83 NCEA Style Question: Sources of Variation

1. Sickle cell disease is caused by a mutation to the gene encoding the oxygen-carrying protein haemoglobin (Hb). The mutation causes an alteration in the phenotype of the red blood cells containing Hb and they take on a sickle shape.

Heterozygotes are carriers of the sickle cell mutation, but do not have the disease. People with two copies of the allele have sickle cell disease. Sickle cell disease causes many medical complications and often results in early death.

Discuss how mutations can lead to phenotypic variation within a population. Your answer should include:

• A definition for allele, heterozygote, and homozygote • A description of mutation and why some detrimental alleles are retained within a population while others are not • State whether sickle cell disease is inherited in a dominant or recessive pattern and justify your answer • Discuss why the sickle cell mutation remains in the population

(a) Discuss how meiosis produces genetic variation. Your answer should include: • A description of meiosis and the type of cells produced • An explanation of how genetic variation is increased through segregation, independent assortment, and crossing over during meiosis • An explanation of why the daughter cells are genetically different to the parent cells

You may use diagrams to illustrate your answer and more paper if you need it.

(b) Explain linkage and discuss its effect on variation in the offspring, contrasting it with recombination: