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

A. Multiple alleles

B. Polygenic traits

C. Incomplete dominance

D. Autosomal inheritance

Incomplete dominance

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?

A. 100%

B. 75%

C. 50%

D. 25%

E. 0%

HC HC

HS HCHS HCHS

HS HCHS HCHS

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.

3. If both parents have wavy hair, what is the phenotype (and genotype) ratio for their offspring?

A.3:1 (curly to straight)

B. All wavy haired offspring

C. 1:2:1 (curly: wavy: straight)

D.9:3:3:1

HC HS

HC HCHC

Curly HCHS

Wavy

HS HCHS

Wavy HSHS

Straight

1 Curly : 2 Wavy: 1 Straight hair

4. Almost all sex-linked traits, such as hemophilia, red-green colorblindness and Duchene’s muscular dystrophy are caused by

A. A gene on the Y chromosome

B. A gene on the X chromosome

C. A gene on chromosome 21

D. Hormonal differences

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.

5. Red-green colorblindness is caused by a recessive sex-linked trait (on the X chromosome). What is the genotype of a colorblind man?

A. XBXB

B. XBY

C. XbY

D. XbXb

E. Can not determine

Males only have one X chromosome.

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

6. If a man is colorblind (a recessive sex-linked trait),

A. All of his sons will be colorblind

B. All of his daughters will be colorblind

C. All of his daughters will be at least carriers

D. Both A and B

E. Both A and C

A father passes his Y chromosome to all sons. So a father being colorblind doesn’t affect as son’s probability of being colorblind.

A Father passes his only X chrosomes to all daughters. So if he is colorblind, all of his daughters will be at least carriers.

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)

A. 100%

B. 75%

C. 50%

D. 25%

E. 0%

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.

Daughters all have normal color vision

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)

A. 100%

B. 75%

C. 50%

D. 25%

E. 0%

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.

All the sons will be colorblind.

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.

A. SS only

B. SS or Ss

C. Ss only

D. ss only

E. Ss or ss

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

A. SS only

B. SS or Ss

C. Ss only

D. ss only

E. Ss or ss

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. A. SS only

B. SS or Ss

C. Ss only

D. ss only

E. Ss or ss

9. You can determine the

genotype of individual I-2

because individuals with the

recessive phenotype must

have two recessive alleles.

(ss)

Explanations

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.)

12. The 4 main types of blood A, B, AB and O are due to

A. Polygenic inheritance

B. Multiple alleles

C. Sex-linked inheritance

D. A and C

E. B and C

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?

A. AB only

B. AB, A, or B

C. A or B

D. A, B, AB or O

IA i

IB IAIB

(AB) Ibi (B)

i Iai (A)

ii (O)

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.

14. A trait that is polygenic is

A. Height

B. Widow’s peak

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

15. An autosomal trait is one that

A. is equally likely in males and females

B. is more likely in males

C. is more likely in females

D. is caused by a dominant allele

E. is caused by a recessive allele

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.

16. Nondisjunction is

A. An extra round of DNA replication in mitosis

B. An extra round of DNA replication in meiosis

C. Improper separation of homologous pairs in meiosis

D. Fertilization of an egg with multiple sperm

17. Having an extra copy of a chromosome is called

A. Trivalent

B. Trisomy

C. Bivalent

D. Monovalent

E. Monosomy

Down’s Syndrome is Trisomy 21

1. C

2. E

3. C

4. B

5. C

6. C

7. E

8. A

9. D

10. B

11. C

12. B

13. D

14.A 15.A 16.C 17.B