Human Reproduction — BIOLOGY STD 12 Science — Question

Differentiate between dominance and co–dominance.

Sakshi's father announced that the children are going to spend this weekend with their grandparents. During the journey, Sakshi saw some farmers who were spraying agrochemicals in their field. She requested her father to stop them. Her father praised her and contacted the farmers. He explained the side effects of such agrochemicals. He also suggested them to use biopesticides and biofertilisers instead of such chemicals. The farmers gave up spraying agrochemicals.

1. What did Sakshi's father explain to the farmers?
2. What are agrochemicals?
3. Why are biofertilisers or biopesticides preferred to chemical fertilisers or pesticides?
4. What values did Sakshi promote?

The biology teacher was explaining about restriction enzymes and came to a point explaining that these enzymes are extracted from bacteria and are called as molecular scissors. Varun got curious and asked some questions for more clarity on the concept to his teacher.

1. From which part of microorganisms are restriction enzymes derived?
2. Why are restriction enzymes called molecular scissors?
3. What if some strands are needed to be cut from within. Would that lead to wastage of DNA?
4. What values are shown by Varun?

Mention any two autosomal genetic disorders with their symptoms.

Samya visited a zoo with her mother, on watching the cheetah, she wondered how he uses his forelimbs for running. While the same forelimbs in bats are used for flying. She wanted to know more about it and so asked her mother (a biology teacher) about it. Her mother explained her how forelimbs are modified in different animal groups for different functions.

1. What are such organs called?
2. Give an example of such organs from the plant world.
3. What led to the origin of such organs?
4. What are the values shown by Samya?

(a) Write the name of primates existing on earth about 15 million years ago. Write its important characteristics also?
(b) (i) From where did the animals similar to human being meet?
(ii) In which sequence were neanderthal, homohabilis and homo erectus evolved on earth?
(iii) When did modern man evolve on this planet?

What is incomplete dominance? Explain it taking the example of snapdragon plant by checker board. Also write the phenotypic and genotypic ratio.

The following is the illustration of the sequence of ovarian events (a – i) in a human female.

Specify the endocrine function of corpus luteum. How does it influence the uterus? Why is it essential?

Describe in detail the development of male gametophyte in angiosperms with well labelled diagram.

Explain with an example, where a gene, which carries a major disadvantage in homozygous state, confers an advantage in heterozygous condition.