Inheritance
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Lilli Howard
BIOL/GEN 313
Dr. Vollbrecht
02/27/14
Vocabulary
1. Complete Dominance: phenotype of heterozygotes is same as one of the homozygotes
2. Incomplete Dominance: phenotype of heterozygote is intermediate between homozygotes
3. Co-dominance: heterozygote phenotype includes phenotypes of both homozygotes
4. Penetrance: : percentage of people having a genotype that express the expected phenotyp
5. Expressivity: the degree to which a character is expressed
6. Lethal Allele: in some particular genotype combination, the allele causes death
7. Multiple Alleles: For a given locus, more than 2 alleles are present in a population
a. How many genotypes are present at a locus with 5 alleles? 15
8. What is incomplete penetrance? What causes it?
-the expected phenotypes of a particular genotypes is not expressed. Environmental or
other gene effects may alter expression.
9. A certain trait is recessive and 75% penetrant. Two heterozygous parents want to know
what the chance is that their first child will have the trait. What is it?
¼ (.75) = 3/16 = .1875
10. If a flower has two alleles, one for red and one for white, what will the phenotype look
like in a heterozygote if the flower exhibits (a) incomplete dominance (b) co-dominance?
a. Pink
b. Red and white
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11. When a Chinese hamster with white spots is crossed with another hamster that has no
spots, approximately ½ of the offspring have white spots and ½ have no spots. When two
hamsters with white spots are crossed, 2/3 of the offspring possess white spots and 1/3
have no spots.
a. What is the genetic basis of white spotting in Chinese hamsters?
b. How might you go about producing Chinese hamsters that breed true for white
spotting?
-2:1 ration indicates lethality. 1:1 ration indicates spotted is heterozygous. Spots are
dominant to no spots.
-You can’t
12. Palomino horses have a golden yellow coat, chestnut horses have a brown coat, and
cremello horses have a goat that is almost white. A series of crosses between the three
different types of horses produced the following offspring:
Cross
Offspring
Palomino x palomino
Chestnut x chestnut
Cremello x cremello
Palomino x chestnut
Palomino x cremello
Chestnut x cremello
13 palomino, 6 chestnut, 5 cremello
16 chestnut
13 cremello
8 palomino, 9 chestnut
11 palomino, 11 cremello
23 palomino
a. Explain the inheritance of the palomino, chestnut, and cremello phenotype.
b. Assign symbols for the alleles that determine these phenotypes and list the
genotypes of all parents and offspring given.
-Cremello and chestnut are true breeding traits (homozygous). Palomino is a heterozygous trait.
Incomplete dominance: palomino as the phenotype of the heterozygotes resulting from chestnuts
crossed with cremellos.
Chestnut: CB CB
Cremello: CRCR
Palomino: CBCR
1060 Hixson-Lied Student Success Center  515-294-6624  sistaff@iastate.edu  http://www.si.iastate.edu