Starter An animal has a diploid chromosome number of 14. Calculate the number of possible genotypes of gametes it produces due to independent segregation . When it breeds, calculate the number of possible zygote genotypes it could produce. How many chromosome combinations would be produced in an organism with n=21? 27 = 128 (27)2 = 16384 2097152

Requirements PRACTICAL Other Per pair:- Pot containing 40 beads – 20 of each of 2 colours Spare ‘discard pot’

Genetic Diversity and Adaptation Pages 229-230 Specification area 4.4

Syllabus

Objectives Explain why organisms are different from one another. Describe what factors influence genetic diversity. Explain how reproductive success affects allele frequency within a gene pool. Explain how genetic diversity enables natural selection

Genetic diversity Genetic Diversity Is the number of different alleles of genes in a population POPULATION – number of organisms of the same species living in the same habitat at the same time Alleles – different forms of the same gene In a population each organism has the same genes, so genetic diversity is expressed as the different alleles of that gene present Genetic diversity is a factor that enables natural selection to occur (ie – if all organisms in a population were identical the natural selection would not work)

Definition of the term “Species” = Organisms that are able to reproduce to produce “fertile offspring” All members of the same species carry the SAME GENES…… What varies is the versions or alleles of those genes!

Differences between individuals of a species Members of the same species have many similarities, but also many differences Members of the same species have same genes But may have different versions or alleles of the genes i.e. different DNA sequences which code for different proteins

What do we mean by the “Genetic Diversity” or “Gene Pool” for a species? TOTAL number of different alleles in a population at a given time

Significance of genetic diversity Which is better for a population/ species survival – High or low Genetic diversity? If a population of a species has a large gene pool i.e. high genetic diversity, then when the environment changes, it is more likely that some individuals in the population will have alleles that enable them to survive in the new conditions. This will allow the population of the species to continue to survive in that area.

White board activity Make a list of points for how natural selection occurs from your GCSE knowledge Start with VARIATION

Natural selection red – bringing it from GCSE to AS level Random mutation results in a new allele (increases variation) When environment changes the new allele gives it’s possessor an advantage over the others These individuals are better adapted so have more reproductive success (i.e they “survive to reproduce”) Their offspring inherit these advantageous alleles The number of individuals with the allele increases The frequency of the allele increases in the population NB most mutations are harmful – it is rare for it to give the possessor an advantage Do not use the word GENE in an exam answer – why not??

Investigating changing allele frequency within a population: Bead model of selection Make a gene pool using 20 beads to represent an “advantageous” dominant allele and 20 beads of another colour to represent the recessive allele. Breed to produce 10 offspring in a generation with bead replacement At the end of the first generation (after 10 offspring), discard the number of recessive alleles that have ‘been selected against’ – e.g. if you have 2 x ‘rr’ individuals, they will not survive to the next generation – so remove 4 ‘r’ alleles from the gene pool. Repeat steps 2 and 3 above for four more generations. Keep a tally for the offspring within each generation. What happens to the allele frequencies? 4 3 3 11 9 27.5 22.5 4 4 2 12 8 34 35.3 23.5

A model showing changes in allele frequency over 5 generations

The Peppered moth case study Two forms of the peppered moth: the melanic (dark) and light form

Homework Complete Summary Questions on page 230 (MACAH) Complete “Natural Selection in Action” green box on page 230 Zig zag match up sheet