Ch. No. 13. Mapping our Genes
Q1. Fill in the blanks
1. In ___________ mode of reproduction the offsprings are with minor differences. (asexual)
2. Both the parents contribute equal amount of ___________ material to the offspring. (genetic)
3. Dominant character masks the ___________ characters. (recessive)
4. Selection by nature is not ____________ but ____________. (deliberate, natural)
Q2. Give scientific reasons:
1. In sexual mode of reproduction greater diversities are generated.
Ans.
i. In sexual mode of reproduction two parents are involved.
ii. Each one has its own DNA copies that are passed on through their nuclei at the time of fertilization of gametes.
iii. Therefore more diversity is produced.
iv. Moreover, the process of meiosis at the time of gamete formation, also produces variations. Hence in sexual mode of reproduction greater
2. Phenotypic and genotypic ratios are different.
Ans.
i. Phenotype is the appearance or any detectable characteristic feature of an individual life red and white flowers.
ii. Genotype is the genetical composition of individuals like RR, Rr and rr.
iii. Hence, phenotypic and genotypic ratios are different.
3. In human beings the gametes from the male parent decides the sex of the baby.
Ans.
i. In human male gametes, two dissimilar chromosomes XY are present whereas in females two similar chromosomes XX are present.
ii. All children inherit ‘X’ chromosomes from their mother and ‘X’ or ‘Y’ from their father.
iii. Hence the gametes from the male parent decide the sex of the baby.
4. Paleontological evidence suggests that invertebrates came into existence before the vertebrates.
Ans.
i. A systematic study of fossils and its occurrence revealed that the deepest layers of land were found to have fossils of invertebrates.
ii. In layers above them were found vertebrates such as fish – like animals, amphibians, reptiles, birds and mammals.
iii. This suggests that invertebrates came into existence before the vertebrates.
Q3. With the help of a diagram (Punnett square) show a Mendelian experiment where tall pea plant bearing red flowers is crossed with a short pea plant bearing white flowers. Write both the phenotypic and genotypic ration for F2 generation.
Q4. Write a short note on:
Darwin’s theory of evolution.
i. Darwin’s theory of evolution is based on natural selection.
ii. Darwin’s theory of natural selection suggests that only the fittest survive.
iii. All those plants and animals which are not fit die.
iv. These fit species reproduce and pass on the relevant characteristics to the following generation which in turn would make them fit for survival.
v. This process of selection of characteristics that contribute to the fitness for survival was called natural selection by Darwin.
vi. The criterion for the natural selection is the only one i.e. successful adaptation for growth and reproduction in the given environment.