3.4.3 Gentic Diversity can arise as a result of mutation or during meiosis Flashcards
Define mutation.
Any change to the DNA of an organism
Either the quantity of DNA or the base sequence
When do most mutations occur?
DNA replication
Cell division
Define gene mutation.
A change in the base sequence of the DNA of an organism
Arise through mistake in DNA replication
Define chromosome mutation.
A change in the number or structure of whole chromosomes
Arise during cell division
If mutation occurs in a body cell will it be passed onto the offspring of that individual?
No
Only passed on from faulty gametes
In which case all the offsprings cells would mutate
When does mutation of gametes occur?
Meiosis
How does a change in base sequence effect the protein made?
Causes change in mRNA base sequence
Changes amino acid sequence
This causes changes in potentially any bond
This changes the tertiary structure of the proteins
It is entirely different now
Define substitution mutation.
Where a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
Define addition mutation.
The insertion of an extra base
Define deletion mutation.
The removal of one base
Define duplication mutation. (not on spec)
Addition of a complete codon
Define inversion mutation. (not on spec)
Where the code is read backwards
Define frame shift.
Where all subsequent codons are altered
When does frame shift have the biggest effect?
The close to the start of a gene it occurs
Define non-sense mutation.
Results in a stop codon
Poly-peptide production stops prematurely
What is a mis-sense mutation?
Different amino acid is coded for
Effect is dependant of the function of the amino acid
How would a mis-sense mutation effect an enzymes function?
The active site would no longer be complementary
Can’t form enzyme-substrate complexes
What is a silent mutation?
The substitutes base still codes for the same amino acid
No effect
Name some key causes of mutations?
Ionising radiation Inherited genetic disorders Random Increased likelihood with age Carcinogens (tar in cigs) Alcohol Infections (HVB)
What is product of meiosis?
4 genetically variable daughter cells
Simply describe meiosis.
Parent cell (diploid)
DNA replicates
Homologous pairs separate (meiosis 1)
Chromatids separate to form 4 daughter cells
Each contains half the number of chromosomes of the parent cell
How many chromosomes does a daughter cell of meiosis contain?
Half that of the parent
What must occur in the parent cell before meiosis 1 can occur?
DNA replication
Why is it important that the chromosome number is halved in meiosis?
The diploid number is restored at fertilisation
If gametes weren’t haploid, the chromosome number would double with each new generation
List all the ways in which meiosis and sexual reproduction lead to variation.
Crossing over
Independent segregation of homologous chromosomes
Independent segregation of chromatids
Random fusion of gametes (only sexual reproduction)
What process could cause blocks of genes to swap between chromosomes?
Crossing over
What stage of meiosis does crossing over take place in?
Metaphase of meiosis 1
Explain how crossing over occurs?
Homologous chromosomes line up on the equator in metaphase of meiosis 1
They sometimes get tangled
The chromosomes are pulled apart in anaphase of meiosis 1
Blocks of genes may get swapped between chromosomes
What are the basic stages that meiosis and mitosis share?
Doubling of DNA
Assembly in centre of cell
Separation of chromosomes
Cell division
How many divisions occur in meiosis?
2
How many divisions occur in mitosis?
1
How many daughter cells are produced in meiosis?
4
How many daughter cells are produced by mitosis?
2
Is there variation in the daughter cells produced by meiosis?
Yes
Genetically variable
Daughters have half the number of chromosomes (haploid)
Is there variation in the daughter cells produced by mitosis?
No
Genetically identical
Full set of chromosomes (diploid)
List the phases of Meiosis.
Interphase 1 Prophase 1 Metaphase 1 Anaphase 1 Telophase and cytokinesis Prophase 2 Metaphase 2 Anaphase 2 Telophase 2
What occurs in interphase 1?
Growth
Synthesis of organelles
DNA replication
What occurs in prophase 1?
Condensing chromosomes Homologous pairs forming Crossing over Nuclear membrane disintegrates Spindle formation
What happens at metaphase 1?
Homologous chromosomes line up on the equator
Spindle fibres starch to each centromere
Independent assortment
What happens in anaphase 1?
Spindle fibres contract (which leads to..) Separation of homologous chromosomes 2 sister chromatids Independent segregation Chromosome number halved
What happens at telophase 1?
Half the number of chromosomes at each pole
Sometimes chromosomes unravel
2 haploid daughter cells
What happens at prophase 2?
Spindle fibres form
Cell membrane disintegrates
What happens at metaphase 2?
Chromosomes line up on equator
Spindle fibres join at the equator
What happens at anaphase 2?
Spindle fibres contract at the poles
Sister chromatids move towards poles
What happens at telophase 2?
4 daughter cells containing two chromatids
What does non-disjunction mean?
The failure of chromatids to separate at anaphase of meiosis 2
Results in one too many/one too few chromosomes
What condition would having an extra chromosome 21 result in?
Down’s syndrome
What is a tetrad?
Two homologous chromosomes together
