Test: Principles of Inheritance & Variation - 2 - NEET MCQ

• The innate tendency of offspring to resemble their parents is called heredity.
• The offspring resembles the parents due to same genetic combination inherited from the parents.

Hence, the correct option is B

Topic in NCERT: Principles of Inheritance and Variation

Line in NCERT: "Inheritance is the process by which characters are passed on from parent to progeny; it is the basis of heredity."

• Monohybrid ratio is the ratio of different phenotypic traits obtained on hybridizing a single pair of traits. It is 3:1.
• When tall pea plant is crossed with dwarf, the offspring obtained are in 3/4 tall and 1/4 dwarf.

Fig: Monohybrid cross

Hence, the correct option is B
NCERT Reference: Topic: " INHERITANCE OF ONE GENE” of chapter "Principles of Inheritance and Variation" of NCERT

Line in NCERT: "The phenotypic ratio of 3/4th tall: (1/4 TT + 1/2 Tt) and 1/4th tt, i.e., a 3:1 ratio, but a genotypic ratio of 1:2:1."

• Gregor Mendel is known as the Father of Genetics.
• He experimented on pea plants and discovered the basic inheritance rules. 

Hence, the correct option is A
NCERT Reference: Topic  MENDEL’S LAWS OF INHERITANCEof chapter "Principles of Inheritance and Variation" of NCERT

Line in NCERT: "Gregor Mendel, conducted hybridisation experiments on garden peas for seven years (1856-1863) and proposed the laws of inheritance in living organisms."

• Mendel studied the common garden pea plant, Pisum sativum because it was easy to cultivate and had a relatively short life cycle of 3 months. The plant exhibited discontinuous characteristics such as flower colour and pea texture.
• Owing to its anatomy, it was easy to control the self-pollination of the plant and cross-fertilization between desired parents could be accomplished artificially.
• The presence of pure breeding varieties and easily visible contrasting characters and presence of F₁ fertile hybrids were the additional advantageous characters for which Mendel choose garden pea as experimental material. 

Hence, the correct option is C

Topic in NCERT: MENDEL'S LAWS OF INHERITANCE

Line in NCERT: "Mendel conducted such artificial pollination/cross pollination experiments using several true-breeding pea lines."

• The physical appearance of a character or organism's observable characteristics or traits is called as phenotype.
• The genetic makeup of an individual is called genotype. Tallness, round, wrinkled, yellow etc. are due to their genetic makeup.

Phenotype Example:

Hence, the correct option is A
NCERT Reference: Topic " MENDEL’S LAWS OF INHERITANCE” of chapter "Principles of Inheritance and Variation" of NCERT

Line in NCERT: "TT and tt are called the genotype of the plant while the descriptive terms tall and dwarf are the phenotype."

In monohybrid and dihybrid cross F₂ generation is obtained by selfing of F₁ hybrids as male and female.

Fig: Monohybrid cross showing F₁ and F₂ generation

Hence, the correct option is B

Topic in NCERT: Gametes

Line in NCERT: "The F1 plant of the genotype Tt when self-pollinated, produces gametes of the genotype T and t in equal proportion."

• In a dihybrid cross, two new kinds of plants with new traits are formed. This is possible only when all traits assort independently and recombine to form a new combination.
• Mendel found that each pair of alleles segregates independently of the other pairs of alleles during gamete formation. 
• This is known as the Law of independent assortment and hence it can be proved by the dihybrid cross.

Hence, the correct option is C

Topic in NCERT: Law of Independent Assortment

Line in NCERT: "Based upon such observations on dihybrid crosses (crosses between plants differing in two traits) Mendel proposed a second set of generalisations that we call Mendel's Law of Independent Assortment."

• Since the yellow seeds are dominant to green, the allele for yellow seeds should be represented with upper case letter while the one for green seeds should be written in lower case letter.
• Let's suppose that the allele for yellow seed is Y and that for green seeds is y. Hence the genotype of the heterozygous yellow seeded plant will be "Yy" and that for green seeded plant will be "yy" (as the recessive allele is expressed only in homozygous conditions).
• The cross between heterozygous yellow seeded plant and green seeded plant will produce 50% yellow seeded plants and 50% green seeded plants.

Hence, the correct option is C

Topic in NCERT: Law of Independent Assortment

Line in NCERT: "When Mendel self hybridised the F plants he found that 3/4th of F₂ plants had yellow seeds and 1/4th had green. The yellow and green colour segregated in a 3:1 ratio."

• Genotype of pure tall plant with green pod = TTGG
• Genotype of pure dwarf plant with yellow pod = ttgg
• P generation:  TTGG    X  ttgg
• F1 generation: TtGg (tall plant, green pod)

Selfing: TtGg X  TtGg

As can be seen from the table, a total 4 short plants with genotypes ttGG, ttGg, ttGg and ttgg are produced.

Hence, the correct option is B

Topic in NCERT: Mendelian Genetics

Line in NCERT: "1/4th of the random fertilisations lead to TT, 1/2 lead to Tt and 1/4th to tt."

In a test cross:

• The organism with the dominant trait is always crossed with an organism with the recessive trait. 
• If any offspring show the recessive trait, the unknown genotype is heterozygous. 
• If all the offspring have the dominant trait, the unknown genotype is homozygous dominant.

Fig: The test cross

Hence, the correct option is A

Topic in NCERT: Test Cross

Line in NCERT: "Therefore, to determine the genotype of a tall plant at F, Mendel crossed the tall plant from F2 with a dwarf plant. This he called a test cross."

A cross between two individuals, one with AB blood group and the other with A blood group will produce four genotypes and three phenotypes.

The genotypes of a husband and wife are I^AI^B and I^Ai.
Four different possible genotypes of their children are: I^AI^B, I^Ai, I^Bi, I^AI^A

The possible number of phenotypes of their children are:

• Blood group A (I^AI^A, I^Ai)
• Blood group B (I^Bi)
• Blood group AB (IAIB)

Fig: Cross between blood groups AB and A 
Hence, the correct option is B.
NCERT Reference: Topic  Co-dominance” of chapter "Principles of Inheritance and Variation"  of NCERT 

Line in NCERT: "Since there are three different alleles, there are six different combinations of these three alleles that are possible, and therefore, a total of six different genotypes of the human ABO blood types."

• Co-dominance is the phenomenon that deviates from Mendel’s law of inheritance.
• Both the alleles appear in offspring instead of one as in Mendel’s experiment.
• ABO blood grouping in human beings is an example of co-dominance in which both I^A and I^B appear simultaneously to form AB blood type.

Hence, the correct option is D.

Topic in NCERT: Co-dominance

Line in NCERT: "A good example is different types of red blood cells that determine ABO blood grouping in human beings."

• If the genotype is AaBb the alleles that are produced will be AB, Ab, aB, ab, since there are two diallelic characters in the genotypes the person must be heterozygous for both genes. AABB is homozygous. So, the correct answer is "AaBb".

Fig: Diallelic characters in the genotype

Hence, the correct option is B.

NCERT Reference: Topic - INHERITANCE OF TWO GENES” of chapter "Principles of Inheritance and Variation"  of NCERT 

• F1 pink flowered plants are heterozygous. When selfing is done the genotype and phenotype develops as 1:2:1 as 40 red, 80 pink and 40 white flowering plants.  It is called Incomplete dominance.
• The appearance of a new phenotype in the progeny but not either of the parents is called Incomplete dominance.

Fig: Cross showing incomplete dominance in Mirabilis jalapa

Hence, the correct option is C.
NCERT Reference: Topic-  Incomplete Dominance” of chapter "Principles of Inheritance and Variation" of NCERT.

Line in NCERT: "When the F, was self-pollinated the F2 resulted in the following ratio 1 (RR) Red: 2 (Rr) Pink: 1 (rr) White."

• In Snapdragon flower, cross between true-breeding white and red coloured flower produce pink coloured flower in the F1 generation.
• This happens due to the incomplete dominance of alleles over the other.

Hence, the correct option is A.
NCERT Reference: Topic -  Incomplete Dominance of chapter "Principles of Inheritance and Variation" of NCERT.

Line in NCERT: "The inheritance of flower colour in the dog flower (snapdragon or Antirrhinum sp.) is a good example to understand incomplete dominance. In a cross between true-breeding red-flowered (RR) and true-breeding white-flowered plants (rr), the F1 (Rr) was pink."

• When two genes are situated very close to one another on the chromosome, hardly any cross-over is produced.
• Such genes are called linkage and do not separate from each other during gamete formation.

Hence, the correct option is A.

Topic in NCERT: Linkage and Recombination

Line in NCERT: "some genes were very tightly linked (showed very low recombination)"

Sex chromosomes of human beings are heteromorphic as they are of different size. Y chromosome is smaller than X chromosome in size.

Hence, the correct option is D.
NCERT Reference: Topic- SEX DETERMINATION of chapter "Principles of Inheritance and Variation" of NCERT.

Line in NCERT: "In human beings and in Drosophila the males have one X and one Y chromosome, whereas females have a pair of X-chromosomes besides autosomes."

Statement I: The bridge between one generation
and the next is sperm and ovum.

• This statement is correct as the fusion of sperm

and ovum during fertilization forms a zygote, which
develops into a new individual.

Statement II: Both sperm and ovum contribute
equally to heredity.

• This statement is incorrect as the ovum

contributes more to heredity as it contains more
cytoplasm and organelles, including the
mitochondria which have their own DNA. The sperm
only contributes genetic material in the form of
chromosomes.

Statement III: Somatic diploid cells possess two
chromosomes as well as two mendelian factors of
each type.

• This statement is correct as somatic cells are

diploid, meaning they contain two copies of each
chromosome and two copies of each gene (known as
mendelian factors).

Therefore, only statements I and III are correct,
making option B the correct answer.

• In humans, the males are heterogametic as they have XY sex chromosomes, so they make 50% sperms with X chromosome and 50% sperms with Y chromosome. Females are homogametic. All gametes made by them have X chromosomes. So, humans show XX-XY type of sex determination.

Hence, the correct option is A.
NCERT Reference: Topic SEX DETERMINATION of chapter "Principles of Inheritance and Variation" OF NCERT.

Line in NCERT: "It has already been mentioned that the sex determining mechanism in case of humans is XY type."

​​​​​​

• In Co-dominance, both alleles for a specific trait are expressed equally in the heterozygous offspring.
• This means that the F1 generation will display traits from both the dominant and recessive parents, rather than resembling only one of the parents.

Hence the correct Answer is " A " 
NCERT Reference: Topic- Co- dominanace of chapter  "Principles of Inheritance and Variation" of NCERT.

Line in NCERT: "In the case of co-dominance the F1 generation resembles both parents."

• Females have the genetic composition XX, while males have the genetic makeup XY.
• The female ovum has an X chromosome, whereas male sperm might have either an X or a Y chromosome.
• When X chromosome-carrying sperm fertilises an egg with an X chromosome, the zygote grows into a female.

Hence, the correct option is B.

Topic in NCERT: Sex Determination and Chromosomal Differences

Line in NCERT: "In case the ovum fertilises with a sperm carrying X-chromosome the zygote develops into a female (XX) and the fertilisation of ovum with Y-chromosome carrying sperm results into a male offspring."

This sex linked recessive disease, which shows its transmission from unaffected carrier female to some of the male progeny has been widely studied. In this disease, a single protein that is a part of the cascade of proteins involved in the clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non-stop bleeding. The heterozygous female (carrier) for haemophilia may transmit the disease to sons.The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic (unviable in the later stage of life).

Hence, the correct option is D.

NCERT Reference: Topic “Haemophilia” of chapter  "Principles of Inheritance and Variation" of NCERT.

Line in NCERT: "The possibility of a female becoming a haemophilic is extremely rare because mother of such a female has to be at least carrier and the father should be haemophilic."

• The father of a colour blind female must be colour blind.
• The mother has to be at least a carrier. This is possible if the maternal grandfather was colour blind [remember criss-cross].

Hence, the correct option is B.

NCERT Reference: Topic- Colour Blindness of chapter "Principles of Inheritance and Variation" of NCERT.

• Yellow pod colour of the pea plant is a recessive trait.
• Mendel studied seven contrasting traits in pea (Pisum sativum), which are as follows:

Hence, the correct option is B.

Topic in NCERT: Contrasting Traits Studied by Mendel in Pea

Line in NCERT: "Contrasting Traits\nS.No.\nCharacters\n1.\nStem height\nTall/dwarf\n2.\nFlower colour\nViolet/white\n3.\nFlower position\n4.\nPod shape\n5.\nPod colour\n6.\nSeed shape\nAxial/terminal\nInflated/constricted\nGreen/yellow\nRound/wrinkled\n7.\nSeed colour\nYellow/green"

• Both tall and dwarf plants produce gametes by mitosis.
• Plants use meiosis only to produce spores that develop into multicellular haploid gametophytes which produce gametes by mitosis.

Therefore, gamete formation in both tall and dwarf plants is by mitosis.

Hence, the correct option is A.
Note: This question is based on basic understanding of inheritance of genes.

Line in NCERT: "only one allele is transmitted to a gamete."

• Gene is a segment of DNA and new alleles arise by mutation - a sudden inheritable change in DNA. Mutations can alter single nucleotides or entire chromosomes.
• The ultimate source of genetic variation is random mutation i.e. changes in nucleotide sequences of DNA. They may involve only a single base pair or many as in chromosomal mutations.
• Change in the allele frequency and introduction of new alleles are the basis of genetic variation occurring in any population.

Fig: Showing Mutation 

Hence, the correct option is C.
NCERT Reference: Topic- MUTATION” of chapter  "Principles of Inheritance and Variation" of NCERT.

Line in NCERT: "Such an alteration or change in the genetic material is referred to as mutation."

According to the Law of Dominance, the correct statement is that in a dissimilar pair of factors, one member of the pair dominates the other. This principle helps explain why only one of the parental characters is expressed in the F1 generation of a monohybrid cross, while both are expressed in the F2 generation. It also elucidates the 3:1 proportion observed in the F2 generation.

Line in NCERT: "In a dissimilar pair of factors one member of the pair dominates (dominant) the other (recessive)."

In the scenario where a true-breeding red-flowered (RR) plant is crossed with a true-breeding white-flowered (rr) plant in the dog flower species, the resulting F1 offspring displays a pink flower color. This outcome is a classic example of incomplete dominance, where neither of the parental traits dominates completely, leading to an intermediate phenotype in the offspring. This phenomenon is crucial in understanding genetic inheritance patterns beyond simple dominant and recessive relationships.

Line in NCERT: "The F1 (Rr) was pink."

In the scenario of co-dominance where both I^A and I^B alleles are present, they express their own types of sugars simultaneously. This occurrence is due to the unique nature of co-dominance, where neither allele suppresses the other, resulting in the expression of both sugar types. This leads to red blood cells displaying both A and B types of sugars, showcasing a co-dominant inheritance pattern.

Line in NCERT: "But when I A and B are present together they both express their own types of sugars: this is because of co-dominance."

The Law of Segregation clarifies that alleles segregate independently during gamete formation, ensuring that each gamete receives only one of the two factors or alleles from a parent. This segregation process underlies the inheritance of traits and explains why both parental traits are not always visible in the F1 generation. Heterozygous parents, which carry two different alleles for a trait, produce gametes with equal proportions of each allele, contributing to genetic diversity in offspring.

Line in NCERT: "Though the parents contain two alleles during gamete formation, the factors or alleles of a pair segregate from each other such that a gamete receives only one of the two factors."