The most obvious outcome of the reproductive process is the generation of individuals of similar design, but in sexual reproduction they may not be exactly alike. The resemblances as well as differences are marked. The rules of heredity determine the process by which traits and characteristics are reliably inherited. Many experiments have been done to study the rules of inheritance.

(i) Why an offspring of human being is not a true copy of his parents in sexual reproduction ? (1 mark)

(ii) While performing experiments on inheritance in plants, what is the difference between $F_1$ and $F_2$ generation ? (1 mark)

(iii) (A) Why do we say that variations are useful for the survival of a species over time ? (2 marks)

OR

(iii) (B) Study Mendel's cross between two plants with a pair of contrasting characters: $RRYY \times rryy$ (Round Yellow x Wrinkled Green). He observed 4 types of combinations in $F_2$ generation. Which of these were new combinations ? Why do new features which are not present in the parents, appear in $F_2$ generation ? (2 marks)

(i) An offspring of a human being is not a true copy of its parents because sexual reproduction involves the fusion of male and female gametes, meaning both parents contribute practically equal amounts of genetic material (DNA) to the child. Each trait is influenced by both paternal and maternal DNA, and minor inaccuracies in DNA copying along with genetic recombination generate unique variations in the offspring.

(ii) In Mendelian experiments:

• In the $F_1$ (first-generation) progeny, only one of the parental traits (the dominant trait) is expressed, and there are no halfway or mixed characteristics (e.g., all plants are tall).
• In the $F_2$ (second-generation) progeny (obtained by self-pollinating $F_1$), the hidden recessive trait also reappears along with the dominant trait in a specific ratio (e.g., $3$ tall to $1$ short).

(iii) (A) Variations are useful for the survival of a species over time because environmental conditions (like temperature, climate, or resources) change constantly. Depending on the nature of these variations, different individuals will have different survival advantages. For example, in a heat wave, only bacteria that have a variation allowing them to withstand heat will survive, preventing the entire species from being wiped out. Thus, selection of variants by environmental factors forms the basis of evolutionary survival.

OR

(iii) (B) In Mendel's dihybrid cross ($RRYY \times rryy$):

• The new combinations (recombinants) observed in the $F_2$ generation are Round Green and Wrinkled Yellow.
• New features appear in the $F_2$ generation because the factors (genes) controlling different traits (like seed shape and seed colour) are present on separate independent pieces of DNA called chromosomes. These traits are inherited independently of each other. During gamete formation and subsequent fertilization, these factors recombine freely, giving rise to novel combinations not present in either of the original parental plants.