Genetics Practice Exam
Jo Wen Wu, Ph.D.

Fullerton College

More Genetics Practice Problems Available on the Internet:

Directions:  Try to work out all these problems on your own.  Show all of your work, including what each allele represents.  Draw pedigrees and Punnett squares as needed.  If you are having trouble, then bring this page and your work to the tutor or instructor.

1) During the cell cycle, replication of the genetic material takes place during the
A) G1 phase of interphase.        B) S phase of interphase.    C) G2 phase of interphase.    D) prophase of mitosis.

2) After the second meiotic division, the number of chromosomes in each progeny cell is _______ the parental cell.
A) half        B) double        C) the same as

3) Cytokinesis refers to the division of the:
A) Cytoplasm        B) Nucleus        C) Mitochondria        D) Centrioles

4)  Meiosis reduces the chromosome number by:
A) Discarding some of the chromosomes
B) Reducing the length of each chromosome by half
C) The formation of polar bodies
D) Duplicating DNA once, followed by 2 cell divisions

5) In sexually reproducing organisms, the source of the nuclear chromosomes in the offspring is:
A) Almost all from one parent, usually the father    B) Almost all from one parent, usually the mother
C) Half from the father and half from the mother    D) A random mix and number of chromosomes from both parents

6) When specifically does the pairing and crossing over of homologous chromosomes occur?
A) anaphase I        B) prophase II        C) metaphase II        D) telophase II        E) prophase I

7) If the centromere on one of your 46 chromosomes does not split during anaphase I of meiosis, the consequence would be the production of
A) four cells, each with 23 chromosomes.
B) four cells, two with 23 chromosomes and two with 46 chromosomes.
C) four cells, two with 45 chromosomes and two with 47 chromosomes.
D) four cells, two with 22 chromosomes and two with 24 chromosomes.
E) four cells, two with 46 chromosomes and two with 47 chromosomes

8)  A person with an extra copy of chromosome 21 will exhibit ______.
A. Klinefelter syndrome        B. Turner syndrome        C. hemophilia       
D. Down syndrome                E. achondroplastic dwarfism

9) A chromosome differs from other non-homologous chromosomes in
A) size & shape        B) centromere position        C) shape only        D) size, shape, centromere position

10) Mendel's "characters" were eventually revealed to be
A) nucleotides.        B) genes.        C) chromosomes.        D) cells.

11) A heterozygote for a particular gene has
A) 2 dominant alleles.        B) 2 recessive alleles.        C) 1 dominant allele and 1 recessive allele.

12) Which is an example of a monohybrid cross?
A) Bb x Bb        B) AaBb x AaBb        C) BB x bb        D) aabb x aabb

13) Righthandness is dominant over lefthandness. Mike and his parents are all righthanded. But Mike's sister is lefthanded. What is the probability that Mike's next sibling will be righthanded? Hint: Drawing a pedigree w/ genotypes might help.
A) 50%        B) 75%        C) 25%        D) 0%        E) 100%

14) In humans, brown eyes are dominant over blue eyes. A brown-eyed woman who has a blue-eyed child has the genotype
A) bb        B) BB        C) either Bb or BB        D) impossible to tell        E) Bb

15) The blue eyed child is ___  for this eye gene.
A) heterozygous   B) homozygous   C) carrier       D) hemizygous      E) pleiotropic

16) Amniocentesis reveals that a fetus has Tay-Sachs disease. What are the genotypes of the parents if they appear normal (t = Tay-Sachs)?
A) Tt x tt        B) TT x Tt        C) tt X tt        D) Tt X Tt        E) TT X TT

17) In humans, red hair is recessive to dark hair. Dark-haired Sue is married to dark-haired Mike. Sue's father and Mike's mother have red hair. What are the chances that Sue and Mike's daughter will be red-haired?
A) 0%        B) 75%        C) 100%        D) 50%        E) 25%

18) In a breeding experiment, 45 of the 107 offspring were tt. The
parents most likely had the following genotype:
A) TT x tt        B) Tt x tt        C) TT x Tt        D) Tt x Tt

19) Polydactyly (extra fingers or toes) is caused by an autosomal dominant gene. John and his mother have polydactyly; his father and sister are normal. Suppose John marries Jane (normal).... what is the probability that their first child will have extra fingers or toes?
A.  50%    B. 75%    C. 100%    D. 25%    E. 0%

20) A woman (type A blood) wants to collect child support for her baby (type A). Which man could be the possible father ?? Jim (type A) or Mike (type O)?
A. only Mike    B. only Jim    C. not Jim nor Mike    D. either Jim or Mike

21) Which of the following could NOT be the parents of a child with blood type O? Assume no epistatic complications from another gene.
A. Type A mother and type O father        B. Type AB mother and type O father
C. Type A mother and type B father        D. Type O mother and type O father

22)  In pea seeds, round (R) is dominant to wrinkled (r) and yellow (G) is dominant to green (g). What percentage of round yellow seeds is expected from the cross: Rr GG x RRGg?
A. 75%    B. 100%    C. 0%    D. 50%    E. 25%

23) All of the following combinations are possible in the gametes of an organism that is AaBb except:
A) aB        B) Ab        C) ab        D) aa        E) AB

24) A boy is color-blind (sex-linked recessive) and left-handed (autosomal recessive). Which could be the genotype of his mother?
A) Bb Xh Xh        B) Xb Y Hh        C) XB Xb Hh    D) bb hh

25) In females, X-inactivation
A) shuts off the Y chromosome in every cell.
B) shuts off the maternally inherited X chromosome in every cell.
C) shuts off the paternally inherited X chromosome in some cells.
D) shuts off one X chromosome in a germinal cell.

26) A colorblind woman marries a man with normal color vision. What is the probability that their first SON will be color blind?
A) 100%        B) 25%        C) 0%        D) 50%        E) 75%

27) If a pure-breeding long-tail cat (LL) is crossed with a pure-breeding cat with no tail (rumpy, ll), and a cat with a short tail (stumpy) is produced, the simplest explanation is
A) an incompletely dominant gene.    B) chromosomal aberration.    C) an X-linked gene.
D) a mutation.            E) a lethal gene.

28) In the pedigree shown below, how is the trait inherited? (8 answer choices)
A) autosomal dominant only        B) autosomal recessive only      
C) X-linked dominant only            D) X-linked recessive only
AB) Both answers A or B are possible    AC) Both answers A or C
BD) Both answers B or D                         E) Another combination not listed above

pedigree 1

29) In the pedigree shown below, how is the trait inherited?
A) autosomal dominant only        B) autosomal recessive only        C) X-linked dominant only
D) X-linked recessive only            AB) Both answers A or B are possible    AC) Both answers A or C
BD) Both answers B or D         E) Another combination not listed above
E) other

Pedigree 4: