CBSE Class 10 Science NCERT Solutions: Heredity and Evolution

Explanation: Genetic material is exchanged during sexual reproduction because it involves the fusion of gametes from two parents. This process leads to the recombination of genes, creating offspring with a mix of parental traits. Vegetative reproduction, asexual reproduction, and budding are all forms of asexual reproduction, where genetic material is not exchanged, and offspring are typically clones of the single parent.

Explanation: This outcome (1 red : 2 pink : 1 white) is characteristic of a monohybrid cross involving incomplete dominance or co-dominance, where the heterozygous condition (pink) results in an intermediate or combined phenotype. This occurs when alleles from two different parents are combined through cross-fertilization, leading to the segregation and recombination of traits in the progeny.

Explanation: In genetics, a dominant trait is expressed in the phenotype even when only one copy of the dominant allele is present. In this cross between a homozygous tall plant (TT) and a homozygous short plant (tt), all the offspring in the first filial (F1) generation inherit one 'T' allele and one 't' allele (Tt). Since tallness is dominant, the 'T' allele masks the effect of the 't' allele, resulting in all tall plants.

Explanation: Genes are segments of DNA that typically code for proteins. Proteins can function as enzymes, hormones, structural components, etc. Therefore, for most hormones and enzymes, there is a corresponding gene that provides the blueprint for their synthesis. However, fats are lipids, and their synthesis is regulated by various enzymes and metabolic pathways, but there isn't a direct gene for 'every molecule of fat' in the same way genes code for specific proteins.

Explanation: This is a dihybrid cross. The genotype RRyy represents a plant with round (R) and green (y) seeds, while rrYY represents a plant with wrinkled (r) and yellow (Y) seeds. In the F1 generation, each parent contributes one allele for each gene. Thus, the offspring will have the genotype RrYy. Since 'R' (round) is dominant over 'r' (wrinkled) and 'Y' (yellow) is dominant over 'y' (green), the phenotype expressed will be round and yellow seeds.

Explanation: Human somatic cells contain 23 pairs of chromosomes, totaling 46. Of these, 22 pairs are autosomes, which are similar in males and females. The 23rd pair consists of sex chromosomes. In human males, the sex chromosomes are XY. While the X chromosome is relatively large and similar to other chromosomes, the Y chromosome is much smaller. These two sex chromosomes (X and Y) do not pair up in the same way as homologous autosomes during meiosis, and they are distinct from each other, hence they are considered the unpaired chromosomes in males.