Genetic Change/Evolution

Evolution• The process in which new species develop from

earlier forms.

Evolution• The process in which new species develop from

earlier forms.• Normally occurs slowly, most often in response to

a change in a species’ environment.

Evolution• The process in which new species develop from

earlier forms.• Normally occurs slowly, most often in response to

a change in a species’ environment. • Life is thought to have evolved from just a few

unicellular organisms three billion years ago.

Evolution• The process in which new species develop from

earlier forms.• Normally occurs slowly, most often in response to

a change in a species’ environment. • Life is thought to have evolved from just a few

unicellular organisms three billion years ago. • Evolution happens through ‘changes in the

frequency of alleles in a population’ – some alleles do better than others.

Evolution• The process in which new species develop from

earlier forms.• Normally occurs slowly, most often in response to

a change in a species’ environment. • Life is thought to have evolved from just a few

unicellular organisms three billion years ago. • Evolution happens through ‘changes in the

frequency of alleles in a population’ – some alleles do better than others.

• Freq. of an allele = occurrence of that alleletotal number of alleles

Example of how to work out allele frequencies• Suppose a gene pool were to contain 50

individuals.

Example of how to work out allele frequencies• Suppose a gene pool were to contain 50

individuals. • 30 – Aa, 10 – AA and 10 – aa

Example of how to work out allele frequencies• Suppose a gene pool were to contain 50

individuals. • 30 – Aa, 10 – AA and 10 – aa• For the A allele it occurs 30 times from Aa

Example of how to work out allele frequencies• Suppose a gene pool were to contain 50

individuals. • 30 – Aa, 10 – AA and 10 – aa• For the A allele it occurs 30 times from Aa• The A allele also occurs 20 times from AA (2x10)

Example of how to work out allele frequencies• Suppose a gene pool were to contain 50

individuals. • 30 – Aa, 10 – AA and 10 – aa• For the A allele it occurs 30 times from Aa• The A allele also occurs 20 times from AA (2x10)• The occurrence of the A allele is now 50 (30 + 20)

Example of how to work out allele frequencies• Suppose a gene pool were to contain 50

individuals. • 30 – Aa, 10 – AA and 10 – aa• For the A allele it occurs 30 times from Aa• The A allele also occurs 20 times from AA (2x10)• The occurrence of the A allele is now 50 (30 + 20)• There are 50 individuals with two alleles so that

the total number of alleles is 100 (50x2)

Example of how to work out allele frequencies• Suppose a gene pool were to contain 50

individuals. • 30 – Aa, 10 – AA and 10 – aa• For the A allele it occurs 30 times from Aa• The A allele also occurs 20 times from AA (2x10)• The occurrence of the A allele is now 50 (30 + 20)• There are 50 individuals with two alleles so that

the total number of alleles is 100 (50x2)• Frequency of the A allele = 50/100 = 0.5

Try these1. Suppose a gene pool were to contain 60

individuals. 20 were BB, 30 were Bb and 10 were bb. Calculate the frequency of the B allele.

2. A gene pool has 120 individuals. 60 were Aa, 20 were AA and 40 were aa. Calculate the frequency of the A allele.

Example of the evolutionary effect of the recessive allele (sometimes the ‘bad allele)

• Sometimes the recessive allele is bad because it makes the individuals phenotypically inferior in some way.

Example of the evolutionary effect of the recessive allele (sometimes the ‘bad allele)

• Sometimes the recessive allele is bad because it makes the individuals phenotypically inferior in some way.

• Remembering we have 50 indiv. = 30 Aa, 10AA, and 10 aa

Example of the evolutionary effect of the recessive allele (sometimes the ‘bad allele)

• Sometimes the recessive allele is bad because it makes the individuals phenotypically inferior in some way.

• Remembering we have 50 indiv. = 30 Aa, 10AA, and 10 aa

• If all the 10 individuals that showed this allele died or were forced to leave the population then:

Example of the evolutionary effect of the recessive allele (sometimes the ‘bad allele)

• Sometimes the recessive allele is bad because it makes the individuals phenotypically inferior in some way.

• Remembering we have 50 indiv. = 30 Aa, 10AA, and 10 aa

• If all the 10 individuals that showed this allele died or were forced to leave the population then:

• Numerator is found from the Aa indiv. (30x1) = 30 a alleles

Example of the evolutionary effect of the recessive allele (sometimes the ‘bad allele)

• Sometimes the recessive allele is bad because it makes the individuals phenotypically inferior in some way.

• Remembering we have 50 indiv. = 30 Aa, 10AA, and 10 aa

• If all the 10 individuals that showed this allele died or were forced to leave the population then:

• Numerator is found from the Aa indiv. (30x1) = 30 a alleles

• Denominator is found from the 30 Aa individuals + the 10 AA individuals (30x2 + 10x2 = 80) – total alleles.

Example of the evolutionary effect of the recessive allele (sometimes the ‘bad allele)

• Sometimes the recessive allele is bad because it makes the individuals phenotypically inferior in some way.

• Remembering we have 50 indiv. = 30 Aa, 10AA, and 10 aa

• If all the 10 individuals that showed this allele died or were forced to leave the population then:

• Numerator is found from the Aa indiv. (30x1) = 30 a alleles

• Denominator is found from the 30 Aa individuals + the 10 AA individuals (30x2 + 10x2 = 80) – total alleles.

• The frequency is now 30/80 = 0.375 – evolution is operating because there has been a change in allele frequencies.

‘Bad’ recessive alleles• Sickle-cell anaemia – red blood cells form a sickle

shape. These abnormally shaped cells cause severe muscle pain and in extreme cases, death.

‘Bad’ recessive alleles• Sickle-cell anaemia – red blood cells form a sickle

shape. These abnormally shaped cells cause severe muscle pain and in extreme cases, death.

• Cystic fibrosis – carried by 1 in 20 pakeha. The affected individual secretes abnormally thick mucus. This affects both their digestive and respiratory systems. In the lungs it provides a thick breeding ground for bacteria.