Natural Selection

Question 1

Around the Java Islands, there are many species of lizards between the lowland lizards and the mountain lizards develop different features from each other. However, the genes of some of these lizards differ widely where species aren’t able to produce a viable offspring.
Name and explain why this process occurs.

(8M)

Y: >=6 G: 6-7 P: 8

Answer 1

• Speciation
• Happens when there is genetic variation in the environment
• Due to geographical barriers of rising sea levels.
• Different environmental/selection pressures will
• cause the favourable alleles of lizards to survive.
• Lizards with favorable alleles will survive and reproduce
• and passed down the favorable alleles
• which increase the frequency of favorable alleles in the gene pool
• This causes speciation, which cause the two species of lizards to not be able to produce a fertile offspring.

Question 2

In farming populations, the allele frequency for lactase persistence can be as high as 96%, whereas in non-farming populations the frequency is only 20%. Explain how natural selection could be responsible for this difference in allele frequency.

(9M)

Answer 2

• Lactase persistance mutation is present
• causing a variation in the gene pool
• in a population that used milk as an energy source
• Those that had the lactase persistance mutation had a better chance of survival
• more offspring are produced with the lactase persistance mutation
• allele frequency of the mutation increases over time
• in population without a milk diet there would be no difference in survival rate
• allele frequency of the mutation remains unchanged