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Number of Chromosome Combinations

Asexual reproduction results in clones. The offspring are genetically identical to the parent and each other.Sexual reproduction leads to variation. One set of chromosomes is inherited from each parent and during meiosis there is genetic recombination.Homologous chromosomes line up on the equator and there is independent segregation as the chromosomes move to the nearest pole. The chromosomes line up independently and the combination of chromosomes is random so there is a huge number of combinations possible. Each gamete will have a different combination of alleles.The number of possible combinations of chromosomes is 2n where n is the number of homologous pairs of chromosomes.Variation is further increased by recombination by crossing over and random fertilisation - any egg cell may be fertilised by any sperm cell.

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Specification: AQA Biology (7401), AS-level, 3.4.3 Genetic diversity can arise as a result of mutation or during. Topic: Genetic Diversity.

Key terms in this lesson

allele
One of the different versions of a gene, arising by mutation, that occupy the same locus on homologous chromosomes.
homologous chromosomes
A pair of chromosomes, one from each parent, that carry the same genes at the same loci but may carry different alleles.
meiosis
A type of nuclear division that produces four genetically different haploid daughter cells (gametes) from a diploid parent cell.
crossing over
The exchange of alleles between homologous chromosomes, occurring at chiasmata during prophase I of meiosis, which increases genetic variation.
independent segregation
The random distribution of maternal and paternal chromosomes, or of sister chromatids, into daughter cells during meiosis, which increases genetic variation.

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