1. 1. When neither allele is dominant, so that a heterzygote has a phenotype that is a blending of each of the homozygous phenotypes (such as one red color allele and one white color allele producing pink flowers) it is called
Multiple alleles
Polygenic traits
Incomplete dominance
Autosomal inheritance

2. Incomplete dominance

3. 2. The curly hair allele (HC) and the straight hair (HS) alleles show incomplete dominance . If one parent has curly hair and one parent has straight hair, what is the probability that they have a child with curly hair?
100%
75%
50%
25% 0%

4. If one parent has curly hair and the other has straight hair, each offspring will inherit one of each allele from parents. All offspring will have wavy hair. HC HS
HCHS

5. 3. If both parents have wavy hair, what is the phenotype (and genotype) ratio for their offspring?
3:1 (curly to straight)
All wavy haired offspring
1:2:1 (curly: wavy: straight)
9:3:3:1

6. HC HS HCHC Curly HCHS Wavy HSHS Straight
1 Curly : 2 Wavy: 1 Straight hair

7. 4. Almost all sex-linked traits, such as hemophilia, red-green colorblindness and Duchene’s muscular dystrophy are caused by
A gene on the Y chromosome
A gene on the X chromosome
A gene on chromosome 21
Hormonal differences

8. Females have two X chromosomes, so they have two copies of any genes on the X chromosome. Females must inherit a recessive allele from both parents to have the recessive phenotype.
Males only have one X chromosome. The Y chromosome does not have the same genes. So males will express a recessive trait if there only X chromosome has the recessive allele.

9. 5. Red-green colorblindness is caused by a recessive sex-linked trait (on the X chromosome). What is the genotype of a colorblind man?
XBXB
XBY
XbY
XbXb
Can not determine

10. Males only have one X chromosome.
A coloblind male has the recessive colorblindness allele on his only X chromosome. (Xb)

11. 6. If a man is colorblind (a recessive sex-linked trait),
All of his sons will be colorblind
All of his daughters will be colorblind
All of his daughters will be at least carriers
Both A and B
Both A and C

12. A Father passes his only X chrosomes to all daughters
A Father passes his only X chrosomes to all daughters. So if he is colorblind, all of his daughters will be at least carriers.
A father passes his Y chromosome to all sons. So a father being colorblind doesn’t affect as son’s probability of being colorblind. Xb Y XB
XBXb
XBY

13. 7. If a mother is colorblind and a father is not colorblind, what is the probability of a daughter being colorblind? (Find the probability just among possible daughter outcomes)
100%
75%
50%
25% 0%

14. XB Y Xb XBXb XbY Daughters all have normal color vision
The father’s only X chromosome always gets passed down to any daughters he has.
Since this father does not have colorblindness, his X chromosome must have the normal color vision allele.
All of his daughters will receive this dominant allele, and will NOT have red-green colorblindness.

15. 8. If a mother is colorblind and a father is not colorblind, what is the probability of son being colorblind? (Find probability just among possible son outcomes)
100%
75%
50%
25% 0%

16. XB Y Xb XBXb XbY All the sons will be colorblind.
Colorblind mother is XbXb. Father with normal color vision is XBY.
With these parents, all the sons will inherit their only X from their colorblind mother and will be colorblind.
All daughters will inherit a dominant color vision gene on the X chromosome from their father, so they will have normal color vision but will be carriers due to the X they receive from their mother.

17. 9. The pedigree below represents a family history for sickle cell anemia which is a recessive trait (ss). Shaded in individual have this recessive genetic condition. Choose the response that includes all of the possible genotypes of individual I-2.
SS only
SS or Ss
Ss only
ss only
Ss or ss

18. 10. The pedigree below represents a family history for sickle cell anemia which is a recessive trait (ss). Shaded in individual have this recessive genetic condition. Choose the response that includes all of the possible genotypes of individual III-2
SS only
SS or Ss
Ss only
ss only
Ss or ss

19. 11. The pedigree below represents a family history for sickle cell anemia which is a recessive trait (ss). Shaded in individual have this recessive genetic condition. Choose the response that includes all of the possible genotypes of individual II-4.
SS only
SS or Ss
Ss only
ss only
Ss or ss

20. Explanations
9. You can determine the genotype of individual I-2 because individuals with the recessive phenotype must have two recessive alleles. (ss)
10. In many cases, you can not determine the genotype of an individual with the dominant phenotype. Individual III-2 could be SS or Ss. There is no way of determining which genotype she has from the pedigree.
11. You can determine that individual II-4 must be heterozygous (Ss) because they have a child with the recessive phenotype. This child must have inherited a recessive allele from both parents. (Also they have a parent with the recessive phenotype- they must have inherited the recessive allele from this parent.)

21. 12. The 4 main types of blood A, B, AB and O are due to
Polygenic inheritance
Multiple alleles
Sex-linked inheritance
A and C
B and C

22. 13. For blood types, the A allele (IA) and the B allele (IB) are codominant. The O allele (i) is recessive. If a mother has blood type B and a father has blood type A, which blood types are possible for their children?
AB only
AB, A, or B
A or B
A, B, AB or O

23. The A blood type parent could have the genotype IA i.
The B blood type parent could have the genotype IB i.
So all 4 blood types are possible. IA i IB
IAIB
(AB)
Ibi
(B)
Iai
(A) ii
(O)

24. 14. A trait that is polygenic is
Height
Widow’s peak

25. There is a wide variation in height because more than one gene controls this trait.

26. 15. An autosomal trait is one that
is equally likely in males and females
is more likely in males
is more likely in females
is caused by a dominant allele
is caused by a recessive allele

27. The autosomal chromosomes are the chromosomes that are found in homologous pairs in both males and females. (chromosomes 1-22 for humans). Since both genders have pairs, these traits are equally likely in males and females.

28. 16. Nondisjunction is An extra round of DNA replication in mitosis
An extra round of DNA replication in meiosis
Improper separation of homologous pairs in meiosis
Fertilization of an egg with multiple sperm

30. 17. Having an extra copy of a chromosome is called
Trivalent
Trisomy
Bivalent
Monovalent
Monosomy

32. Down’s Syndrome is Trisomy 21

33. C E B A D A C B