31 Years NEET Previous Year Questions: Heredity And Variation - 2 Free

Haemophilia is sex linked recesive disease in which a simple protein that is a part of protein cascade involved in clotting of blood is affected. Due to this, in an affected individual a simple cut will result in non stop bleeding.

Tightly linked genes exhibit a strong association, leading to a higher frequency of parental gene combinations compared to non-parental types. This is due to the physical proximity of the genes on the same chromosome, which reduces the likelihood of crossovers during meiosis.

• Independent assortment occurs when genes are not linked, allowing for a mix of traits in offspring.
• If genes are located on the same chromosome, they may experience multiple crossovers, resulting in varied combinations.
• Genes with a recombination frequency of 50% can be on different chromosomes or far apart on the same chromosome.

In summary, genes that show 50% recombination frequency are not tightly linked, as they can assort independently or be located on different chromosomes.

In Co-dominance F₁ generation resemble both the parents. Ex : Blood group inheritance.

ABO blood group system in human beings is an example of codominant, dominant recessive and multiple alletes. Blood groups are controlled by the gene I located on 9^th chromosome that has 3 multiple alleles, out of which any two are found in a person. In codominance both gene express it self completely.

A test cross, first introduced by Gregor Mendel, is used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait. It takes place between F1 - Generation and recessive parent.

Change in single base pair of DNA is also a type of mutations called point mutations. It is a type of mutation that causes the replacement of a single base nucleotide with another nucleotide of the genetic material, DNA or RNA. For example, a point mutation is the cause of sickle cell disease.

Colour blindness is a X-linked disease. So, woman whose father was colourblind will be carrier for the disease. So, possibility of a colourblind daughter (i.e., X^cX^c in F₁ generation is 0%.)

Blood group O is known as the universal donor. This means that individuals with this blood group can donate blood to anyone, regardless of the recipient's blood type.

• Blood group O contains no A or B antigens.
• This absence prevents any adverse reactions during transfusions.
• Therefore, the donor's blood group must be O.

Two X chromosomes would lead to the birth of a normal human female child.

The sex of a child is determined by the combination of chromosomes inherited from the parents:

• Females have two X chromosomes (XX).
• Males have one X and one Y chromosome (XY).

During fertilisation:

• The ovum from the female always carries an X chromosome.
• The sperm from the male can carry either an X or a Y chromosome.

If the sperm carrying an X chromosome fertilises the ovum, the zygote will develop into a female (XX). Thus, the presence of two X chromosomes is essential for a normal female child.

In test cross, genotype of an organism showing dominant phenotype is determined by crossing it with homozygous recessive genotype.

Type Oblood group is considered the universal donor blood group. It can potentially be transfused to any patient regardless of their blood type. In emergency situation, this type of blood can be given to the patient.

Mutation can be induced by gamma radiation.

Gamma radiation is a type of high-energy radiation that can cause changes in the DNA of organisms. Here are some key points:

• Gamma radiation can lead to mutations, which are alterations in the genetic material.
• These mutations can affect an organism's traits and may be passed on to future generations.
• Other forms of radiation, such as UV radiation, can also induce mutations.

Understanding the effects of gamma radiation is important in fields such as genetics and cancer research.

In grasshopper the males lack a Y-sex chromosome and have only an X-chromosome. They produce sperm cells that contain either an X chromosome or no sex chromosome, which is designated as O.

Linkage is the inheritance of genes of same chromosome together and capacity of these genes to retain their parental combination in subsequent generation. The strength of linkage between two genes is inversely proportional to the distance between the two. This means, two linked genes show higher frequency of recombination if the distance between them is higher and lower frequency if the distance is smaller.

Test cross is the cross of an individual with an individual having recessive phenotype. It is used to determine the genotype of a plant showing the dominant phenotype, that means to determine whether the individual exhibiting dominating characters are homozygous or heterozygous.

According to Mendel’s law of Dominance, out of two contrasting allelomorphic factors only one expresses itself in an individual. The factor that expresses itself is called dominant while the other which has not shown its effect in the heterozygous individual is termed as recessive. The option (c) in the given question cannot be explain-ed on the basis of law of dominance. It can only be explained on the basis of Mendel’s Law of independent assortment, according to which in a dihybrid cross, the two alleles of each character assort independently of the alleles of other character and separate at the time of gamete formation.

A point mutation is a simple change in one base of the gene sequence. This is equivalent to changing one letter in a sentence, such as this example, where we change the ‘e’ in cat to an ‘h’: Original: The fat cat ate the wee rat. Point Mutation: The fat hat ate the wee rat.

Option B is correct.

Sickle cell anaemia results from a single base substitution (point mutation) in the β-globin gene, which changes the codon GAG to GUG.

This base change causes the substitution of glutamic acid (Glu) by valine (Val) at the 6th amino acid position of each β-globin chain, converting normal haemoglobin (HbA) into sickle haemoglobin (HbS).

Because of the hydrophobic nature of valine at that position, haemoglobin molecules polymerize under low-oxygen conditions and distort red blood cells into a sickle (elongated) shape, which impairs their flexibility and causes clinical problems.

Statement evaluations:

Statement 1 is not presented as the correct option here because it now specifies the α-globin gene, which is not the gene mutated in sickle cell anaemia; the mutation occurs in the β-globin gene.

Statement 2 correctly describes the amino acid substitution (Glu → Val at position 6 of β-globin) and is therefore true.

Statement 3 is incorrect because mature human red blood cells are anucleate; although sickled RBCs are elongated, they do not contain a nucleus.

Statement 4 is incorrect because sickle cell anaemia shows an autosomal recessive pattern of inheritance, not dominant.

Final answer: Option B.

The chart shows the inheritance of a condition like phenylketonuria as an autosomal recessive trait. Parents’ needs to be heterozygous as two of their children are known to be sufferer of the disease. It cannot be recessive sex linked inheritance because then the male parent would also be sufferer.

Klinefelter's syndrome is a genetic disorder affecting men in which an individual gains an extra X chromosome, so that the usual Karyotype of XY is replaced by one of XXY. Symptoms of  Klinefelter's syndrome  named after us physician H.P. Klinefelter, include female characteristics (such as breast enlargement).