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Lecture 10

GN 301 Lecture Notes - Lecture 10: Rett Syndrome, Learning Disability, Hypertrichosis

Course Code
GN 301
Marian- Elizabeth B.Gardner

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2.5 Sex Determination and Development
Tuesday, October 3, 2017
10:10 AM
Sex Determination in organisms with no X or Y chromosome
o Clamydomonas
single cell organisms
Two Isogametes (one + and one -) make a pairing
Single gene changes sex
o Slipper Limpet
Stack of microorganisms
Depending on what level on the stack they are, that determines gender
Sequential hermaphroditism (constantly changing)
o Corn
Monoecious: both type of sex flowers found on one plant
Silk (pistil) is Female Part and Tassel (makes pollen) is male part
Single gene mutations can cause one flower to not develop at all
Female Only: ts (tassel-seed mutation so no pollen)
Male Only: sk (no silks so no seeds)
Can be affected by cytoplasmic or nuclear genes
Cytoplasmic: genes transferred outside nucleus
Nuclear: genes transferred within nucleus
o Haplodiploidy
Bees and wasps
Live males are haploid and females diploid
Male bees develop from unfertilized egg so only receive half of chromosomes. A
bee that comes from fertilization and is heterozygous for sex gene becomes
female. Homozygous for that gene is male. But males never survive.
Sex Determination in organisms with X and Y Chromosome
Sex Chromosomes
o Protenor Mode of Sex Determination
XX for one sex and XO for another sex
Diff. Sex have diff. Number of chromosomes
Ex: grasshoppers
o Lygaeus Mode of Sex Determination
XX vs XY
XX is homogametic and XY is heterogametic
Y chromosome has sex determining region
Sexes have equal number of chromosomes
Ex: humans, fruit flies, mealworms
Exception: birds and fish; platypus
Males are homogametic and female are heterogametic (ZZ/ZW system in
Platypus has same # of chromosomes for each sex, but females get 10 X and
males get 5 X and 5 Y
Sex Development
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