Very Short Answer Type Questions (1 Mark each)
1. Name two important factors that cause development of a new species.
2. How can the chromosomes be identified?
3. When does the process of gene flow take place?
Short Answer Type I Questions (2 Mark each)
4. Define the following terms.
(a) Genes
(b) Dihybrid cross
5. Write down the ratio of the progeny obtained from the following cross.
(a) Tt         X         Tt
Tall plant     Tall plant
(b) RRyy         X            rrYY
Round green      Wrinkled yellow
6. What is the contribution of Charles Darwin on our knowledge of evolution?
7. Why the small number of a species is a matter of worry from genetics point of view?
8. Plant A shows the growth of leaves in axillary position and plant B shows the growth
of tendrils in it. Do the leaf and tendrils of the two plants share any relationship with
each other? Explain.
9. If a round, green seeded (RRyy) pea plant is crossed with wrinkled, yellow seeded
(rrYY) pea plant, what will be the genotype of seeds produced in F,- generation?
10. Aditya is trying to observe some organisms in lab and to compare them. How can he
confirm that they share an evolutionary history?

Short Answer Type II Questions (3 Marks each)
11. What are heredity and variation? Why did Mendel select garden pea plant to
conduct his genetics experiments?
12. ‘Variations that confer advantage to an individual organism only will survive in
population’. Justify.
13. What does help scientists to reconstruct the pattern and trends that existed in. the
history of life on the Earth?
Long Answer Type Questions (5 Marks each)
14. Ovum and sperm are both female and male gametes, respectively. But what is so
intricate in sperm which makes it solely responsible for determining the sex of the
child? Explain.
15. Define the following
(a) Speciation
( c) Recessive trait
( e) Genetics
(b) Genetic drift
(d) Evolution

1.New species usually develop due to the following two factors
(a) Geographical isolation (b) Reproductive isolation                    (1)
2. In human beings, the individual chromosomes are identified by their lengths, position of centromere.
and banding pattern on staining. (1)
3. Gene flow or gene migration takes place in between the populations that are partly, but not completely
separated. ( 1)
4. (a) Genes These are the factors present on chromosomes and help to carry traits from one generation
to another.
(b) Dihybrid cross The cross in which two characters are considered at a time.
5. (a) 3 : 1, i.e. 3 tall and 1 short plant.
(b) The progeny of F2-generation results into the ratio of 9 : 3 : 3 : 1.

6. Charles Robert Darwin was a British naturalist who formulated his hypothesis that evolution took place
due to natural selection and proposed the theory of natural selection, also known as Darwinism. (2)
7. The small number of a species is a matter of worry from genetics point of view because if they all die
and become extinc , heir genes will be lost forever. Also, the small number of a species reduces the
chances of variations ~d hence, their population declines rapidly. (2)
8. Both these structures share homology with each other. Their origin is same, but function is different.
Leaves perform photosynthesis while tendrils provide support to the plant. (2)
9. The cross between RRyy an rrYY seeds will produce RrYy (round and yellow) seeds in F1-generation,
because round and yellow are dominant traits  (2)
10. He can confirm this by looking at the homologous organs. These organs are present in organisms
which share an evolutionary history, but they perform different functions in different organisms. (2)
11. Heredity – It deals with the resemblances and differences among related organisms.
Variations These are differences in the traits or characters among the individuals of a species. (1)
Mendel selected garden pea plants because of the following reasons:
(a) They grow quickly and are easy to study.
(b) Pea plants can be crossed or self-pollinated and have a flower structure that limits accidental
contact. (2)
12. Variation is the difference in the characters or traits among the individuals of a species. Sexual
reproduction of organisms produces variation. The variations produced in organisms during
successive generations get accumulated in the organism. The significance of variations shows up
only if it continues to be inherited by the offspring for several generations. {3)

13. Fossils are dead remains of animals and plants of the past. By providing information about previous
time, they help in tracing the process of evolution. The layers in which they are present in sedimentary
rocks help to determine the complexity of organisms that existed in the past. They also help to
establish the analogous and homologous characteristics among organisms. Hence, they help –
reconstructing the patterns and trends that existed in the history of life on Earth.
14. The sperm is responsible for the determination of sex of a child. A male cell has one X-chromosome
and one Y-chromosome, so it produces two types of sperms with genotype A + X and A + Y.
Female sex is homogametic. A female cell has both X-chromosomes, so it produces similar type c
eggs with genotype A + X.
Sex of the child depends upon what happens during fertilisation.
(a) If a sperm carrying X-chromosorne fertilises the egg, the child born will be a female (XX).
(b) If a sperm carrying Y-chromosome fertilises the egg, the child born will be a male (XY).

15. (a) Speciation It is the process of formation of new species over the course of evolution.
(b) Genetic drift It is the stage in which a part of population (sub-population) migrates to other plac~
and interbreeds with the local population to alter the gene frequency of the remaining populatior
(c) Recessive trait The trait which is unable to express itself in heterozygous state or in the presence ::;
dominant trait is called as recessive trait.
(d) Evolution it is a constant, gradual and irreversible change occurring in the organisms since tri=
origin of life giving rise to a variety of complex organisms.
(e) Genetics The study of heredity and variations is called genetics.

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