Lecture 3

Question 1

Which is the wild type allele in V/V+? (just a nomenclature question!)

Answer 1

V+

Question 2

2 genes, 2 pathways

Answer 2

complementation, no interaction between the genes, often a 9:3:3:1 ratio– 4 phenotypes, different pathways

Question 3

2 genes, ONE pathway

Answer 3

noncomplementation, loss of function for either gene results in lack of functional product, gives yield of 9:7 because:

9 A-;B-

3 A-;bb (one nonfunctional product)

3 aa;B- ((one nonfunctional product)

1 aa;bb (one nonfunctional product)

3+3+1=7

Question 4

2 genes, ONE pathway (gene order!)

Answer 4

recessive epistatis (if intermeditaae products look different from each other, it must mean that allelic state of one affects the allelic state of the other)- -labradors

9:4:3 suggests epistasis and gene order

Question 5

recessive epistasis

Answer 5

interaction of two genes where the allelic state of one gene affects the phenotypic expression of the other– must be recessive null mutations

Question 6

9:3:4 is an example of___.

Answer 6

recessive epistasis—pic helps to explain why 3 and 4! :) you can do it!

Question 7

9:3:3:1 is an example of ______.

Answer 7

Two genes, two pathways.

Question 8

9:7 is an example of ______.

Answer 8

two genes, one pathway.

Question 9

synthetic lethality

Answer 9

recessive double mutant dies as an embryo– do not confuse with recessive lethality which is the outcome of a single gene!!! for synthetic lethality both genes must be recessive

Question 10

complementation

Answer 10

two strains of an organism with different homozygous recessive mutations that are the same mutant phenotype can produce a wild-type phenotype offspring when crossed

alleles on different genes

Question 11

non-complementation

Answer 11

when recessive mutations in two different loci fail to complement each other

alleles are on the same gene

Question 12

Same complementation group refers to alleles .

Answer 12

On the same gene. (lack of complementation)

Question 13

Why are yeast great model organisms?

Answer 13

1. Great for looking at secretion because they have to secrete their enzymes in order to eat food (extracellular digestion)
2. Most of the lifecycle of a yeast exists as a haploid cell, so to test a function, you only need to knock out one allele instead of two.
3. They can go into starvation mode to produce sexually through meiosis.

Question 14

essential genes

Answer 14

genes required for viability of the organism. Homozygosity for null alleles of essential genes is lethal.

Question 15

conditional allele

Answer 15

alleles that are only fully penetrant under defined conditions (eg., cold, heat, salt concentration)

Question 16

epistasis

Answer 16

when one gene completely masks another gene

Question 17

The normal # of chromosomes in a human cell is _______.

Answer 17

46 chromosomes, 23 pairs.

Question 18

p represents the ___ arm.

Answer 18

smaller (petite)

Question 19

centromere

Answer 19

a region of DNA on the chromosome, it is NOT a connecting protein

Question 20

packing ratio

Answer 20

the length of DNA divided by the length into which it is packaged

Question 21

constitutive heterochromatin

Answer 21

regions that are ALWAYS heterochromatic, permanently inactive in regard to transcription—

telomeres and centromeres

Question 22

facultative heterochromatin

Answer 22

regions that can interconvert between euchromatin and heterochromatin– helps for the differentiation of cells by

Question 23

During interphase, most chromosomal regions are ______.

Answer 23

euchromatic

Question 24

What are the 3 key features scientists use to identify chromosomes?

Answer 24

1) size
2) banding pattern
3) centromere position

Question 25

euploid

Answer 25

(true ploid) a cell having any number of complete chromosome sets haploid (1n), diploid (2n), triploid (3n) etc

Question 26

aneuploid

Answer 26

a cell having a chromosome number that differs from the normal chromosome number for the species by a small number of chromosomes

• monosomic (2n-1) – Turners*
• trisomic (2n+1) – Down’s Syndrome*

Question 27

polyploidy

Answer 27

a cell having more than 2 sets of homologous chromosomes

can arise from two diploid gametes

Question 28

True or false: Nondisjunction can occur in both divisions of meiosis.

Answer 28

False. It can only occur in one division not both.

Question 29

There is NO crossover in _____ chromosomes.

Answer 29

X & Y. Since x and y chromosomes are not homologues they do not crossover.

Question 30

homologous chromosomes

Answer 30

• contain the same arrangement of genes
• are visibly identical
• pair during meiosis I
• in nature they are not usually identical but typically exhibit alleleic differences

Question 31

sex lethal gene

Answer 31

the master switch gene for determining sex in fruit flies- if a fly has XX, sxl gene becomes activated and produces female sex characteristics. In XY flies, the gene remains inactive and male development ensues

Question 32

SRY gene

Answer 32

a key transcription factor– SRY is necessary for transcription of genes required to form male gonads

Question 33

dosage compensation in drosophila

Answer 33

In XX, both chromosomes active, in XY, the X is hyperactive

Question 34

dosage compensation in humans

Answer 34

one chomosome inactivated in XX, single chromosome active in XY

Question 35

dosage compensation in c elegans

Answer 35

In XX, both chromosomes hypoactive, in X0, single chromosome active

Question 36

Barr body

Answer 36

a small, condensed, inactive x chromosome in the cell nuclei of female mammals

Question 37

genetic mosaic

Answer 37

denotes the presence of two populations of cells with different phenotypes in one individual who has developed from a single fertilized egg— x-inactivation in calico cats