Name: __________________________________________ Period: ________________

 

Allelic Frequency and Evolution

 

Example 1: let's consider a gene with only two alleles. In rabbits, Black fur color (BB or Bb) is dominant to white fur color (bb). In a population of 100 rabbits, 36 rabbits are homozygous dominant (BB), 48 rabbits are heterozygous (Bb) and 16 are white (bb).

Calculating the frequency of the B allele for Generation 1:

Frequency of B= # of B alleles in the population

                            # of total alleles in the population

 

Frequency of B= (36 x 2) + (48 x 1)= _____________ = _________________%

                                 (100 x 2) = 200

 

Calculating the frequency of the b allele for Generation 1:

Frequency of b= # of b allele in the population

                            # of total alleles in the population

 

Frequency of b= (16 x 2) + (48 x 1) = ____________= __________________%

                              (100 x 2) = 200

 

Note that the two allele frequencies add up to 1. This is a law of population genetics: The sum of all allele frequencies will always be equal to 1. This is because 1 represents the frequency of all possible alleles within the population.

0.6 + 0.4 =1.0

The population of 100 rabbits have offspring. In Generation 2, there are 300 rabbits, 100 rabbits are homozygous dominant (BB), 160 rabbits are heterozygous (Bb) and 40 are white (bb).

 

  1. Calculate the frequency of the B allele for Generation 2.

 

Frequency of the B=

 

 

 

 

  1. Calculate the frequency of the b allele for Generation 2.

 

Frequency of the b=

 

 

 

  1. Has the allelic frequency changed from generation 1 to generation 2? Explain your answer.

 

 

  1. Has evolution occurred from generation 1 to generation 2? Explain your answer.

 

 

Example 2: Letís consider a gene with multiple alleles. In humans, IA (Type A blood) and IB (Type B blood) are codominant and i (Type O blood) is recessive. In a population of 100 people for Generation 1:

Blood Type

Genotype

Number of people in the population

Type A

IAIA

10

Type A

IAi

15

Type B

IBIB

10

Type B

IBi

15

Type AB

IAIB

14

Type O

ii

36

 

  1. Calculate the frequency of the IA allele for Generation 1.

 

 

Frequency of the IA allele= 10+10+15+14  = _____________ = ____________%

                                                   200

 

 

  1. Calculate the frequency of the IB allele for Generation 1.

 

Frequency of the IB allele=

 

 

 

  1. Calculate the frequency of the  i allele for Generation 1.

 

Frequency of the i allele=

 

 

 

 

 

 

Note that the three allele frequencies should add up to 1.

 

 

 

 

In a population of 100 people for Generation 2:

Blood Type

Genotype

Number of people in the population

Type A

IAIA

5

Type A

IAi

7

Type B

IBIB

15

Type B

IBi

15

Type AB

IAIB

14

Type O

ii

44

 

  1. Calculate the frequency of the IA allele for Generation 2.

 

Frequency of the IA allele=

 

 

 

 

  1. Calculate the frequency of the IB allele for Generation 2.

 

Frequency of the IB allele=

 

 

 

 

  1. Calculate the frequency of the  i allele for Generation 2.

 

Frequency of the i allele=

 

 

 

 

Note that the three allele frequencies should add up to 1.

 

 

  1. Has the allelic frequency changed from generation 1 to generation 2? Explain your answer.

 

 

 

 

  1. Has evolution occurred from generation 1 to generation 2? Explain your answer.