The gingham dog and the calico cat
Side by side on the table sat;
There was going to be a terrible spat.
But the truth about the cat and pup
Is this: they ate each other up!
Now what do you really think of that!
(The old Dutch clock it told me so,
And that is how I came to know.)
by Eugene Field (1850-1895)
(Poems of Childhood)
Campbell and Reece., Chapter 15
Of course, genes come on chromosomes.
There are autosomes and sex chromosomes.
Independent assortment (Mendel's 2nd law) does not apply to genes (near
enough to each other) on the same chromosome.
TRANSPARENCY (Fig. 15.7) map location is based on cross-over probability
(determined with a genetic cross)
TRANSPARENCY (Fig. 15.3) Sex linked inheritance in Drosophila, white x red
eye cross. Note that there is no corresponding gene on the Y, hence the
TRANSPARENCY (Fig. 15.8) Different organisms have different chromosomal
means of sex determination.
Drosophila males are XY, but tissues that are XO are male (though if fly
or germ cells are X0, fly is sterile) and XX tissues are female, thus sex
is based on number of X chromosomes. grasshopper XO male
TRANSPARENCY (Fig. 15.10) X inactivation in tortoiseshell cat
SLIDE calico cat
XX Barr body, X inactivation Mary Lyon
TRANSPARENCY (Fig. 15.11) Nondisjunction e.g. trisomy
lethal, spontaneous abortions
X abnormalities survive
1968 prison if taller than 71 inches 1/11 XXY or XYY
population XXY - .08-.092%
XYY - .069-.095%
Research to find if people have X or Y abnormalities is controversial, for
instance because of self-fulfiling prophesy.
It was widely rumored that Richard Speck, known for his mass murder of 8
student nurses in Chicago in 1966, was XYY.
Turner X0 (SLIDE) 1/2000 females
spatial sense abnormal
In humans, Y determines male-ness and there are virtually no genes on Y
except to differentiate testes in male. CARTOON (Science 1993 vol261 p.
Autosomal aneuploidies are often lethal
Trisomy 21 = Down's syndrome
The TV show "Life goes on" featured Corkey who had Down's syndrome.
(the term "Mongulism" is used less in this era of political correctness,
especially in light of Down's
unsavory attitude toward non-European races in his writings)
retarded but nice, increases with increasing maternal age and is in percents
for women over 40
age 40 almost 1% age 50 almost 10%
In the reproduction
lecture (second semester), you can see that all human "eggs"
are already made around the time of birth (while sperm are made throughout
life). It seems likely that either "eggs" suffer from aging (alternatively
the good ones are used in the earlier reproductive years).
This page was last updated 7/18/02
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