Mendel’s laws

In Mendel’s monohybrid cross, a pure tall plant is crossed with a pure dwarf plant. The first-generation offspring receive one allele for each form of the trait, but only the tall phenotype is visible. This shows that the tall allele masks the dwarf allele and is dominant. The dwarf allele is not destroyed; it remains present in the hybrid genotype. Therefore option A is correct.

Let the dominant tall allele be T and the recessive dwarf allele be t. A pure tall parent is TT and a pure dwarf parent is tt. Every F1 offspring receives T from the first parent and t from the second, giving genotype Tt. Because T is dominant, all F1 plants appear tall, while the t allele remains present but hidden. Therefore option A is correct; the dwarf information was not destroyed or absent.

Mendel’s law of independent assortment states that, during gamete formation, the allele pair for one trait can separate independently of the allele pair for another trait, provided the genes are not linked in a way that prevents independence. In a dihybrid cross this produces new combinations of traits, commonly reflected in the classic 9:3:3:1 ratio under ideal conditions. Thus option A is correct.

A pure-breeding line produces offspring with the same form of a trait generation after generation because it is genetically uniform for that characteristic. Mendel could therefore begin a cross with known parental forms and attribute differences in the offspring to the cross rather than to unknown variation in the parents. This made dominant and recessive inheritance patterns easier to detect. Option A is correct; the other choices contradict the purpose of controlled breeding.

In a monohybrid cross, the heterozygous F1 generation produces two types of gametes in equal proportions because the two allelic forms separate during gamete formation. Self-pollination then gives genotypes in a 1:2:1 ratio and, with complete dominance, phenotypes in a 3:1 ratio. The reappearance of the recessive phenotype demonstrates segregation. Thus option A is correct; blending would not restore the recessive form.

The governing principle is Mendel’s law of segregation. In a cross such as Tt × Tt, the two alleles separate during gamete formation. Random fusion produces TT, Tt, Tt, and tt in a 1:2:1 genotype ratio; because T is dominant, the visible phenotypes occur in a 3 tall:1 dwarf ratio. Therefore option B is correct. Independent assortment concerns the inheritance of two different traits, not the basic one-trait 3:1 result.

The governing concept is Mendel’s law of independent assortment. During gamete formation, the allele pair for one trait can separate and combine independently of the allele pair for another trait, when the genes are considered independently. This allows offspring to receive new combinations of characteristics. Thus option B is correct. The law of dominance explains why one allele can mask another, conservation of energy belongs to physics, and natural selection is an evolutionary process rather than the specific inheritance rule described here.

The governing concept is the paired-allele model of inheritance. In sexual reproduction, each parent forms gametes carrying one allele for a trait. At fertilisation, the offspring receives one allele from the mother and one from the father, restoring a pair. For example, Tt may result from T supplied by one parent and t by the other, allowing dominant and recessive relationships to be observed. Therefore option A is correct; the other choices deny biparental inheritance or confuse inherited traits with acquired characteristics.