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Section 11.1: The Work of Gregor Mendel

Exercise 1

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The principle of dominance involves the dominant and recessive alleles. Dominant alleles exhibit their effect in the form of a trait in an organism. On the other hand, recessive allele is masked by the dominant allele. It would only show if it is teamed up with another recessive allele. For example, if the allele for blue eyes is dominant and the allele for brown eyes is the recessive one, the blue eyes will manifest in a person. However, if a person has two recessive alleles of brown eyes, the brown eyes will show.

Exercise 2

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The law of segregation explains how genes are separated during meiosis. During the formation of gametes in an organism, the pair of alleles segregates from each other in order for each gamete to carry one of the two alleles. In this way, an offspring acquires one allele from each parent.

Exercise 3

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Gregor Mendel concluded that biological inheritance is influenced by chemical factors that determine the traits which are passed to the next generation. This chemical factor is called genes. Genes produce the characteristics of an organism’s trait in two contrasting forms called alleles. For example, a gene of a person occurs in one allele that produces black hair and another allele that produces brown hair.

Exercise 4

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Mendel cross-pollinated pea plants by opening the flower buds and cutting off the male part (stamen) of one flower to prevent self-pollination. Then, he dusted the stigma with pollen from another flower. By doing this, he was able to cross-bred peas using 7 pairs of traits and recorded the results. He noticed that the first generation showed dominant traits, whereas the recessive traits appeared in the second generation.

Exercise 5

Step 1

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The reappearance of the recessive allele for shortness reappeared in F2 plants happened because of the law of segregation. This explains how a pair of alleles are separated from each other in order for an offspring to acquire one allele from each parent. Each F1 plant has one dominant allele for tallness, which is represented by capital T, and one recessive allele for shortness, which is represented by small t. When plants undergo segregation, the combinations produced for their offspring would be TT, Tt, Tt, and tt. TT, Tt, and Tt contain dominant allele T which is responsible for the tallness, whereas tt contains two recessive alleles that represent shortness. This is why only one of the four F2 plants exhibit the recessive trait.

T = dominant allele for tallness

t = recessive allele for shortness

Combinations produced:

Tf $times$ Tf = TT, Tt, Tt, and tt

TT, Tt, and Tt = contain dominant allele T (tallness)

tt = contains two recessive alleles (shortness)

Exercise 6

Result

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A true-breeding organism passes down the exact same traits that they have to its offspring. These traits are manifested physically by its offspring, in turn, they look very similar to each other. Because of these conditions, Mendel used them as his basis for his investigation. The presence of observable traits in the pea plants made it easier for Mendel to tell any differences in the plants’ form during his experiment.

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Section 11.1: The Work of Gregor Mendel

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