Jones (extranuclear inheritance) Flashcards
1
Q
In what organisms are chloroplasts present?
A
- green plants
- photosynthetic protists
- blue-green algae
2
Q
What are the diff parts of a chloroplast?
A
- DIAG*
- OM and IM are phospholipid bilayers
- stroma = fluid containing DNA and ribosomes
- thylakoids = membrane bound structures, w/ lumen containing chlorophyll
- grana = stacks of thylakoids
3
Q
What are the characteristics of cpDNA?
A
- ds and circular genome
- majority of species 100-225kb
- low GC content (36%), compared to 64% in nucleus
- genes arranged into operons (like proks)
- contains introns (unlike proks)
- copy no. varies –> 10-1000 copies per chloro and up to 50 choros, in all species
- assoc w/ thylakoid membrane or IM
4
Q
What does cpDNA encode?
A
- subunits from PS1 and PS11 (also parts encoded by nucleus)
- ribosomal proteins
- pols
- tRNAs and rRNAs
5
Q
What does cpDNA contain?
A
- 2 inverted repeats of varying length (10-76kb) = most variable part between species
- long single copy region
- small single copy region
6
Q
How are chloroplasts inherited, and why?
A
- during cell division
- highly dynamic and divide by binary fission
- rep before chloro division (mol mechanisms vary between species)
7
Q
What result would a white leaf/stem mutation have?
A
- lethal
- no chlorophyll, so can’t photosynthesise
- can germinate, but then dies
8
Q
How did Correns study variegation in Mirabilis jalapa, and what did he observe?
A
- some plants white, some green and some mixed (variegated)
- utilised fact plants can have stems of diff colours and carried out self fertilisations to see how inherited
- saw if egg from white branch all progeny white and if egg from green branch all progeny green, regardless of phenotype of branch providing pollen
- when variegated phenotypes provided egg, phenotype of progeny could be white, green or variegated
- random segregation in every cell division, so female gametes can be derived from cells which are homoplasmons or heteroplasmons
9
Q
What is homoplasmy and heteroplasmy?
A
- DIAG*
- heteroplasmon = combo of chloros containing WT and mutant DNA (due to foreign pop coming in or mutation
- homoplasmon = all copies in organelle are identical
10
Q
What was Correns conclusion?
A
- inheritance of leaf/stem colour is “non-Mendelian” and maternal
11
Q
What do we know now about Correns experiment?
A
- cpDNA mutation leads to loss of chlorophyll
- cpDNA inherited from egg only = maternal inheritance
- variegation results from WT and mutant tissue
- indiv cells can contain mixture of WT and mutant chloros = heteroplasmon
12
Q
What is the maternal effect?
A
- maternal nuclear gene products (proteins and RNA) stored in egg (large w/ lots of cyto) and get transmitted to offspring following fertilisation
- these maternally encoded proteins can exert phenotypic effect on offspring, regardless of offspring genotype
- in some species, req for successful embryo dev, in others just changes certain aspects of phenotype
13
Q
How does shell coiling differ in Limnaea to most snail species?
A
- in most species all individuals share same coiling pattern
- Limnaea shells can be coiled in either direction
- -> dextral = right-handed (DD or Dd)
- -> sinistral = left handed (dd)
14
Q
How was Limnaea peregra studied to show its an example of the maternal effect?
A
- DIAG*
- maternal effect observed in gens II and III
- maternal parent genotype controls offspring phenotype
- spiralling of shell happens v early in fertilisation, so permanent phenotype determined due to maternal phenotype
15
Q
What are 2 other examples of maternal effect?
A
- Ephestia kuehniella –> maternal effect dictates pigmentation of larvae, but mutation starts to become visible in adults, as cytoplasmic proteins diluted and become spread out
- Drosophila –> maternal effect impacts on genes related to embryonic dev and allows homozygous mutants to dev normally
16
Q
What is the structure of mito?
A
- IM, IMS and OM
- IM contains OXPHOS proteins
- cristae = folds in IM
- matrix contains enzymes, DNA and ribosomes
17
Q
What are the characteristics of mtDNA?
A
- ds closed circle genome
- generally smaller than cpDNA (16-18kb in mammals, 75kb in yeast, up to 367kb in plants)
- introns rare –> present in some larger genomes, eg. yeast
- encodes ETC proteins (also partly encoded by nucleus)
- D loop is largest noncoding part and part most variable between species
- vertebrates have multiple copies, plants have more, but varies lots between species
18
Q
How was Neurospora crassa used to look at maternal inheritance of mtDNA?
A
- slow growing mutant strain (= poky) has impaired mito function
- 2 mating types = A and a, fuse together, either can be maternal, dep on which parent had poky genotype
- results of crosses between WT and poky strains revealed maternal inheritance
- offspring either all poky or all WT, dep on which parent had poky genotype
19
Q
How is mtDNA inherited?
A
- generally maternally in most species
- yeast don’t follow this
20
Q
Why is yeast a useful model organism for looking at mtDNA?
A
- facultative anaerobe, so can gen energy through glycolysis, so can survive loss of mito function
- can still grow, but smaller, as not respiring as efficiently = petites
21
Q
What causes petites in S. cerevisiae?
A
- deficiency in cellular resp due to defective ETC –> ETC proteins encoded in mito and nucleus so could be mutation in either genome
22
Q
What diff results came from crossing haploid petite w/ haploid normal, and what conclusions can be drawn from these?
A
All prod diploid zygote, then sporulation and meiosis prod following acrospores:
- segregational –> half petite and half normal, ∴ petites can be from mutations in nuclear DNA
- neutral –> all normal, ∴ inheritance of mtDNA bi-parental in yeast (both passing on mtDNA, so some WT from each is enough to prod WT)
- suppressive –> all petite, ∴ mutations can behave dominantly = preferential rep?
