One Marks Questions

Answer: The transmission of characteristics from one generation to another is known as heredity.

Answer: Cellular DNA is the information source for making proteins in the cells.

i) Genetics is the study of the mechanism by which variations are created and inherited.

ii) Evolution is used for studying the development of a new type of organisms from the existing ones.

Answer: No two individuals are absolutely alike in a population because variations arise due to DNA copying.

Answer: Comparing the DNA of different species gives a direct estimate of how much the DNA has changed during the information of these species. Thus it helps us to a great extent in tracing the evolutionary pathways.

Answer: Genes carry information for producing proteins, which in turn control the various body characteristics.

Answer: Black

Two Marks Questions

Characteristics are details of the appearance of behaviour, in other words, a particular form or a particular function. The presence of four limbs in humans is an example of characteristics.

Genes are located on chromosomes in a linear sequence and at fixed positions.
Chemically genes are made up of nucleic acids which constitute DNA.

The genes controlling a particular trait separate from each other during gamete formation. Hence gamete is always pure as far as contrasting characters are considered and will possess only one gene set.

Answer: In asexually reproducing organisms. there is no mixing of genes of two different individuals since only one partner is involved. There are very minor variations generated in such organisms due to small inaccuracies in DNA copying.

A male individual has 46 chromosomes but because the gametes are always haploid i.e they have half the number of chromosomes sperms will be haploid (23 chromosomes) Female individual also contains only 23 chromosomes in the egg. it is the fusion of the sperm and egg which leads to offspring with 46 chromosomes.

F1 generations F2 generations
F1 generations refer to the offspring resulting immediately from a cross between the first set of parents. F2 generations, on the other hand, refers to the offspring resulting from among the members of F1 generation.
The nucleus first divides automatically into two, followed by the division of the cytoplasm The nucleus of the cell divides repeatedly producing many nuclei.

Answer: In crossing, if two or more traits are involved, their genes assort independently, irrespective of the combinations present in the parents.
So, new combinations of genes appear in the offsprings leading to new traits.

Answer: The experiences of an individual may only affect the somatic cells, but will not changes the DNA of the germ cells.

Three Marks Questions

(i) When a cross was made between a tall pea plant with round seeds and a short pea plant with wrinkled seeds, the F1 progeny plants are all tall with round seeds. This indicates that tallness and round seeds are the dominant traits.
(ii) When the F1 plants are self-pollinated, the F2 progeny consisted of some tall plants with round seeds and some short plants with wrinkled seeds which are the parental traits.
(iii) There were also some new combinations like tall plants with wrinkled seeds and short plants with round seeds.
(iv) Thus it may be concluded that tall and short traits and round and wrinkled seed traits have been inherited independently.

i)The structure of the DNA molecule resembles a spirally twisted ladder.
(ii) Each strand of the ladder is made up of pentose sugar and phosphate arranged alternatively.
(iii) There are two types of nitrogenous bases namely purines and pyrimidines.

(i)Genetics is the branch of biology that deals with the study of heredity and variations.

(ii)Gregor Johann Mendel/ garden pea.

(iii) Garden pea plants were easily available / they grow in one season/ fertilization was easy.

Such traits are called acquired traits. Acquired traits are experienced by an individual during his lifetime. These traits involve changes in non-reproductive cells (somatic cells) which are not transferred to germ cells. So, these traits cannot be passed on to the next generation. For example Learning skills like swimming, dancing, cooking, bodybuilding, etc are acquired traits and cannot be passed on to the next generation.

Mendel conducted breeding experiments with garden peas:
(i) He studied (pure) plants of tall/short varieties.
(ii) He crossed them and obtained F1 progeny.
(iii) He found that F1 progeny was all tali plants.
(iv) Heselfed the (hybrid) plants of F1 progeny.
(v) He found that in F2progeny there were tall as well as short plants.
(vi) The three-quarter plants were tall and one quarter was short.


Four Marks Questions

Difference between dominant trait and recessive trait
Dominant Trait Recessive trait
The trait which appears in the F1 progeny is dominant The trait which remains hidden or which does not appear in the F1 progeny in the recessive trait
It appears in more numbers. It appears in fewer numbers.
75% of the plants were with round seeds.

. (a) Reasons
(i) Pea plant is small and easy to grow.
(ii) A large number of true-breeding varieties of the pea plant are available. (iii) Short life cycle.
(iv) Both self and cross-pollination can be made possible. (Any two reasons)

(b) Contrasting characters:
Round/Wrinkled seeds
Tall/Short plants
White/purple flowers
Green/yellow seeds

(c) When Mendel crossed two pea plants with a pair of contrasting characters only one character appeared in all the members of F1 progeny, the others remain hidden. On selfing F1, the hidden characters reappeared in just 259% of the offsprings and the other 75% shared the characters expressed in F1.
Mendel concluded that the character which expresses itself in F1 and in 75% of the individuals of F2, is dominating while the other is recessive.

(i) Mendel conducted an experiment on the garden pea plant selecting seven visible contrasting characters. He selected and crossed a homozygous tall pea plant having the genotype TT with a homozygous dwarf pea plant having the genotype tt. F generation consists only of tall plants having genotype Tt.
The expressed allele T for tallness is dominant over the unexpressed allele t for dwarfness. Hence the trait of tallness is dominant while dwarfnessor shortness is the recessive characteristics. Thus, Mendel's experiment showed that traits may be dominant or recessive.

(ii) Mendel performed an experiment in which he took two different traits like tall and dwarf plant and round and wrinkled seeds. In F2 (second)generation, some plants were tall with round seeds and some were dwarf with wrinkled seeds. There would also be dwarf plants having round seeds. Thus, the tall/short traits and round/wrinkled seed traits are independently inherited.

(i) Traits: A characteristic feature is called a trait.

(ii) Inherited Traits are the traits that are transferred from parents to young ones. Acquired Traits are the traits that an organism acquires in its lifetime.

(iii) Formation of new species from the existing ones is called speciation. Factors that could lead to the rise of new species are geographical isolation, genetic drift, tt natural selection.

(i) This is to show that each trait is influenced by both paternal and maternal DNA.

(ii) No. This is because all the F progeny plants show the genetic makeup Pp, which results in purple flowers.

(iii) Dominant trait is a genetic trait that is expressed in a person who has only one copy of that gene. A recessive trait is a genetic trait that is expressed only when two copies of the gene are present

(i) Yes, eye colour and height are genetically inherited traits, as these are expressed by genes. No, weight lifting and reading French are acquired traits.

(ii) Variations in individuals during sexual reproduction gives survival advantages to them, and help them to adapt even in extreme environments.