Mendel's law of inheritance Questions in English

(B) Mendel originally proposed two fundamental laws of inheritance based on his experiments with pea plants.
First, the $Law of Segregation$ (also known as the law of purity of gametes) was derived from his monohybrid cross experiments.
Second, the $Law of Independent Assortment$ was derived from his dihybrid cross experiments.
The $Law of Dominance$ is often considered a conclusion or a principle derived from the monohybrid cross rather than a primary law discovered independently in the same sequence. Among the options provided, the $Law of Segregation$ is the fundamental principle that Mendel established first through his work on single-trait inheritance.

(B) To determine the genotype of an organism showing a dominant phenotype,we perform a test cross. In a test cross,the individual with the unknown genotype is crossed with a homozygous recessive individual.
In this case,the dominant phenotype is orange leaves $(G-)$. The recessive phenotype is green leaves $(gg)$.
If the unknown plant is $GG$,the cross $GG \times gg$ will produce all orange offspring $(Gg)$.
If the unknown plant is $Gg$,the cross $Gg \times gg$ will produce $50\%$ orange $(Gg)$ and $50\%$ green $(gg)$ offspring.
Thus,by crossing with a homozygous recessive plant $(gg)$,we can determine the genotype of the unknown plant.

(A) The law of segregation of characters is also known as the law of purity of gametes. This is because,during the formation of gametes,the two alleles of a gene pair separate from each other such that each gamete receives only one of the two alleles. Thus,the gametes are always pure for a particular trait,meaning they do not contain a mixture of alleles.

(C) Mendel's law of independent assortment states that, "the alleles of different genes segregate independently of each other during meiosis".
Since the gene for blood group (located on chromosome $9$) and the gene for hair color (located on a different chromosome) are inherited independently, an individual can possess any combination of these traits.
This demonstrates that the inheritance of one trait does not influence the inheritance of another trait, which is the core concept of independent assortment.

(C) Mendel's Law of Segregation states that during the formation of gametes (germ cells),the two alleles of a gene pair separate from each other so that each gamete receives only one of the two alleles. This ensures that the offspring receive one allele from each parent,maintaining the diploid condition in the next generation.

(B) The provided figure illustrates the process of meiosis,specifically focusing on the behavior of two pairs of homologous chromosomes during Anaphase-$I$ and Anaphase-$II$.
This diagram demonstrates Mendel's Law of Independent Assortment.
It shows that during the formation of gametes,the segregation of one pair of chromosomes is independent of the segregation of another pair.
As seen in 'Possibility $I$' and 'Possibility $II$',the chromosomes can align in different ways at the metaphase plate,leading to different combinations of chromosomes in the resulting germ cells.
This random alignment and subsequent independent segregation result in the production of various genetic combinations in the offspring.

(B) In $X$-linked recessive inheritance,a carrier female (heterozygous,$X^cX$) carries one recessive allele on one of her $X$ chromosomes.
When she reproduces with a normal male $(XY)$,there is a $50\%$ chance that her sons will inherit the $X$ chromosome carrying the recessive allele $(X^cY)$,resulting in the expression of the trait because males are hemizygous for the $X$ chromosome.
This pattern is known as criss-cross inheritance,where the trait is passed from the mother to the son.
Therefore,the correct option is $B$.

(N/A) The study of inheritance of a single pair of alleles or factors of a trait at a time (monohybrid cross) is called one gene inheritance.
Based on his observations on monohybrid crosses,Mendel proposed two general rules in order to consolidate his understanding of inheritance in monohybrid crosses.
These rules are called the principles or laws of inheritance.
They are:
$1$. Law of Dominance (First Law): $(i)$ Characters are controlled by discrete units called factors. $(ii)$ Factors occur in pairs. $(iii)$ In a dissimilar pair of factors,one member of the pair is dominant while the other is recessive.
This law explains the expression of only one of the parental characters in a monohybrid cross in the $F_1$ generation and the expression of both in the $F_2$ generation. It also explains the $3:1$ phenotypic ratio obtained in the $F_2$ generation.
$2$. Law of Segregation (Second Law): This law states that although the parents contain two alleles,during gamete formation,the factors or alleles of a pair segregate from each other such that each gamete receives only one of the two factors.
Hence,the alleles do not show any blending and both characters are recovered as such in the $F_2$ generation,even though one of these is not seen in the $F_1$ generation.

(N/A) Every gene contains the information to express a particular trait.
In a diploid organism,there are two copies of each gene,i.e.,as a pair of alleles.
These two alleles need not always be identical,as in a heterozygote.
One of them may be different due to some changes that it has undergone,which modifies the information that particular allele contains.
Let us take an example of a gene that contains the information for producing an enzyme.
Now,there are two copies of this gene,the two allelic forms.
Let us assume that the normal allele produces the normal enzyme that is needed for the transformation of a substrate $S$.
Theoretically,the modified allele could be responsible for the production of: $(i)$ the normal/less efficient enzyme,or $(ii)$ a non-functional enzyme,or $(iii)$ no enzyme at all.
In the first case,the modified allele is equivalent to the unmodified allele,i.e.,it will produce the same phenotype/trait,resulting in the transformation of substrate $S$.
Such equivalent allele pairs are very common.
However,if the allele produces a non-functional enzyme or no enzyme,the phenotype may be affected.
The phenotype/trait will only be dependent on the functioning of the unmodified allele.
The unmodified (functioning) allele,which represents the original phenotype,is the dominant allele,and the modified allele is generally the recessive allele.
Hence,in the example above,the recessive trait is seen due to a non-functional enzyme or because no enzyme is produced.

(A) The Law of Dominance states that:
$1$. Characters are controlled by discrete units called factors.
$2$. Factors occur in pairs.
$3$. In a dissimilar pair of factors,one member of the pair dominates the other (dominant),while the other is recessive.
Option $A$ states that alleles remain together without blending. This is actually a postulate of the Law of Segregation (or Purity of Gametes),which states that alleles do not show any blending and that both the characters recover as such in the $F_2$ generation. Therefore,it is not a statement of the Law of Dominance.

(C) Gregor Mendel proposed three fundamental laws of inheritance based on his experiments with pea plants:
$1$. Law of Dominance
$2$. Law of Segregation
$3$. Law of Independent Assortment
Incomplete Dominance and Codominance are deviations from Mendelian inheritance and were discovered after Mendel's work. Therefore,only the Law of Dominance was proposed by Mendel.

(A) According to Mendel's Law of Dominance:
$(1)$ Characters are controlled by discrete units called factors $(D)$.
$(2)$ Factors occur in pairs $(C)$.
$(3)$ In a dissimilar pair of factors,one member of the pair dominates (dominant) the other (recessive) $(A)$.
$(4)$ The Law of Dominance explains why only one of the parental characters is expressed in a $F_1$ generation monohybrid cross $(E)$.
Statement $(B)$ describes the Law of Segregation,which states that alleles do not show any blending and both characters are recovered as such in the $F_2$ generation.
Therefore,statements $A, C, D,$ and $E$ are explained by the Law of Dominance.

(B) Mendel's law of segregation states that the two alleles of a gene pair segregate from each other during the formation of gametes,such that each gamete receives only one of the two alleles.
This law is a fundamental principle of inheritance and applies to all sexually reproducing organisms,regardless of whether the inheritance of one trait (monohybrid cross) or two or more traits (dihybrid or polyhybrid cross) is being studied.
Therefore,the law of segregation is applicable to both monohybrid and dihybrid crosses.

(B) The law of independent assortment states that the segregation of one pair of unit factors is independent of the other pair of unit factors.
Option $A$ is a correct statement.
Option $B$ is false because the independent alignment of chromosome pairs occurs during metaphase-$I$,not telophase-$I$.
Option $C$ is a correct statement as it describes the phenotypic ratio of a dihybrid cross under independent assortment.
Option $D$ is a correct statement because independent assortment only applies to genes located on different chromosomes (or far apart on the same chromosome).

(C) Mendel's experiments on garden pea demonstrated that the factors (alleles) governing contrasting traits do not blend or mix when they coexist in a hybrid.
During gamete formation,these factors segregate from each other,ensuring that each gamete receives only one of the two factors.
This principle of segregation confirms that traits remain distinct and do not show blending in either the $F_1$ or $F_2$ generations.

(C) Mendel's $Law$ $of$ $Segregation$ states that the two alleles of a gene pair segregate from each other during the formation of gametes,such that each gamete carries only one allele for each trait.
In a monohybrid cross,such as $Rr \times Rr$,the $F_1$ hybrid $(Rr)$ produces two types of gametes ($R$ and $r$) in equal proportions.
This segregation ensures that the $F_2$ generation exhibits the phenotypic ratio of $3:1$ and the genotypic ratio of $1:2:1$,which confirms the purity of gametes.

(D) The Law of Segregation is considered universally applicable because it is the only law of inheritance without any known exceptions.
It states that each trait consists of two alleles that segregate during the formation of gametes.
Since gametes are always haploid $(n)$,they contain only one allele for each trait,which ensures that the offspring receive one allele from each parent during fertilization.

(D) मेंडल का युग्मकों की शुद्धता का नियम (Law of Segregation) यह बताता है कि युग्मक निर्माण के दौरान,युग्मविकल्पी जोड़े (allelic pairs) एक-दूसरे से अलग हो जाते हैं,जिससे प्रत्येक युग्मक को केवल एक ही एलील (allele) प्राप्त होता है। इस प्रक्रिया के कारण युग्मक हमेशा शुद्ध होते हैं,अर्थात वे कभी भी मिश्रित नहीं होते हैं। इसलिए,विकल्प $D$ सही उत्तर है।

(B) The $Law$ $of$ $Segregation$ (also known as the $Law$ $of$ $Purity$ $of$ $Gametes$) states that although the two alleles of a gene pair live together in an individual, they do not blend or mix with each other. During the formation of gametes, these alleles separate (segregate) so that each gamete receives only one of the two alleles. This ensures that the traits remain distinct and pure in subsequent generations.

(C) The $Law$ $of$ $Dominance$ states that in a heterozygous condition, only one allele (the dominant one) expresses its phenotype in the $F_1$ generation, masking the other (recessive) allele. However, during gamete formation, these alleles segregate, allowing the recessive trait to reappear in the $F_2$ generation when the recessive alleles pair up again. Thus, the appearance of only one trait in $F_1$ and both traits in $F_2$ is explained by the $Law$ $of$ $Dominance$.

(C) In human genetics,the $Rh$ factor is determined by the presence or absence of the $Rh$ antigen on the surface of red blood cells. The presence of the $Rh$ antigen is controlled by a dominant allele,while its absence is recessive. Therefore,the $Rh+ve$ blood group is a genetically dominant trait. In contrast,$O$ blood group is recessive (genotype $ii$),colour blindness is an $X$-linked recessive disorder,and albinism is an autosomal recessive disorder.