Meiosis and genetic variationEdexcel International A Level Biology: Mind map

Exam questions on Meiosis and genetic variation

1. A diploid human cell in the testis contains 46 chromosomes and begins meiosis to produce sperm cells.
   Ignoring crossing over, calculate the number of genetically different combinations of maternal and paternal chromosomes that could be present in the sperm cells produced by this person.2 marks
2. In the fruit fly Drosophila the gene for body colour (grey G, dominant to black g) and the gene for wing length (long L, dominant to vestigial l) are close together on the same chromosome. A fly heterozygous for both genes, with G and L on one chromosome and g and l on its homologue, was crossed with a black, vestigial-winged fly. Out of 1000 offspring, 462 were grey with long wings, 458 were black with vestigial wings, 42 were grey with vestigial wings and 38 were black with long wings.
   Calculate the percentage of the offspring that were recombinants.2 marks
3. A diploid cell has the genotype AaBb. Alleles A and B are on one chromosome of a homologous pair, and alleles a and b are on the other chromosome of the pair. In this cell, one chiasma forms between the loci of the two genes during prophase I of meiosis.
   Describe what happens during crossing over in this cell.3 marks