Genetics and Plant Breeding

One gene having more than one effect is called pleiotropy.

Different forms of the same gene are called alleles, e.g., T and t are alleles for stem height.

Since blood groups in humans are controlled by 3 alleles, i.e., I^A, I^B and i, it is an example of multiple allelism.

Pleiotropy is an instance where one gene has more than one effect. In this case, amount of starch grain produced as well as seed shape are the two effects.

Here, both genotypic and phenotypic ratios are the same, i.e., genotypic ratio is 1 RR:2Rr:1rr and phenotypic ratio is 1 red:2 pink:1 white.

Blood group AB can have only one genotype option and blood group A can also have only one option. After crossing, it can be concluded that their children can have blood groups A, B or AB.

Blood groups O and AB have only one genotype. By crossing them, the possible blood groups of their children are A or B.

The phenotypic ratio of dominant to recessive phenotypes of F₂ generation in a monohybrid cross is 3 : 1.

In genetics, a contrasting trait refers to a characteristic that manifests in two distinct, opposite forms such as tall vs short, or round vs wrinkled seeds. Mendel's work on pea plants focused specifically on such contrasting traits because they were easily observable and followed predictable inheritance patterns. Recessive and dominant describe how traits are inherited, not their appearance in opposite forms. Polygenic traits involve multiple genes and don't appear as simple opposites.

Every human inherits approximately half of their DNA from their mother and half from their father. This equal contribution occurs because each parent contributes one set of chromosomes (23 in humans) to form the complete set of 46 chromosomes in the offspring. While siblings share some DNA, they are not the primary source of an individual's genetic material - that comes from the two biological parents.

Gregor Mendel studied seven pairs of contrasting traits in pea plants: plant height (tall/dwarf), seed shape (round/wrinkled), seed color (yellow/green), pod shape (inflated/constricted), pod color (green/yellow), flower position (axial/terminal), and flower color (purple/white). These seven traits formed the foundation of his laws of inheritance.

When a pure tall plant (TT) is crossed with a dwarf plant (tt), all F1 offspring receive one dominant allele (T) and one recessive allele (t), making them all heterozygous (Tt). Since tallness is dominant over dwarfness, the T allele masks the expression of the t allele, resulting in all F1 plants appearing tall. This demonstrates Mendel's law of dominance. The plants won't be intermediate in height because height in peas shows complete dominance, not incomplete dominance.

Each offspring receives two versions (alleles) for each trait - one from the mother and one from the father. These alleles may be identical (homozygous) or different (heterozygous), but there are always exactly two versions present for each trait in a diploid organism like humans. This is why the possible genotype combinations follow predictable patterns in inheritance.

In sexual reproduction, each parent contributes exactly half of the offspring's genetic material. A human offspring receives 23 chromosomes from the mother and 23 chromosomes from the father, creating a total of 46 chromosomes. This means the ratio of maternal DNA to paternal DNA is exactly 1:1. Neither parent contributes more genetic material than the other.

In Mendelian genetics, a dominant trait (T) only needs one copy to be expressed. Therefore, both homozygous dominant (TT) and heterozygous (Tt) genotypes will produce tall plants, while only homozygous recessive (tt) produces short plants.