9. genetic diversity and adaptation

gene mutation

a change in the sequence of base pairs in a DNA molecule that may result in an altered polypeptide chains

DNA base sequence determines what

the sequence of amino acids that make up a protein

mutations lead to what

a change in the polypeptide that the gene codes for

most mutations don’t alter the polypeptide, or only slightly, because the genetic code is what

the genetic code is degenerate

3 types of mutation

insertion, deletion and substitution

insertion mutation

occurs when a nucleotide (with a new base) is randomly inserted into the DNA sequence

what does the insertion mutation change

the amino acid that would have been coded for by the original base triplet, frameshift changing the rest of the triplets

deletion mutation

occurs when a nucleotide is randomly deleted

substitution of nucleotides

occurs when a base in the DNA sequence is randomly swapped for a different base

what is different in substitution mutation compared to a deletion and insertion mutation

only the amino acid for the triplet is changed - no knock on effect

3 forms of substitution mutation

silent, missense and nonsense

silent (substitution) mutation

mutation does not alter the amino acid sequence of polypeptide (codons may code for same amino acid)

missense (substitution) mutations

mutation alters a single amino acid in polypeptide chain

example of a missense mutation

sickle cell anaemia

nonsense (substitution) mutation

the mutation creates a premature stop codon (signals for the cell to stop translation)

nonsense mutation example

cystic fibrosis

ways the mutation may affect the ability of the protein to perform its function

change the shape of the active site on an enzyme - substrate may no longer fit

examples of natural mechanisms that take place within cells to ensure accuracy of DNA replication

proofreading and repairing damaged DNA

mutagenic agents

environmental factors that increase the mutation rate of cells

3 examples of mutagenic agents

high energy radiation (uv light), ionising radiation (xrays), and toxic chemicals (peroxides)

nondisjunction (mutation in chromosomes)

when chromosomes fail to separate during meiosis

implications of non-disjunction mutation (chromosomal)

gametes may end up with one extra copy of a chromosome or no copies of a chromosome - gametes have different number of chromosomes compared to normal haploid number

what happens if the abnormal gametes take part in fertilization as a result of a non-disjunction mutation

chromosome mutation occurs as the diploid cell will have an incorrect number of chromosomes

example of chromosome mutation

down syndrome - individuals have 47 chromosomes as they have 3 copies of chromosome 21

chromosome mutations involve

a change in the number of chromosomes

meiosis produces

daughter cells that are genetically different to each other and the parent cell - haploid from diploid cells

what processes make the daughter cells genetically different

independent assortment and crossing

independent assortment

the alleles of two different genes get sorted into gametes independently of one another

what is a polyploidy chromosome mutation

where an individual has 3 or more sets of chromosomes instead of 2

meiosis

a form of cell division that produces 4 genetically different haploid cells known as gametes

inversion

occurs when a section of triplets get inverted

Using an example, explain why an unrepaired mutation could affect the function of a protein (5)

1\.Amino acid structure is different 2. altered position of disulfide/ ionic bonds 3. protein will fold differently so different shape/ tertiary structure 4. structural protein like collagen may lose its strength as active site gets altered, the substrate will no longer bind

crossing over process (meiosis I)

homologous chromosomes pair up, non-sister chromatids can cross over, places stress on DNA molecule - a section of chromatid from another chromosome may break and rejoin with the chromatid

crossing over

non-sister chromatids exchange alleles

why is crossing over beneficial

swapping of alleles can result in a new combination of alleles on the two chromosomes

how is meiosis different from mitosis

meiosis produces 4 genetically different cells with half the number of chromosomes as the parent cells whereas mitosis produces 2 genetically identical cells with the same number of chromosomes as the parents

the stages in both divisions meiosis I and II

prophase, metaphase, anaphase and telophase

prophase I (5)

1. dna condenses and becomes visible as chromosomes
2. chromosomes arranged in homologous pairs
3. crossing over may occur
4. centrioles migrate to opposite poles and spindle is formed
5. nuclear envelope breaks down

name of the point where crossing over occurs

chiasma

metaphase I

bivalents line up along equator of spindle, spindle fibres attached to centromeres

Bivalent

a pair of homologous chromosomes

anaphase I

bivalents are separated as microtubules pull whole chromosomes to opposite ends of the spindle - centromeres do not divide

telophase I (3)

1. chromosomes arrive at opposite poles
2. spindle fibres break down
3. nuclear envelope forms around 2 groups of chromosomes

cytokinesis meiosis I

division of the cytoplasm - two haploid cells

cytokinesis (meiosis I)animal cell

cell surface membrane pinches inwards- cleavage furrow in the middle of the cell - contracts and cytoplasm divides

cytokinesis (meiosis I) plant cell

vesicles from golgi apparatus gather along equator of the spindle - vesicles merge forming new cell surface membrane

prophase II

nuclear envelope breaks down and chromosomes condense, spindle forms at right angle to old one

metaphase II

chromosomes line up in single file along equator of spindle

anaphase II

centromeres divide and individual chromatids are pulled to opposite poles - creates 4 groups of chromosomes

telophase II

nuclear membranes form around each group of chromosomes

cytokinesis meiosis II

cytoplasm divides - cell surface forms creating 4 haploid cells

independent assortment

the production of different combinations of alleles in daughter cells due to random alignment of homologous pairs along the equator of the spindle

when does independent assortment usually take place

metaphase I

what forms during fertilisation when a male gamete fuses with a female gamete

zygote

how can variation be generated in the fusion of zygotes

the fusion of male and female gametes is random - unique combination alleles

formula to calculate the number of combinations of chromosomes after random fertilisation of two gametes

(2^n)^2 - n is the haploid number and the ^2 is the number of gametes

meiosis I

homologous chromosomes pair up, crossing over at the chiasmata may take place - cell then divides

meiosis II

the chromatids of each chromosome are separated producing 4 haploid daughter cells

genetic diversity

total number of different alleles in the population

population

a group of individuals of the same species that live in the same place and are able to reproduce

niche

it’s role within the environment

natural selection

fitter individuals, who are better adapted to the environment survive and pass on advantageous genes to future generations

evolution

the process by which the frequency of alleles in a gene pool changes over time as a result of natural selection

what is there a variety of within a population

phenotypes

what happens as a result of environmental change occurs

selection pressures changes

what do advantageous alleles provide some individuals with

a selective advantage allowing them to survive and reproduce

what produces new alleles of a gene

random mutation

example of natural selection

variation in fur colour to adapt with environment

3 types of selection

directional, stabilising and disruptive

what type of selection

directional

what type of selection

stabilising

what type of selection

disruptive

stabilising selection

natural selection that keeps allele frequencies constant - phenotypes around the mean of the population are selected

example of stabilising selection

birth weights

directional selection

natural selection that produces gradual change in allele frequencies over generations

directional selection happens as a result of what

change in environment or new allele

3 adaptations produced as a result of natural selection

anatomical, physiological and behavioural

anatomical adaptation

structural / physical features - fur used as camouflage to hide from prey

physiological adaptations

biological processes within the organism - mosquito produce chemicals that stop the animals blood clotting when they bite

behavioural adaptations

way an organism behaves -swallows migrate from uk to Africa in autumn to avoid food shortages in uk winter

adaption and selection are major factors in what process

evolution

explain how selection produces changes within a population

1. variation and chance mutation within a species

2. some individuals develop a phenotype with survival advantages like live longer etc

3. repeated over generations, mutated phenotype is the normal

4. if the genetic differences accumulate and the population is isolated then a new species may evolve

3 examples of ways phenotypes / characteristics can provide survival advantages a species. they allow species to:

live longer, breed more and be more likely to pass their genes on

why is it essential that aseptic techniques are used

ensure microbes being investigated don’t escape or become contaminated with another unwanted, pathogenic microbe

3 aseptic techniques with explanations

1. wash hands to remove microbes

2. disinfect bench to kill microbes/ prevent contamination

3. flame instruments to sterilise/kill microbes

4 differences between mitosis and meiosis

1. one division in mitosis, two in meiosis

2. daughter cells genetically identical in mitosis, genetically different in meiosis

3. two cells produces in mitosis, four in meiosis

4. crossing over is only in meiosis

what method is used to test for bacterial antibiotic resistance

the disc diffusion method - allows for multiple antibiotics at once

what is the MIC - minimum inhibitory concentration

the lowest concentration of a substance that will inhibit the growth of a microorganism

when prescribing antibiotics , why is the recommended dose always greater than the MIC? give 3 reasons

1. not all of the antibiotic may be absorbed

2. some of the antibiotic mat get broken down

3. some bacteria may have antibiotic resistance