Gene Inheritance Flashcards
What happens to DNA that allows for inheritance of genes?
It’s replicated
What are the stages of the cell cycle?
- G 1
- S
- G 2
- M
At what stage of the cell cycle is division happening?
M
What happens at G 1 ?
Cell content replication
What happens at S?
DNA replication
What happens at G 2 ?
Double check and repair
Where are the cell cycle checkpoints?
At the end of G 1 and G 2
What can happen if something is found to be wrong at one of the cell cycle checkpoints?
Can decide to stop and perform autolysis
What is the part of the cell cycle where division is not happening known as?
Interphase
What is G 0 ?
A stage outside of the cell cycle where the cell is not dividing anymore
What is the model for DNA replication called?
Semi-conservative DNA replication
Why is semi-conservative DNA replication used?
Best way to make sure that an accurate copy of the old strand is made
What is DNA replication catalysed by>?
DNA polymerase
Where does DNA polymerise extend from?
3’ end
How is DNA extended?
Get a nucleotide with a complementary base to the template strand, which then makes a phosphodiester bond with the OH on the 3’ end of the primer
What happens to the DNA double helix in semi-conservative replication?
It is seperated
How is the DNA replication reaction carried out?
Stepwise
What is the DNA replication reaction driven by?
Pyrophosphate hydrolysis
In what direction is DNA chain growth?
5’ to 3’
What are the stages of DNA replication in prokaryotes?
- Starts with circular ‘naked’ chromosome
- Initiation
- Elongation
- Termination
What happens in the initiation stage of DNA replication of prokaryotes?
Separating of the double strand in both directions
What is the result of DNA replication in prokaryotes?
2 identical bits of plasmid DNA
What is the first step in initiation of DNA replication?
Recognition of origins of replication
What is meant by the origins of replication?
The DNA sequence that tells the cellular machinery to start there
What does initiation require?
- The recruitment of DNA polymerase, plus other specific proteins
- ‘Kickstart’ by primase
Why does initiation require a ‘kickstart’ by primase?
As DNA polymerase can only extend from 3’ end
What is the main feature of elongation?
Moving replication forks
What needs to happen to the double helix in elongation?
It needs to be unwinded
What unwinds the double helix?
Helicase
Why does the DNA helix need to be unwinded?
To open up new areas where DNA polymerase can bind
What does the fact that DNA polymerase extends from 3’ ends only lead to?
A continuous leading strand, and a discontinuous lagging strand
What does the discontinuous lagging strand produce?
Okazaki fragments
What joins the Okazaki fragments?
DNA ligase
When is DNA replication terminated?
When replication forks bump into one another
What must happen to finish DNA replication?
DNA ligase joins the lagging and leading strands
Does DNA replication start at the end of the molecule?
No
Where do DNA replication forks start?
From specific positions
Do DNA replication forks all go in the same direction?
No
How many DNA molecules are there in a chromosome?
1
How many DNA molecules are there in a replicated chromosome?
2
Why are chromosomes still so called when they are being replicated?
So the chromosome number stays the same, even when dividing
What does the classical X shape of chromosome consist of?
2 identical DNA molecules, as it has been replicated
What are chromatid telomeres?
Sequences that protect DNA from degredation
What are the different types of chromosomes?
NAME?
What is metacentric?
When the centromere is exactly central
What is submetacentric?
When the centromere is slightly off centre
What is acrocentric?
When the centromere is almost at the end of the chromatid
What is telocentric?
When the centromere is right at the end of the chromatid, so there is no p arm
Do humans have all types of chromosomes?
Not telocentric
What does one replicated chromosome consist of?
2 sister chromatids
What is mitosis?
The cell division for somatic cells
What does mitosis produce?
2 identical daughter cells
What does each daughter cell produced from mitosis have?
The same chromosome content as the parental cell
How many mitotic rounds are there during development?
~50
For what tissues is mitotic growth necessary?
- Epidermis
- Mucosae
- Bone marrow
- Spermatogonia
What are the stages of mitosis?
NAME?
What happens during prophase?
The nuclear membrane disintegrates
What happens during prometaphase?
Spindles connect to the chromosome
What are the spindles formed in prometaphase called?
Kinetochore spinde fibres
Where do spindle fibres connect to the chromosomes?
At the kinetochore
What is the kinetochore?
A complex of proteins that binds to the centromere
What happens in metaphase?
Chromosomes line up at the metaphase plate
Where is the metaphase plate?
In the middle
In what fashion to chromosomes line up?
Randomly
What happens to the spindles in metaphase?
They connect to either end of the cell
What happens in anaphase?
Chromosomes split and are pulled towards opposite ends of the cell
What happens in telophase?
NAME?
What is meiosis?
Specialised cell division for germ line cells
What do germ line cells eventually produce?
Gametes
What does meiosis produce?
4 non-identical cells
What does each cell produced by meiosis contain?
Half the chromosomal content of parental cells
What is one round of replication followed by in meiosis?
Two rounds of division called meiosis I and II
What reduction occurs in meiosis?
Diploid (2n) reduced to haploid (n)
What are the ultimate products of meiosis?
Egg and sperm
What happens in prophase I?
- Disintegration of nuclear membrane
- Homologous chromosomes pair up
What is the pairing up of homologous chromosomes dependant on?
Sequence
Why is it said that the pairing of homologous chromosomes is sequence dependant?
They find the same sequence
What do the chromosomes have when they pair up?
Paternal copy and maternal copy
What is the result of the chromosomes having a maternal and paternal copy when they pair up?
They are non-sister, and so have a slightly different DNA sequence
When does crossing over occur?
In late prophase 1
What happens in crossing over?
Non-sister chromatids cross over and swap DNA strands
What is the result of crossing over?
End up with DNA that has paternal and maternal DNA, as well as one chromatid that has completely paternal and one that has completely maternal
What happens in metaphase 1?
The chromosomes line up in the metaphase plate in pairs
In what order to the chromosomes line up in metaphase 1?
Randomly
What is the result of the random lining up in metaphase 1?
Random assortment of chromosomes
What happens in anaphase 1?
Each replicated chromosome goes to either end of the cell
What happens in telophase 1?
2 cells are formed
What happens to the 2 cells formed from telophase 1?
They go into meiosis II
What happens in prophase II?
The nuclear envelope disintergrates
What happens in metaphase II?
The chromosomes line up on the metaphase plate
What happens in anaphase II?
Chromatids split and are pulled to opposite ends of the cell
What happens in telophase II?
Both cells split into 2, producing 4 in total
What are the consequences of meiosis?
- Maintains constant number of chromosomes from generation to generation
- Generation of genetic diversity
How does meiosis generate genetic diversity?
NAME?
What is spermatogenesis?
Cell division to produce male gametes
What are the stages of spermatogenesis?
Spermatogonium (2n) → Primary spermatocyte (2n) → 4x spermatids (4 x n) → 4x mature sperm (4 x n)
So how many sperm come from each spermatocyte?
4
How long does spermatogenesis take ?
~48 days
What is oogenesis?
Cell division to produce female gametes
What are the stages of oogenesis?
Oognium (2n) → Primary oocyte (2n) → 4x polar bodies (4 x n) → 1 mature ovum (n) leaving 3 polar bodies remaining
What comes from 1 oocyte?
1 egg and 3 polar bodies
What is the length of oogenesis?
12-50 years
What happens if crossing over doesn’t occur?
Both of the pair may go into the same cell, resulting in an empty cell, therefore an empty gamete, and the other gamete would have 2 copies of the chromosome
What is the error rate for meiosis?
~3 in 10 are mis-segregated
What are the consequences of faulty meiosis?
- Cause of 1/3 of all identified miscarriages
- Infertility
- Leading cause of mental retardation
