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genetics 1 > becky barnes > Flashcards

becky barnes Flashcards

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Biology 101 flashcards
1
Q

what cross would you do to figure out which phenotype is dominant?

A

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

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2
Q

if you have a dominant phenotype but want to figure out it’s genotype (hetero or homo) how would you do it?

A

cross with homozygous recessive, if yours is homozygous dominant all offspring will have dominant phenotype, if heterozygous it’ll be a 50/50 split

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3
Q

chi squared - what is the equation, what is degrees of freedom, what does a low/high chi squared mean?

A

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

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4
Q

what type of genes is independent assortment not applicable to?

A

genes carried close to each other - almost always inherited together - this is easily spotted as the expected ratios are not the found

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5
Q

if ratios are not as expected, for linked or not linked, what is the most likely explanation?

A

crossing over

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6
Q

what is the recombination frequency? what is it proportional to and what is it always between?

A

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%

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7
Q

go look at the transforming principle (griffith) bacteriophage lifecycle (hershey and chase) and discovering structure of DNA from molecular and cell

A
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8
Q

eukaryotic chromosomes are made of…

A

chromatin - DNA wrapped around histones

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9
Q

structure of linear chromosomes?

A

centromere at centre as binding site of kinetochore proteins

telomeres at end to protect from degradation

p arm = short arm, q arm = long one

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10
Q

cytogenetics is the?
common staining technique is?
karyotype is?

A

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

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11
Q

how does cytoplasmic inheritance work?

A

mitochondria and chloroplasts inherited from the cytoplasm of the egg

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12
Q

euchromatin vs heterochromatin?

A

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

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13
Q

what happens in prophase?

A

chromosomes condense (now visible threads) and now have two chromatids attached at centromere
chromatids held together by cohesin

nuclear membrane breaks down (prometaphase)

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14
Q

what is the cytoskeleton made of?
what are centromeres and how are sister chromatids separated?

A

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

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15
Q

what happens in metaphase?

A

centromeres align along equator, microtubules attach toe ach pole and the tension between these keeps the chromosomes central

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16
Q

what happens in anaphase?

A

cohesin breaks down, chromatids become separate chromosomes
centromeres start moving to opposite poles

17
Q

what happens in telophase?

A

Chromosomes arrive at the cell poles
Chromosomes decondense – no
longer recognisable thread structures
Daughter nuclei reform

18
Q

is cytokinesis symmetrical?

A

not always, can give unevenly sized daughter cells

19
Q

what are the 5 stages of meiotic prophase 1?

A

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

20
Q

polyploidy vs aneuplody?

A

polyploidy = unusual number of chromosome sets
so 3n, 4n etc…

aneuploidy = one or few individual extra chromosomes like 2n + 1

21
Q

what is a null allele?

A

total loss of function

22
Q

what are auxotrophic mutants?

A

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

23
Q

allelic vs non-allelic mutations? what kind of yeast is used?

A

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

24
Q

describe the nuclear cycle of saccharomyces cerevisiae

A

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

25
Q

what are Mendel’s three laws?

A

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

26
Q

how can saccharomyces cerevisiae be used in genetic experiments?

A

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

27
Q

what is a parental ditype?

A

when all four products of meiosis are the same as one of the parents, happens with LINKED GENES

28
Q

when two genes are unlinked what ditype do you get?

A

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

29
Q

what is a tetratype?

A

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)

30
Q

if there are loads more PDs than NPDs when analysing tetrads you conclude…

A

the genes are likely to be linked

31
Q

if you see roughly the same number of PDs and non-PDs you conclude…

A

genes are most likely not linked

32
Q

how can you calculate recombinant frequency using number of PDs an NPDs?

A

NPD + 1/2 tetrad all over total PD + NP + TT

then x 100

33
Q

look at tetrad powerpoint

A
34
Q

what is a pericentric inversion vs paracentric?

A

pericentric = when a centromere is within the inverted segment of chromosome

paracentric = when it’s not in the inverted segment

35
Q

if crossing over occurs within a paracentric inversion then…

A

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

36
Q

what are plasmids?

A

circular extra-genomic DNA elements ranging from a few hundred bps to many kbps

37
Q

how can mutagens be used?

A

some mutagens cause specific mutations and so can be used to induce this

genetics 1 (4 decks)

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