Complex Patterns of Inheritance

Sometimes two traits can be dominant at the same time

What’s the difference between incomplete dominance and co-dominance? Incomplete Dominance : Complex inheritance pattern in which the heterozygous phenotype is intermediate between those of the two homozygous parent organisms…huh? RR W W RW Mixes like paint!

What’s the difference between incomplete dominance and co-dominance? Co-Dominance : Complex inheritance pattern that occurs when neither allele is dominant and both alleles are expressed. B B W W BWBWBWBW BWBWBWBW

Multiple Alleles Inheritance that involves more than 2 alleles for a trait Ex: Blood types!

ABO Blood Groups Alleles Type A: I A Type B: I B Type O: i i – recessive to I A & I B I A & I B – codominant with each other

Multiple Alleles Let’s list all the possible genotypes for each blood type. Human Blood Group Genotypes A: I A I A (homozygous dominant) or I A i (heterozygous) B: I B I B (homozygous dominant) or I B i (heterozygous) AB: I A I B (co-dominant) O: ii (homozygous recessive)

Sex Determination Sex chromosomes – 1 pair of your 23 2 types : X and Y XX: female XY: male (the other 22 pairs of chromosomes are autosomes)

X-linked Genes (“Sex-linked”) An allele inherited on the X chromosome X-linked recessive: more males are affected than females Females have 2 X’s – 1 likely to be normal, mask the effect X H X h (Carrier female) Males have 1 X – if he gets the bad allele, he has the disorder for sure X h Y

Polygenic Inheritance Many gene pairs act together to produce a single trait Examples: skin color, fingerprints, height

Polygenic Traits More intermediate phenotypes than extremes (Example: Height)

Karyotype Micrograph showing pairs of homologous chromosomes 22 matching autosomes and pair of sex chromosomes

Review from last unit: Nondisjunction Chromosomes fail to separate properly during meiosis Gamete does not have correct # of chromosomes Results in zygote with too many or few chromosomes 3 copies – trisomy 1 copy – monosomy

Nondisjunction

Down Syndrome “Trisomy 21” – 3 copies of chromosome 21 Distinct facial features, heart defects, mental disabilities Frequency increases with age of mother 1 out of 800 in born in US

Which person has Down Syndrome?