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
what are Mendel’s three laws?
law of equal segregation = during gamete formation (meiosis) gene pairs separate equally
law of independent assortment = chromosome pairs segregate independently of each other
law of dominance = alleles can be dominant or recessive
how can saccharomyces cerevisiae be used in genetic experiments?
two haploid parents = fuse = transient diploid = meiosis and four haploids that can be segregated and cultured, then studied individually to give us information about LINKAGE RELATIONSHIPS
what is a parental ditype?
when all four products of meiosis are the same as one of the parents, happens with LINKED GENES
when two genes are unlinked what ditype do you get?
50% of the time you get a non-parental ditype
this is when all products are non-parental genotypes
the other 50% you get a parental ditype
what is a tetratype?
when a single crossover occurs between two loosely linked genes, giving two parental genotypes and two non-parental genotypes
(has four different genotypes, two different recombinants and two different parental, unlike non-parental ditype which has only two genotypes, both of which are recombinants there’s just two of each)
if there are loads more PDs than NPDs when analysing tetrads you conclude…
the genes are likely to be linked
if you see roughly the same number of PDs and non-PDs you conclude…
genes are most likely not linked
how can you calculate recombinant frequency using number of PDs an NPDs?
NPD + 1/2 tetrad all over total PD + NP + TT
then x 100
look at tetrad powerpoint
what is a pericentric inversion vs paracentric?
pericentric = when a centromere is within the inverted segment of chromosome
paracentric = when it’s not in the inverted segment
if crossing over occurs within a paracentric inversion then…
one of the chromatids won’t have a centromere and be lost, another one will have two centromeres and form a bridge in anaphase and then break at some point along it’s length
what are plasmids?
circular extra-genomic DNA elements ranging from a few hundred bps to many kbps
how can mutagens be used?
some mutagens cause specific mutations and so can be used to induce this
