31 Years NEET Previous Year Questions: Principles of Inheritance & Variation

• Polygenic traits are traits controlled by multiple genes, often located on different chromosomes. These genes collectively contribute to the phenotype, and their effects are additive.
• Unlike single-gene traits studied by Mendel, polygenic traits do not follow simple dominant-recessive inheritance. Instead, they exhibit a Non-Mendelian inheritance pattern.
• Examples of polygenic traits include skin color, height, eye color, and weight in humans. These traits show a continuous range of variation rather than discrete categories.
• Environmental factors also play a significant role in the expression of polygenic traits.
• Polygenic traits are inherited in a manner that does not conform to Mendel’s laws of inheritance. The phenotypes result from the interaction of multiple genes, each with a small, cumulative effect.

Other Options:

• Mendelian inheritance pattern: This applies to single-gene traits where one gene determines the phenotype, with clear dominant and recessive alleles. Polygenic traits do not follow this pattern, as they are influenced by multiple genes and exhibit a range of phenotypes.
• Autosomal dominant pattern: In this inheritance pattern, a single copy of a dominant allele on an autosome is sufficient to express the trait. 
• X-linked recessive inheritance pattern: This pattern refers to traits caused by recessive alleles on the X chromosome. These traits are often seen more in males due to their single X chromosome. 

• A pedigree chart is a diagram that shows the occurrence and appearance of phenotypes of a particular gene or organism and its ancestors, often used to determine inheritance patterns.
• Carriers are individuals who have one recessive allele (disease mutation) and one normal allele. They do not show symptoms of the disease but can pass the mutation to their offspring.

X-linked Recessive Mutation:

• Typically, X-linked recessive traits are more common in males because they only have one X chromosome.
• Affected males pass the trait to all their daughters, who are carriers, and to none of their sons.
• Carrier females (having one normal and one affected X chromosome) can pass the trait to both sons and daughters.

Thus, the correct answer is 1/4 (XX^c)

In pea plants:

• The round seed (R) is dominant over the wrinkled seed (r)
• The yellow color (Y) seed is dominant over the green color seed (y)

The cross is in the following,

F1: RrYy (Round and yellow)
​Selfing of F1:  RrYy (Round and yellow)   X   RrYy (Round and yellow)
​Gametes:  RY, Ry, rY, ry      X     RY, Ry, rY, ry

The phenotypic ratio produced is 9 : 3 : 3 : 1.

• 9 - Round yellow
• 3 - Round green
• 3 - Wrinkled yellow
• 1 - Wrinkled green

Therefore, in F2 generation two new combination of seeds Round yellow and wrinkled green seeds would be produced that differ from the parent type.

To correctly match List I with List II concerning medical conditions and their associated chromosomes, it's essential to have some understanding of genetics and chromosome abnormalities related with each condition. Here's the correct matching based on that information:
Down's syndrome: This genetic disorder is characterized by an extra copy (trisomy) of the 21^st chromosome, which makes it associated with 21^st chromosome (III).
α -thalassemia: This condition is related to a mutation or deletion in the alpha globin genes located on the 16^th chromosome (IV).
β -thalassemia: This is a blood disorder caused due to mutations in the beta globin gene found on the 11^th chromosome (I).
Klinefelter's syndrome: This syndrome arises from the presence of an extra X chromosome in males (usually XXY), so it is related to abnormality in the 'X' chromosome (II).
Given these matches:
A - III
B - IV
C - I
D - II
The correct option based on the details above is: Option C: A-III, B-IV, C-I, D-II

The ABO blood group is determined by alleles I^A, I^B, and i, which are responsible for producing A, B, and O blood types, respectively. The I^A and I^B alleles are codominant, meaning both can be expressed if both are present, whereas the i allele is recessive.

Given the blood types in the problem statement:

To find the correct pairing:
The child has an O blood type, meaning their genotype must be ii, indicating they inherited an i allele from each parent. Therefore, both parents must have at least one i allele.

Given this information:
Father's Genotype: It must include i since the child inherited i. Thus, the father's genotype could be I^Bi.
Mother's Genotype: It must also include i for the same reason, so the mother's genotype could be I^Ai.
Child's Genotype: It is confirmed as ii.

Matching this analysis with the provided options:
Option A: I^Bi/I^Ai/ii - This matches the reasoning provided.
Option B: I^BI^B/I^AI^A/ii - This is incorrect because it suggests that neither parent has a recessive i allele to pass to the child, which is necessary for the child’s blood type O.
Option C: iI^B/iI^A/I^AI^B - This is incorrect and does not match the required genotypes for the child to inherit ii.
Option D: I^Ai/I^Bi/I^Ai - This includes a typo in the children's genotype and misalignment with blood types.
Option E: iI^B/iI^A/I^AI^B - This is incorrect, mismatches the inheritance mechanism.
So the correct pairing based on the genotypes and blood groups mentioned, along with genetic laws, would be Option "A",
So the answer is: Option A

The correct answer is: Option B: A, C, D and E only Explanation:
Mendel's Law of Dominance states that in a heterozygote, the dominant allele will mask the expression of the recessive allele. Let's analyze the options:
A. Out of one pair of factors one is dominant and the other is recessive: This is the core principle of Mendel's Law of Dominance.
C. Factors occur in pairs in normal diploid plants: This is a fundamental concept in genetics, as diploid organisms have two copies of each chromosome, thus two copies of each gene (factors).
D. The discrete unit controlling a particular character is called factor: Mendel used the term "factor" to describe what we now know as genes.
E. The expression of only one of the parental characters is found in a monohybrid cross: This is a direct consequence of the law of dominance, where the dominant trait masks the expression of the recessive trait in the F1 generation of a monohybrid cross.

Option B is incorrect:
B. Alleles do not show any expression and both the characters appear as such in F2 generation: This statement is incorrect. While the recessive allele is not expressed in the F1 generation, it reappears in the F2 generation in a 3:1 ratio (dominant:recessive). This is due to the Law of Segregation, not the Law of Dominance.

Let's analyze each term in List-I with the definitions presented in List-II:

A. Two or more alternative forms of a gene: These are called alleles. Thus, A matches with III 'Allele'.
B. Cross of F₁ progeny with homozygous recessive parent: This specific type of cross is known as a test cross, often used to determine the genotype of an individual having dominant phenotype. Therefore, B matches with IV 'Test cross'.
C. Cross of F₁ progeny with any of the parents: This is defined as a back cross, which can be used for multiple purposes, including the testing of the parental genes in the offspring. So, C matches with I 'Back cross'.
D. Number of chromosome sets in plant: This describes how many sets of chromosomes are present, i.e., the level of ploidy of the organism. Therefore, D matches with II 'Ploidy'.

From the analysis:

• A matches with III
• B matches with IV
• C matches with I
• D matches with II

Accordingly, the correct answer that matches all the descriptions is: Option C: A-III, B-IV, C-I, D-II.

To determine the genotype of a black seed plant that could either be homozygous dominant (BB) or heterozygous (Bb), you need to perform a test cross. A test cross involves crossing the individual in question with a homozygous recessive individual. In this scenario, that would be a plant with white seed color, or genotype bb.
A test cross is used because it can reveal whether the black seed plant carries the recessive b allele. When crossed with a homozygous recessive (bb) plant:
By observing the seed colors of the offspring, you can determine whether the black seed plant was homozygous dominant or heterozygous. If any white seeds appear among the offspring, the black seed plant must be heterozygous (Bb). If no white seeds appear, the black seed plant is likely homozygous dominant (BB).
Therefore, the correct option for crossing to determine the genotype of the black seed plant is: Option B bb

Pink colour flower in snapdragon have genotype Rr
Red flowered snapdragon have genotype RR when they both are crossed

So the progeny that we get are red and pink flowered plants only.

When a single gene affects multiple phenotypic expression, the gene is called pleiotropic gene and the phenomenon is called pleiotropism.

B. Such an individual has overall masculine development. However, the feminine development is also expressed. People with Klinefelter syndrome are male (XY), but they often have certain physical characteristics that may be typically associated with female development, such as wider hips, less body hair, and sometimes breast tissue development.
E. Such individuals are sterile. Often, individuals with Klinefelter syndrome produce little to no sperm and are therefore usually infertile. However, there are cases where fertility treatments can help some men with Klinefelter syndrome to father children.
For the other options :
A. This disorder was first described by Langdon Down (1866). This is incorrect. Klinefelter's syndrome was first described by Dr. Harry Klinefelter in the 1940s, not by Langdon Down.
C. The affected individual is short statured. This is incorrect. In fact, individuals with Klinefelter's syndrome are often taller than average.
D. Physical, psychomotor and mental development is retarded. This is also incorrect. While individuals with Klinefelter syndrome may have some learning difficulties or delays, particularly with language and speech, it is not accurate or appropriate to say that their physical, psychomotor, and mental development is "retarded". They may face some challenges, but with support they can lead healthy, productive lives.

A broad palm with a single palmar crease, also known as a "simian crease," is often associated with Down's Syndrome. Down's Syndrome is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is characterized by certain physical features, including a flat facial profile, an upward slant to the eyes, and a single palmar crease.
So, the correct answer is : Option A : Down's syndrome.

• Alfred Sturtevant used the frequency of recombination between gene pairs on the same chromosome as a measure of the distance between genes and ‘mapped’ their position on the chromosome.
• Sutton and Boveri proposed chromosomal theory of inheritance.
• Henking discovered X-chromosome.
• Thomas Hunt Morgan proved chromosomal theory of inheritance and proposed the concept of linkage.

Hence (b) & (c) are correct which makes option (c) as correct option.

• The symptoms described in the question are characteristic of Down syndrome, a genetic disorder caused by the presence of an extra copy of chromosome 21. This results in a trisomy of chromosome 21.
• Option A : Trisomy of chromosome 21 - Individuals with Down syndrome typically exhibit a range of physical and developmental features, such as a small round head, furrowed tongue, partially open mouth, and a broad palm with a characteristic single palmar crease. They also tend to have delayed physical, psychomotor, and mental development. Karyotype analysis of an individual with Down syndrome will show three copies of chromosome 21 instead of the normal two copies.

The other options describe different chromosomal abnormalities:

• Option B : 47 chromosomes with XXY sex chromosomes - This karyotype is characteristic of Klinefelter syndrome, a condition in which males have an extra X chromosome. Affected individuals have 47 chromosomes, and their symptoms are different from those described in the question.
• Option C : 45 chromosomes with XO sex chromosomes - This karyotype is characteristic of Turner syndrome, a condition in which females have only one X chromosome. Affected individuals have 45 chromosomes, and their symptoms are different from those described in the question.
• Option D : 47 chromosomes with XYY sex chromosomes - This karyotype is characteristic of XYY syndrome, a condition in which males have an extra Y chromosome. Affected individuals have 47 chromosomes, and their symptoms are different from those described in the question.

(G) Green pod colour is dominant over yellow pod colour (g)
(I) Inflated pod is dominant over constricted pod (i)

Expected percentage of F₂ progeny with yellow – inflated pod in this cross is
1/4  x 3/4 x 100 = 18.75%

Sutton and Boveri proposed chromosomal theory of inheritance. Thomas Morgan experimentally verified the chromosomal theory of inheritance. Gregor Mendel proposed laws of inheritance.

Crossing over and exchange of genetic material between homologous chromosomes occurs during pachytene stage of meiosis. The enzyme involved in this process is recombinase.

Grasshopper is an example of XO type of sex determination in which the males have only one X-chromosome besides the autosomes, whereas females have a pair of X-chromosomes.

• Sickle cell anaemia is autosomal recessive disorder, whereas, haemophilia is sex linked recessive disorder.
• Both sickle cell anaemia and haemophilia are the genetic disorders related to blood.

In sequence annotation, the whole set of genome containing all coding and non-coding sequences is sequenced and the functions are assigned to different segments. It could be used for marking specific features in a DNA, RNA or protein sequence with descriptive information about structure or function. It helps in describing regions or sites of interest in the protein sequence, such as enzyme active sites, secondary structure or other characteristics reported in the cited references.

Step 1: List the Recombination Frequencies
We have the following recombination frequencies:
- A & C: 5%
- B & C: 15%
- B & D: 9%
- A & B: 20%
- C & D: 24%
- A & D: 29%

Step 2: Identify Closest Genes
The recombination frequency indicates the distance between genes. The smaller the percentage, the closer the genes are on the chromosome. From the list, we see:
- A & C (5%) are the closest.
- B & D (9%) are the next closest.
- A & B (20%) and B & C (15%) are further apart.
- C & D (24%) and A & D (29%) are the farthest apart.

Step 3: Arrange the Genes
Start with the closest pair:
- Place A and C together since they have the smallest recombination frequency (5%).

Next, consider the other pairs:
- B is closer to C than A (B & C is 15% vs A & B is 20%). So, we can place B next to C.
- Now we have A - C - B.

Next, we need to incorporate D:
- B & D is 9%, which is closer than A & D (29%) and C & D (24%). Thus, D should be placed next to B.

Step 4: Final Arrangement
Putting it all together, we can arrange the genes as follows:
- A - C - B - D

Step 5: Verify with Remaining Frequencies
Now, let's check the recombination frequencies:
- A & C: 5% (correct)
- B & C: 15% (correct)
- B & D: 9% (correct)
- A & B: 20% (correct)
- C & D: 24% (correct)
- A & D: 29% (correct)

All the recombination frequencies match the given data.

Final Sequence
The sequence of the genes on the linear chromosome is:
A - C - B - D

If mother of man is colour blind, then man will also be colour blind as colour blindness is a X-linked recessive trait and shows criss-cross inheritance.

Closely located genes do not show independent assortment. Mendel's law of independent assortment holds good for those genes which are located on different chromosomes.

• Haemophilia is a X-linked recessive disorder. Thalassemia is an autosomal recessive disorder. Sickle cell anaemia is an autosomal recessive disorder.
• Myotonic dystrophy is an autosomal dominant disorder i.e. it occurs due to the presence of autosomal linked dominant trait.

Gregor J. Mendel, conducted hybridisation experiments on garden peas and selected 14 true breeding pea plant varieties (seven contrasting traits). Contrasting traits studied were smooth or wrinkled seeds, yellow or green seeds, inflated on constricted pods, green or yellow pods, tall or dwarf plants, violet or white flowers and axial or terminal flower positions.

The production of gametes by the parents, the formation of the zygotes, the F₁ and F₂ plants can be understood from a diagram called Punnett Square. It helps in identifying the possible allelic combinations.

Fig: Punnett Square