3.4.3 genetic diversity can arise as a result of mutation or suring meiosis Flashcards
3.4.3 genetic diversity can arise as a result of mutation or suring meiosis
there are two types of mutation that cause the quantity or structure of DNA to cahnge what are they
Gene (point ) mutation – a change in one or more nucleotides bases or a change in the sequence of bases, caused by errors in DNA replication.
Chromosome mutation – a change in the number or structure of chromosomes, caused by errors in cell division.
what are the three types of gene mutaitons
base substitutiojn
base deletion
base insertion
what does conservative/ non-conservative mean in the context of gene mutation
conservative - means that the amino acid has changed however the property of that amino acid e.g hydophilic has not changed
non-conservative - means that the amino acid has changed and also the property has changed as well.
what effects does :
silent mutations have
those that do not alter the amino acid sequence of the polypeptide even through the nucleotide sequnce has changed
aka
what effects does :
missense mutations have
those that do alter the amino acid sequnce of the polypeptide
these are normally non-conservative or conservative
what effects does :
nonsense mutations have
involve a change from a normal codon to a termination codon. they cause the synthesis of the polypeptide to be terminated
what can base deletion and insertion cause
a framshift which can then lead to a non functional protein
what is sickle cell anamia and how is it caused
Sickle Cell Anaemia – a genetic disease caused by a base substitution
fects on blood flow. The sickle shaped cells cannot carry as much oxygen and get caught in the capillaries cutting off the blood supply to the organs
what is the substatution effect
The significance of the difference depends on the role of the amino acid that’s changed. If it is important in forming bonds that determine the tertiary structure of the final protein, then the replacement amino acid may not form the same bonds. The protein may then be a different shape and therefore not function properly. For example, if the protein is an enzyme then its active site may no longer fit the substrate.
If the new triplet still codes for the same amino acid then the mutation will have no effect. This is one of the advantages of the degenerate code.
what is the fram shift effect
So called because they shift the way that the sequence is read.
Caused by insertions or deletions of bases.
Since mRNA is translated 3 nucleotides at a time insertions or deletions that do not involve multiples of three change how all of the mRNA nucleotides down stream of the mutation are translated.
Almost always result in a non functional protein.
what is mutagenic agents and list some
Can increase the rate of gene mutation:
Uv radiation
X-rays
cigarette smoking
nitrate and nitrate preservatives
barbecuing
benzoyl peroxide - common product in acne products
human papillomavirus - sexually transmitted virus
helicobacter pylori- bacteria spread through contaminated food
why would a mutation in a gamete have more of a profound biological consequence than a mutaion in a somatic cell?
effects all cells in body, which will effect the protein production which causes a non viable embrio
aslo somata cells (all cells but gamates) have introns , so mutations there would have zero effect while in a gamate it will as all genes are switched on
what protects the coding strand (sense strand) during transcription
antisense strand protects the sense strand and cannot code for mRNA
descrtibe the process of mieosis and draw it out and compar with a sourse
interphase 1
prophase 1 :
condensation
centrioles move to poles
cross over causing in a bivalent arms
recombination
diploid
metaphase :
line in the middle next to there homologous pair
cross over at chiasma
recombination
anaphase :
making a haploid cell moves the sister chromasomes aside
telophase and cytokinesis :
formation of two daughter cells with haploid number of chromasomes
prophase 2 —> cytokinesis 2
just regular mitosis but with haploid number of chromasomes
what is crosing over and when does it happen in mieosis
it happens during prophase 1
2 sister chromastids cross over each other and join at the chiasma , they then do reformation of genes at spesific loci , causes cariaty and more able to survice
what is independant segrigation and when does it happen is meiosis
metaphase 1
they live up at the equator , it is compleatly random, they then seperate
therefor one gamate could have all the chromasomes from dad or mum
what is random fertilisation
thurther genetic combinations are increases through the random pairing of male and female gametes at fertilisation
info card read and recite
when chromasomes undergo crossing over they form a chiasma , and then anything PAST that point change with its partner bivalent arm
what is non disjunction
Changes in the number of individual chromosomes
Resulting from homologous pairs of chromosomes or sister chromatids failing to separate during mitosis or meiosis. Known as non disjunction.
for example n-1 or n+1
what is the definition of :
diploid
Diploid – a term applied to cells that have two sets of chromosomes
what is the definition of :
haploid
Haploid – a term referring to cells that contain only a single copy of each chromosome eg sex cells (gametes)
what is the definition of :
Chromosome
Chromosome – a thread like structure made of protein and DNA by which hereditary information is physically passed from one generation to the next.
what is the definition of :
Chromatid
Chromatid – one of two strands of a chromosome that are joined together by a single centromere prior to cell division.
what is the defintion
homologous
Homologous – a pair of chromosomes, one maternal and one paternal that have the same gene loci and therefore determine the same features.
what is the definition of :
gene
Gene – a length of DNA that codes for a polypeptide
what is the definition of :
allele
Allele – one of a number of alternative forms of a gene.
what are homologous chromasomes
Pairs of chromosomes carrying alleles of same gene loci and therefore determine the same features.
One of the pair is derived from the female parent (maternal chromosome), one is derived from the male parent (paternal chromosome)
what is a locus
a spesific place for a gene
What are chromatids?
One of the two copies of a chromosome that are joined by a single centromere prior to cell division
what happens in meiosis 1
This is the reduction division when the homologous chromosomes separate, the number of chromosomes in the nucleus halves (2 to 1 in this diagram)
But the DNA content does not half because each chromosome is still composed of two chromatids.
Two daughter cells are made.
what happens during prophase 1
DNA condenses and chromosomes become visible with chromatids in the well known x shape.
If centrioles present they move to poles of cells and microtubules begin to radiate from them forming asters.
This leads to the formation of spindle fibres.
Homologous chromosomes pair up forming Bivalents. Each bivalent consists of 4 chromatids, made up from 2 chromosomes that have replicated themselves
Chromatids wrap around each other and partially repel each other. They stay attached at certain points called chiasmata.
Crossing over occurs by breaking of maternal and paternal DNA which is then interchanged.
At the end of prophase the nuclear envelope disintegrates and the nucleolus disappears.
what happens during metaphase 1
Bivalents move to the equator
Chromosomes attach to the spindle at Centromeres
Maternal and paternal chromosomes are arranged randomly (Random Assortment)
This produces new genetic combinations
what happens during anaphase 1
Spindle fibres contract pulling chromosomes in bivalents to opposite poles
Each pole receives only one chromosome from each homologous pair thus achieving a random mixture of maternal and paternal chromosomes
Nuclear envelope reforms around each group of haploid chromosomes
what happens during telophase 1
Spindle fibre breaks down
In animal cells cytokinesis occurs to give two haploid cells
Many plant cells go straight into prophase II
what happens during Prophase II/metaphase II
A new spindle forms at right angle to the first
Each of the pair of sister chromatids (chromosomes) move to the equator of the cell
Each chromosome attaches to the Spindle fibre by the centromere
what happens during anaphase 2
The centromeres divide
The spindle fibres contract to pull the two chromatids to the opposite poles
what happens during telophase 2
The chromosomes lengthen becoming chromatin
The spindle fibre breaks down
Nuclear membrane reforms
Cytokinesis occurs resulting in 4 haploid cells being formed which show genetic variation
what is the Importance of Meiosis
meiosis during gamete formation
When gametes fuse the zygote retains diploid number of chromosomes
Meiosis introduces genetic variation
Crossing over at prophase 1 – different forms of same allele exchanged
Independent assortment of homologous chromosomes on the spindle in metaphase 1 leading to random separation at poles
Genotype of one parent mixed with that of another parent when haploid gametes fuse to form zygote
to find the possbile combination of combinations of daughter cells what is the formula
for a single gamte
2^n
n= number of pairs of homologous chromasomes
to find the number of combinations of zygote when two gamets are involved
give the formula
(2^n)^2
n= number of pairs of homologous chromasomes
