Chapter 22. Population Genetics Hi everybody!! TWO more classes !!!! . Where we’re going. WHAT is population genetics Allelic frequencies, and calculating them p& q, P,H,&Q (I’ll explain later) Hardy-Weinberg principle- application of a little algebra “Fun” things you can do w/ H-W.
TWO more classes !!!!
So the Δ32 deletion both deletes 32 bases, and shifts the reading frame.
P= 0.79, Q= 0.01, H= 0.2
q= Q + 1/2H
If a gene is sex-linked, then Q is q2 in females, q in males; the male:female ratio is then q/q2, or 1/q.
How can you tell if a population is in H-W equilibrium? by using chi2 analysis:
You’d think there’d be 2 degrees of freedom, but according to your book there’s only one. Has to do with the fact that there are only 2 alleles.
Sickle cell anemia; population of 1000: Note we have data, NOT assuming H-W equilibrium !!!
Note that SS is underrepresented, AS is overrepresented
The next slide shows how to calculate what q will be after a certain number of generations, if being homozygous means that your fitness is 0
(Note that this equation deals with the situation when the homozygous individual has 0 fitness.)
Think of warming, antibiotic resistance, prey size, etc.
Think of a population moving into a cold and warm place, living low on a mtn and high up…
Back-mutation becomes an issue; a-> A happens also; I don’t think this graph considers this.
Drift is an IMPORTANT factor, OFTEN overlooked! We WANT differences to be due to selection!
From Weaver & Hedrick, Basic Genetics, 2nd Ed., p. 420
The allelic frequencies over 30 generations for four replicate population of size 20 (flies). The mean is represented by the broken line
It turns out that being heterozygotic tends to be good for a population- severely inbred populations tend to have more problems- less fertility, more disease, etc., that outbred populations. You’ve all probably heard of diseases in dogs that are more prevalent in certain breeds, such as hip dysplasia in German shepherds. Mongrels, on the other hand, are often healthier.
Full & Half-brother-sister:
Half first cousins: