Chromosomal Mutations

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

Aneuploidy

• 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.

Polyploid

• Multiple haploid sets (triploid=3, tetraploid=4).
• Relatively common in plant kingdom.
• Important evolutionary process.

Parental Imprinting

• Expression of disorders seem to depend on which parent contributed the defective chromosome.