question_answer

A true breeding pea plant homozygous for axial violet flowers (AAW) was crossed with another pea plant having terminal white flowers (aavv).

(i) Predict the phenotype and genotype of \[{{F}_{1}}\]- generation.

(ii) Find out the phenotypic ratio of \[{{F}_{2}}\] - generation.

(iii) Discuss the Mendel's generalisation that can be derived from the above cross.

Or

(i) What are variations?

(ii) How is genetic drift important in evolution?

(iii) Fitness of a population helps in evolution. Give reason.

Answer:

The cross between true breeding pea plant homozygous for axial voilet flowers (AAVV) with another pea plant having terminal white flowers (aavv) :

(i) Phenotype of \[{{F}_{1}}\]-generation: Axial violet flower

Genotype of \[{{F}_{1}}\]-generation: AaVv (Heterozygous)

(ii) Phenotypic ratio of \[{{F}_{2}}\]-generation.

(iii) Based on the above cross Mendel?s ??Law of independent assortment?? can be derived.

The law states that ??when two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent of the other pair of characters.??

Or

(i) Variations are morphological, physiological, cytological and behavioristic differences amongst the individuals of the same species and the offspring of the same parents.

They are found in all characters and in every conceivable direction. Therefore, two individuals are not similar.

(ii) Genetic drift refers to a change in the population of alleles in the gene pool. Genetic drift is also known as ??Sewall

Wright Effect?? (named after its discoverer). It is random in gene (allele) frequency. It occurs only by chance. It is non-directional. Genetic drift can cause elimination of certain alleles and fixation of the other alleles in the population.

Due to this, genetic drift affects the frequency of alleles in the population which leads to evolution. Therefore, genetic drift is important in the process of evolution.

(iii) Fitness is a measure of how well organisms survive and reproduce. It is also defined as the number of offspring that organisms with a particular genotype or phenotype leave behind, on average, as compared to others in the population.

The phenotypes and genotypes favoured by natural selection are not necessarily just the ones that survive best. Instead, they are the ones with the highest overall fitness. The fitness of a population thus helps in evolution.