Ans: Father (blood group A) can have genotype I^A I^A or I^A i. Mother (blood group O) has genotype ii. Case 1: Father I^A I^A × Mother ii → All children I^A i → All blood group A. Case 2: Father I^A i × Mother ii → Children: I^A i (blood group A) and ii (blood group O) in 1:1 ratio. So possible blood groups of children are A and O (depending on father's exact genotype). This illustrates Mendel's Law of Segregation — alleles separate during gamete formation. Blood group is determined by multiple alleles: I^A, I^B (codominant), and i (recessive).

Ans: Evidence for evolution: (1) Fossil record: Fossils are preserved remains of ancient organisms in sedimentary rock layers. Older/simpler organisms in deeper layers; more complex in upper layers. Shows gradual change over time and existence of extinct species. (2) Homologous organs: Structurally similar organs with different functions (e.g., forelimbs of whale, bat, human, frog) indicating descent from a common ancestor (divergent evolution). (3) Analogous organs: Functionally similar but structurally different organs (e.g., wings of birds and insects) showing convergent evolution due to similar environmental pressures. (4) Embryological similarities: Embryos of fish, amphibians, reptiles, birds, and mammals look nearly identical in early stages, suggesting common ancestry. (5) Molecular evidence: Similar DNA/protein sequences across species.

Ans: Traits acquired during a lifetime (acquired traits) are changes in somatic (body) cells caused by environment, use, or injury — not changes in the DNA of reproductive cells (germ cells/gametes). Since only germ cell DNA is passed to offspring, somatic changes cannot be inherited. Example: A person who loses a finger in an accident will not have children born with missing fingers. Weismann's experiment: mice had their tails cut off for 22 generations — none were born tailless, proving acquired traits are not inherited. Only mutations in germ cells (sperm/egg DNA) can be inherited.

Ans: Speciation is the evolutionary process by which a new species originates from existing species. A species is a group of organisms that can interbreed and produce fertile offspring. Factors leading to speciation: (1) Geographic isolation — populations separated by mountains, rivers, or oceans cannot interbreed; each population accumulates different genetic changes over time. (2) Genetic drift — random changes in gene frequencies (especially in small, isolated populations) lead to different gene pools. (3) Natural selection — different environments favor different traits, driving populations apart. (4) Mutations — different mutations arise in isolated populations. Over many generations, differences accumulate until the two populations can no longer interbreed even if brought together — new species formed.

Ans: XY.

Ans: The dominant trait.

Ans: The wings of a bird and the wings of an insect: they perform the same function (flight) but differ in structure and origin.

Ans: F1: all Tt (tall). F2: 1 TT : 2 Tt : 1 tt, i.e. 3 tall : 1 short.

Ans: Homologous organs have a similar basic structure but may perform different functions. Example: the forelimb of a human, the wing of a bat and the flipper of a whale have the same bone arrangement.

Ans: Variations give some individuals features that help them survive and reproduce in a changing environment. Over generations these features accumulate, causing evolution.

Ans: Parents: TT × tt. F1: all Tt (tall). F1 × F1: gametes T and t from each parent. The Punnett square gives TT, Tt, Tt, tt in F2. Phenotypic ratio = 3 tall : 1 short; genotypic ratio = 1 : 2 : 1.

Ans: It had feathered wings like birds, but also teeth in its jaw, claws on its wings and a long tail like reptiles. Having features of both groups shows that birds evolved from reptiles.

Ans: Genetic drift is a random change in the frequency of genes in a small population by chance events and not due to any advantage. Example: if a few individuals of a beetle population are killed by an elephant stepping on the bush, the survivors' traits become common by chance.

Ans: Law of dominance: when two contrasting traits are crossed, only one (dominant) appears in F1 (tall × short gives all tall). Law of segregation: the two alleles of a trait separate during gamete formation, so each gamete has one allele; recessive trait reappears in F2 (3:1). Law of independent assortment: alleles of different traits are inherited independently, as in a dihybrid cross where F2 shows 9:3:3:1 and new combinations (round green, wrinkled yellow) appear.

Ans: Relationships are traced by comparing homologous organs, fossils, embryos and the DNA of species; more similar DNA means a closer relationship. Humans (Homo sapiens) evolved in Africa, and groups migrated to other continents. Variations in skin colour are due to adaptation and genetic variation, but all humans belong to one species. Evolution is not a ladder of progress; it is a branching of species through variation, natural selection and chance.