becky barnes Flashcards
what cross would you do to figure out which phenotype is dominant?
cross the two pure lines, then self fertilise F1, expecting 75% dominant phenotype
Double check - cross fertilise F1 with homozygous recessive, expecting 50/50 phenotype split
if you have a dominant phenotype but want to figure out it’s genotype (hetero or homo) how would you do it?
cross with homozygous recessive, if yours is homozygous dominant all offspring will have dominant phenotype, if heterozygous it’ll be a 50/50 split
chi squared - what is the equation, what is degrees of freedom, what does a low/high chi squared mean?
sum of: (O-E)^2, all over E
number of classes minus 1
if chi squared is low there is a good agreement between observed and expected, there is a high probability the deviation you’ve seen is no biggie
what type of genes is independent assortment not applicable to?
genes carried close to each other - almost always inherited together - this is easily spotted as the expected ratios are not the found
if ratios are not as expected, for linked or not linked, what is the most likely explanation?
crossing over
what is the recombination frequency? what is it proportional to and what is it always between?
recombinants/total x100
it is proportional to the distance between the genes on the chromosome, further apart = more likely they are to be recombinants
always between 0% and 50%
go look at the transforming principle (griffith) bacteriophage lifecycle (hershey and chase) and discovering structure of DNA from molecular and cell
eukaryotic chromosomes are made of…
chromatin - DNA wrapped around histones
structure of linear chromosomes?
centromere at centre as binding site of kinetochore proteins
telomeres at end to protect from degradation
p arm = short arm, q arm = long one
cytogenetics is the?
common staining technique is?
karyotype is?
study of chromosomes
common technique used is called G-banding using Giesma to satin chromosomes in a unique banding pattern
karyotype = chromosome complement of an individual
how does cytoplasmic inheritance work?
mitochondria and chloroplasts inherited from the cytoplasm of the egg
euchromatin vs heterochromatin?
euchromatin = loosely packed and readily transcribed
heterochromatin = condensed structure that does not allow gene expression, controlled by addition of methyl and acetyl groups to the histone proteins
what happens in prophase?
chromosomes condense (now visible threads) and now have two chromatids attached at centromere
chromatids held together by cohesin
nuclear membrane breaks down (prometaphase)
what is the cytoskeleton made of?
what are centromeres and how are sister chromatids separated?
cytoskeleton = microtubules (polymers of tubulin)
centromere = specialised region of the chromosome that direct equal segregation
NOT ALWAYS CENTRAL
microtubules connect to kinetochore and shorten to separate the sister chromatids
what happens in metaphase?
centromeres align along equator, microtubules attach toe ach pole and the tension between these keeps the chromosomes central
what happens in anaphase?
cohesin breaks down, chromatids become separate chromosomes
centromeres start moving to opposite poles
what happens in telophase?
Chromosomes arrive at the cell poles
Chromosomes decondense – no
longer recognisable thread structures
Daughter nuclei reform
is cytokinesis symmetrical?
not always, can give unevenly sized daughter cells
what are the 5 stages of meiotic prophase 1?
leptotene - replicated chromosomes start to contract
zygotene - chromosomes line up in
homologous pairs (synapsis) and are held together by the synaptonemal complex
pachytene - crossing over between non-sister chromatids
diplotene - chromosomes separate a bit but sites of crossing over still visible
diakinesis - chromosomes contract even further
polyploidy vs aneuplody?
polyploidy = unusual number of chromosome sets
so 3n, 4n etc…
aneuploidy = one or few individual extra chromosomes like 2n + 1
what is a null allele?
total loss of function
what are auxotrophic mutants?
mutants that are unable to synthesise essential compounds
this is useful when distinguishing between WT and mutants, WT can grow in minimal growth media (only the nutrients an organism cannot synthesise by itself) and in complete media (contains extra nutrients)
auxotrophic mutants require the extra nutrients of complete media to grow
allelic vs non-allelic mutations? what kind of yeast is used?
allelic = this is when you have mutations in both of the alleles for e.g. an enzyme in a biosynthetic pathway, so that enzyme cannot be made correctly at all
non-allelic = mutations not in the same allele, so there is at least one functional copy for each one and it should be all good
yeast in it’s transient diploid stage, when two haploid parent yeast have combined, is used in these experiments
describe the nuclear cycle of saccharomyces cerevisiae
haploid through most of the life cycle, two mating types = a and alpha
an a and alpha must combine to give a transient diploid stage that results in meiosis and four haploid products, these can be separated and cultured
