Question

9. Which evolutionary processes can increase genetic variation in a population?

10. Is it possible to have evolution without natural selection?

Answer 1

Answer 9.

Which evolutionary processes can increase genetic variation in a population

Those developments which do not change gene frequencies in the population are:

·         Crossing-over.

The exchange of genetic information between members of a homologous pair of chromosomes at meiosis that results in new combinations of alleles on chromosomes.

·         Recombination.

Mendel's Law of Independent Assortment that results in new combinations of chromosomes in both gamete (egg or sperm).

·         Mating.

Random combination of parents for most alleles resulting in a new combinations of chromosomes in every child. Every child is a unique combination with 50% of genes coming from each parent.

Those processes which do change gene frequencies in the population (i.e. they cause evolution directly) are:

·         Mutation.

A change in genetic code called as a mutation that comprises of changes in the hereditary instructions present within a gene. A mutation, the definitive source of all genetic variation occur in reproductive cells to cause genetic change in offspring. The process of mutation involves random genetic change predominantly due to chemical compounds and ionizing radiations. It may be:

1.      Advantageous. Produce a better allele.

2.      Neutral. Do not affect functioning of allele.

3.      Disadvantageous. Disturbs functioning of allele.

·         Gene Flow (immigration)

Movement of genes from one population to another, the process of the loss or gain of genes in a population due to the emigration or immigration of fertile individuals, or the transfer of gametes, between populations. The process bring together new genes into a population which result in populations becoming more similar to one another

Answer 10

Natural selection is a process which reduces genetic variation with populations (cause evolution directly). It refers to the discrepancy in survival and reproduction of organisms based on their biological characteristics.

ü "Garden variety" natural selection

Selective reduction in genetic variation leads to the changes in gene frequencies through time as individuals carrying alleles not well-adapted to that particular environment reproduce not as much of successfully than individuals having alleles suited to that specific habitat. It reduces variation by removing all the alleles carried by poorly adapted individuals. Results in population changing to become better and better adapted to their environment, as long as the environment remains the same. If the environment changes, the game begins anew. Differential net Reproductive success is measured by the number of offspring who survive to reproduce. However small difference in reproductive success can cause major changes in the gene frequencies.

ü Artificial Selection

When natural humans are the agents, the foundation of all plants and animals, including such wonders as the modern strawberry and Chihuahuas.

ü Sexual Selection

Natural selection with female choice of males for mating partners (genetically derived traits) as the agents; the source of most sexually dimorphic features like lions' manes, antlers in deer and canines in baboons.