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Genetics Take Home Study Guide
Mendelian Genetics
Red eyes (R) in fruit flies are dominant over white eyes (r). Using Punnett squares, find the
possible eye colors of the F1 generation for each of the following crosses. Identify the genotypic
ratios and the phenotypic probability as a percentage.
A. Rr x rr
B. rr x RR
C. Rr x Rr
In an experiment, Mendel grew 216 green pea plants with either wrinkled seed-coats (dominant)
or smooth (recessive). If the ratio of the wrinkled seed-coat plants to smooth seed-coat plants
was 3:1, how many smooth seed-coat plants did he grow?
Non-Mendelian Genetics
Sex-Linked Traits
1.
In fruit flies, the gene for white eyes is sex-linked recessive. (R) is red and (r) is white.
Cross a white-eyed female with a normal red-eyed male.
a.
What percent of the males will have red eyes? White eyes?
b.
What percent of the females will have red eyes? White eyes?
c.
What total percent of the offspring will be white-eyed?
d.
What percent of the offspring will be carriers of the white eye trait?
2.
In humans, hemophilia is a sex-linked recessive trait. If a female who is a carrier for
hemophilia marries a male with normal blood clotting, answer the following questions.
a.
What fraction of the female children will have hemophilia?
b.
What fraction of the female children will be carriers?
c.
What fraction of the male children will have normal blood clotting?
d.
What fraction of the male children will be carriers?
e.
What fraction of the male children will have hemophilia?
Incomplete Dominance
In snapdragons, flower color is controlled by incomplete dominance. The two alleles are red (R)
and white (W). The heterozygous genotype is expressed as pink.
a) What is the phenotype of a plant with the genotype RR? ___________
b) What is the phenotype of a plant with the genotype WW? ___________
c) What is the phenotype of a plant with the genotype RW? ___________
A pink-flowered plant is crossed with a white-flowered plant. Show the Punnett Square. What is
the probability of producing a pink-flowered plant? ____%
In Andalusian fowls, black individuals (B) and white individuals (W) are homozygous. A
homozygous black bird is crossed with a homozygous white bird. The offspring are all bluishgray. Show the cross as well as the genotypes and phenotypes of the parents and offspring.
What are the genotypic and phenotypic ratios if a black individual is crossed with a bluish-gray
individual? Show the Punnett Square.
If two bluish-gray individuals were crossed, what would be the ratios for both phenotype and
genotype of the offspring? Show the Punnett Square.
Codominance
1. If a Red (RR) and White flower (WW) were crossbred, resulting in 100% RW, what
phenotype(s) would been seen according to the rules of CO-dominance?
2. In cows, the red and white coat color alleles are codominant. We can choose an initial to
represent this trait, like “C” for coat. Then we can give the codominant alleles superscripts.
Show a cross between a white cow (CWCW) and a red cow (CRCR)
What will be the phenotype of the offspring?
Polygenic Traits
- What are polygenic traits and what are some examples?
Nature versus Nurture
- Both genes and the ________________ define our individual traits. This is an
example of nature versus nurture. Nature refers to your genes and nurture refers to the
__________________.
- Provide three specific examples:
- ________________________
- ________________________
- ________________________
Pedigrees
1. By looking at a pedigree, how do you know that it is sex-linked?
2. By looking at a pedigree, how do you know if it is autosomal?
3. By looking at a pedigree, how do you know if the trait is dominant or recessive?
Examine the following pedigree. Indiviuals with the trait under investigation are shaded.
1. What is the mode of inheritance (autosomal dominant, autosomal recessive, sex-linked
dominant, sex-linked recessive)
2. Identify the genotype of each individual in the pedigree.
3. How many individuals have the disorder?
4. If individual II-4 were to marry an individual who was homozygous recessive, what
would be the probability that their offspring would display the phenotype of the trait?
1.
Which family pedigree shows an autosomal dominant mode of inheritance? Give
reasons for your choice.
2.
What type of inheritance is demonstrated by the other family? Why did you decide on
that type of inheritance?
Karyotypes
1. Is this karyotype abnormal?
2. If so, what is the chromosomal abnormality?
3. Abnormalities such as this often occur in ___________.
a. Meiosis
b. Mitosis
c. Genetics
d. Mendel