Week 10 Flashcards
What are the two theories of how eggs can generate whole organisms?
Preformationism and Epigenesis
What is preformationism?
Adult is preformed in egg or sperm, all organisms were generated at the same time
What is epigenesis?
Organisms are progressively built anew in each generation
Aristotle supported this
Which cells contain the complete genome? and what does this mean?
The nucleus of the zygote and every cell that is produced during ontogenesis contains the complete genome.
Every cell, somatic and germ line cells can be used to make a new animal - as in Dolly sheep where a somatic cell was used.
what is differentiation?
Making cells different by regulation of gene expression
In broad terms how are the different cell types established during development?
the genotype contains a developmental programme that unfolds and results in the expression of different sets of genes in different cell types
what are 5 factors that control gene expression?
chromatin structure initiation of transcription RNA processing initiation of translation post-translational modifications
Genes within highly packed ____ are usually not expressed. Why?
heterochromatin
Because dont have access to the genes, it is not naked.
What can affect whether a gene is transcribed?
the location of the gene promoter relative to nucleosome
sites where DNA is attached to the chromosome scaffold or nuclear lamina
Chemical modifications to histones and DNA influence both chromatin structure and gene expression = 3 types?
acetylation
methylation
phosphorylation
What is methylation?
The addition of methyl groups to certain bases in DNA, is associated with reduced transcription in some species. The methylation pattern is past on to daughter cell
what 2 things are used in genomic imprinting?
DNA methylation and histone modifications
What is genomic imprinting?
process by which epigenetic modifications regulate expression of either the maternal or paternal alleles of certain genes at the start of development
What is epigenetic inheritance?
Epigenetic modifications can be passed on to emerging cells during development, however, epigenetic tags are removed in germ line cells.
Some epigenetic tags avoid reprogramming and are inherited by the next generation - this is epigenetic inheritance
Example of epigenetic inheritance in plants?
When wild radish plants are attacked by caterpillars they produce distasteful chemicals ad grow protective spines. The offspring of the caterpillar damaged plants also develop these defences, even in the absence of caterpillars.
(no nucleotide changes)
INDIRECT EVIDENCE
Example of epigenetic inheritance in invertebrates?
waterfleas respond to predators by growing helmets. This defensive trait is inherited by the offspring and maintained in the absence of predators over several generations. Not known the substance which induces the helmet growth but something the preadtor does.
INDIRECT EVIDENCE
Example of epigenetic inheritance in mammals?
Rats.
Feeding vinclozolin to pregnant rats causes life long changes in the pups. As adults, the offspring have low sperm counts, among others. this trait is maintained over 3 generations.
DIRECT EVIDENCE - the sperm DNA had an abnormally high level of methyl tags.
Regulation of transcription by transcription factors. How?
Chromatin modifying enzymes provide initial control of gene expression by making a region of DNA either more or less able to bind the transcription machinery.
Transcription factors then control levels of transcription
What is a gene?
a section of DNA that contains the information required for the production of a biologically active RNA molecule
What is the organisation of a typical eukaryotic gene?
most eukaryotic genes have control elements, segments of noncoding DNA that help regulate transcription by binding certain transcription factors.
What is critical to the precise regulation of gene expression in different cell types?
control elements and the transcription factors they bind
Which control elements are located close to the promoter?
proximal control elements
What are enhancers?
groups of distal control elements
where are distal control elements located?
far away from a gene or even located in an intron