryonic development. This inactive $X$ chromosome appears as a deeply stained,dense body near the nuclear envelope,known as the Barr body. Therefore,the correct answer is $B$.

(A) The dark-stained body observed near the nuclear membrane in interphase cells is known as a Barr body.
Barr bodies represent inactivated $X$-chromosomes in cells with more than one $X$-chromosome.
The number of Barr bodies in a cell is calculated using the formula: $N = (\text{Number of } X\text{-chromosomes}) - 1$.
For an individual to have a visible Barr body, they must have at least two $X$-chromosomes (e.g., $XX$, $XXY$, $XXX$).
Among the given options, $XX$ is the only genotype that possesses two $X$-chromosomes, resulting in $2 - 1 = 1$ Barr body.

(D) According to the Lyon hypothesis,in human females,one of the two $X$ chromosomes in each somatic cell is randomly inactivated during early embryonic development to ensure dosage compensation.
This inactivated $X$ chromosome becomes highly condensed and is visible as a dark-staining structure known as a Barr body.
Since the inactivation is random,it can involve either the $X$ chromosome inherited from the mother or the $X$ chromosome inherited from the father in different cells.

(A) Gynandromorphs in Drosophila are organisms that exhibit both male and female characteristics.
They originate from a zygote that is initially female $(2A + XX)$.
During the early cleavage stage (two-celled proembryo),one of the $X$ chromosomes fails to move to the daughter cell due to non-disjunction or chromosome loss.
As a result,one daughter cell retains the normal female genotype $(2A + XX)$,while the other daughter cell receives only one $X$ chromosome $(2A + X)$,which develops into male tissue.
Therefore,the correct chromosomal configuration is $2A + XX$ in one cell and $2A + X$ in the other.

(B) The genic balance theory of sex determination was proposed by $C.B. Bridges$ in $1921$ based on his studies on $Drosophila$ $melanogaster$.
According to this theory,sex 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 it is $0.5$,the individual is a male; and if it is between $0.5$ and $1.0$,the individual is an intersex.

(D) In humans,sex determination is based on the type of sperm that fertilizes the egg. The father produces two types of sperms: $50\%$ containing the $X$ chromosome and $50\%$ containing the $Y$ chromosome. The egg always contains an $X$ chromosome. If an $X$-bearing sperm fertilizes the egg,a daughter $(XX)$ is born,and if a $Y$-bearing sperm fertilizes the egg,a son $(XY)$ is born. The birth of five daughters is a matter of probability; each fertilization event is independent,and by chance,an $X$-bearing sperm fertilized the egg in every instance.

(C) In humans,the sex of an individual is determined by the presence of specific sex chromosomes. Females possess two $X$ chromosomes $(XX)$,while males possess one $X$ chromosome and one $Y$ chromosome $(XY)$. The presence of the $Y$ chromosome is the primary factor that triggers the development of male characteristics,thus determining the genetic identity of a human male.

(B) The $Genic$ $balance$ $theory$ of sex determination was proposed by $C.B.$ $Bridges$ in $Drosophila$ $melanogaster$.
According to this theory,the sex of an individual is determined by the ratio of the number of $X$-chromosomes $(X)$ to the number of sets of autosomes $(A)$.
This ratio is expressed as $X/A$ ratio.
If the $X/A$ ratio is $1.0$,the individual is a female; if it is $0.5$,the individual is a male; and if it is between $0.5$ and $1.0$,it is an intersex.

(D) The chromosomal theory of sex determination was proposed by the American biologist $C.E. McClung$ in $1902$,based on his studies of chromosomes in grasshoppers. Since this name is not listed in the options provided,the correct choice is $D$.

(A) In humans,the sex determination mechanism is $XX-XY$ type.
Female individuals are homogametic,meaning they possess two identical sex chromosomes,which are $XX$.
Male individuals are heterogametic,meaning they possess two different sex chromosomes,which are $XY$.
Therefore,the sex chromosomes in females are $XX$.

(A) In Melandrium (a type of garden flower),sex determination follows the $XX-XY$ type or Lygaeus type of chromosomal mechanism,which is similar to the mechanism observed in many animals,including humans. In this system,the female is homogametic $(XX)$ and the male is heterogametic $(XY)$.

(C) The Barr body is a condensed, inactive $X$ chromosome found in the cells of individuals with more than one $X$ chromosome.
In humans, females typically have two $X$ chromosomes $(XX)$, one of which is inactivated to form a Barr body.
Normal males have only one $X$ chromosome $(XY)$ and therefore do not possess a Barr body.
Thus, the presence of a Barr body in the $WBC$ (white blood cell) indicates that the individual is a normal female.

(B) Sex determination in $Drosophila$ $melanogaster$ is determined by the ratio of the number of $X$ chromosomes to the number of sets of autosomes $(A)$.
This is known as the Genic Balance Theory,proposed by $C$.$B$. Bridges.
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.
Therefore,the sex is determined by the genetic balance between the $X$-chromosome and autosomes.

(A) In the $Melandrium$ plant,sex determination follows the $XY$ type mechanism.
$1$. The female plants are homogametic with $XX$ chromosomes.
$2$. The male plants are heterogametic with $XY$ chromosomes.
$3$. The $Y$ chromosome in $Melandrium$ carries the male-determining factors,making it responsible for the development of male sex organs. Therefore,the presence of the $Y$ chromosome determines the male sex.

(C) Barr bodies are the inactive $X$ chromosomes in the somatic cells of female mammals.
They appear as condensed,dark-staining masses of chromatin located at the periphery of the nucleus.
Because they stain intensely with basic dyes,they are referred to as chromatin-positive.

(A) In humans,sex determination is based on the $XY$ chromosome system. During fertilization,the male gamete (sperm) carries either an $X$ or a $Y$ chromosome,while the female gamete (ovum) always carries an $X$ chromosome.
Each pregnancy is an independent event. The probability of having a boy or a girl remains $50\%$ for every conception,regardless of the gender of the previous children.
Therefore,the probability of the $6^{th}$ child being a son is $1/2$ or $50\%$.

(A) The correct answer is $A$. The chromosomal basis of sex determination was first discovered in the plant $Melandrium$ (also known as $Lychnis$ $dioica$). In this plant,sex is determined by the presence or absence of the $Y$-chromosome. Individuals possessing a $Y$-chromosome are male,while those lacking it are female.

(B) In $Drosophila$,sex determination is based on 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 $(A)$.
This ratio is known as the sex index ratio $(X/A)$.
For example,in a superfemale,the number of $X$-chromosomes is $3$ and the number of sets of autosomes is $2$,resulting in a ratio of $3/2 = 1.5$.

(B) Sex-linked characters are traits controlled by genes located on the sex chromosomes ($X$ or $Y$).
In humans,most sex-linked traits are recessive and are located on the non-homologous region of the $X$-chromosome.
Because males have only one $X$-chromosome $(XY)$,they express these recessive traits even if they have only one copy of the gene.
Therefore,sex-linked characters are predominantly recessive in nature.

(C) Sex-linked inheritance refers to the transmission of traits whose genes are located on the sex chromosomes ($X$ or $Y$).
These genes are inherited along with the sex of the individual.
Since sex chromosomes determine the sex of an organism,any gene located on these chromosomes is termed sex-linked.
Therefore,the correct answer is that the gene is carried on $X$ and $Y$ chromosomes.

(A) Traits controlled by genes located on the sex chromosomes ($X$ or $Y$) are known as sex-linked traits.
Since the $X$ chromosome is a sex chromosome,genes present on it exhibit sex-linked inheritance.
Examples include color blindness and hemophilia in humans.

(C) The $Y$ chromosome is present only in males ($XY$ genotype).
During gametogenesis,a male produces two types of sperms: one carrying the $X$ chromosome and the other carrying the $Y$ chromosome.
Since the gene is located on the $Y$ chromosome,every son who inherits the $Y$ chromosome from his father will receive this gene.
Therefore,a man will transmit his $Y$-linked gene to all of his sons.

(C) Sex-linked characters are those whose genes are located on the sex chromosomes ($X$ or $Y$).
$1$. Genes located on the $X$-chromosome show criss-cross inheritance,where the trait is passed from the father to the daughter and then to the grandson.
$2$. However,genes located on the $Y$-chromosome (holandric genes) are passed directly from father to son.
$3$. Since sex-linked genes can be located on either the $X$ or $Y$ chromosome,they are not restricted to the $X$-chromosome alone,and they do not always follow criss-cross inheritance (as $Y$-linked traits do not).
$4$. Therefore,the most accurate statement among the choices is that they may be present on the $Y$-chromosome.

(A) Sex-linked genes are genes that are located on the sex chromosomes ($X$ or $Y$).
In humans,the majority of sex-linked genes are located on the $X$-chromosome because it is much larger and contains more genes than the $Y$-chromosome.
Genes located specifically on the $X$-chromosome are called $X$-linked genes,while those on the $Y$-chromosome are called $Y$-linked or holandric genes.
Since the question asks for the general location of sex-linked genes in humans,the most accurate and primary location is the $X$-chromosome.

(D) Sex-linked inheritance refers to the transmission of traits whose determining genes are located on the sex chromosomes.
In humans,sex chromosomes include both the $X$ and $Y$ chromosomes.
$X$-linked traits are determined by genes located on the $X$ chromosome,while $Y$-linked (holandric) traits are determined by genes located on the $Y$ chromosome.
Since both $X$ and $Y$ chromosomes carry genes that can be inherited,sex-linked inheritance occurs through both.

(C) The inheritance pattern described is known as holandric inheritance.
In humans,the $Y$ chromosome is passed directly from father to son.
Since the character is transmitted from a father to all his sons and subsequently to all their sons,the gene responsible for this trait must be located on the non-homologous region of the $Y$ chromosome.
Therefore,the correct option is $C$.

(A) In fruit flies ($Drosophila$ $melanogaster$),the sex determination is of the $XY$ type.
When a male is heterozygous for sex-linked genes,he possesses one $X$ chromosome and one $Y$ chromosome.
During meiosis,the $X$ chromosome and the $Y$ chromosome segregate into different gametes.
As a result,$50\%$ of the sperm cells receive the $X$ chromosome and $50\%$ receive the $Y$ chromosome.
Therefore,the ratio of male-specific chromosomes ($X$ and $Y$) entering the gametes is $1:1$.

(D) In this scenario,the father is diseased and the mother is normal.
All daughters inherit the $X$ chromosome from their father,while all sons inherit the $Y$ chromosome from their father.
Since all daughters are diseased and all sons are normal,the disease-causing gene must be located on the $X$ chromosome inherited from the father.
Because the trait is expressed in all daughters (who receive the $X$ chromosome from the father),it indicates that the gene is $X$-linked dominant.
If it were $X$-linked recessive,the daughters would be carriers but not necessarily diseased unless the mother was also a carrier or affected.
Therefore,the pattern of inheritance is $X$-linked dominant.

(A) Sex is determined at the time of fertilization by the nature of the sperm that fertilizes the egg.
In humans,females are homogametic $(XX)$ and males are heterogametic $(XY)$.
Sperms produced by males are of two types: $50\%$ carry the $X$ chromosome and $50\%$ carry the $Y$ chromosome.
If a $Y$-bearing sperm fertilizes the egg $(X)$,the resulting zygote is $XY$,which develops into a male child.
If an $X$-bearing sperm fertilizes the egg $(X)$,the resulting zygote is $XX$,which develops into a female child.

(C) In humans,sex determination is of the $XY$ type.
Females possess two $X$ chromosomes $(XX)$,making them homogametic.
Males possess one $X$ chromosome and one $Y$ chromosome $(XY)$,making them heterogametic.
Therefore,the male human is represented by $XY$ sex chromosomes.

(A) In humans,sex determination is of the $XX-XY$ type.
Females are homogametic,producing gametes with $22 + X$ chromosomes.
Males are heterogametic,producing gametes with either $22 + X$ or $22 + Y$ chromosomes.
When a sperm carrying an $X$ chromosome $(22 + X)$ fertilizes an egg $(22 + X)$,the resulting zygote has a chromosomal composition of $44 + XX$,which develops into a female.
Therefore,the correct composition for a female-destined zygote is $44 + XX$.

(D) In humans and many other organisms,chromosomes are classified into two types: autosomes and sex chromosomes (allosomes).
Autosomes are the homologous chromosomes that are present in both males and females and carry genes for somatic traits.
In humans,there are $22$ pairs of autosomes.
Sex chromosomes (heterosomes or allosomes) differ between males and females (e.g.,$XY$ in males and $XX$ in females).
Therefore,the correct term for homologous chromosomes present in both sexes is autosomes.