Question

How does Mendels show traits are inherited independently

Answer 1

this is shown as he crossed between two pea plants and sees that it is having tallness and shortness ratio as 2*2 and after crossing with each other 3*1

Answer 2

Our understanding of how inherited traits are passed between generations comes from principles first proposed by Gregor Mendel in 1866. Mendel worked on pea plants, but his principles apply to traits in plants and animals – they can explain how we inherit our eye colour, hair colour and even tongue-rolling ability.

Genes located on different chromosomes will be inherited independently of each other. Mendel observed that, when peas with more than one trait were crossed, the progeny did not always match the parents. This is because different traits are inherited independently – this is the principle of independent assortment.

Mendel’s principles of inheritance

1. Fundamental theory of heredity
Inheritance involves the passing of discrete units of inheritance, or genes, from parents to offspring.

Mendel found that paired pea traits were either dominant or recessive. When pure-bred parent plants were cross-bred, dominant traits were always seen in the progeny, whereas recessive traits were hidden until the first-generation (F1) hybridplants were left to self-pollinate. Mendel counted the number of second-generation (F2) progeny with dominant or recessive traits and found a 3:1 ratio of dominant to recessive traits. He concluded that traits were not blended but remained distinct in subsequent generations, which was contrary to scientific opinion at the time.

Inheritance of a single trait in peas

Mendel followed the inheritance of 7 pea traits. Dominant traits, like round peas, appeared in the first-generation hybrids (F1), whereas recessive traits, like wrinkled peas, were masked. However, recessive traits reappeared in the second generation (F2). Each individual carries a pair of factors for each trait, and they separate from each other during fertilisation. This is the basis of Mendel’s principle of segregation.

2. Principle of segregation
During reproduction, the inherited factors (now called alleles) that determine traits are separated into reproductive cells by a process called meiosis and randomly reunite during fertilisation.

Mendel proposed that, during reproduction, the inherited factors must separate into reproductive cells. He had observed that allowing hybrid pea plants to self-pollinate resulted in progeny that looked different from their parents. Separation occurs during meiosis when the alleles of each gene segregate into individual reproductive cells (eggs and sperm in animals, or pollen and ova in plants).

3. Principle of independent assortment
Genes located on different chromosomes will be inherited independently of each other.

Mendel observed that, when peas with more than one trait were crossed, the progeny did not always match the parents. This is because different traits are inherited independently – this is the principle of independent assortment. For example, he cross-bred pea plants with round, yellow seeds and plants with wrinkled, green seeds. Only the dominant traits (yellow and round) appeared in the F1 progeny, but all combinations of trait were seen in the self-pollinated F2 progeny. The traits were present in a 9:3:3:1 ratio (round, yellow: round, green: wrinkled, yellow: wrinkled, green).

Inheritance of multiple traits in peas

Mendel cross-bred plants with 2 or more traits and found that each trait was inherited independently of the other and produced its own 3:1 ratio. For example, a plant with round, yellow seeds crossed with a plant with wrinkled green seeds gives a ratio of 9:3:3:1. This is the basis for Mendel’s principle of independent assortment.