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HL 10.2: Dihybrid crosses, gene linkage and recombination

HL 10.2: Dihybrid crosses, gene linkage and recombination. Working out dihybrid crosses. Dihybrid cross: a mating between two individuals who have different alleles at TWO gene loci. Working out dihybrid crosses. Always list: EACH parent’s phenotype (e.g. green pea/ wrinkly skin)

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HL 10.2: Dihybrid crosses, gene linkage and recombination

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  1. HL 10.2: Dihybrid crosses, gene linkage and recombination

  2. Working out dihybrid crosses Dihybrid cross: a mating between two individuals who have different alleles at TWO gene loci

  3. Working out dihybrid crosses Always list: • EACH parent’s phenotype (e.g. green pea/ wrinkly skin) • EACH parent’s genotype (2 alleles for each parent, each containing 2 genes) • Up to 4 different gametes for each parent • F1 generation genotypes (and proportions) • F1 generation phenotypes (and proportions)

  4. Past paper Question (c) In a species of plant, tallis dominant to short and the production of round seeds is dominant to that of wrinkled seeds. The alleles are unlinked. A plant heterozygous for both characteristics is crossed with a plant homozygous for tall with wrinkled seeds. Use the letters: T—allele for tall t — allele for short R — allele for round seed r—allele for wrinkled seed. Determine the phenotypes and genotypes of the offspring of this cross. (2)

  5. Linked genes

  6. Linked genes • Any two (or more) genes which are found on the same chromosome are said to be linked to each other • Linked genes tend to be inherited together • (Crossing over and recombination during prophase 1 of meiosis can alter the allele arrangement of linked genes) • Note that linked genes are NOT THE SAME as ‘sex linked genes’ • Linked genes can be linked on autosomes • Linked genes can be linked on the sex chromosomes

  7. Youmust know the standard notation to show linked genes

  8. Inheritance of linked genes • Linkage groups are carried on the same chromosome, and thus do NOT assort independently • They will be inherited together • [but they CAN be re-assorted (mixed up) by crossing over and re-combination during prophase 1 of meiosis] • Gametes are termed ‘parental’ or ‘recombinant’ gametes

  9. Linkage groups in plants: sweet peas

  10. Linkage groups in plants: Sweetcorn Kernel colour and waxiness are linked genes

  11. Past paper Questions

  12. Past paper questions

  13. Past paper Questions

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