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 allelesB. Polygenic traitsC. Incomplete dominanceD. Autosomal inheritance

Multiple a

lleles

Polygenic

traits

Inco

mplete dominance

Autosomal in

heritance

25% 25%25%25%

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%

100%75%

50%25% 0%

20% 20% 20%20%20%

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 offspringC. 1:2:1 (curly: wavy: straight)D.9:3:3:1

3:1 (curly

to st

raight)

All wavy h

aired offsp

ring

1:2:1 (curly

: wavy

: straight)

9:3:3:1

25% 25%25%25%

HC HS

HC HCHCCurly

HCHSWavy

HS HCHSWavy

HSHSStraight

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 chromosomeB. A gene on the X chromosomeC. A gene on chromosome 21D. Hormonal differences

A gene on the Y ch

romo...

A gene on the X ch

romo...

A gene on chro

mosome 21

Hormonal

differences

25% 25%25%25%

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. XBYC. XbYD. XbXb

E. Can not determineXBXB

XBYXbY

XbXb

Can not determ

ine

20% 20% 20%20%20%

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 BE. Both A and C

All of h

is sons w

ill be co

l...

All of h

is dau

ghters will

..

All of h

is dau

ghters will

b...

Both A and B

Both A and C

20% 20% 20%20%20%

Xb YXB XBX

bXBY

XB XBXb

XBY

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%

100%75%

50%25% 0%

20% 20% 20%20%20%

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.

XB YXb XBXb XbYXb XBXb XbY

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%

100%75%

50%25% 0%

20% 20% 20%20%20%

XB YXb XBXb XbYXb XBXb XbY

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 onlyB. SS or SsC. Ss onlyD. ss onlyE. Ss or ss

SS only

SS or S

s

Ss only

ss only

Ss or

ss

20% 20% 20%20%20%

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 onlyB. SS or SsC. Ss onlyD. ss onlyE. Ss or ss

SS only

SS or

Ss

Ss on

lyss

only

Ss or s

s

20% 20% 20%20%20%

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 onlyB. SS or SsC. Ss onlyD. ss onlyE. Ss or ss

SS on

ly

SS or

Ss

Ss only

ss only

Ss or s

s

20% 20% 20%20%20%

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 inheritanceB. Multiple allelesC. Sex-linked inheritanceD. A and CE. B and C

Polygenic i

nheritance

Multiple alleles

Sex-linked in

heritan

ce

A and C

B and C

20% 20% 20%20%20%

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 onlyB. AB, A, or BC. A or BD. A, B, AB or O

AB only

AB, A, o

r BA or B

A, B, A

B or O

25% 25%25%25%

IA iIB 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. HeightB. Widow’s peak

Height

Widow’s p

eak

50%50%

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 malesC. is more likely in femalesD. is caused by a dominant

alleleE. is caused by a recessive

alleleis e

qually lik

ely in m

ales ...

is more lik

ely in m

ales

is more lik

ely in fe

males

is cause

d by a dominant a...

is cause

d by a recessi

ve al...

20% 20% 20%20%20%

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

An extra r

ound of DNA re

...

An extra r

ound of DNA re

...

Improper s

eparation of...

Ferti

lization of a

n egg wi..

25% 25%25%25%

17. Having an extra copy of a chromosome is called

A. TrivalentB. TrisomyC. BivalentD. MonovalentE. Monosomy

Trivalent

Trisomy

Bivalent

Monovalent

Monosomy

20% 20% 20%20%20%

Down’s Syndrome is Trisomy 21

1. C2. E3. C4. B5. C6. C7. E8. A9. D10. B11. C12. B13. D

14.A15.A16.C17.B