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Sex Linkage and Polygenic Inheritance

Sex Linkage and Polygenic Inheritance. Higher Human Biology. Lesson Aims. To revise sex chromosomes To examine effects of sex-linked genes To look at polygenic inheritance. Normal Body Cells. In the nucleus of every body cell there are 46 chromosomes

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Sex Linkage and Polygenic Inheritance

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  1. Sex Linkage and Polygenic Inheritance Higher Human Biology

  2. Lesson Aims • To revise sex chromosomes • To examine effects of sex-linked genes • To look at polygenic inheritance

  3. Normal Body Cells • In the nucleus of every body cell there are 46 chromosomes • 22 homologous pair and one pair of sex chromosomes

  4. Female and Male Sex Chromosomes

  5. Red Green Colour Blindness • Inability to distinguish between red and green • A red green colour blind person does not see the number 29 on the right • In humans normal vision is completely dominant to red-green colour blindness

  6. Genetics of Colour Blindness • Normal vision C • Red-green colour blindness c • Heterozygous females are called carriers • Work out the genotypes of the following family tree

  7. Answers • Carrier mother XCXc • Nomal father XCY • Normal daughter XCXC • Carrier daughter XCXc • Normal son XCY • Colour-blind son XcY

  8. Haemophilia • Haemophiliacs cannot make the blood clotting protein Factor VIII. • It caused by a recessive allele carried on the X but not the Y chromosome • Hence is sex-linked

  9. Family Tree of Haemophilia

  10. Muscular Dystrophy • Skeletal muscles loose their normal structure and fibrous tissue develops in their place • Caused by a recessive allele carried on the X chromosome and is sex-linked

  11. Family Tree of Muscular Dystrophy

  12. Polygenic Inheritance • Polygenic inheritance is a characteristic showing continuous variation and is controlled by the alleles of more than one gene • The more genes involved the more intermediate phenotypes that can be produced • The effects of the genes are additive (each dominant allele of each gene adds a contribution towards the characteristic controlled by the gene)

  13. Polygenic Inheritance

  14. Examples include skin colour, height, weight Polygenic Inheritance in Humans

  15. Polygenic Inheritance in Humans

  16. Effect of Environment • Many of these characteristics are influenced by the environment. • Polygenic inheritance + environmental factors = phenotypic characteristic which shows a wide range of continuous variation and a normal pattern of distribution.

  17. Facts you need to know • P6 from “sex-linked genetics problems…” • to p7 “weight or height or skin colour…”

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