Lecture 3 Flashcards
Which is the wild type allele in V/V+? (just a nomenclature question!)
V+
2 genes, 2 pathways
complementation, no interaction between the genes, often a 9:3:3:1 ratio– 4 phenotypes, different pathways
2 genes, ONE pathway
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
2 genes, ONE pathway (gene order!)
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
recessive epistasis
interaction of two genes where the allelic state of one gene affects the phenotypic expression of the other– must be recessive null mutations
9:3:4 is an example of___.
recessive epistasis—pic helps to explain why 3 and 4! :) you can do it!
9:3:3:1 is an example of ______.
Two genes, two pathways.
9:7 is an example of ______.
two genes, one pathway.
synthetic lethality
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
complementation
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
non-complementation
when recessive mutations in two different loci fail to complement each other
alleles are on the same gene
Same complementation group refers to alleles .
On the same gene. (lack of complementation)
Why are yeast great model organisms?
- Great for looking at secretion because they have to secrete their enzymes in order to eat food (extracellular digestion)
- 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.
- They can go into starvation mode to produce sexually through meiosis.
essential genes
genes required for viability of the organism. Homozygosity for null alleles of essential genes is lethal.
conditional allele
alleles that are only fully penetrant under defined conditions (eg., cold, heat, salt concentration)
epistasis
when one gene completely masks another gene
The normal # of chromosomes in a human cell is _______.
46 chromosomes, 23 pairs.
p represents the ___ arm.
smaller (petite)
centromere
a region of DNA on the chromosome, it is NOT a connecting protein
packing ratio
the length of DNA divided by the length into which it is packaged
constitutive heterochromatin
regions that are ALWAYS heterochromatic, permanently inactive in regard to transcription—
telomeres and centromeres
facultative heterochromatin
regions that can interconvert between euchromatin and heterochromatin– helps for the differentiation of cells by
During interphase, most chromosomal regions are ______.
euchromatic
What are the 3 key features scientists use to identify chromosomes?
1) size
2) banding pattern
3) centromere position
euploid
(true ploid) a cell having any number of complete chromosome sets haploid (1n), diploid (2n), triploid (3n) etc
aneuploid
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*
polyploidy
a cell having more than 2 sets of homologous chromosomes
can arise from two diploid gametes
True or false: Nondisjunction can occur in both divisions of meiosis.
False. It can only occur in one division not both.
There is NO crossover in _____ chromosomes.
X & Y. Since x and y chromosomes are not homologues they do not crossover.
homologous chromosomes
- 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
sex lethal gene
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
SRY gene
a key transcription factor– SRY is necessary for transcription of genes required to form male gonads
dosage compensation in drosophila
In XX, both chromosomes active, in XY, the X is hyperactive
dosage compensation in humans
one chomosome inactivated in XX, single chromosome active in XY
dosage compensation in c elegans
In XX, both chromosomes hypoactive, in X0, single chromosome active
Barr body
a small, condensed, inactive x chromosome in the cell nuclei of female mammals
genetic mosaic
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
