COMPLEX INHERITANCE

Chapter 12- Simplified Version

CHROMOSOMES:Humans have 23 pairs of chromosomesOne pair is sex chromosome:

XX in females, XY in malesIt is the presence of Y chromosome that determines maleness.

Y CHROMOSOMEDoes not have a homologous partner, and does not experience recombination during meiosisY chromosome a son inherits from his father is identical to Y chromosome his father inherited from his father (grandfather)This can be used to establish paternity

X-LINKED GENESLocated on X chromosomeDisorders inherited on X chromosome are called X-linked disordersMore common in males than in females

INCOMPLETE DOMINANCEEX: hair typeHeterozygotes have a phenotype intermediate between homozygous dominant and homozygous recessive

CODOMINANT TRAITEX: ABO blood typeBoth maternal and paternal alleles contribute equally and separately to the phenotype

POLYGENIC TRAITSTraits that are influenced by additive effects of multiple genesShow a normal distribution in the population

MULTIFACTORIAL INHERITANCE

A persons phenotype is determined by both his or her genotype at a number of different genes as well as by environmental influenceEX: human height, cardiovascular disease, and depression

EXTRA CHROMOSOMESSome genetic disorders result from having a chromosome number that differs from the usual 46EX: down syndrome (trisomy 21) has an extra copy of chromosome 21