Download Genetics Test Review Sheet

Genetics Test Review Sheet - KEY
1. Two parents with the genotype Ss for a genetic disorder caused by a recessive allele are crossed. What
would the genotype for the genetic disorder be? Show the Punnett square and give the phenotypic ratio.
Genotype for genetic disorder: ss
Phenotypic Ratio: 3:1
3 Normal
1 Disorder
2. Show the cross for a genetic disorder caused by a dominant allele between two heterozygous parents. Will
any of their children inherit this disorder?
75% of children with inherit disorder
3. Using letter R, create the following.
Homozygous dominant:
RR
Homozygous recessive:
rr
Heterozygous:
Rr
4. Why is a Punnett Square useful?
Predicting possible offspring genotypes and phenotypes
5. Describe each of Mendel’s two laws.
Law of Segregation: Organisms inherit two copies of each gene, one from each parent
Law of Independent Assortment: Traits are inherited as separate discrete units
6. What is genotype?
Arrangement of genes (letters)
7. What is phenotype?
Physical characteristics (what we see)
8. What is a trait?
A distinguishing characteristic
9. Why might a recessive allele not be expressed (not show up)?
Because it is masked by the dominant allele
10. In order to show the phenotype of a disorder caused by a recessive allele, what must the
genotype be?
Homozygous recessive (dd)
11. What must a female’s genotype be if she shows the phenotype for a sex-linked trait?
XbXb
12. What does crossing over result in?
Genetic variation
13. What is co-dominance?
Genes are equally dominant resulting in a phenotype showing BOTH genes
14. How does the phenotype appear when co-dominant alleles are present?
You see both alleles (ex: seeing both brown and white in roan cattle)
15. What is incomplete dominance?
Genes are equally dominant resulting in a phenotype showing a mixture of the genes
16. How does the phenotype appear when incompletely dominant alleles are present?
You see a blending of the alleles (ex: red and white flowers creating pink flowers)
17. What are sex-linked traits?
Genes found only of the sex chromosomes (X chromosome)
18. Give three examples of sex-linked traits.
Hemophilia, Color Blindness, Pattern Baldness
19. What type of alleles cause most human genetic disorders: dominant or recessive?
Recessive
20. What type of gene is Huntington’s disease caused by: dominant or recessive?
Dominant
21. Define the following:
Dihybrid:
Heredity:
Haploid:
Homozygous:
Cross involving two different traits
Passing on of characteristics from parent to offspring
Cell that contains one member of each chromosome pair
Alleles present for a trait are the same
Gray feathers are dominant over white in turkeys. Fill in the allele combinations for each turkey in the cross
below. You will need to determine the CORRECT letter to represent the alleles (complete the key first):
Gray =
White =
X
gg
Gg
Gg
G
g
Gg
gg
gg
Use complete sentences to answer the following:
1. Is the white turkey in the P generation heterozygous or homozygous? How do you know?
The white turkey is homozygous because the only way you get a white turkey is if it has 2 alleles for white.
2. Is the gray turkey in the P generation heterozygous or homozygous? How do you know?
The gray turkey is heterozygous because the only way a white turkey and a gray turkey can produce a
white turkey is if the gray turkey carries and allele for white.
3. If the gray turkey in the P generation was homozygous, what would you expect the offspring to look like?
I would expect all of the offspring to be gray since all of the offspring would receive an allele for gray from
the homozygous gray parent.