Mat + Paternal genomes

Question 1

how do embryos take control of their own development

Answer 1

• first hours after fertilization, maternal factors in oocyte dictate early dvlpmnt. then zygotes genes take over
• maternal to zygote transition needs epigenetic reprogramming (changes to chromatin structure, and resetting methylation on genome)

Question 2

Explain the chromatin and methylation changes

Answer 2

C - chromatin in pronuclei take on open configuration then re-establishes local + global features

M - methyl marks removed. Paternal genome has rapid demethylation. Mat genome loses methylation passively after cell divisions

Question 3

explain the transcirption changes and cell fate determination.

Answer 3

T - mRna in oocyte slowly depletes over 1st week dvlpmnt. But zygotic genome has multiple activations so genes expressed early for embryonic organisation + cell fate.

F - by 4-8 cell stage, some cells express genes causing them to become embryonic lineage (forms fetus) Other cells express genes linked with extraembryonic lineage (placenta)

Question 4

what is parthenogenesis

Answer 4

** development without fertilisation (alternates with sexual repro)

some insects, haploid males develop from unfertilised eggs. Other parthenogenic organisms are diploid (oocyte genome replicated or Polar body not ejected.

• they lack microtubule organiser.

Question 5

Brief explain parthenogenesis in mouse (pic pg 7)

Answer 5

. If polar body not ejected, egg is diploid.
. But the parth fatuus is too small + placenta abnormal. (so degenerates till mid pregnancy)
. this happens too if foetus develops from zygote with 2 F pronuclei
. If zygote 2 M pronuclei, placenta big enough but foetus more underdeveloped.

Question 6

what is genomic imprinting and where does it occur

Answer 6

related to diff methylation of maternal / paternal genes in mammals.
In humans 9 chromosomes known to hv regions of genes that are imprinted.

Question 7

Briefly explain what genomic imprinting involves

Answer 7

> During meiosis methylation of Mat +Pat DNA equal. then ovaries all chromosomes methylated as maternal, testes paternal.

> Some imprinted gens, only 1 copy (m or P) of same gene need be active.
Error in imprinting may mean gene that is tuned off when shud be on (vice versa)
Result = activation of both genes/ blocking of them

Question 8

What is Prader Willi + Angelman syndrome. what causes it

Answer 8

PW - only maternal genes expressed
A - only paternal genes expressed

• defect = small section of chromosome 15 is missing/partially expressed

Question 9

what is chorioandenoma (abnormal fertilisation)

Answer 9

. type of uterine cancer, tumour origin = growing placenta without foetus.
. usually when a zygote doesn’t hv female pronucleus with diploid male.
CAN SPREAD TO OTHER PARTS - also called invasive hyatidiform mole

Question 10

Give the 2 mechanisms to develop uniparental chorioadenoma

Answer 10

> oocyte without viable chromatin fuses with 1 spermatazoon, male pronucleus then does replication

> oocyte without viable chromatin fuses with 2 spermatozoa, then 2 male pronuclei fuse + forms diploid nucleus.
** tumour tissue = pat genome (androgenic hydatidiform mole)

Question 11

how does Biparental chorioadenoma form

Answer 11

gene mutations that totally disturb imprinting mechanisms in embryo,

> maternally imprinted genes BLOCKED
paternally imprinted genes OVEREXPRESSED

• result = trophoblast (cells that normally turn into placenta) is overdeveloped, therefore foetus not developed.