Equal genetic contribution of male and female parents in the progeny is ensured by the equal inheritance of chromosome from each parent.
Human possesses 23 pairs of chromosomes, of which 22 pairs are autosomes and 1 pair is the sex chromosomnes.
The two sex chromosomes in human are X and Y. Females have 2X chromosomes and males have a X and Y chromosome.
During the process of fertilization, a haploid sperm fuses with a haploid ovum to produce a diploid zygote. Zygote receives equal amount of genetic material from each parent and thus, retains the diploid narure on fertilizarion.

(1) Complex organs may have evolved because of the survival advantages of the intermediate state.
(2) Complex organ like eyes are created bid by bid over generation.
(3) The structure of the eye in all organisms is different enough to have separate evolutionary origin.
(4) Organs may be adapted to new functions during the course of evolution, e.g., feathers are thought to have evolved for warmth and later adapted for flight.
(5) Some dissimilar looking structures also evolved from common ancestor, e.g., different vegetation like cauliflower, cabbage, broccoli, kale, etc. are generated by artificial selection from wild cabbage.
(6) Changes in DNA during reproduction are the basic events of evolution.

(a) Cabbage, broccoli, kale, kohirabi are evolved from wild cabbage by artificial selection.
(b)Sometimes an evolutionary change produced in an organism for one purpose later on becomes more useful for an entirely different function. For example: Birds have evolved feathers as a means of providing insulation to their bodies in cold weather but later on these feathers became more useful for the purpose of flying.

(i) Homologous organs. Those organs, which have the same basic structure but different functions are called homologous organs.
For example: The forelimbs of a man, a lizard, a frog, a bird and a bat have the same basic design of bones but they perform different functions.
The presence of homologous organs in different animals provides evidence for evolution that they are derived from the same ancestor who has the basic design of the organ on which all the homologous organs are based.
(ii) Analogous organs. Those organs, which have different basic structure but have similar appearance and perform similar functions are called analogous organs.
For example: The wings of an insect and a bird have different structures but they perform the same function of flying.
Analogous organs provide evidence for evolution that the organisms from different ancestors perform similar functions to survive, flourish and keep on evolving in prevailing environment.
(iii) Fossils. The remains of dead animals or plants that lived in the remote past are known as fossils. The fossils provided evidence for evolution.
For example: A fossil of a bird called Archaeopteryx looks like a bird but it has many other features found in reptiles. Therefore Archaeopteryx is a connecting link between the reptiles and birds and hence suggests that the birds have evolved from the reptiles.

A male has one X chromosome and One Y chromosome. Thus half the sperms will have X chromosomes and the other half will have Y chromosome. A female has two X chromosomes. So all the female gametes will have only X chromosomes. If a sperm carrying X chromosome fertilizes an ovum then the child born will be a girl. If a sperm carrying Y chromosome fertilizes an ovum then the child born will be a boy.
Thus the chromosomal difference between sperms and eggs of humans determines the sex of the child.

(a) All tall
(b) Tall plants (3) : Dwarf plants (1)
(c) Dwarf plants this is because, in F₁ generation only the dominant traits is expressed.

50%

The small number of tigers are causing a worry for the genetics because if they become extinct then the genes of this species will be lost forever. There will be no scope of again getting this species back to life without their genes.

Only dominant trait appeared in F₁ generation.

The process by which new species develop from the existing species is known as speciation.

Male - I^A I^B Female - I^O I^A Blood groups will be :
(i) A (ii) A (iii) B (iv) AB

TT

The process by which new species develop from the existing species is known as speciation.
Factors leading to speciation:
(i)Geographical isolation of a population caused by various types of barriers like mountain ranges, rivers, sea etc. The geographical isolation leads to reproductive solation due to which there is no flow of genes between separated groups of population.
(ii)Genetic drift caused by drastic changes in the frequencies of particular genes by chance alone.
(iii)Variations caused in individuals due to natural selection.
(iv)Drastic change in the genes or DNA called mutation is also a cause of speciation. Reproductive isolation cannot be major factor in the speciation of a self-pollinating
plant species. This is because, it does not depend on any other plant for its reproduction process.

(a) Mendel choose garden pea for his experiment because pea plants was self fertilising and have short life cycle.
(b) Mendel performed experiments on a garden pea (Pisumsativum) with different visible contrasting characters. He selected seven contrasting pairs of characters such as tall / short plants, purple / white flower colour etc.
(c) Mendel performed his experiment on tall and dwarf plant and interpreted his results to show that the traits may be dominant or recessive. Parent plants: True breeding tall pea plant was crossed with true breeding dwarf pea plant. Production of F₁ plants: All F₁ plants were found to be tall. Results of self-pollination ofF₁ plants or F₂plants: Mendel found that on self-pollination of F₁ plants, the progenies obtained in F₂ generations were not all tall plants. Instead, one- fourth of F₂plants were found to be dwarf.
Mendel's explanation for the reappearance of the short trait: From this experiment, Mendel concluded that the F₁ tall plants were not true breeding. They were carrying
both the traits. They appeared tall, because the tall trait was dominant over the dwarf trait.