3.4.3 genetic diversity can arise as a result of mutation or suring meiosis

Question 1

there are two types of mutation that cause the quantity or structure of DNA to cahnge what are they

Answer 1

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.

Question 2

what are the three types of gene mutaitons

Answer 2

base substitutiojn
base deletion
base insertion

Question 3

what does conservative/ non-conservative mean in the context of gene mutation

Answer 3

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.

Question 4

what effects does :
silent mutations have

Answer 4

those that do not alter the amino acid sequence of the polypeptide even through the nucleotide sequnce has changed

aka

Question 5

what effects does :
missense mutations have

Answer 5

those that do alter the amino acid sequnce of the polypeptide

these are normally non-conservative or conservative

Question 6

what effects does :
nonsense mutations have

Answer 6

involve a change from a normal codon to a termination codon. they cause the synthesis of the polypeptide to be terminated

Question 7

what can base deletion and insertion cause

Answer 7

a framshift which can then lead to a non functional protein

Question 8

what is sickle cell anamia and how is it caused

Answer 8

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

Question 9

what is the substatution effect

Answer 9

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.

Question 10

what is the fram shift effect

Answer 10

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.

Question 11

what is mutagenic agents and list some

Answer 11

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

Question 12

why would a mutation in a gamete have more of a profound biological consequence than a mutaion in a somatic cell?

Answer 12

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

Question 13

what protects the coding strand (sense strand) during transcription

Answer 13

antisense strand protects the sense strand and cannot code for mRNA

Question 14

descrtibe the process of mieosis and draw it out and compar with a sourse

Answer 14

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

Question 15

what is crosing over and when does it happen in mieosis

Answer 15

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

Question 16

what is independant segrigation and when does it happen is meiosis

Answer 16

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

Question 17

what is random fertilisation

Answer 17

thurther genetic combinations are increases through the random pairing of male and female gametes at fertilisation

Question 18

info card read and recite

Answer 18

when chromasomes undergo crossing over they form a chiasma , and then anything PAST that point change with its partner bivalent arm

Question 19

what is non disjunction

Answer 19

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

Question 20

what is the definition of :
diploid

Answer 20

Diploid – a term applied to cells that have two sets of chromosomes

Question 21

what is the definition of :
haploid

Answer 21

Haploid – a term referring to cells that contain only a single copy of each chromosome eg sex cells (gametes)

Question 22

what is the definition of :
Chromosome

Answer 22

Chromosome – a thread like structure made of protein and DNA by which hereditary information is physically passed from one generation to the next.

Question 23

what is the definition of :
Chromatid

Answer 23

Chromatid – one of two strands of a chromosome that are joined together by a single centromere prior to cell division.

Question 24

what is the defintion
homologous

Answer 24

Homologous – a pair of chromosomes, one maternal and one paternal that have the same gene loci and therefore determine the same features.

Question 25

what is the definition of :
gene

Answer 25

Gene – a length of DNA that codes for a polypeptide

Question 26

what is the definition of :
allele

Answer 26

Allele – one of a number of alternative forms of a gene.

Question 27

what are homologous chromasomes

Answer 27

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)

Question 28

what is a locus

Answer 28

a spesific place for a gene

Question 29

What are chromatids?

Answer 29

One of the two copies of a chromosome that are joined by a single centromere prior to cell division

Question 30

what happens in meiosis 1

Answer 30

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.

Question 31

what happens during prophase 1

Answer 31

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.

Question 32

what happens during metaphase 1

Answer 32

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

Question 33

what happens during anaphase 1

Answer 33

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

Question 34

what happens during telophase 1

Answer 34

Spindle fibre breaks down

In animal cells cytokinesis occurs to give two haploid cells

Many plant cells go straight into prophase II

Question 35

what happens during Prophase II/metaphase II

Answer 35

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

Question 36

what happens during anaphase 2

Answer 36

The centromeres divide

The spindle fibres contract to pull the two chromatids to the opposite poles

Question 37

what happens during telophase 2

Answer 37

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

Question 38

what is the Importance of Meiosis

Answer 38

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

Question 39

to find the possbile combination of combinations of daughter cells what is the formula

for a single gamte

Answer 39

2^n

n= number of pairs of homologous chromasomes

Question 40

to find the number of combinations of zygote when two gamets are involved

give the formula

Answer 40

(2^n)^2

n= number of pairs of homologous chromasomes