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Chromosomes & Inheritance

Chromosomes & Inheritance. Sex Chromosomes : contain genes determining sex (gender) of an individual Autosomes : Not involved in determining sex What is the name of the diagram shown? How many chromosomes do you see? Point of the centromere , sex chromosomes, and sister chromatids . .

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Chromosomes & Inheritance

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  1. Chromosomes & Inheritance • Sex Chromosomes: contain genes determining sex (gender) of an individual • Autosomes: Not involved in determining sex • What is the name of the diagram shown? • How many chromosomes do you see? • Point of the centromere, sex chromosomes, and sister chromatids.

  2. Sex Determination • Set up a Punnett Square using XX and XY homologous pairs to determine the ratio of a cross between a male and female.

  3. SRY gene • The Y chromosome contains a Sex-determining Region Y gene coding for the protein determining sex. • Controls expression of other genes that determine characteristics • Vital role in development

  4. Sex Linked Traits & Genes • Thomas Hunt Morgan experimented with fruit flies • While doing research it was noticed that only white males were ending up with the recessive white eye trait, both males and females could have dominant red eyes. • Sex Linked Trait: a trait that is coded for by an allele on a sex chromosome • X-linked genes • Y-linked genes

  5. Example Sex-Linked genes

  6. Linked Genes • Pairs of genes that tend to be inherited together are linked genes. • Linkage group is a set of linked genes. • Morgan hypothesized that linked genes are found on the same chromosome. • Remember crossing over: • Does not create new genes or delete old ones • Rearranges allele combinations

  7. Mutations • Mutation is a change in the nucleotide-base sequence of a gene or DNA molecule. • Mutations can involve an entire chromosome or a single DNA nucleotide • Germ cell mutations – do not affect organism • Somatic cell mutations- affect organism, cannot be inherited • Skin cancer & Leukemia

  8. Chromosome Mutations • Deletion: loss of a piece of chromosome due to breakage • Inversion: chromosomal segment breaks off, flips around backward, and reattaches • Translocation: piece of one chromosome breaks off and reattaches to a nonhomologous chromosome. • Nondisjunction: chromosome fails to separate, extra copy

  9. Down’s syndrome

  10. Gene Mutations • Point mutation: substitution, addition, or removal of a single nucleotide

  11. Discussion questions • Compare sex chromosomes with autosomes. • How do sex-linkage and crossing over show that genes are found on chromosomes? • Describe how nondisjunction can change chromosome number.

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