Genetics Pt. 2

• 22 pairs of autosomes and one set of sex chromosomes (XX for female and XY for male)
• X chromosome has many genes while Y chromosome has few
• genes on the X and Y chromosomes are sex-linked because they determine the sex of an individual
• sex-linked traits are caused by recessive alleles and since males carry one X chromosome, they inherit the disorder from one copy of the allele
• females inherit two copies of the allele, one on each chromosome, so sex-linked genetic disorders occur more in males than females
• the sperm always determines the sex of a child because it can either bring an X or a Y chromosome
• the female egg always brings an X
• sex linkage: certain traits are attached or linked to the X chromosome
• since females have two X chromosomes, they can be normal, carriers, or have the disease
• males only have one X chromosome, so they can either be normal or have the disease
• a pedigree is a chart that shows the inheritance of a trait over several generations
• pedigrees outline inheritance patterns of genetic disorders and traits
• pedigree helps determine the probability that offspring will inherit a genetic disorder
• on a pedigree, squares represent males and circles represent females

  • shaded circles/squares represents a trait being considered
• the X linked recessive trait is not commonly seen in female carriers, however the females can pass to their sons and daughters (only sons are affected)
• affected males pass the trait to ALL daughters
• the trait appears to skip a generation when only female carriers are present
• autosomal recessive: all affected individuals will be homozygous recessive
• autosomal dominant: all affected individuals will have at least one dominant allele (homozygous dominant or heterozygous)
• if the trait is present in every generation then the trait is probably dominant
• if the trait skips generations then it is recessive
• if the trait is found in mostly males then the trait is mostly sex-linked
• polygenic inheritance: the determination of a given characteristic is the result of the interaction of many genes
• polygenic inheritance: when more than one gene controls a trait, showing only small differences