developmental genetics

Question 1

how many cells and cell types are in humans?

Answer 1

around 10-50 trillion cells in one person
more than 200 cell types

Question 2

define totipotent, pluripotent and multipotent

Answer 2

toti = can form a whole new organism, including embryo and placenta

pluri = can form embryo and almost all cell types but not placenta/extraembryonic membrane

multi = can form fewer but still many cell types

Question 3

what term is given to the daughter cell of a stem cell that starts a new line?

Answer 3

progenitor cell

Question 4

cells from a

zygote
blastocyst
adult
organ

are what kind of stem cell/progenitor and can they self-renew?

Answer 4

zygote = totipotent
blastocyst = pluripotent they are embryonic stem cells and can self renew

adult = multipotent and can self renew

organ = can be limited, either a progenitor, committed progenitor (can’t renew) or a completely differentiated cell

Question 5

how are embryonic stem cells generated? what are these able to form and how can they be used?

Answer 5

extracted from the inner cell mass/ICM of the blastocyst

placed in a tissue culture, a small number of the cells start to divide

these stem cells are pluripotent and cannot form a trophectoderm or placenta

they can be used to produce transgenic mice for knockout experiments or introduction of a new gene, chromosomal rearrangements etc.. a lot can be investigated

Question 6

how do you get transgenic mice from embryonic stem cells?

Answer 6

your embryonic stem cells you’ll design to be homozygous dominant for something like fur colour and banding, e.g. a grey mouse with no banding AACC

you shove these embryonic stem cells in a mouse blastocyst, which you shove into a pseudopregnant mother that is homozygous recessive aacc, resulting in a chimeric 1st gen mouse, its cells will be either aacc from mother or AACC from embryonic stem cells, both were in the blastocyst

you want one cell type only, derived from your embryonic stem cells - so it should have whatever edits you’re investigating in all the cells of that mouse

to get this you cross your 1st gen with a homozygous recessive

this can give you homozygous recessive 2nd gen which you’re not interested in because it means the chimeric mouse contributed it’s maternal derived cells, the aacc, to this 2nd gen

the other option is the chimeric mouse contributed its embryonic stem cells, AACC, giving AaCc 2nd gen showing the dominant phenotypes so identifiable, you know no stripe grey mice have embryonic stem cell derived cells

Question 7

what are induced pluripotent stem cells?

Answer 7

made using Yamanaka factors - specific transcription factors that go in and make adult stem cells revert to pluripotent stem cells, so use no embryos and skirt the ethical issues

Question 8

somatic nuclei can be reprogrammed to be…

Answer 8

totipotent

Question 9

drosophila have how many chromosomes and genes?

Answer 9

4 pairs of chromosomes, X/Y, 2, 3, 4
16000 genes 140Mb long

Question 10

what can be observed between the organisation of larvae and adult drosophila?

Answer 10

both segmented, the segments can be mapped from the larvae to the adult, it’s consistent

Question 11

how is the body plan determined?

Answer 11

by a hierarchy of developmental genes

Question 12

zygotic genes vs maternal effect genes?

Answer 12

zygotic - still involved in segmentation, zygotic genes the phenotype of the individual is determined by it’s genotype

for maternal effect genes - the phenotype of the progeny is determined by the mother’s genotype

Question 13

if you are homozygous for a mutated maternal effect gene, does that automatically make you have the mutant phenotype?

Answer 13

no, as long as the mother was not homozygous for the mutant

Question 14

using an example, how do maternal effect genes (in drosophila) effect polarity?

Answer 14

transcripts (mRNA) from maternal effects genes can be seen in the unfertilised egg

Bicoid mRNA is tethered at the anterior pole and ensures head development

nanos mRNA is tethered at the posterior pole and determines that end’s formation (idk the ass)

even after fertilisation the proteins Bicoid and nanos are found in much higher concentrations at their respective poles

Question 15

what happens with mutations in zygotic and maternal effect genes that is different from homeotic mutants? use the ultrabithorax mutant as an example

Answer 15

maternal effect genes when mutated have a complete deletion of the respective structure, like if you mutate the mother’s Bicoid alleles, the progeny will not have an anterior end at all (which is lethal)

in homeotic genes the mutation usually means there is a replacement, e.g. in drosophila the wings form on the T2 segment, the ultrabithorax mutation is in a homeotic gene that causes the T3 (no wings) to be replaced with the T2 so that there are two T2 segments and two pairs of wings

Question 16

what is special about the arrangement of the homeotic genes?

Answer 16

their order on the chromosome reflects the body plan of where the genes are expressed

Question 17

what are homeotic genes?

Answer 17

they are transcription factors with a homeodomain (a specific DNA binding domain)
though all homeotic genes have this domain, having the domain doesn’t automatically make something a homeotic gene

Question 18

do humans have homeotic genes?

Are humans as likely to have phenotypic homeotic issues (like two sets of wings)?

Answer 18

yes, humans and mice have four hox complexes while drosophila has just the one, Hom-C

humans and mice, having four copies, are less likely to have homeotic phenotypic abnormalities tho it is not impossible - polydactyly for example

it’s much easier to happen in drosophila with only one copy (two alleles need to be mutated but stull more likely than humans and mice)

Question 19

why can homeotic mutations be harder to spot in plants?

Answer 19

could look like complete loss - a zygotic or maternal effect gene mutation

but really it’s a replacement - petals are not completely lost, but replaced by another organ

Question 20

what is pattern formation and why is it important?

Answer 20

the concept that positional information is used to give cells positional values in a coordinate system, which they interpret by developing in particular ways to give rise to spatial patterns

you need your organs in the right place/right size with respect to one another

Question 21

what is polarity?

Answer 21

basically you need your feet to develop at one end and your head at the other

a shark needs it’s dorsal fin on top