problem set 7

 For each of the following chromosome rearrangements, describe the physical nature of the

rearrangement, and give a specific example of how the arrangement has affected the evolution

of humans, or another species. (You can use the class lecture notes and/or Google to help)

a. duplication

b. deletion

c. translocation

d. inversion

a. Extra copy of a chromosome
ex: globin genes


b. loss of chromosome part
ex: cri-du-chat

c. part moves to another chromosome
ex: Philadelphia chromosome

d. Part flips around
ex: human vc chip chromosome 4

 Compare and contrast DNA transposons and retrotransposons. What properties do they share and what is unique about each type?

DNA: moves by cut and paste

Retro: move by cut and paste (Use RNA)

Both: jumping gene

Transposons, or jumping genes, are DNA elements that move within the genome. In which organismic groups are transposons found?
A) bacteria

B) eukaryotes

C) mammals

D) ancient bacteria

E) all organismic groups

E

 All insertion sequences (IS elements) contain two structural elements that are essential for their movement. What are these two elements?

A) transposase and inverted terminal repeats

B) integrase and pseudogenes

C) integrase and oncogenes

D) proto-oncogenes and oncogenes

E) transposase and oncogenes

A

Barbara McClintock discovered mobile elements in corn by analyzing the genetic behavior of

two elements, Ds and Ac. The interplay between these two elements has become one of the

most interesting stories of discovery in the field of genetics. How do Ds and Ac interact?

A) Ds causes a deletion next to the insertion site of Ac.

B) Ac causes a deletion next to the insertion site of Ds.

C) While Ds moves only if Ac is present in the genome, Ac is capable of autonomous movement.

D) The movement of Ac is dependent on two forms of Ds.

E) Both elements can move only within chromosome 9.

C

What is NOT a potential consequence of a copy number variation (a type of duplication)?

A) none

B) higher protein levels of specific genes

C) phenotypic consequences leading to enhanced ability to fight infection

D) loss of function at multiple loci

E) phenotypic consequences that track with the number of each gene

D

A geneticist examines an ear of corn in which most kernels are yellow, but she finds a few kernels with purple spots, as shown here. Give a possible explanation for the appearance of the purple spots in these otherwise yellow kernels, accounting for their different sizes.

Different size: Excision happens earlier/later

Purple sport: happens when transposon jumps out restoring color

 The following diagrams represent two nonhomologous chromosomes:

A B • C D E F G

R S • T U V W X

What type of chromosome mutation would produce each of the following groups of

chromosomes? Include which genes are affected in your answer.

a. A B • C D

R S • T U V W X E F G3

b. A U V B • C D E F G

R S • T W X

c. A B • T U V F G

R S • C D E W X

d. A B • C W G

R S • T U V D E F X

a. translocation
EFG

b. Translocation
UV

c. Reciprocal translocation
TUV, CDE

d. Inversion
DEF

 Can Turner Syndrome (female with a single X chromosome, XO) be caused by nondisjunction

in (yes or no for a-d):

a. Meiosis I of the patient’s father?

b. Meiosis II of the patient’s father?

c. Meiosis I of the patient’s mother?

d. Meiosis II of the patient’s mother?

all yes

 In humans, hemophilia is caused by an X-linked recessive (h) and achondroplastic dwarfism

is caused by an autosomal dominant (D). A female dwarf, who is not a hemophiliac, marries a phenotypically normal man and produces a hemophiliac XXY son of normal stature. Determine the most likely genotype of the mother and then diagram the meiosis that produced the egg that gave rise to this son and circle the meiotic product that became the egg. Show and label all of the mother's chromosomes that carry genes marked in this cross (use the designations of the alleles they carry) at the indicated stages:

Metaphase I Telophase I Telophase II

Mother X+XH Dd
Nondis in mom XX egg + Y sperm = XXY son.

 Unicorns are typical diploid eukaryotes with a sex determination mechanism like that of

humans. An X-linked gene with two alleles (B and b) determines coat color in unicorns B/B

females and B/Y males are black; b/b females and b/Y males are white; B/b females are mottled black and white (i.e., black and white patches).

(a) Why are the heterozygous females mottled?

The following three crosses each produce a baby unicorn with an unexpected coat color. In

each case, the exceptional offspring can be explained by invoking nondisjunction in one of the

parents.


(b) For each cross, determine the genotypes of the mother, the father, and the exceptional

child, using the allele notations given above. Also determine the parent in which nondisjunction

must have occurred and the meiotic division(s) at which it could have happened.

a. X-inactivation (randomly silences one X in each cell)



Father MII ( white female)
Father MI (mottled male.)
Mother MI or II ( white female.)

 Coat color in cats is determined by an X-linked locus B, with two alleles: Bb (black) and By

(yellow). Heterozygous females are mottled black and yellow, the so-called tortoise-shell

pattern. Male tortoise shell cats occur, but are very rare and very sterile.

(a) Why are the heterozygous females mottled?

(b) What is the most likely genotype of a mottled male cat?

Suppose that a cross between a tortoise-shell female and a yellow male produces a male

tortoise- shell cat. Assuming that one of the parents produced an aberrant gamete that gave

rise to the exceptional son...

(c) Show how the yellow male parent could have produced the aberrant gamete. Diagram and

label the yellow male’s sex chromosomes, indicate their movements at each stage of meiosis,

and identify the aberrant meiotic product that gave rise to the tortoise-shell son.

(d) A litter of four kittens consists of one yellow male, one black male, one yellow female, one

tortoise-shell female. What are the phenotypes and the relevant genotypes of the parents of

this litter?

x inactivation

XXY: X^B X^y Y

XY sperm (nondisjunction I) + X^B egg = tortoiseshell male.


Girl=X^B X^Y x boy=X^Y Y boy= yellow/black girl= yellow tortoseshell

 Give three important characteristics of cloning vectors.

Origin (ori), marker gene, restriction site (MCS).

The following are four processes common to most cloning experiments:

i) transforming bacteria

ii) plating bacteria on selective medium

iii) cutting DNA with restriction endonucleases

iv) ligating DNA fragments

Place the components of this list in the order in which they would most likely occur during a

cloning experiment.

3,4,1,2

When using a plasmid with the lacZ gene, there are two possible colony colors that result. What are those two colors? Which color are we interested in? Why are we interested in that

color?

Blue = no insert, White = insert present (desired).

 How does CRISPR work in eukaryotic cells? Your answer should include the components of CRISPR and how the cell might try to repair what CRISPR does.

Cas9 + gRNA cut DNA; cell repairs by NHEJ (mutations) or HDR (template repair