Download Worksheet 20 - Iowa State University

BIO 313 Worksheet 20
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Laura
Bio 313
Dr. Rodermel
12/7/15
Warm-up:
What are the 3 main points about the Lyon Hypothesis?
1.
2.
3.
Answer the following questions about Calico Cats:
1. Coat color in cats is a codominant trait and is also located on the X chromosome. Cats can be
black, orange or calico. A calico cat has black and orange splotches. In order to be calico. the cat
must have an allele for the black color and an allele for the orange color. Use a punnett square to
show why there are no male calico cats.
2. A female calico cat is crossed with a male black cat. What are the phenotypes of the offspring and
in what proportion?
3. Also located on the X chromosome of a cat is a gene that codes for deafness. This gene is
recessive. A black female cat that is heterozygous for deafness (Dd) is crossed with a orange male
cat that is not deaf. Show the cross. What are the phenotypes of the offspring and in what
proportion? Hint: place two letters on the X chromosome in your cross. (You will need to use two
superscript letters on your X chromosome) the female cat has the following alleles BD and Bd; the
male cat has only OD, setting up the square will show that the offspring will be:
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4. Match the term with the definition:
Term
Definition
Penetrance
A trait that is penetrant in males OR females
Expressivity
A trait that has a larger penetrance in males or
females
Sex-limited trait
Causes death at an early stage in development, so
some genotypes do not appear among the
progeny
Epigenetics
Densely staining areas in the nuclei of females
Sex-influenced trait
Interactions between alleles of a single gene, or
rather interactions between the gene products of
these alleles
Barr Bodies
Heritable alterations in the DNA that do not
involve base changes, but affect the way DNA
sequences are expressed
Dominance
The degree to which a character is expressed
Lethal Allele
Percentage of individuals having a particular
genotype that express the expected phenotype
5. Another type of non-mendelian trait: Multiple alleles. Human hair color is controlled by one gene
with four alleles (with some incomplete dominance):
HBr = brown HBd = blonde hr = red hbk = black
The possible genotypes and phenotypes:
HBd HBd or HBd hbk = blonde HBd hr = strawberry blonde HBrhR = auburn
hRhR or hRhbk = red
hbk hbk = black
What do you think your parent’s phenotypes and genotypes for hair color are?
6. What are your phenotype and genotype for hair color?
7. If someone with auburn hair has children with someone with red hair (but whose mother had black
hair), what are the genotype and phenotype probabilities for their children?