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Gene Linkage

Gene Linkage. Inheritance Patterns for ---Two Genes on the Same Chromosome ---Genes on the Sex Chromosomes . Sex Determination. Sex Chromosomes : homologous chromosomes that differ in size and genetic composition between males and females. Sex Determination.

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Gene Linkage

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  1. Gene Linkage Inheritance Patterns for ---Two Genes on the Same Chromosome ---Genes on the Sex Chromosomes

  2. Sex Determination Sex Chromosomes: homologous chromosomes that differ in size and genetic composition between males and females

  3. Sex Determination Autosome: any chromosome that is not a sex chromosome Humans have 22 autosome pairs and 1 pair of sex chromosomes

  4. Sex Determination Female Male XX x XY X X XX XX X Y XY XY Phenotypic Ratio of Offspring ½ Female + ½ Male

  5. Xh Females can be homozygous or heterozygous for traits on the X chromosome Males are hemizygous for traits on the X chromosome Dad XhY Sex Linked Genes Hemophilic Male Non-hemophilic Female (father is hemophilic) XhY x XHXh XH Xh XHXh XhXh Xh Y XHY XhY Phenotypic Ratio of Offspring ¼ hemophilic males + ¼ non-hemophilic males ¼ hemophilic females + ¼ non-hemophilic females

  6. Patterns of Inheritance • Autosomal Dominant • Autosomal Recessive • Sex-Linked Dominant (X-linked) • Sex-Linked Recessive (X-linked)

  7. Pedigree for An Autosomal Dominant Trait

  8. Pedigree for Albinism: An Autosomal Recessive Trait

  9. Pedigree forHemophilia, An X-linked Recessive Trait

  10. Pedigree forColorblindness, An X-linked Recessive Trait

  11. Patterns of Inheritance • Autosomal Dominant • Autosomal Recessive • Sex-Linked Dominant (X-linked) • Sex-Linked Recessive (X-linked) • Mitochondrial Inheritance

  12. Linked Genes

  13. How Do We Study Gene Linkage? Example from the Fruit Fly Red eyes, x Pink eyes Beige body Ebony body RRBB rrbb F1: Red eyes, Beige body RrBb

  14. How Do We Study Gene Linkage? Testcross: cross to individual of known genotype F1: Red eyes X Pink eyes Beige body Ebony body RrBb rrbb

  15. How Do We Study Gene Linkage?

  16. R B r b R B r b R B r b How Do We Study Gene Linkage? If genes are linked: Red eyes, x Pink eyes Beige body Ebony body F1: Red eyes, Beige body

  17. R B r b R B R b r b r B How Do We Study Gene Linkage? F1: Red eyes, Beige body X Alleles are inCis Configuration Four types of gametes are produced Parental Recombinant

  18. r b R b r b R B R B r B r b r b r b r b r b r b r B R B r b R b r b How Do We Study Gene Linkage? F1:Red eyes X Pink eyes Beige body Ebony body

  19. How Do We Study Gene Linkage?

  20. Genetic Map Units 1% recombination = 1 map unit 108 + 112 x 100 = 22% 1000 These genes are located 22 map units apart on the same chromosome. Map is drawn as: R B I 22 map units I

  21. r B R b 39% 11% r B r b 39% 11% R b R B 78% 22% How Do We Study Gene Linkage? Knowing the gene distance allows us to predict the expected percentages of each type of gamete. Alleles are inTrans Configuration X Parental Recombinant

  22. Gene Linkage Summary • Linked genes tend to be inherited together in their original, parental arrangement. B. Alleles of linked genes can be separated by crossing over (recombination) during meiosis. • Distance between genes is calculated as 1% recombination = 1 map unit. • Gene distances can be calculated for genes that are less than 50 map units apart. At 50 map units and beyond, we cannot distinguish between genes far apart on the same chromosome and genes on separate chromosomes.

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