Midterm 1 - Notes 6 Flashcards
What percentage are protein coding regions in the human?
1.5%
How are genes placed throughout the body
They are scattered
- flanked and interrupted by non-coding DNA
- very messy
Are coding regions conserved or not conserved?
Conserved
- non coding regions are not
How % do introns make up of the human genome?
20%
The vast majority of Euk. have what?
Has no known function
- half is unique sequences (introns)
- other half is repeated sequences (junk DNA)
What % of the human genome is transcribed?
75%
What kind of change is histone modification?
Epigenetic change
Repetitive sequences (3)
- Long, but low copy
- Short, but many local repeats
- Intermediate length, scattered throughout the genome
What does 80% of the human genome made up of? (4)
- Transcribed
- Associated with modified histones
- Found in open chromatin areas
- Binding transcription factors
What do most Euk. have a large number of?
Transposons
Transposons
A chromosomal segment that can undergo transposition
What is another name for transposons?
Jumping genes
What can lead to duplication of transposons? (2)
- Excison
2. Reintegration
What are the 2 major categories of transposons?
- Tranpose as DNA (DNA transposons)
2. Transpose via RNA intermediate (retro-transposons)
Transpose as DNA (4)
- Involves transposase
- Cut and paste mechanism
- cut out a piece of DNA and reverses it and makes it back to intermediate - Can intergrate elsewhere into the genome at a random integration
- Can become a stable part of it
Transposase
Is an enzyme that binds to the end of a transposon and catalyzes the movement of the transposons to another part of the genome by a cut and paste mechanism or replicative transposition mechanism
Transpose via RNA intermediate (retro-transposons) (3)
- Involves reverse transcriptase and integrase
- Copy and paste mechanism
- Causes an amplification and duplication
What was the study of discovery of transposons done on?
Maize
Gene C
Necessary for kernel colour development
What was c/c phenotype?
White kernels
- mutant
What was C/C phenotype?
Purple kernels
- wildtype
What kind of markers were used in the maize study?
Morphological markers
What 2 things can happen when an Ac (a dominant allele) is present in c/c?
- High frequency of revertants back to C/c
- Revertants can affect whole kernel or only sectors
- the earlier in development reversion happens, the larger the wildtype sector
What caused the mutation in C-gene?
Integration of another genetic element called Ds
What is reversion caused by?
Dissociation of Ds from C-locus
What was the advantage to using maize?
Each kernel contains a seedling from one plant that came from the true parents
When can Ds only move?
When Ac is present
What can Ds and Ac both do?
Can change location in the genome
What are Ds and Ac?
Transposons
What element is Ds?
Non-autonomous
What element is Ac?
Autonomous
Excision of Ds during kernel development causes what?
Reversion to wildtype phenotype in affected sectors
What does Ds not encode for?
Proteins for movement
Can Ds be moved?
Yes
What does the insertion of Ds into the genome disrupt? (2)
- The C gene
2. Effects kernel colour
What does Ds cause when it moves?
A mix pigment of mutant and wildtype
What did Barbar McMlintock discover?
Jumping genes and transposition
- 1940-1950s
When did Barbar receive her nobel prize?
1983
What are 4 reasons why Barbar did not receive her prize till 1983?
- Peer discrimination
- eccentric and a women - Study seemed only limited to maize
- but then was expanded to bacteria - Only fully appreciated when it came on a larger scale
- MAIN REASON = she miss interpreted her results as a regulatory mechanism, not as a random process
Ds integration into C
A repressor of gene C activity
Ac
A repressor of the repressor
- eg. an activator of gene C
What was Barbars hypothesis? (3)
- If Ds located away from target gene = no repression
- Ac activates Ds translocation into target gene = repression
- Ds translocation reversible by Ac action (dissociation) = no repression
- all to do with gene control mechanism
Did Barbars hypothesis hold true?
NOPE
