Populations & evolution

Question 1

What is Allelic frequency?

Answer 1

-the number of times an allele occurs within the gene pool is referred to as the allelic frequency

Question 2

What is an example of Allelic frequency?

Answer 2

• the gene responsible for cystic fibrosis, a disease of humans in which the mucus produced by affected individuals is thicker than normal
• the gene has a dominant allele (F) that leads to normal mucus production and a recessive allele (f) that leads to normal mucus production and a recessive allele (f) that leads to the production of thicker mucus and hence cystic fibrosis
• any individual human has two of these alleles in every one of their cells, one on each of the pair of homologous chromosomes on which the gene is found
• as these alleles are the same in every cell of a single person, we only count one pair of alleles per gene per individual when considering a gene pool
• if there are 10000 people in a population, there will be twice as many (20000) alleles in the gene pool of this gene
• the pair of alleles of the cystic fibrosis gene has three different possible combinations, namely homozygous dominant (FF), homozygous recessive (ff) and heterozygous (Ff)
• when we look at allele frequencies, however, it is important to appreciate that the heterozygous combination can be written as Ff or fF (its just conventional to put the dominant allele first in all cases)

Question 3

In a population of 10000 people if all 10000 had the genotype FF what would happen?

Answer 3

• the probability of anyone being FF would be 1.0 and the probability of anyone being ff would be 0.0
• the frequency of the F allele would be 100% and the frequency of the f allele would be 0%

Question 4

In a population of 10000 people if all 10000 had the genotype Ff what would happen?

Answer 4

-the probability of anyone being Ff would be 1.0 and the frequency of the F allele would be would be 50% and the frequency of the f allele would also be 50%

Question 5

What is the Hardy-Weinberg principle?

Answer 5

• the Hardy-Weinberg principle provides a mathematical equation that can be used to calculate the frequencies of the alleges of a particular gene in a population
• the principle makes the assumption that the proportion of dominant and recessive alleges of any gene in a population remains the same from one generation to the next this can be the case provided that the five conditions are met
• although these conditions are probably never totally met in a natural population, the Hardy-Weinberg principle is still useful when studying gene frequencies

Question 6

What are the five conditions needed for the Hardy-Weinberg principle?

Answer 6

• no mutations arise
• the population is isolated so there is no flow of alleges into or out of the population generation
• the population is large
• mating within the population is random
• there is no selection so all alleges are equally likely to be passed to the next

Question 7

What is a population?

Answer 7

• a population is a group of organisms of the same species that occupies a particular space at a particular time and that can potentially interbreed
• any species exists as one or more populations

Question 8

What is a gene pool?

Answer 8

-all the alleges of the genes of all the individuals in a population at a given time are known as the gene pool