Human Genetics and Medicine - BIOL 272    EXAM II - March 9, 2010    NAME:

DO NOT USE ANY OTHER PAPER AT ANY TIME WITHOUT INSTRUCTOR PERMISSION

Part I: [46 points] Variable units.  Answer all the questions.

1.  Fill in the table for each of the following human genes.  The letters for the gene’s name is given in all uppercase; you must decide what should really be upper and lower case in the symbol. [24 points]

trait which is passed on as ...	achondroplasia (ACH) - dominant (a type of dwarfism)	Gaucher disease (GD) recessive (a lysosomal storage disorder)
wild type allele
mutant allele
dominant allele
recessive allele
“normal” genotypes
“abnormal” genotypes
show mating heterozygote x normal
offspring genotype (s)
offspring phenotype (s)
show mating heterozygote x abnormal
offspring genotype (s)
offspring phenotype (s)

2.  Solve the following pedigree. For each individual, write the genotype [write it next to the symbol in the pedigree]. Is the inheritance pattern for the indicated trait recessive, dominant, other? Explain.  [11 points]

Name the propositus (proband):

 _______________

Inheritance pattern: 

_______________
(explain)

What phenotypic ratio would one expect among
the offspring if II-2 and II-6 had children?  Is this
mating legal in the USA (assuming these are people)?

 _______________

What phenotypic ratio would one expect among
the offspring if III-2 and II-6 had children?  Is this
mating legal in the USA (assuming these are people)?

 _______________

At the right of the pedigree, indicate what Mendel
would have called each generation.

3.  While you are working as a genetic counselor, a couple asks you for advice.  They have had one child who died of Tay Sachs, a lethal recessive disorder.  They hope to have more children, and want to know: [11 points]

    a. What is the chance that their next child will have Tay Sachs?

    b.  If their next child is healthy, what is the chance that the third child will be healthy as well?

    c. What is the chance of their having four normal children, in their next four attempts?

    d. What is the chance of their having four normal girls, in their next four attempts?

        e.  If there is a prenatal test for Tay Sachs, why might this couple chose to have such a test done with subsequent pregnancies?  That is, for what purpose would such a test be done?


4.  Fill in the following table.  Show your work for possible partial credit; if you choose to do this, be sure that your work is legible and labeled sufficiently clearly to be understood by someone other than yourself.  Be sure to list the genotypes & phenotypes in a sensible order in the first column, and then to use the table as a table. [10 pts]
 

genotypes	AaBb x AaBb	AB/ab x Ab/aB	Ab/aB b x Ab/aB
phenotypes

bonus: Write a question that you studied for, and forgetful me, I neglected to ask.  Answer your question.  PLEASE ask yourself something you can answer well!  PLEASE answer the question you actually ask.  [up to 5 points awarded based on question & answer]

Part II: [44 points]  Choose the one BEST answer.  Circle its letter. Read each question and all 5 choices carefully because more than one answer might seem correct at first glance.  2  point each

1.  An SP/sp female that underwent one crossover event during meiosis could produce which of the following gametes?
    a. Sp and sP
    b. SP and sp
    c. Ss and Pp
    d. a and b
    e. all of the above

2.  An abnormal condition in which one extra or one too few chromosomes is present is called
    a. euploidy
    b. aneuploidy
    c. monosomy
    d. trisomy
    e. haploidy

3.  Characteristics of a normal human karyotype include
    a.  23 chromosomes per haploid genome
    b.  46 chromosomes per somatic cell
    c.  24 different types of chromosomes
    d. a and b
    e. all of the above

4.  Non-disjunction can occur during
    a.  the first meiotic event
    b.  the second meiotic event
    c.  spermatogenesis
    d.  oogenesis
    e.  a and b
    f.  c and d
    g.  all of the above

5.  Karyotype analysis can determine all of the following EXCEPT
    a. gender
    b. trisomy
    c. monosomy
    d. presence of a recessive allele
    e. loss of a piece of a chromosome

6.  The term "wild type" indicates
    a. organisms found outside captivity
    b. the accepted "standard" strain of an organism, or allele of a gene (genotype or phenotype)
    c. organisms particularly prone to mutate
    d. organisms out of control
    e. organisms which breed true

7.  An organism's expressed physical trait, such as seed color or pod shape, is its
    a.  genotype  
    b.  cytosol
    c.  phenotype
    d.  gamete
    e.  trait

8.  Two genes are known to be 10 map units apart. The expected percentage of nonparental (recombinant) offspring from a testcross is
    a. 1%
    b. 5%
    c. 10%
    d. 20%
    e. not enough information given

9.  A man with a rare recessive disorder marries a woman who is phenotypically normal.  If the woman is homozygous at that locus, the probability that their offspring will have the disorder is
    a. 0% because the disease is rare
    b. 0% because the child will receive a dominant allele from the mother
    c. 100% because the child would receive the trait from the father
    d. 50%
    e. 25%

10. A child of the parents described in #9 marries a heterozygote at this locus. The probability that they will have a child with the disorder is:
    a. 0% because the disease is rare
    b. 0% because the child will receive a dominant allele from the mother
    c. 100% because the child would receive the trait from the father
    d. 50%
    e. 25%

11.  The number of chromosomes in a gamete (any gamete) is
    a.  1N
    b.  2N
    c.  4N
    d.  46
    e.  23 pairs

12.  Non-disjunction tends to occur more frequently in women over 35 because
        a.  primary oocytes stop at metaphase 1 of meiosis from when they start, prenatally, until they are released into the uterine tube
    b.  sperm that have less chromatin in nucleus swim faster
    c.  women over 35 tend to have more children, thus the probability of non-disjunction increases
    d.  Barr bodies accumulate in the oocytes of women over 35
    e.  sperm carrying both a Y and an X swim slower

13.  A phenotypic ratio of 3:1 among offspring of a cross between two organisms heterozygous for a single gene is expected when
    a.  the alleles separate randomly and independently during meiosis
    b.  each allele contains two mutations
    c.  the alleles are identical
    d.  the alleles are incompletely dominant
    e.  only recessive traits are scored

14.  In order to map genes one must
    a. sequence DNA
    b. mate large numbers of individuals with known genotypes
    c. have a chromosomal library
    d. measure recombination rates between genes during sexual reproduction
    e. any of the above may contribute to a gene map

15.  To identify the genotype of yellow-seeded pea plants as either homozygous dominant (YY) or heterozygous (Yy), one would do a test cross using plants of genotype
    a.  y
    b.  Y
    c.  yy
    d.  YY
    e.  Yy

16.  Two people of normal phenotype have had a child with Niemann-Pick disease, a lethal recessive trait.  What is the probability that their next child will be afflicted?
    a. 1 (100%)
    b. 1/2 (50%)
    c. 1/4 (25%)
    d. 3/4 (75%)
    e. not possible to predict from information given

17.  A monohybrid cross (Dd x Dd) can illustrate Mendel's observations of
    a. dominance and recessiveness
    b. random segregation
    c. independent assortment
    d. a and b
    e. all of the above

18. In order to demonstrate the phenomena described above, how many generations are required?
    a. 1 (parental only)
    b. 2
    c. 3
    d. 4
    e. insufficient information

19.  The genetic cross predicted to give a phenotypic ratio of 9:3:3:1 is
    a.  SSYY x ssyy
    b.  SsYY x SSYy
    c.  SsYy x SsYy
    d.  SSyy x ssYY
    e.  ssYY x ssyy

20.  An example of monosomy is
    a.  46,XX
    b.  47,XXX
    c.  69,XYY
    d.  45,X
    e.  none of the above; monosomy is not designated or written this way

21.  A chromosome with its centromere located in the middle is
    a.  metacentric
    b.  telocentric
    c.  submetacentric
    d.  acrocentric
    e.  holocentric

22.  An example of a genetic mosaic is someone with
    a.  many cells with one or the other of two different genotypes
    b.  skin cells, about half each with the maternal, and half with the paternal X inactivated
    c.  too many chromosomes
    d.  a and b
    e.  all of the above