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Complex Patterns of Inheritance

Complex Patterns of Inheritance . Sometimes two traits can be dominant at the same time. What’s the difference between incomplete dominance and co-dominance?.

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Complex Patterns of Inheritance

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  1. Complex Patterns of Inheritance

  2. Sometimes two traits can be dominant at the same time

  3. 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? Mixes like paint! R R W RW RW W RW RW

  4. 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 BW BW W BW BW W

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

  6. ABO Blood Groups Alleles • Type A: IA • Type B: IB • Type O: i • i – recessive to IA & IB • IA & IB – codominant with each other

  7. Multiple Alleles Let’s list all the possible genotypes for each blood type. Human Blood Group Genotypes A: IAIA(homozygous dominant) orIAi(heterozygous) B: IBIB(homozygous dominant) orIBi(heterozygous) AB: IAIB (co-dominant) O: ii (homozygous recessive)

  8. 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)

  9. 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 • XHXh(Carrier female) • Males have 1 X – if he gets the bad allele, he has the disorder for sure • XhY

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

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

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

  13. 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

  14. Nondisjunction

  15. 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

  16. Which person has Down Syndrome?

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