1 When neither allele is dominant so that

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%

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. C H S H C S HH

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

C H S H C C HH Curly C S HH Wavy S H C S HH Wavy S S HH 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. Xb. Y D. Xb 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 sexlinked trait), A. All of his sons will be B. C. D. E. colorblind All of his daughters will be at least carriers Both A and B Both A and C

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

7. If a mother is colorblind 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%

B X b X Y B b b X X XY 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.

8. If a mother is colorblind 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%

B X b X Y B b b X X XY All the sons will be colorblind. Colorblind mother is Xb. 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.

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. B. C. D. E. SS only SS or Ss Ss only ss only Ss or ss

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 phenotypethey 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. B. C. D. E. Polygenic inheritance Multiple alleles Sex-linked inheritance A and C 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. B. C. D. AB only AB, A, or B A, B, AB or 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. IB i IA I AI B (AB) I ai (A) i I bi (B) ii (O)

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. B. C. D. E. Trivalent Trisomy Bivalent 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