Hardy Weinberg population genetic problems:
1. A certain homozygous recessive geneotype occurs in 4% of a
population. What is the frequency of its two alleles, T (.8) and t (.2)?
2. What percentage of the population is heterozygous (Tt) 32%?
3. In a certain species of plant where red and white flowers are
determined by a single pair of alleles, R (red) and r (white), a grower counted
90 white flowering plants in a field of 1000. If random pollination is occurring,
what proportion of the field is heterozygous? 42%
4. In the United States, 16% of the population is Rh-, due to a
homozygous recessive pair of alleles. From this data, determine:
a. The frequency of the recessive gene .4
b. The frequency of the dominant gene .6
c. The percentage of heterozygotes in the population 48%
5. The frequency of a particular recessive gene is 0.5.
a. What percentage of the population will be homozygous recessive?
25%
b. What are the percentages of each of the three genotypes in the
population? DD 25%, hetero 50%, dd 25%
6. A certain gene (k) is recessive; the dominant gene (K) is one
of the genes necessary to produce chlorophyll in plant leaves. In a particular
variety of corn, 36% of the seedlings are found to lack chlorophyll and appear
yellow when they sprout, then die. Determine:
a. The frequency of K .4
b. The frequency of k .6
c. The percentage of individuals that are Kk 48%
7. About 1 in 10,000 Caucasians born in the U.S.A. have the
homozygous recessive condition where they lack the ability to produce the
enzyme PKU. Without treatment, this is a fatal condition. This is a fairly
difficult problem.
What is the frequency of the recessive
gene? q2 = .0001
therefore
q = .01 therefore p = .99
What percentage of individuals are heterozygous?
2pq = .0198
8. Native Africans who immigrated to the American Colonies as
slaves had an estimated sickle cell allele frequency of .25. Assume that all of
the homozygous recessive children died before producing offspring , calculate the
percentage of homozygous dominant and heterozygous individuals in that
African-American founders population. What was the percentage that died?
(Ignore deaths due to malaria as the US is not in a malaria zone).
If q= .25 then p= .75
p2= . .5625
q2= .0625 die
2pq = .375
9. In a population of cats containing 4 with white fur, 64 with
solid brown fur, and 32 with tan fur, what is the white gene frequency? So we have incomplete dominance at work
here: 4/100 were white fur this is q2 or .04 therefore q = .2
10. Explain the
difference between an adaptation and the term "natural selection".
Natural selection "picks" those variations that increase
an organism's chance to survive and reproduce (adaptations).
11. If evolution is
defined as "change through time", what really is
changing during biological evolution?
Allele frequencies.
12. Is the global human gene pool in equilibrium? Why or why not? Cite at least three reasons. Not,
mutations, non-random mating, genetic drift, natural selection are some of the
reasons.
13. Darwin could not
explain the origins of the variations he observed, you can, and what are they?
Multiple alleles, mutations, incomplete dominance, co-dominance,
multiple gene inheritance, multifactorial inheritance
14. In wooba-wooba
plants, petal color is co-dominant. The three petal phenotypes are black, grey and white. The black allele frequency is greater
than the white allele frequency.
48% of the population is grey.
What percent of the population should have the elegant
black petals?
THINK (start with a punnet square, fill in what
information is given and then solve the entire square) SHOW YOUR WORK. This is kind of difficult.
If .48 is the grey or heterozygous = 2 pq then pq = .24, ask yourself what pq =.24 and p + q =
1? .6 and .4 from the
problem I told you black was the larger allele frequency so b2 =.36
15. If 30% of a
population shows a recessive phenotype, how would you figure out p and q? Obviously if you do not have access to calculators you will leave your
work in unfinished form. Again use
a punnet square, remember I am asking only for p and q.
q2 = .3
then q= square root of .3
then subtract that answer from 1 and that will give us p
16. Define and
give an example of the following terms:
gene flow-
genetic drift-
17. Within an
isolated population of 10,000 rats (that are in equilibrium) 3600 individuals
have white fur, a homozygous recessive trait. How many rats should be homozygous dominant for their fur
color? Show work. yes, start with your
punnet square.
q 2 = .36
q = .6 therefore p = .4 and finally p therefore p2 = .16 or
16%
18. Gene frequencies
will NOT change if a population's gene pool is in equilibrium. Give three examples of these conditions
that will keep a population in equilibrium.
random mating, large population, no selection, no mutation, no
migration, no genetic drift
19. What factors/circumstances favored the dark allele frequency in
the peppered moth gene pool to increase? What factors/circumstances favored the light allele frequency in
the peppered moth gene pool to increase?
Read 16.4 p. 423
dark favored in a polluted forest
light favored in a clean forest
20. The following
list is a gene pool that is in equilibrium of a very small
breeding population of nerdy birdies (I made it up) for the dominant trait, Albinism.
A A A A a a A a A A A a a a a a
What is the predicted percent of the F1 that will have the albino
phenotype? Show work.
Since the allele frequencies are p =.5 and q = .5 (COUNT THE A AND
a), then p2 = .25
21. Explain how the
use of antibiotics has actually resulted in antibiotic resistant bacteria now
becoming a serious health concern.
Assuming
we have a multi factorial inheritance at work here and as we keep killing the
weaker/less antibiotic resistant bacteria, leaving the naturally more resistant
bacteria to reproduce, subsequently within the next generation a higher percent
of resistant bacteria are created.
Another real problem is people tend to stop taking the medications too
early. The number of days has been
experimentally arrived at. Take
the pills for the entire duration.
Stopping early has killed the "weaker" bacteria and perhaps
not all of the "stronger".
So in a few years doctors have to increase the dosage of antibiotics,
once again killing the less resistant and having the more resistant
reproduce. Also coloring the
discussion are random mutations that could amplify the results even
faster. Quite a problem, should we
not use antibiotics because we are afraid of creating these future populations
of super bacteria? No, but doctors
must be very insistent on only prescribing antibiotics when severe health
consequences would occur in the absence of the medicine and to INSIST that the
entire prescription is taken for the prescribe number of days.