Download Genetics Test Review Sheet

Name: ___Key_______
Genetics Test Review Sheet
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 with genetic disorder
S
s
S
SS
s
Ss
Ss
ss
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
G
g
G
GG
Gg
g
Gg
gg
3. Which type of cross would yield a 3:1 ratio?
A cross between two heterozygotes
4. Using letter R, create the following.
Homozygous dominant: __RR______
Homozygous recessive: __rr_________
Heterozygous:__Rr________________
5. Why is a Punnett Square useful? Predicting possible offspring genotypes
and phenotypes
6. Describe each of Mendel’s three laws.
Law of Segregation: Organisms inherit two copies of each gene, one from
each parent
Law of Dominance and Recessiveness: One factor in a pair may mask the
effect of the other
Law of Independent Assortment: Traits are inherited as separate discrete
units
7. What is genotype? Arrangement of genes (letters)
8. What is phenotype? Physical characteristics (what we see)
9. What are alternate forms of a gene called? Alleles
10. What are homologous chromosomes? Two similar chromosomes inherited
from each parent
11. What is a trait? A distinguishing characteristic
12. Why might a recessive allele not be expressed (not show up)? Because it
is masked by the dominant allele
13. In order to show the phenotype of a disorder caused by a recessive
allele, what must the genotype be? Homozygous recessive (dd)
14. What must a female’s genotype be if she shows the phenotype for a sexlinked trait? XbXb
15. What is a clone? A genetically identical copy of a gene
16. What happens during crossing over? An area of chromatid is exchanged
(or crossed over) with the matching area on its homologous chromosome
17. What does crossing over result in? Genetic variation
18. What might a mutation of a person’s skin cell cause? Skin cancer, reduced
functioning of the skin cell, or no change in the person’s skin
19. What is co-dominance? Genes are equally dominant resulting in a
phenotype showing BOTH genes
20. How does the phenotype appear when co-dominant alleles are present?
You see both alleles (ex: seeing both brown and white in roan cattle)
21. What is incomplete dominance? Genes are equally dominant resulting in a
phenotype showing a mixture of the genes
22. 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)
23. What are sex-linked traits? Genes found only of the sex chromosomes (X
chromosome
24. Give three examples of sex-linked traits. Hemophilia, Color Blindness,
Pattern Baldness
25. What type of alleles cause most human genetic disorders: dominant or
recessive?
26. What type of gene is Huntington’s disease caused by: dominant or
recessive?
27. Define the following:
Meiosis: cell division that produces gametes
Dihybrid: a cross involving two different traits
Heredity: passing on of characteristics from parent to offspring
Haploid: cell that contains one member of each chromosome pair
Homozygous: alleles present for a trait are the same