Ch15

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

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.

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.

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.

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.

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.