Question: Cytogenetics and Bacterial Mapping Practice Problems
1. A normal chromosome has several
loci with…
Cytogenetics and Bacterial Mapping Practice Problems
1. A normal chromosome has several
loci with the order ABC • DEFGHI (the dot is the centromere). A
person inherits one copy of this chromosome from one parent, but
the second copy from the other parent has an inversion of the C •
DEF segment.
What type of inversion is this?
Draw how the two chromosomes will synapse at Prophase I of
meiosis. Include the gene loci and centromeres in the drawing.
Suppose that during Prophase I there is a crossover between the
D and E loci. What are the contents and orders of loci in the four
chromatids produced from meiosis? Indicate which of these products
would likely lead to inviable offspring.
2. Two nonhomologous chromosomes in a
woman’s primary oocyte have the gene loci FGHI • JKLMN and PQ •
RSTUVW. In that cell there is a reciprocal translocation in which
the LMN and VW segments are mutually exchanged. Both translocated
chromosomes are segregated to an ovum which is then fertilized by a
sperm that has no chromosomes with rearrangements, leading to a
daughter. Later, as that daughter matures, her oocytes begin
meiosis.
Draw how the four chromosomes (2 translocated, 2 normally
arranged) will synapse at Meiosis I. Include the gene loci and
centromeres in the drawing.
There are two common ways in which these chromosomes may
segregate at Anaphase I. For each of those ways, draw the contents
of the gametes that will result, and indicate which of them would
likely lead to inviable offspring.
3. A bacterial geneticist hopes to map
genes a through g by means of interrupted mating experiments using
three Hfr strains designated X, Y, and Z. In all crosses the Hfr
parent is prototrophic for each gene and is streptomycin sensitive,
whereas the recipient F– strain is multiply auxotrophic and
streptomycin resistant.
How does an Hfr strain differ from an F+ strain?
Why does it matter that the Hfr is streptomycin sensitive while
the F– strain is streptomycin resistant?
From the data in the accompanying table, showing times of entry
in minutes, deduce the genetic map of the markers a through g.
Write the genes in correct order and between adjacent pairs of
genes write the distance in minutes.
4. E. coli cells were infected with
two strains of T2 phage, one wild type for two plaque traits and
the other doubly-mutant. The lysate from this mixed infection
experiment was plated out, with the following results:
186 + +
127 a +
139 + b
198 a b
What is the map distance between locus
a and locus b?
