4A DNA, RNA and Protein Synthesis Flashcards
What is Nondisjunction?
Nondisjunction is where chromosomes fail to segregate during meiosis
What can Nondisjunction be due to?
A failure of homologous chromosomes to segregate in meiosis 1 or a failure of sister chromatid to segregate in meiosis 2
What happens if a gamete with the incorrect no. chromosomes is fertilised?
The resulting embryo may not be viable and might die or else an individual may be born with a genetic disease
What are the two ways which meiosis is a source of variation?
- Independent Assortment
2. Crossing Over
What is a homologous chromosome?
Homologous chromosomes are a pair chromosomes, one maternal and one paternal, that have the same gene loci
What is an allele?
An allele is a form of a gene
What is a gene locus?
A gene locus is a fixed position on a chromosome that is occupied by a gene
When does crossing over occur?
Phase 1 of meiosis
Why does crossing over happen?
Crossing over occurs as piece of chromatid from one chromosome touches a piece of chromatid from the homologous partner.
What happens during crossing over?
The chromatids of each pair become twisted around each other (crossing over). This creates tensions and causes portions of the chromatids to break off.
What is recombination?
After crossing over, the broken portions might then rejon with the chromatids of its homologous partner
What does recombination result in?
The exchange of genetic material between homologous chromosomes
–> Each homologous chromosome has a different combo of alleles compared to what they had originally
Why do chromosomes stay the same length in crossing over?
The genetic material is exchanged between homologous chromosomes and at the same gene loci, no genetic material is lost
In meiosis, how many chromosomes from each homologous pair enters a gamete?
One
Which of the two chromosomes from each pair enters a gamete is dependant on what?
Dependent on how the homologous pairs line up at the equator of the cell ( THAT MAKES BLOODY SENSE DONT IT)
Shut up Dan
In metaphase 1, how do chromosomes align along the equator of the cell?
Chromosomes randomly align along the equator of the cell (independent assortment)
What is independent assortment?
Chromosomes randomly align along the equator of the cell in metaphase 1
What does the random alignment of chromosomes actually refer to?
The way in which one homologous pair lines up at the equator in meiosis is independent of how any other pair aligns
How does the random alignment of chromosomes affect the chromosomes in daughter cells?
The combo of chromosomes of maternal & paternal origin that go into the daughter cell at meiosis 1 is a matter of chance
(independent segregation)
What do you need to know to calculate the number of possible combinations in the gametes?
The haploid number –> 2^n where n is the haploid no.
What is cross fertilisation?
Where the female and male gametes fuse
What can cause further variation other than meiosis?
Cross fertilisation
What mixes up allelic combination?
Independent assortment and crossing over during meiosis and the random nature of fertilisation
What is genetic novelty?
New variations of alleles or genes produced