NCERT Solution Class 12 Biology Chapter 5 ” Principle of Inheritance “

 

1. Mention the advantages of selecting pea plant for experiment by Mendel.

AnS : Advantages of selecting pea plant for experiment by Mendel:

• Pea plants have a relatively short life cycle, which allowed Mendel to conduct multiple generations of experiments within a short period of time.
• Pea plants have both male and female reproductive organs, which enabled Mendel to easily control the breeding of the plants.
• Pea plants produce large numbers of offspring with distinct and easily observable traits, making it easier for Mendel to analyze the inheritance patterns of these traits.
• Pea plants have several traits that are easily distinguishable, such as seed color, seed texture, and flower color, which allowed Mendel to conduct experiments on multiple traits simultaneously.

2. Differentiate between the following –
(a) Dominance and Recessive

(b) Homozygous and Heterozygous
(c) Monohybrid and Dihybrid.

(a) Dominance and Recessive: Dominance refers to the phenomenon where one allele masks the expression of the other allele in a heterozygous individual, resulting in only the dominant allele being expressed. Recessive refers to the allele that is masked by the dominant allele and is only expressed in the homozygous recessive individual.

(b) Homozygous and Heterozygous: Homozygous refers to an individual with two identical alleles at a specific gene locus, while heterozygous refers to an individual with two different alleles at a specific gene locus.

(c) Monohybrid and Dihybrid: Monohybrid refers to a cross between two individuals that differ in only one trait, while dihybrid refers to a cross between two individuals that differ in two traits.

3. A diploid organism is heterozygous for 4 loci, how many types of gametes
can be produced?

Ans : A diploid organism that is heterozygous for 4 loci can produce 16 different types of gametes (2 to the power of 4).

4. Explain the Law of Dominance using a monohybrid cross.

The Law of Dominance states that in a heterozygous individual, the dominant allele will be expressed while the recessive allele is masked. This can be demonstrated through a monohybrid cross between two heterozygous individuals, where the offspring will have a 3:1 phenotypic ratio. For example, if we cross two pea plants that are heterozygous for seed color (yellow is dominant and green is recessive), we would expect the offspring to have a 3:1 ratio of yellow to green seeds.

5. Define and design a test-cross.

A test-cross is a cross between an individual with an unknown genotype and an individual that is homozygous recessive for a specific trait. The purpose of the test-cross is to determine the genotype of the unknown individual. If any offspring of the test-cross exhibit the recessive trait, then the unknown individual must be heterozygous for that trait.

6. Using a Punnett Square, workout the distribution of phenotypic features in the first filial generation after a cross between a homozygous female and a heterozygous male for a single locus.

If a homozygous female (YY) is crossed with a heterozygous male (Yy) for a single locus, the Punnett square would show that all offspring will have the dominant phenotype (Yy). However, all offspring will be heterozygous because the female parent is homozygous dominant and the male parent is heterozygous.

 

7. When a cross in made between tall plant with yellow seeds (TtYy) and tall plant with green seed (Ttyy), what proportions of phenotype in the offspring could be expected to be
(a) tall and green.
(b) dwarf and green.

(a) In a cross between a tall plant with yellow seeds (TtYy) and a tall plant with green seeds (Ttyy), the expected phenotypic ratio of tall and green offspring would be 1:1. (b) In a cross between a tall plant with yellow seeds (TtYy) and a dwarf plant with green seeds (ttyy), the expected phenotypic ratio of dwarf and green offspring would be 1:1.
8. Two heterozygous parents are crossed. If the two loci are linked what would be the distribution of phenotypic features in F1 generation for a dibybrid cross?

If two heterozygous parents are crossed and the two loci are linked, the distribution of phenotypic features in the F1 generation for a dihybrid cross would not follow the expected 9:3:3:1 ratio. Instead, the phenotypic ratios would depend on the degree of linkage between the two

9. Briefly mention the contribution of T.H. Morgan in genetics.

T.H. Morgan was a geneticist who made significant contributions to the understanding of inheritance and the role of chromosomes in heredity. He studied the fruit fly Drosophila melanogaster and discovered that genes are located on specific chromosomes, and that certain traits are sex-linked. Morgan’s work provided evidence for the chromosomaltheory of inheritance, which states that genes are located on chromosomes and are transmitted from parents to offspring during reproduction.

10. What is pedigree analysis? Suggest how such an analysis, can be useful.

Pedigree analysis is the study of the inheritance patterns of traits in families over several generations. It involves constructing a family tree that shows the relationships between family members and their traits. Pedigree analysis can be useful in identifying the inheritance pattern of genetic disorders, determining the risk of an individual developing a genetic disorder, and identifying carriers of genetic disorders. It can also help in making decisions regarding genetic counseling and family planning.

11. How is sex determined in human beings?

In human beings, sex is determined by the presence of sex chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY). The sperm from the father determines the sex of the offspring, as it can carry either an X or a Y chromosome. If the sperm carries an X chromosome, the offspring will be female, while if it carries a Y chromosome, the offspring will be male.

12. A child has blood group O. If the father has blood group A and mother blood group B, work out the genotypes of the parents and the possible genotypes of the other offsprings.

If a child has blood group O and the father has blood group A and the mother has blood group B, the possible genotypes of the parents are IAi and IBi, respectively. The child’s genotype would be ii. The possible genotypes of the other offspring would be IAi or IBi.

13. Explain the following terms with example
(a) Co-dominance
(b) Incomplete dominance

(a) Co-dominance is a type of inheritance pattern in which both alleles of a gene are expressed in the heterozygous individual. An example of co-dominance is the ABO blood group system, where both the A and B alleles are expressed in individuals with AB blood type.

(b) Incomplete dominance is a type of inheritance pattern in which the heterozygous individual has an intermediate phenotype between the two homozygous parents. An example of incomplete dominance is the flower color in snapdragons, where a red-flowered plant crossed with a white-flowered plant produces offspring with pink flowers.

14. What is point mutation? Give one example.

Point mutation is a type of mutation that involves a change in a single nucleotide base in DNA. An example of point mutation is sickle cell anemia, which is caused by a mutation in the beta-globin gene. The mutation results in a change in a single nucleotide base, which leads to the production of abnormal hemoglobin.

15. Who had proposed the chromosomal theory of the inheritance?

The chromosomal theory of inheritance was proposed by Walter Sutton and Theodor Boveri in 1902. The theory states that genes are located on specific chromosomes and that the behavior of chromosomes during meiosis explains the inheritance patterns of traits.

16. Mention any two autosomal genetic disorders with their symptoms.

Two examples of autosomal genetic disorders are:

Sickle cell anemia is a genetic disorder caused by a mutation in the hemoglobin gene, which affects the shape of red blood cells. Instead of the normal round shape, the red blood cells become crescent-shaped (sickle-shaped), which can block blood flow and cause tissue damage. Symptoms of sickle cell anemia include anemia, fatigue, jaundice, pain episodes, and increased risk of infections. Sickle cell anemia is most commonly found in people of African descent, but it can also occur in individuals of Mediterranean, Middle Eastern, or Indian ancestry.

Phenylketonuria (PKU) is a genetic disorder caused by a mutation in the gene that helps produce the enzyme phenylalanine hydroxylase (PAH). Without this enzyme, the body cannot properly break down the amino acid phenylalanine, which can build up to toxic levels and damage the brain. Symptoms of PKU include intellectual disability, seizures, skin rashes, and behavioral problems. PKU can be managed with a special diet low in phenylalanine and supplementation of certain nutrients.

Both sickle cell anemia and PKU are inherited in an autosomal recessive manner, which means that an individual needs to inherit two copies of the mutated gene (one from each parent) to develop the disorder.