Autosomal Recessive Inheritance
- Recessive allele mutation of autosomal cell.
- Either male or female can carry.
- Affects homozygous recessive only.
- Examples: albinism, sickle-cell anemia, phenylketonuria.
Autosomal Dominant Inheritance
- Dominant allele mutation of autosomal cell.
- Doesn't die out because may not affect reproduction or onset occurs after reproductive age.
- Examples: Huntington's disease, polydactyly.
Sex (X) - linked Recessive Inheritance
- Mutation on the X-chromosome.
- Homozygous dominant females - don't express, don't carry.
- Heterozygous females - don't express, do carry.
- Since males have XY, they will express the trait, carry to daughters, not to sons.
- Examples: hemophilia.
Change in Chromosome Structure
- Deletion - loss of a segment.
- Duplication - gene fragment joins homologous chromosome (evolutionarily important).
- Translocation - gene fragment joins non-homologous chromosome.
Changes in Chromosome Number
- One or more chromosomes.
- Major cause of human reproductive failure (higher than most mammals).
- Occurs when homologous chromosomes don't separate in anaphase I,
- or when sister chromatids don't separate in anaphase II (called nondisjunction).
- Trisomy - when the genotype has three copies of a chromosome.
- Examples: Down's syndrome, Turner syndrome (X0), Klinefelter syndrome (XXY), XYY condition.
- Multiple haploid sets (triploid=3, tetraploid=4).
- Relatively common in plant kingdom.
- Important evolutionary process.
- Expression of disorders seem to depend on which parent contributed the defective chromosome.