Question

Explain how a trait might seem to “disappear” for a generation, and then “reappear” in the following generation.

Answer 1

If all of the individual in a generation receives one dominant allele and one recessive allele, then they will all show the dominant trait.

If they are bred, they will pass on the dominant allele to some of their offspring and recessive allele to others.

If an offspring receives two recessive alleles, it will show the recessive trait and therefore it will reappear.

Answer 2

When two true-breeding or homozygous individuals for dominant and recessive traits are crossed, the resultant is always a dominant trait. The recessive character appears in the following generation when the F1 progeny is self-crossed due to independent segregation and random fusion of gametes.

Further Explanation:

Consider Mendel's experiment on a pea plant in which he used the trait of height as tall and short. On self-pollinating the tall plants, the resulting progeny were all tall while when self-pollination was done for short plants, the resultants were all short. It was found that when true-breeding short (t) plants are bred with the true breeding tall (T) plants, the offspring results in all tall plants in the F1 generation. When this progeny is self-crossed, the F2 generation results in both tall and short plants in a 3:1 ratio.

Mendel stated that the traits are controlled by genes that are present in pairs of alleles. Each parent contributes the alleles in the pair. Allele 'T' is received from a tall parent while short parent contributes to allele’t’ and they together produce a tall plant. This is because the 'T' allele suppresses the expression of’t’ allele because of its dominant nature. Therefore,’t’ is a recessive allele, and 'T' is a dominant allele.

Cross between true-breeding tall (TT) and short (tt) plant:

Parents: TT x tt

Gametes: T x t

Progeny: Tt (tall, F1 generation)

When F1 generation is self crossed:

Parents: Tt x Tt

Gametes: T, t x T, t

Progeny: TT, Tt, Tt, tt

In the F1 generation, the recessive trait (short plant) was suppressed because of the dominance of the 'T' allele over the’t’ allele. In the following generation, the recessive trait reappeared because of the independent segregation of gametes and their random association with each other.

Learn More-

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Answer Details:

Grade: High School

Chapter: Gene interaction

Subject: Biology

Keywords:

True-breeding, homozygous, genes, alleles, dominant, recessive, independent segregation, random fusion, gametes, progeny, F1 generation, F2 generation.