Download Problems in Genetics Use the class notes for how to solve punnett

Problems in Genetics
Use the class notes for how to solve punnett squares and review pgs. 262-269 to help solve the following problems. Show your
work on a separate piece of paper! And list all parts of the problem clearly. Be sure to have a full understanding of the terms
homozygous and heterozygous. Remember: heterozygous=hybrid and homozygous=pure breeding
Monohybrid Crosses:
1. In guinea pigs, the gene for black coat color is dominant to the gene for white coat color. If two heterozygous black individuals
mate, what will be the phenotype and genotype of the offspring? (B=black; b=white)
2. In some of Mendel’s later crosses he found that the gene for purple flowers was dominant over the gene for white flowers.
What type of offspring would you expect if you crossed a pure purple flower with a white flower?
(P=purple; p=white – be careful using Ps as capital and lowercase can look similar – use a different letter if you like)
nd
3. What would the genotype and phenotype be of the 2 generation from the above problem? (cross any two of the offspring
from the F1 offspring)
4. What results would you expect if you crossed a F1 offspring from #2 with a plant bearing white flowers?
5. In Holstein cattle, the spotting of the coat is due to a recessive gene while the solid colored coat is dominant. What types of
offspring might be produced by crossing 2 spotted cattle? (solid coat=____; spotted coat=____)
6. The polled (hornless) condition in cattle is dominant over horned. A cattleman in Texas has a range stocked with polled cattle
only, but some horned cattle occasionally appear. These are removed from the range before they can breed. Assuming the man
has good fences to keep stray cattle out, how could explain the appearance of horned cattle?
7. In sheep the color white is due to a dominant allele, black is the recessive allele. A white ewe (female) is mated to a white ram
produced a black lamb. If they produce another offspring, could it be white? If so, what are the chances of it being white?
(Remember to show all your work and genotypes)
Incomplete Dominance:
8. Superboy came from the planet Xenon where people were either red skinned, white skinned, or pink skinned. If redskin is
dominant and white skin recessive, could parents with pink skin and white skin have a red skinned boy? Show all your work.
9. In northeast Kansas there is a creature know as a wildcat. It comes in three colors, blue, red, and purple. This trait is controlled
by a single gene with incomplete dominance. A homozygous (BB) individual is blue, a homozygous (bb) individual is red, and a
heterozygous (Bb) individual is purple. What would be the genotypes and phenotypes of the offspring if a blue wildcat were
crossed with a red one?
10. What are the genotypic ratio and phenotypic ratio of a F2 generation of the cross above?
Co-dominance:
11. A cattleman has a roan bull and some white cows and wants a purely red herd on his ranch. Outline a breeding program for
him to follow which will allow him to get results without bring in other stock cattle. Assume red is dominant (RR), white is
recessive (rr), and roan is the heterozygous blend (Rr). Show the crosses for each generation leading up to the desired results
for your breeding program.
12. The lubber grasshopper is a very large grasshopper, and is black with red and yellow stripes. Assume that red stripes are
expressed from the homozygous RR genotype, yellow stripes from the homozygous YY genotype, and both from the
heterozygous genotype. What will be the phenotypic ratio of the F1 generation resulting from a cross of two grasshoppers, both
with red and yellow stripes (red : both : yellow)?
13. Genetic scientists working in Tulipville have discovered a rare striped purple/white tulip. Until this time only dominant purple
tulips and white recessive tulips were known to exist. What types of offspring are expected when two of these striped tulips are
cross pollinated?
Multiple alleles:
st
nd
rd
th
14. A couple have 4 children. Their 1 child has blood type A, the 2 has blood type O, the 3 has type AB, and the 4 has type B.
What are the genotypes of the parents?
15. A mother with blood type AB and a father with blood type O have a child. What is the likelihood that the child will have
blood type O? What is the likelihood of blood type B?
Sex-linked Traits:
16. In hamsters, dominant black coat and a recessive white coat is sex-linked. What type of offspring would you expect from
mating a heterozygous black female with a white male? Show your work
17. A woman who has the recessive trait of red-green color-blindness marries a man with normal vision. What is the probability
that they have a son who has red-green color-blindness?
18. What is the probability that they have a daughter with red-green color-blindness?
19. The woman who has red-green color-blindness has a mother with normal vision. What is the father’s genotype?
20. In fruit flies, red eye color is dominant over white eye color and this trait is sex-linked on the X-chromosome. What genotypes
and phenotypes will result from a cross between a red eyed male and a heterozygous red eyed female?
Dihybrid Crosses:
Review your notes, pgs. 270, 271, and figure 11-10 in your text. Remember to use only one letter per trait.
Remember to show all work!
21. In the fruit fly, vestigial wings (extremely short wings) is recessive to normal long wings. Ebony (black) body color is recessive
to the dominant normal gray body color. What type of offspring would be expected from a cross between a vestigial ebony
female and a homozygous normal long winged gray body male? (male is homozygous for both traits)
22. If the F1 offspring in the above problem were allowed to breed among themselves, what types of offspring would be
expected?
23. If a vestigial winged female who is heterozygous for body color is crossed with an ebony male who is heterozygous for long
wings, what are the expected results for the F1 offspring?
24. Some dogs of one species bark while others are silent. The barking trait is dominant. Erect (pointy) ears are dominant to
droopy ears. What kind of pups would be expected from a heterozygous erect-eared barker mated to a droopy eared, silent
individual?
25. In tomatoes, yellow fruit is recessive to red fruit and dwarfed vines are recessive to tall vines. If a dwarf plant bearing pure
red fruit were crossed with a pure tall plant bearing yellow fruit, what would the expected F1 generation be?
26. If the F1 plants from #24 were allowed to cross among themselves, what would be the expected F2 generation?
Pedigree Problems:
27. In man, normal pigmentation is due to a dominant gene, albinism is its recessive allele. A normal man marries an albino
st
woman. Their 1 child is an albino. What are the genotypes of these three persons? If there are more children, what would they
probably be like? Use a pedigree style diagram to show this.
28. A normally pigmented man whose father was an albino marries an albino woman whose parents were both normally
pigmented. They have 3 children, 2 normally pigmented and 1 who is albino. List the genotypes of all persons on a pedigree style
diagram.
Alternatives Inheritance Problems
Incomplete & Co-Dominance – Read page 272
1.
What is meant by incomplete dominance?
2.
The heterozygote condition displays (both or a blend) of the two traits?
3.
Using Figure 11-11 as a guide, show the results of a cross between two of the pink flowered offspring in the incomplete
dominance punnett square below – color your results!
4.
How is codominance different than incomplete dominance?
5.
Using Figure 11-11 as a guide, show the results of a cross between two of the pink flowered offspring in the codominance
punnett square below if the genes demonstrate codominance – color your results!
Incomplete
Dominance
Codominance
Vs.
Multiple Alleles – Read pages 273 & 344
1.
Define multiple alleles.
2.
No matter the number of allele types that exist for a particular gene, an individual can only have
their genotype.
3.
Blood type is an example of multiple alleles in humans. Complete the table below related to this information.
Possible Alleles for Blood Type
alleles that determine
Blood Phenotype
Dominant Alleles =
Recessive Alleles =
A Genotypes
B Genotypes
AB Genotype
O Genotype
This phenotype
demonstrates what
else?
4.
Solve the following multiple allele problems.
a.
Suppose that a female with AB blood mates with a male with type O blood. Predict what type of blood their
offspring will have.
b.
A male heterozygous for B blood mates with a heterozygous A female. Predict the blood types of their kids.
Sex-linked genes - Read pages 350-351
1. What are sex-linked genes?
2. True or False? The Y chromosome does not contain any genes at all?
3. Why are all X-linked alleles expressed in males?
4. Using the information provided, complete the table below for sex-linked information.
R
r
In fruit flies eye color is sex-linked. Red is dominant (X ) and white is recessive (X )
Female
Male
Dominant
X X or X X
X Y
Recessive
X X
X Y
5. If ‘Mom’ has white eyes, which sex of fly has the best chance of having white eyes?
What do you think the percentage is?
%
6. Complete the table describing sex-linked disorders.
Sex Linked Disorders in Humans
Disorder
Description
Cause
Colorblindness
A recessive allele in either of 2 genes
resulting in a missing protein that is
required for normal blood clotting.
Defective version of a gene that codes for
a muscle protein.
Polygenic Traits – Read page 273, 395-396
1.
What is meant by polygenic inheritance?
2.
Give an example of this type of inheritance in humans, other than the one mentioned in the book.
3.
If a gene is controlled by a single gene and it’s simple dominant/recessive, how many phenotypes will result?
4.
If a gene is controlled by polygenic inheritance, how many phenotypes would result?
5.
Label the graphs below as SINGLE GENE or POLYGENIC INHERITANCE based on their phenotype results
# of Individuals
Height in cm
Dihybrid Crosses - Read pgs. 270-272
1. Thinking about Mendel’s earlier studies, does the gene that determines the shape of a seed have anything to do with
seed color?___________. Why/why not?
.
2.
What did Mendel do to answer the question above?
.
His experiment is known as a ____________________________________________________________________.
3.
Write the genotypes of the true-breeding plants that Mendel used in his two-factor cross.
Phenotype
Genotype
a. round yellow peas
______________________
b. wrinkled green peas
______________________
4.
Did the genotypes of the F1 offspring indicate to Mendel that genes assort independently? ______________.
What did he learn from mating true-breeding parents?
5.
Circle the letter(s) that best describes the F1 offspring of Mendel’s two-factor (dihybrid) cross.
.
a. Homozygous dominant with round yellow peas
b. Homozygous recessive with wrinkled green peas
c. Heterozygous dominant with round yellow peas
d. Heterozygous recessive with wrinkled green peas
6.
Complete the Punnett square below to show the predicted results of Mendel’s two-factor cross between individuals of
the F1 generation (RrYy x RrYy)
RY
Ry
rY
ry
RY
Ry
rY
ry
Genotypic Ratio
RRYY: RRYy: RrYY: RrYy: RRyy: Rryy: rrYY: rrYy: rryy
Phenotypic Ratio
7.
State Mendel’s principle of independent assortment : __________________________________________________
8.
State Mendel’s law of segregation:
9.
Summarize Mendel’s principles, which are the basis of genetics into your own words:
Karyotypes & Pedigrees: Read pages 341- 342
1.
2.
3.
What is a karyotype? ____________________________________________________________________________
A karyotype is the result of _______________________________________________________________________
How do biologists make a karyotype? (It is on the page!)
4.
5.
What is a karyotype used for? _______________________________________________________________________
Two of a human’s 46 chromosomes or one pair are called _________ __________________ because
__________________________________________________________________________________________________
That means the other 44 chromosomes or 22 pairs are called _____________________________________________
Using the words given label the diagram
6.
7.
autosome
8.
sex chromosome
karyotype
Why are females and males born in roughly a 50% ratio? _______________________________________________
________________________________________________________________________________________________
Read pages 345-348, 349-353
9. What percentage of DNA in your chromosomes actually functions as genes? ________.
What is the average base pair length? ____________________.
10. As we know already, females have 2 X chromosomes. How does the cell ‘adjust’ to the extra X chromosome in female
cells? __________________________________________________________________________________________
__________________________________________________________________________________________________
__________________________________________________________________________________________________
11. What is a Barr body? _______________________________________________________________________________
They are only found _________, because
.
12. If you see a cat with orange and black spots, is it most likely a male or female? Explain. __________________________
_________________________________________________________________________________________________.
Chromosomal disorders
13. What occurs during nondisjunction? _________________________________________________________________
_________________________________________________________________________________________________
14. True or False, If nondisjunction occurs, gametes may have abnormal numbers of chromosomes? ___________.
15. When exactly would the greatest chance of nondisjunction occur during Meiosis? _________________________
Compare/Contrast Table for Genetic Disorders
Type of
Disorder
Autosomal
Cause
1.
Can it be
Inherited?
Yes
Affects both males
and females?
Yes
Examples
2.
3.
Sex-linked
Caused by alleles on the X or
Y chromosome
Yes
4.
Colorblindness, Hemophilia
Chromosomal
5.
No
Yes
6.
7.
Read pages 342-343
16. What does a pedigree chart show? ___________________________________________________________________
17. Use the labels to identify the parts of the pedigree chart shown below.
A person who expresses the trait
A Male
A person who does not express the trait
A Female
Represents a marriage
Connects parents to child
18. Give 2 reasons why it is impossible to associate some of the most
obvious human traits with single genes?
•
______________________________________________________________________________________________
•
______________________________________________________________________________________________
A little review……….
1. What is a sex-linked disorder? _______________________________________________________________________.
2. Why are females less likely to show a trait caused by a recessive allele linked to an X chromosome?
_____________________________________________________________________________________________________.
3. What common error in meiosis leads to the production of gametes with abnormal numbers of chromosomes?
_____________________________________________________________________________________________________.
4. Why could you conclude that the X chromosome is essential for the development of a human embryo, but the Y chromosome
is not? _________________________________________________________________________________
___________________________________________________________________________________________________.
5. If you know that a woman has hemophilia, what can you infer about her parents’ genotypes. Diagram a simple pedigree
below to explain.