population genetics

Question 1

population genetics

Answer 1

• The study of genetic variation within populations
• Via the frequency of genes and alleles
• There is huge variation within populations at the nucleotide level

Question 2

what is a population

Answer 2

• A group of individuals of the same species living in a specific region at the same time
• In this context species refers to individuals who interbreed and produce viable offspring

Question 3

factors affecting population size

Answer 3

• Birth
• Death
• Immigration
• Emigration

Question 4

population genetics and evolution

Answer 4

• Mendelian principles are used to understand the genetic composition of a population
• The set of genes is a population is called the gene pool
• A population evolves via changes in the gene pool

Question 5

measuring genetic variation

Answer 5

How to measure the numbers of genotype and alleles in a population

• Need to be able to tell the difference of the phenotype level
• Differences maybe in coding or non-coding DNA eg polymorphisms used for forensics

Question 6

calculation genetic frequencies

Answer 6

• For large populations where it is not possible to sample all individuals, a representative sample is usually taken
• The frequency of a genotype or an individual allele can be calculated
• To calculate a genotypic frequency we add up the number of individuals possessing the genotype and divide by the total number of individuals in the population (N)

Question 7

genotypic frequencies

Answer 7

• For a locus with 3 possible genotypes, AA, Aa and aa, the frequency of each genotype (f) is:
• f(AA)= number of AA individuals/N
• f(Aa)= number of Aa individuals/N
• f(aa)= number of aa individuals/N
• The sum of all the genotypic frequencies always equals 1

Question 8

what is a frequency

Answer 8

A frequency is a proportion or percentage usually expressed as a decimal fraction
- Eg if 20% of a population has allele A, the frequency of allele A is 0.2

Question 9

allelic frequencies

Answer 9

• It is the alleles that are passed from generation to generation within a population rather than the genotypes therefore it is important to be able calculate allele frequencies as well
• Can be determined from the genotype frequency
• p= F(A)= f(AA)+ ½ f(Aa)
• q= F(a)= f(aa)+ ½ f (Aa)
• If a locus only has two alleles the frequencies are usually represented by p and q. p+q = 1

Question 10

allelic frequencies can also be determined by counting observed alleles

Answer 10

• And then calculating the frequency

- Frequency of an allele= number of copies of the allele number of copies of all alleles at locus

Question 11

blood group examples of allelic frequencies

Answer 11

-	298 MM, 489 MN, 213 NN 
So for each genotype there are: 
-	298 MM = 596 M alleles 
-	489 MN = 489 M alleles + 489 N alleles 
-	213 NN = 426 N alleles
-	Add these figures as below to get the frequencies:
f(M) = 596 + 489 = 1085 / 2000 = 0.542 
f(N) = 489 + 426 = 915 / 2000 = 0.458

Question 12

mendelian laws- the law of segregation

Answer 12

• States that allele pair separate during gamete formation and randomly unite at fertilisation. Allows formation of heterozygotes and homozygotes

Question 13

mendelian laws- the laws of independent assortment

Answer 13

• States hereditary factors assort independently during gamete formation

Question 14

the relationship between genotype and allele frequencies

Answer 14

• The hardy Weingberg law is a mathematical representation of the relationship between genotype and allele frequencies in an ideal population
• Key to forensic genetics