Human Reproduction — BIOLOGY STD 12 Science — Question

What are the various routes by which transmission human immunodeficiency virus take place?

Are parthenocarpy and apomixis different phenomena? Discuss their benefits.
Hint: Yes, they are different. Parthenocarpy leads to development of seedless fruits. Apomixis leads to embryo development. 

How did Hershey and Chase differentiate between DNA and protein in their experiment while proving that DNA is the genetic material?

Why is the length of a food chain in an ecosystem generally limited to 3-4 trophic levels? Explain with an example.

In the 1950s, there were hardly any mosquitoes in Delhi. The use of pesticide DDT on standing water killed their larvae. It is believed that now there are mosquitoes because they evolved DDT resistance through the interaction of mutation and Natural selection. Pointwise, state in a sequence how that could have happened.

i. Why is the collection of white-winged moths and dark-winged moths made in England between 1850-1920 considered a good example of natural selection?
ii. Evolution is based on chance events in nature and chance mutations in organisms. Justify the statement.

Removal of gonads cannot be considered as a contraceptive option. Why?

Why are the males of Grasshoper and Drosophila said to show heterogamete? Explain female heterogamete with the help of an example.

A cross is made between different homozygous pea plants for contrasting flower positions.

1. Find out the position of flowers in F₁ generation on the basis of genotypes.
2. Work out the cross upto F₂ generation.
3. Compute the relative fraction of various genotypes in the F₂ generation?

State Mendel's law of dominance. How did he deduce the law? Explain with the help of a suitable example.