Chapter 11
Chromosomes
Two kinds of chromosomes
Autosomes
Sex chromosomes
Mammals have XY sex determination
One or more Y chromosomes, develop into a male
Birds have ZW, male has homologous sex
chromosomes, female has non-homologous sex
chromosome ZW
Reptiles sex is determined by incubation
temperate
Karyotype
Aneuploidy (unusual numbers of chromosome)
XO Turner’s syndrome (shorter than usual,
fertility problems)
XXX (Trisomy X) very little effect
XXY (Klinefelter’s Syndrome)
XYY (supermale)
Normal XX, you have dosage compensation
Only one X is uncondensed during interphase
Barr bodies (the second uncondensed X
chromosome)
Mosaicism (find this only in female mammals)
Calico cat
Sex-linked traits
Sex-linked trait is found on the X chromosome
Some examples: hemophilia, red-green colorblind
Hemophilia is recessive, more often seen in males
Woman who carries hemophilia
Man who is not hemophiliac
Crossed
How many hemophiliac sons? 25% of all offspring
normal sons? 25% of all offspring
Hemophiliac daughters? 0%
Normal daughters? 50% of offspring (half of
these are carriers)
Duplication
Deletion
Inversion
Translocation
If a man and woman have a child, and the woman
makes a normal egg with one X chromosome, but
the man has a non disjunction, producing one XY
sperm, and one 0 sperm, what offspring might
result?
In chromosome 21, the woman has non
disjunction, one egg has two C21s, the other has
zero C21s. What kinds of offspring may result?