Ch15

Chapter 15: Sex Chromosomes, Linked Genes, & Organelle Inheritance

15.1 The X and Y Chromosomes

• Mendelian Genetics

  • Mendel studied simple traits using peas.

  • Peas can self-fertilize; reciprocal crosses yield same offspring.

  • Pea plants do not have different adult sexes or sex chromosomes.

• Sex Determination in Other Organisms

  • Some animals exhibit genetic differences between sexes.

  • Both sexes may share similar autosomes, but have distinct sex chromosomes.

  • Inquiry into alternative sex determination methods.

15.2 Inheritance of Genes on the X Chromosome

Humans and Sex Chromosomes

• Humans have X and Y chromosomes.

  • XX = Female; XY = Male.

  • X chromosome contains ~1000 genes; Y chromosome has ~50.

  • Small region of homology required for pairing during meiosis.

  • Question regarding necessity of X and Y pairing in mitosis.

15.3 Linkage

• Definition of Linkage

  • Linked genes reside on the same chromosome,

  • Linked traits appear together more frequently than expected by chance.

  • Example: If genes for green and wrinkled are tightly linked, most offspring will not show independent assortment.

15.4 Inheritance of Genes on the Y Chromosome

• Genes on the Y chromosome are limited in number compared to the X chromosome.

  • All sons inherit Y-linked traits from their fathers.

  • No daughters inherit Y-linked traits.

  • Discussion of Y-linked recessive mutations.

15.5 Inheritance of Mitochondrial and Chloroplast DNA

• Endosymbiotic Hypothesis

  • Mitochondria and chloroplasts have their own circular DNA.

  • Most mitochondrial proteins are encoded by nuclear genes; a small number by mitochondrial genome.

• Maternal Inheritance of Mitochondrial DNA

  • Mitochondria are inherited exclusively from the mother.

  • All offspring of a mother with mitochondrial abnormalities will inherit the trait.

• Genetic Context and Comparison

  • Overview of genetic characteristics in humans, focusing on maternal vs. paternal inheritance.