Chromosomes• Autosomes– Chromosomes that do not

determine the sex of an individual• We have 44 autosomes or 22

pairs

• Sex chromosomes• 2 sex chromosomes

– XX female – XY male

• Karyotype– The picture of the

chromosomes in their condensed form

Sex Determination

• Humans & many animals – X & Y

• the presence of the Y determines male – contains the region SRY (sex-determining

region of Y)– XX or X or XXX all female– XY of XXY both male (Y by its self is not

viable)

– X-O system (grasshopper) • XX vs X • XX female, X male

– Z-W System (chicken) • ZW female, ZZ male

– Haploid/diploid system (bees) • diploid - female, haploid - male

Expression of Traits - Recessive

• Recessive disorders – homozygous individuals

are called carriers – cystic fibrosis – sickle-cell – mating of close

relatives increases the penetrance of recessive disorders

Expression of Traits - Dominant

• Dominant disorders – achondroplasia (dwarfism)– Huntington's

• Multifactorial (Nature + Nurture) – Polygenetic inheritance

• Many genes affect a single trait

– diseases that have a genetic basis but there penetrance are tied to environmental issues • heart disease • diabetes (type II)

Expression of Traits - Codominant

• An intermediate expression or expression of both phenotypes– ABO Blood System

Expression of Traits – Sex Linked

• Sex linked– Expressed ALWAYS in the

male (Xd of XD)– May have low penetrance

(expression) due to random X inactivation unless homozygous (XDXd)

Pedigree Chart • Pedigree charts help track the

expression of traits through generations.– Recessive… only expressed if

homozygous recessive (dd)– Dominant expressed…expressed

always (DD or Dd or D_)