4.3-4.4- diversity and mutation or meiosis/genetic diversity and adaptation

what is genetic diversity?

what is a gene?

what is an allele?

what is a gene pool?

the number of different alleles in a population

section of DNA that codes for the production of a polypeptide chain and functional RNA

different versions of a gene

all the alleles in a population

what does a bigger gene pool mean?

what does greater genetic diversity mean?

greater variation within that species, and the greater the genetic diversity

the better the survival chances of that species as they are more likely to be able to adapt to a change in the environment

what are the three causes of genetic diversity?

of these causes, which is the only way asexually reproducing organisms show variation?

mutations, meiosis and random fusion of gametes

mutations

what are mutations and what can they cause?

how do they lead to the production of non-functioning proteins?

why would this prevent an enzyme functioning?

1) change in the base sequence of DNA- causes change in characteristics

2) sequence of bases altered- changes sequence of amino acids

change in primary structure of protein causes change in tertiary structure- bonds form in different places

loss or reduction in function of protein

3) active site of enzyme changes- no longer complementary to substrate- less ES complexes forms

what happens in meiosis?

how many nuclear divisions?

what is formed?

what is haploid and diploid?

what does meiosis ensure?

1) formation of gametes

2) 2 nuclear divisions

3) 4 genetically different daughter cells

4) daughter cells have half the number of chromosomes in a normal body cell (23)- haploid

normal number of chromosomes found in a body cell- (46)- diploid

5) when male and female gametes join together at fertilisation, the diploid number is restored

therefore, meiosis ensures that the chromosome number is kept constant from one generation to the next

what happens in meiosis 1?

what happens in meiosis 2?

homologous pairs separate, and the cells become haploid

centromere breaks and chromatids separate

what is chromosome non-disjunction?

what happens to the zygote as a consequence?

homologous chromosomes don’t separate properly during meiosis and both chromosomes of a pair go into the same cell

the zygote can end up with an extra copy of a particular chromosome

how does meiosis lead to variation in the offspring produced by fertilisation of the gametes?

do these two processes occur during meiosis 1 or meiosis 2?

independent segregation- random shuffling between maternal and paternal chromosomes

crossing over- parts of chromatids are exchanged between homologous chromosomes

alleles are exchanged between the maternal and paternal chromosmes- genetic recombination occurs

both during meiosis 1

What happens in crossing over? (3)

Homologous pairs of chromosomes associate to form a bivalent

Non sister chromatids entangle and chiasmata form

Non sister chromatids are exchanged

(Results in new combination of alleles)

during which two stages, is the chromosome number 2n i.e. diploid and n i.e. haploid

draw what the cells look like in meiosis?

diploid = interphase + meiosis 1

haploid = meiosis 2 + at the end

How to calculate possible combinations of chromosomes in daughter cells?

2 to the power of n

N = number of homologous pairs

Why may mutations still produce a functional protein?

Substitution- one nucleotide changed

Same amino acid coded for- genetic code is degenerate

So tertiary structure not changed

Change could be in an interim

Removed during splicing

what is natural selection and what are some factors that are involved in it?

What does variation in the population do?

process by which frequency of ‘advantageous’ alleles gradually increase in a population’s gene pool over time

predation, disease and competition, e.g. for food and breeding sites in animals, and for water, space and light in plants.

variation- some organisms possess phenotypes that give them a selective advantage in their environment

what is directional selection and give an example?

one extreme of organism’s phenotype selected, and the other extreme is acted against

antibiotic resistance in bacteria:

random mutations some bacteria have allele which gives them resistance to antibiotics

In the presence of antibiotics only those bacteria that have the allele for resistance will be able to survive and reproduce

The next generation of bacteria inherit this allele as they divide (vertical gene transmission)

Over time, the frequency of the allele for antibiotic resistance will increase in the population.

Bacteria can also transfer this allele to different species of bacteria in a process (horizontal gene transmission)

what is stabilising selection and give an example (what are the two extremes selected against and why?)

acts against both the extremes in a range of phenotypes i.e. it selects and favours the intermediate phenotype and so acts to prevent change

e.g. human birth weight- two extremes that are selected against e.g. high birth weight- damage to mother;s body + low birth weight- lose heat faster- ill from infectious diseases

what is disruptive selection?

both extremes of a phenotype have a selective advantage over those in the middle

intermediate phenotypes are selected against

what are the three types of adaptations?

physiological e.g. having haemoglobin with different oxygen affinity

anatomical- visible changes to organism’s body

behavioural e.g. better food search strategy more elaborate songs in whales