Mendelism Questions in English

(D) Mendel studied seven pairs of contrasting traits in pea plants $(Pisum \text{ } sativum)$.
In the case of flower position, the axial position is dominant, while the terminal position is recessive.
Violet flower color, round seed shape, and green pod color are all dominant traits.
Therefore, the terminal flower position is the correct recessive trait among the given options.

(C) Gregor Mendel selected $7$ pairs of contrasting traits in pea plants ($Pisum$ $sativum$) for his experiments. These traits are:
$1$. Stem height (Tall/Dwarf)
$2$. Flower color (Violet/White)
$3$. Flower position (Axial/Terminal)
$4$. Pod shape (Inflated/Constricted)
$5$. Pod color (Green/Yellow)
$6$. Seed shape (Round/Wrinkled)
$7$. Seed color (Yellow/Green)
Flower shape is not among the traits studied by Mendel. Therefore,the correct option is $C$.

(D) recessive gene is a type of allele that does not produce a trait at the phenotypic level when present in a heterozygous condition (i.e.,paired with a dominant allele).
$1$. In a heterozygous state $(Aa)$,the dominant allele $(A)$ masks the expression of the recessive allele $(a)$.
$2$. The recessive trait is only expressed phenotypically when the organism is homozygous for the recessive allele $(aa)$.
$3$. Therefore,statements $A$,$B$,and $C$ are all correct descriptions of a recessive gene.

(B) In genetics, a gene that expresses its phenotype even in the heterozygous condition (where two different alleles are present) is known as a $Dominant$ gene.
Conversely, a $Recessive$ gene is one that only expresses its phenotype when it is in a homozygous condition (where both alleles are identical).
Therefore, the correct answer is $B$.

(A) $Test \ cross$ is a genetic cross between an individual with an unknown genotype and a homozygous recessive individual.
It is specifically used to determine whether an individual exhibiting a dominant phenotype is homozygous dominant or heterozygous.
If the offspring show a $1:1$ phenotypic ratio,the parent is heterozygous.
If all offspring show the dominant phenotype,the parent is homozygous dominant.

(A) Gregor Mendel selected $7$ pairs of contrasting traits in pea plants $(Pisum \text{ } sativum)$.
Although the pea plant has $7$ pairs of chromosomes, Mendel's $7$ traits were located on $4$ different chromosomes.
Specifically, these traits are distributed across chromosomes $1, 4, 5,$ and $7$.

(B) In genetics,the trait that expresses itself in the $F_1$ generation is called the dominant trait.
Given that the plant with white flowers is the dominant one,the alleles for white color will mask the expression of the alleles for red color.
Therefore,all offspring in the $F_1$ generation will exhibit the dominant phenotype.
Since white is the dominant color,the $F_1$ generation will have white flowers.

(C) According to Gregor Mendel,the units of inheritance are called 'factors'.
These factors exist in alternative forms that control the expression of a trait.
In modern genetics,these alternative forms of a gene are known as 'alleles' or 'allelomorphs'.
Therefore,the term used by Mendel for these alternative forms was 'factors'.

(A) The phenotype of an organism is determined by its genotype and the environment.
Growth hormones (like gibberellins) can induce temporary phenotypic changes in a plant,making a genetically dwarf plant appear tall.
However,these changes are purely physiological and do not alter the genetic makeup (genotype) of the plant.
The genotype of the dwarf plant remains homozygous recessive $(tt)$.
When this treated dwarf plant $(tt)$ is crossed with another dwarf plant $(tt)$,all offspring in the $F_1$ generation will have the genotype $tt$.
Therefore,all offspring will be phenotypically dwarf.

(A) $Test \ cross$ is a genetic cross between an individual of unknown genotype (showing a dominant trait) and a homozygous recessive individual.
This method is used to determine whether the individual with the dominant phenotype is homozygous dominant or heterozygous.
If the offspring show both dominant and recessive traits, the parent is heterozygous.
If all offspring show the dominant trait, the parent is homozygous dominant.

(C) Mendel selected $7$ pairs of contrasting traits in pea plants. These traits were:
$1$. Stem height (Tall/Dwarf)
$2$. Flower color (Violet/White)
$3$. Flower position (Axial/Terminal)
$4$. Pod shape (Inflated/Constricted)
$5$. Pod color (Green/Yellow)
$6$. Seed shape (Round/Wrinkled)
$7$. Seed color (Yellow/Green)
Out of these,the traits related to the pea pod are Pod shape and Pod color. Therefore,there are $2$ traits related to the pea pod.

(C) In diploid organisms,chromosomes exist in homologous pairs.
Genes (alleles) also exist in pairs within the somatic cells of diploid organisms.
However,gametes are haploid $(n)$ cells produced through meiosis.
During gametogenesis,the homologous chromosomes and alleles segregate,resulting in gametes that contain only one set of chromosomes and one allele for each trait.
Therefore,gametes do not contain characteristics in pairs.

(D) Mendel's laws of inheritance are based on the principles of segregation and independent assortment,which occur during the formation of gametes in sexual reproduction.
Vegetative propagation and asexual reproduction involve the production of offspring from a single parent without the fusion of gametes or genetic recombination.
Therefore,in plants that reproduce exclusively through vegetative or asexual means,the genetic variation and segregation patterns described by Mendel do not occur.
Thus,Mendel's laws are not applicable to plants showing vegetative propagation or asexual reproduction.

(C) In genetics,a gene contains the information to produce a specific enzyme. If a modified allele produces a normal enzyme,it functions exactly like the original wild-type allele. Since the enzyme produced is normal and functional,it will catalyze the same biochemical reaction as the original enzyme. Consequently,the trait expressed by the organism will be the same as the wild-type,meaning the phenotype will remain unchanged.

(C) In genetics,a gene that expresses its phenotype only when present in a homozygous condition (e.g.,$aa$) is known as a recessive gene.
Dominant genes are expressed in both homozygous $(AA)$ and heterozygous $(Aa)$ conditions.
Therefore,the correct answer is the recessive gene.

(A) The probability of having a boy or a girl in a single birth is $1/2$ each.
Since the gender of each child is an independent event,the probability of having four sons in a row is calculated by multiplying the individual probabilities.
Probability = $(1/2) \times (1/2) \times (1/2) \times (1/2) = 1/16$.
Therefore,the probability of a couple having four sons is $1/16$.

(D) The term 'gene' was coined by the Danish botanist $W.L. Johannsen$ in $1909$.
He used this term to replace the word 'factor' used by Gregor Mendel to describe the units of heredity.
Therefore,Johannsen is credited with introducing the term 'gene' to represent Mendelian factors.

(A) The gene is defined as the functional unit of inheritance. It is a segment of $DNA$ that codes for a specific polypeptide or functional $RNA$ molecule. While $DNA$ is the genetic material,the gene represents the specific sequence that carries the instructions for biological traits.

(A) Gregor Mendel,through his experiments on pea plants,proposed that characters are controlled by discrete units called 'factors' (now known as genes). He demonstrated that these factors are inherited from parents to offspring and determine the physical appearance or phenotype of the organism.

(A) Gregor Mendel selected $7$ pairs of contrasting characters in the garden pea plant ($Pisum$ $sativum$) for his hybridization experiments.
These characters include stem height,flower color,flower position,pod shape,pod color,seed shape,and seed color.

(A) The genotypic ratio of a monohybrid cross is $1:2:1$ for $TT, Tt,$ and $tt$ genotypes.
This ratio corresponds to the expansion of the binomial expression $(ax + by)^n$,where $n$ represents the number of gene pairs involved.
For a monohybrid cross,$n = 2$ (as it involves one pair of alleles,$T$ and $t$,resulting in $1TT : 2Tt : 1tt$).
Therefore,the expression is $(ax + by)^2 = a^2x^2 + 2abxy + b^2y^2$,which mathematically represents the $1:2:1$ ratio.

(A) Mendel obtained the recessive character in the $F_{2}$ generation by self-pollinating the $F_{1}$ plants.
Mendel cross-pollinated a pure tall pea plant and a pure dwarf pea plant. He called them the parental generation,denoted by the symbol $P$.
This hybridization is popularly called a monohybrid cross.
In the $F_{1}$ generation,all plants are tall. When these $F_{1}$ plants are self-pollinated,they produce the $F_{2}$ generation.
In the $F_{2}$ generation,the phenotypic ratio is $3:1$ (three tall and one dwarf). Thus,the recessive dwarf character reappears in the $F_{2}$ generation due to the self-pollination of $F_{1}$ hybrids.

(A) homozygous individual possesses identical alleles for a particular trait (e.g.,$AA$ or $aa$).
Since both alleles are the same,the individual can only produce one type of gamete (either $A$ or $a$).
Therefore,the number of types of gametes produced by a homozygous individual is $1$.

(D) Dominant alleles are expressed in both homozygous and heterozygous conditions.
According to the Principle of Dominance:
In heterozygous individuals or hybrids,a character is represented by two contrasting factors called alleles or allelomorphs. Out of the two contrasting alleles,only one is able to express its effect in the individual. It is called the dominant factor or dominant allele.
The other allele,which does not show its effect in the heterozygous individual,is called the recessive factor or recessive allele. The cross between a pure tall and a pure dwarf plant gives all progeny $(F_{1})$ as tall.
The character shown by the $F_{1}$ generation is called the dominant character.

(C) Mendel worked on garden pea $(Pisum \text{ } sativum)$ and formulated the laws of inheritance, including the Law of Segregation, which is demonstrated by a monohybrid cross.
However, Mendel did not discover linkage; in fact, he failed to observe it because the genes he studied were either far apart or on different chromosomes.
The phenomenon of linkage was discovered and fully explained as a theory by $T. H. Morgan$ in $1911$.

(C) Gregor Mendel died in $1884$,long before his work was recognized by the scientific community.
In $1900$,three scientists independently rediscovered the principles of heredity that had already been established by Mendel.
These three scientists were:
$1.$ Hugo de Vries (Holland)
$2.$ Carl Correns (Germany)
$3.$ Erich von Tschermak (Austria)
Therefore,the correct individuals are $II, III,$ and $IV$.

(C) test cross is a genetic cross between an individual with a dominant phenotype (whose genotype is unknown,i.e.,either homozygous dominant or heterozygous) and a homozygous recessive individual.
This cross is used to determine the genotype of the dominant individual.
If the dominant individual is heterozygous $(Aa)$,the test cross with a homozygous recessive parent $(aa)$ results in a $1:1$ phenotypic ratio of dominant to recessive offspring.
If the dominant individual is homozygous dominant $(AA)$,all offspring will exhibit the dominant phenotype.

(A) Gregor Mendel selected $7$ pairs of contrasting traits in pea plants for his experiments.
Each pair consists of one dominant trait and one recessive trait.
Therefore,there are $7$ dominant traits and $7$ recessive traits in total.

(C) The term 'gene' was coined by the Danish botanist Wilhelm Johanssen in $1909$. He introduced this term to replace the term 'factor' used by Gregor Mendel to describe the unit of heredity.

(B) Gregor Mendel is known as the father of genetics. His primary contribution was the formulation of the laws of inheritance (Law of Dominance,Law of Segregation,and Law of Independent Assortment). These laws provide a clear mechanism that explains the patterns of inheritance observed in living organisms,specifically how traits are passed from parents to offspring.

(B) The correct answer is the Dominant character.
According to the Law of Dominance:
In heterozygous individuals or hybrids,a character is represented by two contrasting factors called alleles or allelomorphs.
Out of these two contrasting alleles,only one is able to express its effect in the individual. This is called the dominant factor or dominant allele.
The other allele,which does not show its effect in the heterozygous individual,is called the recessive factor or recessive allele.
For example,a cross between a pure tall plant and a pure dwarf plant results in all progeny in the $F_{1}$-generation being tall,as the tall trait is dominant over the dwarf trait.

(D) Mendel performed experiments on pea plants by manually transferring pollen grains from the anther of one flower to the stigma of another flower. This process is known as artificial pollination or cross-pollination. By using true-breeding lines (e.g.,$TT$ and $tt$),he ensured controlled hybridization to study the inheritance of traits.

(C) Mendel's work was rediscovered independently in $1900$ by three scientists: Hugo de Vries (Dutch),Carl Correns (German),and Erich von Tschermak (Austrian). Among the given options,Carl Correns is one of the rediscoverers.

(A) The principles or laws of inheritance were enunciated by $Gregor \text{ } Mendel$. He proposed these laws based on his experiments with garden peas $(Pisum \text{ } sativum)$.
There are three main laws of inheritance:
$1.$ $\text{Law of Dominance}$: In a heterozygote, one allele masks the presence of another allele for the same character.
$2.$ $\text{Law of Segregation}$: Alleles of a gene pair segregate from each other during gamete formation so that each gamete carries only one allele.
$3.$ $\text{Law of Independent Assortment}$: The alleles of different genes assort independently of one another during gamete formation.

(A) The father of experimental genetics is $TH$ Morgan.
He is also known as the 'fly man of genetics' because he selected the fruit fly ($Drosophila$ $melanogaster$) as his primary research material for his experiments in genetics.

(A) Punnett square was developed by the British geneticist Reginald $C.$ Punnett.
It is a graphical representation used to calculate the probability of all possible genotypes of offspring in a genetic cross.

(C) Mendel's success was due to several key factors:
$(i)$ Selection of the pea plant ($Pisum$ $sativum$),which is easy to grow and has distinct contrasting traits.
$(ii)$ He studied one or two characters at a time,which simplified the analysis of inheritance patterns.
$(iii)$ He maintained a complete and systematic record of every cross and generation.
$(iv)$ He applied statistical methods and laws of probability to analyze his data,which was a novel approach at the time.
Knowledge of history $(II)$ did not contribute to his success in genetics. Therefore,factors $I, III,$ and $IV$ are correct.

(C) When an $F_{1}$ hybrid is crossed with its recessive parent,it is called a test cross.
By performing a test cross,the heterozygosity and homozygosity of an organism can be determined.
The test cross ratio in a monohybrid cross is $1:1$,and in a dihybrid cross,the ratio is $1:1:1:1$.

(A) Gregor Johann Mendel conducted his hybridization experiments on garden pea $(Pisum\, sativum)$ for $7\, years$, specifically from $1856$ to $1863$.

(B) Mendel's monohybrid cross between tall and dwarf plants resulted in a $3: 1$ phenotypic ratio in the $F_{2}$-generation.
$1$. Law of Dominance: This law explains that in a heterozygous condition,one allele expresses itself (dominant) while the other remains masked (recessive). The $3: 1$ ratio supports this.
$2$. Law of Segregation: This law states that alleles separate during gamete formation so that each gamete carries only one allele for a trait. This is the basis for the $3: 1$ ratio.
$3$. Law of Independent Assortment: This is deduced from dihybrid crosses,not monohybrid crosses.
$4$. Incomplete Dominance: This is a deviation from Mendelian inheritance where the $F_{1}$ phenotype is intermediate,not dominant.
Therefore,only $I$ and $III$ are deduced from this specific result.

(A) Gregor Johann Mendel,known as the father of genetics,conducted his hybridization experiments on the garden pea plant.
The scientific name of the garden pea is $Pisum \ sativum$.
He chose this plant because it has several contrasting traits,a short life cycle,and is easy to cultivate.

(C) Allelomorphs,or simply called alleles,represent a pair of contrasting characters. An allele is one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome.

(A) test cross is performed to determine the genotype of an organism showing a dominant phenotype.
In a test cross,an organism with an unknown genotype (exhibiting a dominant trait) is crossed with a homozygous recessive individual.
If the unknown organism is homozygous dominant,all offspring will show the dominant phenotype.
If the unknown organism is heterozygous,the offspring will show a $1:1$ ratio of dominant and recessive phenotypes.
Therefore,Mendel used the test cross to identify the genotype of $F_{1}$ individuals.

(A) The condition in which the alleles at a given locus are identical is called homozygous.
In a homozygous condition,an organism possesses two similar alleles for a particular character on homologous chromosomes,$e.g., TT$ or $tt$.
Conversely,an organism containing two different alleles for a particular character,$e.g., Tt$,is known as heterozygous.

(A) The $Rh$ factor is a protein found on the surface of red blood cells. The presence of the $Rh$ factor is determined by a dominant allele. Individuals who possess the $Rh$ factor are classified as $Rh^+$ (Rh-positive),while those who lack it are $Rh^-$ (Rh-negative). The $Rh^+$ allele is dominant over the $Rh^-$ allele,meaning that even a single copy of the $Rh^+$ allele results in the expression of the $Rh$ factor. In contrast,Haemophilia,Albinism,and Colour blindness are all recessive genetic traits.

(C) Gregor Mendel selected $7$ pairs of contrasting characters in pea plants ($Pisum$ $sativum$) for his hybridization experiments.
These characters include: $(1)$ Stem height,$(2)$ Flower colour,$(3)$ Flower position,$(4)$ Pod shape,$(5)$ Pod colour,$(6)$ Seed shape,and $(7)$ Seed colour.
Therefore,the total number of contrasting character pairs studied by Mendel is $7$.

(B) In Mendel's monohybrid cross,the recessive trait (dwarfness) is masked in the $F_{1}$ generation because all offspring are heterozygous tall.
The recessive trait first reappears in the $F_{2}$ generation,where the phenotypic ratio is $3$ tall : $1$ dwarf.
In the $F_{3}$ generation,the dwarf plants from the $F_{2}$ generation,when self-pollinated,continue to produce only dwarf plants (breeding true),while the tall plants from the $F_{2}$ generation show mixed results (some breed true as tall,others produce both tall and dwarf offspring).
Therefore,the recessive character is expressed in both the $F_{2}$ and $F_{3}$ generations,but it is first observed in the $F_{2}$ generation. Given the options,the most accurate description of where the recessive character appears is the $F_{2}$ generation.

(D) Mendel's work remained unrecognized for a long time due to several reasons:
$(i)$ Communication was not easy at that time,so his work could not be widely publicized.
$(ii)$ The concept of factors (genes) as stable and discrete units that did not blend was not accepted by his contemporaries,who believed in the 'blending inheritance' theory.
$(iii)$ The use of mathematics and statistics to explain biological phenomena was a completely new approach and was largely unacceptable to the biologists of that era.
$(iv)$ He could not provide any physical proof for the existence of factors,as the concept of chromosomes and $DNA$ was not known at that time.
Therefore,all the given statements are correct.

(B) true breeding line is one that,having undergone continuous self-pollination,shows the stable trait inheritance and expression for several generations.
Option $(B)$ is incorrect because a true breeding line maintains the expression of traits for many generations,not just a few.

(C) In $Pisum$ $sativum$ (edible pea),Mendel identified seven pairs of contrasting traits.
$1$. Seed colour: Yellow is dominant,while Green is recessive.
$2$. Flower position: Axial is dominant,while Terminal is recessive.
$3$. Pod shape: Inflated is dominant,while Constricted is recessive.
$4$. Pod colour: Green is dominant,while Yellow is recessive.
Therefore,Green seed colour is a recessive trait,not a dominant one.