Meiosis and genetic variationEdexcel A-Level Biology A: Mind map

Exam questions on Meiosis and genetic variation

1. The gene for the beta-globin polypeptide of haemoglobin is found at one position on chromosome 11 in humans. Two alleles of this gene are common in some populations: HbA, which codes for normal beta-globin, and HbS, which codes for the beta-globin found in sickle cell haemoglobin.
   State what is meant by an allele and explain why HbA and HbS are found at the same locus.2 marks
2. Red-green colour blindness is caused by a recessive allele on the X chromosome. A woman who is a carrier of the allele and a man with normal colour vision have a family together.
   Explain why none of the daughters of this couple will be colour blind, although some may be carriers.2 marks
3. In fruit flies, the gene for body colour (grey G, dominant, or black g) and the gene for wing length (long L, dominant, or vestigial l) are on the same autosome. A heterozygous grey, long-winged fly, with G and L on one chromosome and g and l on its homologue, was crossed with a black, vestigial-winged fly. Among 1000 offspring, 462 were grey and long-winged, 458 were black and vestigial-winged, 41 were grey and vestigial-winged and 39 were black and long-winged.
   Explain the results of this cross.3 marks