chromosomes autosomes – chromosomes that do not determine the sex of an individual we have 44...
TRANSCRIPT
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_)