Mendelism Questions in English

(C) The year $1900 \, AD$ is highly significant in the history of genetics because it marks the rediscovery of Gregor Mendel's work on the laws of inheritance.
Three scientists,Hugo de Vries,Carl Correns,and Erich von Tschermak,independently rediscovered Mendel's results on the inheritance of characters in plants,which had been published earlier but remained largely ignored until this time.

(A) In diploid organisms,genes are present in pairs known as alleles. These alleles occupy the same locus on homologous chromosomes. Homologous chromosomes are pairs of chromosomes that have the same gene sequence and structure,one inherited from each parent. Therefore,the correct answer is $A$.

(D) Mendel selected $7$ pairs of contrasting traits in pea plants ($Pisum$ $sativum$).
Among these $7$ traits,there were $2$ traits specifically related to the pea pod:
$1$. Pod shape (Inflated vs. Constricted)
$2$. Pod color (Green vs. Yellow)
Therefore,Mendel studied $2$ traits of the pea pod.

(A) Mendel studied $7$ pairs of contrasting traits in pea plants $(Pisum \text{ } sativum)$.
These traits are categorized as follows:
$1$. Flower: $2$ traits (Flower color, Flower position).
$2$. Pod: $2$ traits (Pod shape, Pod color).
$3$. Seed: $2$ traits (Seed shape, Seed color).
(Note: The remaining trait is Stem height).
Therefore, the number of traits for flowers, pods, and seeds are $2, 2, 2$ respectively.

(D) Mendel studied $7$ pairs of contrasting traits in pea plants. These traits are controlled by genes located on $4$ different chromosomes in the pea plant $(Pisum \text{ } sativum)$.
Specifically, the distribution is as follows:
- Chromosome $1$: $2$ genes (e.g., seed shape and flower color).
- Chromosome $4$: $3$ genes (e.g., pod shape, pod color, and flower position).
- Chromosome $5$: $1$ gene (e.g., stem height).
- Chromosome $7$: $1$ gene (e.g., seed color).
Therefore, the correct distribution is $2$ on chromosome $1$, $3$ on chromosome $4$, $1$ on chromosome $5$, and $1$ on chromosome $7$.

(C) $Drosophila$ $melanogaster$,commonly known as the fruit fly,is a model organism used extensively in genetics.
In laboratory conditions,$Drosophila$ are typically cultured on a medium that provides necessary nutrients and moisture.
Ripe banana is considered the most suitable and natural medium for their culture because it provides the necessary carbohydrates and yeast growth,which serves as the primary food source for both larvae and adults.
Therefore,option $C$ is the correct answer.

(C) The unit of inheritance is the $Gene$.
According to Mendelian genetics,genes are the discrete units of heredity that are passed from parents to offspring.
They contain the information necessary to express specific traits.
Phenotype refers to the observable characteristics,while genotype refers to the genetic makeup of an organism.

(C) Mendel's Law of Dominance states that in a dissimilar pair of factors (alleles),one member of the pair dominates (dominant) the other (recessive).
Option $C$ is incorrect because it states that in a 'similar' pair of factors,one dominates the other,whereas dominance only occurs in a 'dissimilar' (heterozygous) pair.
In a homozygous (similar) pair,both factors are identical,so there is no dominance relationship between them.

(B) The phrase "$Like\, begets\, like$" refers to the biological principle that organisms produce offspring that resemble themselves. This continuity of traits from parents to offspring is known as heredity. Heredity is the transmission of genetic characters from parents to their progeny, ensuring that the fundamental characteristics of a species are maintained across generations.

(C) $Drosophila$ $melanogaster$ (fruit fly) is an ideal organism for genetic studies because:
$1$. It completes its life cycle in about two weeks.
$2$. $A$ single mating produces a large number of progeny.
$3$. It has clear sexual dimorphism (male and female are easily distinguishable).
$4$. It has many types of hereditary variations that can be seen with low-power microscopes.
Option $C$ is incorrect because it states that variations can be seen with 'high-power' microscopes (implied by the original phrasing context),whereas the standard textbook states they are visible under 'low-power' microscopes. Therefore,the statement claiming it requires high-power is false.

(A) In Mendel's experiments on monohybrid crosses,he crossed two true-breeding plants differing in a single trait (e.g.,tall and dwarf).
He observed that all the plants in the $F_1$ generation resembled only one of the parents (the dominant trait).
For example,in a cross between tall and dwarf plants,all $F_1$ plants were tall.
This observation led to the Law of Dominance,which states that in a heterozygous condition,only the dominant allele expresses its phenotype.

(D) In $1900$,three scientists independently rediscovered Mendel's work on the inheritance of characters. These scientists were Hugo de Vries,Carl Correns,and Erich von Tschermak. Thomas Hunt Morgan is known for his work on linkage and recombination in Drosophila,not for the rediscovery of Mendel's laws. Therefore,the correct option is $D$.

(D) In pea plants,the flower color follows Mendelian inheritance where red is dominant over white.
When a pure red $(RR)$ plant is crossed with a pure white $(rr)$ plant,the $F_1$ generation consists of all heterozygous red $(Rr)$ plants.
Since the question implies a cross between pure-breeding parents,the $F_1$ offspring will all express the dominant trait.
Therefore,all $120$ plants will be red.

(D) The $Rh$ factor is inherited as a dominant trait.
An individual is $Rh^+$ (Rh positive) if they possess at least one dominant allele $(R)$.
Therefore,the possible genotypes for an $Rh^+$ individual are homozygous dominant $(RR)$ or heterozygous $(Rr)$.
Since both $RR$ and $Rr$ result in an $Rh^+$ phenotype,the correct answer is $A$ or $B$.

(B) Gregor Mendel chose the garden pea plant $(Pisum \ sativum)$ for his experiments due to several key reasons:
$1$. The pea plant possesses several clearly defined,contrasting traits (e.g.,tall/dwarf,violet/white flowers,round/wrinkled seeds).
$2$. It has a short life cycle,allowing for the study of multiple generations in a relatively short period.
$3$. It is easy to cultivate and can be cross-pollinated artificially.
$4$. The flowers are bisexual and typically undergo self-pollination,which helps in maintaining pure lines.
Therefore,the presence of contrasting traits was a primary factor for his genetic studies.

(D) In diploid organisms,most cells (somatic cells) contain two sets of chromosomes,meaning genes are present in pairs (alleles).
However,gametes (sperm and egg) are haploid $(n)$,meaning they contain only one set of chromosomes.
Therefore,genes are not found in pairs in gametes,as they carry only one allele for each trait.

(D) According to Mendel's experiments on $Pisum \text{ } sativum$ (garden pea), he identified seven pairs of contrasting traits.
In the case of pod color, green pod color is dominant over yellow pod color.
Terminal position of flower is recessive to axial position.
Wrinkled seed is recessive to round seed.
Green seed color is recessive to yellow seed color.
Therefore, the green color of the pod is a dominant trait.

(D) test cross is a genetic cross between an individual showing a dominant phenotype (whose genotype is unknown) and a homozygous recessive individual.
In the context of a monohybrid cross involving height,where $T$ is dominant (tall) and $t$ is recessive (dwarf),the test cross involves crossing an individual of unknown genotype (either $TT$ or $Tt$) with a homozygous recessive individual $(tt)$.
Therefore,the cross $Tt \times tt$ is a classic example of a test cross used to determine the zygosity of the dominant phenotype.

(A) An allele is defined as one of two or more alternative forms of a gene that arise by mutation and are found at the same place (locus) on a chromosome.
Alleles are responsible for the variations in inherited characteristics,such as different eye colors or blood types.
For example,in the gene for plant height,one allele may code for tallness $(T)$ and another for dwarfness $(t)$.

(A) In $1900$,three scientists independently rediscovered Mendel's work on the inheritance of characters. These scientists were Hugo de Vries (from the Netherlands),Carl Correns (from Germany),and Erich von Tschermak (from Austria). They recognized the significance of Mendel's laws of inheritance and brought them to the attention of the scientific community.

(B) Mendel chose the pea plant ($Pisum$ $sativum$) for his experiments because it possesses several advantageous characteristics:
$1$. It has a short life cycle,allowing for the study of multiple generations in a short time.
$2$. It produces a large number of offspring.
$3$. It exhibits distinct,easily observable contrasting traits.
$4$. Most importantly,pea flowers are bisexual and naturally undergo self-pollination,which allows for the production of pure-breeding lines.
$5$. Artificial cross-pollination can also be easily performed.
While animals are difficult to maintain and have complex breeding patterns,the self-pollination capability of pea plants was a critical factor for Mendel to establish pure lines.

(C) Gregor Mendel selected $7$ pairs of contrasting traits in garden peas $(Pisum \text{ } sativum)$ for his hybridization experiments.
These traits include:
$1$. 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).

(B) test cross is a cross between an individual with an unknown genotype (usually an $F_1$ hybrid) and a homozygous recessive parent.
It is used to determine the genotype of the $F_1$ individual.
If the offspring show a $1:1$ phenotypic ratio,the $F_1$ individual is heterozygous.
If all offspring show the dominant trait,the $F_1$ individual is homozygous dominant.

(C) Gregor Mendel published his research work titled 'Experiments on Plant Hybridization' (Versuche über Pflanzen-Hybriden) in $1866$. This work was published in the proceedings of the Natural History Society of Brünn,which is known as 'Verhandlungen des naturforschenden Vereines in Brünn'.

(C) मेंडल के अनुसार,'कारक' (जिन्हें अब 'जीन' के रूप में जाना जाता है) आनुवंशिकता की इकाइयाँ हैं। ये माता-पिता से संतानों में लक्षणों के संचरण के लिए जिम्मेदार होते हैं और विशिष्ट लक्षणों की अभिव्यक्ति के लिए आनुवंशिक जानकारी रखते हैं। इसलिए,विकल्प $A$ और $B$ दोनों सही हैं।

(C) Mendelism,or the laws of inheritance proposed by Gregor Mendel,is based on the principles of segregation and independent assortment. These laws are observed when crossing pure-breeding (homozygous) parents with contrasting traits to produce $F_1$ hybrids,which are then self-pollinated or crossed to study the $F_2$ generation. Option $C$ describes the fundamental starting point of Mendelian experiments,where pure-breeding lines (e.g.,Tall $TT$ and Dwarf $tt$) are crossed to observe the inheritance patterns.

(C) In genetics,a dominant allele $(T)$ expresses its trait even in the presence of a recessive allele $(t)$.
$1$. Individuals with the genotype $TT$ (homozygous dominant) will be tasters.
$2$. Individuals with the genotype $Tt$ (heterozygous) will also be tasters because the dominant allele $T$ masks the effect of the recessive allele $t$.
$3$. Individuals with the genotype $tt$ (homozygous recessive) lack the dominant allele $T$ required to express the tasting trait. Therefore,they are non-tasters and are unable to taste $PTC$.

(D) Mendelism was strengthened by the concept that traits are controlled by discrete units called 'factors' (now known as genes).
These factors occur in pairs and do not blend,which explains the inheritance patterns observed in his experiments.
While the Law of Independent Assortment is a key part of Mendelism,it is derived from dihybrid crosses,not monohybrid crosses.
Incomplete dominance is actually an exception to Mendel's laws,not a point that strengthens them.

(B) Mendel studied $7$ pairs of contrasting traits in pea plants $(Pisum \text{ } sativum)$.
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)
Leaf shape was not one of the traits studied by Mendel. Therefore, the correct option is $B$.

(B) The different forms of a gene that occupy the same locus on homologous chromosomes and control the same trait are known as alleles or allelomorphs. For example,in pea plants,the gene for height has two alleles: one for tall $(T)$ and one for dwarf $(t)$.

(C) Genes are defined as the fundamental units of heredity or inheritance. They are specific segments of $DNA$ that carry instructions for the synthesis of proteins or functional $RNA$ molecules. Through the process of inheritance,these genes are passed from parents to offspring,thereby determining the traits and characteristics of the progeny. Therefore,genes are correctly identified as the units of inheritance.

(D) An organism is said to be $Homozygous$ for a trait if it carries two identical alleles for that specific gene (e.g.,$TT$ or $tt$).
In contrast,$Heterozygous$ organisms carry two different alleles for a gene (e.g.,$Tt$).
Therefore,organisms with identical genetic factors (alleles) are called $Homozygous$.

(A) An allele is one of two or more alternative forms of a gene that arise by mutation and are found at the same place (locus) on a chromosome. These alleles are responsible for coding for contrasting traits (e.g.,tall vs. dwarf). Therefore,the correct answer is $A$.

(A) In genetics, when two different alleles for a trait are present in a hybrid (heterozygous condition), the trait that manifests or is expressed in the phenotype is known as the $Dominant$ trait. The trait that remains masked or hidden in the presence of the dominant allele is called the $Recessive$ trait. Therefore, the correct option is $A$.

(B) The probability of having a daughter in a single birth is $1/2$.
Since each birth is an independent event, the probability of having three daughters in three consecutive births is calculated by multiplying the individual probabilities.
Probability = $P(\text{daughter}) \times P(\text{daughter}) \times P(\text{daughter})$
Probability = $(1/2) \times (1/2) \times (1/2) = 1/8$.
Therefore, the probability of having three daughters is $1/8$.

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

(C) $Test \ cross$ is a genetic cross between an individual exhibiting a dominant phenotype and a homozygous recessive individual.
It is used to determine the genotype of the dominant individual.
If the offspring are all dominant, the parent is homozygous dominant $(AA)$.
If the offspring show a $1:1$ ratio of dominant and recessive phenotypes, the parent is heterozygous $(Aa)$.

(C) test cross is a genetic cross between an individual of unknown genotype (usually showing a dominant phenotype) and a homozygous recessive individual.
It is specifically used to determine whether the individual showing the dominant phenotype is homozygous or heterozygous for a particular trait.
If the offspring show a $1:1$ ratio of dominant to recessive phenotypes,the parent was heterozygous.
If all offspring show the dominant phenotype,the parent was homozygous dominant.

(D) $Test \text{ } cross$ is a genetic cross between an individual of unknown genotype and a homozygous recessive individual.
If the offspring show a $1:1$ phenotypic ratio, the unknown individual is heterozygous.
If all offspring show the dominant phenotype, the unknown individual is homozygous dominant.
Therefore, it is the standard method to determine the zygosity of an organism.

(D) In $1865$,Gregor Mendel proposed that characters are controlled by discrete units called 'factors'.
These factors are now known as 'genes'.
According to Mendel,factors occur in pairs,and they represent the units of inheritance that are passed from parents to offspring.
Therefore,factors are essentially the units of heredity,which we now identify as genes.

(B) Allelic genes (alleles) are alternative forms of a gene that occupy the same locus (position) on homologous chromosomes.
Since homologous chromosomes carry the same genes at the same loci,one allele of a gene is present on one chromosome of the homologous pair,and the other allele is present at the corresponding position on the other chromosome of the same pair.

(A) Dominance is a fundamental principle of genetics,specifically $Mendelian$ genetics. It refers to the phenomenon where,in a heterozygous condition,one allele (the dominant allele) expresses its phenotype while masking or suppressing the expression of the other allele (the recessive allele). Therefore,the dominant gene completely masks the effect of the recessive gene in the $F_1$ generation.

(A) Mendel studied $7$ pairs of contrasting traits in pea plants. Although he assumed independent assortment for all of them,it was later discovered that some of these genes are linked because they reside on the same chromosome.
Specifically,the genes for 'Pod shape' and 'Stem height' are both located on chromosome number $4$ in $Pisum$ $sativum$.
Because they are located on the same chromosome,they exhibit genetic linkage and do not follow the law of independent assortment as strictly as Mendel predicted.
Therefore,the correct pair of traits is 'Pod shape' and 'Stem height'.

(C) In genetics,an allele is a variant form of a gene. $A$ modified allele is considered equivalent to an unmodified (wild-type) allele if it produces the same phenotype. This occurs when the modified allele produces a 'normal enzyme' that functions exactly like the enzyme produced by the unmodified allele,thereby resulting in the same biological effect.

(C) In Mendel's experiments,traits such as seed coat color,flower nature,flower position,pod color,and stem height represent the observable physical characteristics of the pea plant.
These observable characteristics or traits are collectively known as the $Phenotype$.
$Genotype$ refers to the genetic makeup of an organism,while $Alleles$ are different forms of a gene.
Therefore,the correct option is $C$.

(B) test cross involves crossing an individual of unknown genotype with a homozygous recessive individual to determine the genotype of the former. This method requires controlled breeding experiments. In humans,controlled breeding is ethically and socially impossible,making it difficult to perform a standard test cross. In contrast,organisms like $Neurospora$,pea plants,and dogs can be subjected to controlled breeding experiments.

(C) test cross is a genetic cross between a homozygous recessive individual and a corresponding suspected heterozygote or dominant phenotype individual.
It is primarily used to determine the genotype of an organism showing a dominant trait.
By crossing the individual with a homozygous recessive parent,the offspring's phenotypes reveal whether the parent was homozygous dominant or heterozygous.

(A) Mendel studied $7$ pairs of contrasting traits in pea plants $(Pisum \text{ } sativum)$.
These traits include:
$1$. Seed shape: Round/Wrinkled
$2$. Seed color: Yellow/Green
$3$. Flower color: Violet/White
$4$. Pod shape: Inflated/Constricted
$5$. Pod color: Green/Yellow
$6$. Flower position: Axial/Terminal
$7$. Stem height: Tall/Dwarf
Analyzing the options:
Option $A$: Round seeds (Correct), constricted pods (Correct), axial flower position (Correct).
Option $B$: Green seeds (Correct), inflated pods (Correct), axial flower position (Correct).
However, looking at the specific combinations provided in the options, Option $A$ lists three traits that Mendel studied: Seed shape (Round), Pod shape (Constricted), and Flower position (Axial). All these are valid traits from Mendel's list.

(B) Albinism is an autosomal recessive trait. Let $A$ be the allele for normal skin pigmentation and $a$ be the allele for albinism.
An albino man must have the genotype $aa$.
$A$ normal woman can be either $AA$ or $Aa$.
If the woman were $AA$ (homozygous normal),all offspring would be $Aa$ (normal phenotype).
If the woman is $Aa$ (heterozygous normal),the cross $Aa \times aa$ results in $50\%$ $Aa$ (normal) and $50\%$ $aa$ (albino) offspring.
Since the offspring are half albino and half normal,the woman must be heterozygous normal $(Aa)$.

(B) In genetics,a heritable feature is referred to as a $Character$ (e.g.,height of the plant).
Each character can have different detectable variants,which are known as $Traits$ (e.g.,tall or dwarf).
Therefore,a heritable feature and its detectable variant are collectively referred to as a trait.