Isolated communities in rural Finland, Hungary and some of the Scottish islands have a high incidence of red-green colour blindness. Describe the inheritance of red-green colour blindness.

Outline the causes of variation in one example of continuous variation in humans.

Explain how evolution occurs and which factors can cause the process to be rapid.

a. sex linked/gene is on the X chromosome ✔ 

b. allele «for red-green colour blindness» is recessive/colour blindness is recessive trait/disorder ✔

c. heterozygous females are unaffected/carriers ✔

d. X^B denotes normal allele and X^b denotes colour blindness allele ✔

e. more frequent in males because they only have one X chromosome ✔

f. 50% chance of colour blindness in sons whose mother is heterozygous/X^BX^b ✔

Accept any other letter for the alleles.

Award mpb, mpc, mpd and mpf if these points are clearly made on a Punnett grid.

a. height/skin colour/other valid example ✔

b. with continuous variation any level of the variable/phenotype is possible/OWTTE ✔

c. polygenic inheritance/combined effect of more than one gene on the trait ✔

d. additive effects on the trait of alleles of multiple genes/OWTTE ✔

e. histogram showing effects of alleles of multiple genes ✔

f. environment «may» also affect the trait/sunlight affects skin colour/other example ✔

g. normal distribution curve drawn or described to show typical pattern with continuous variation ✔

a. evolution is a change in the heritable characteristics «of a species» ✔ 

b. natural selection «causes evolution» ✔

c. overpopulation/over-reproduction/more offspring «than the environment can support» ✔

d. competition «for resources/mates» ✔

e. variation in population/species ✔

f. mutation/meiosis/sexual reproduction contributes to variation ✔

g. adaptation increases chance of survival ✔

h. reproduction/offspring produced «by the better adapted/by those that survive» ✔

i. characteristics passed to offspring by reproduction/variation is heritable ✔

j. allele frequencies/number of organisms carrying a gene changes/gene pool changes ✔

k. environmental change stimulates/triggers/speeds up natural selection/evolution ✔

l. increase in rainfall/introduction of antibiotic/pollution on tree trunks/other valid example of environmental change/new selection pressure ✔

m. artificial selection/selective breeding can speed up evolution ✔

Mark points can be awarded if explained using an example.