Gene pools and evidence of evolution

Question 1

Natural selection

Answer 1

process by which a species becomes better adapted to its environment.
Based on 3 observations: variation, birth rate, nature’s balance.
survival of the fittest: organisms with favourable characteristics survived, while many of those with favourable characteristics died before they had an opportunity to reproduce and pass on the trait.
Selective agent: environmental factor acting on the population, survivors pass on favourable alleles to offspring.

Question 2

NS summary

Answer 2

There is variation of characteristics within a species.
more offspring of a species are produced than can possibly survive to maturity.
Because of excessive birth rate and limited resources, there is a struggle for existence or competition for survival.
individuals wt characteristics best suited to the environment have more chance of surviving and reproducing. (Survival of the fittest)
Favourable characteristics are passed on to the next generation.
in gene pool, the proportion of alleles that produce favourable characteristics gradually increases.
The change in allele frequency in populations as a result of a selective agent.

Question 3

examples of natural selection

Answer 3

Body stature
Sickle-cell anaemia
Tay-sachs disease
thalassemia

Question 4

Genetic drift

Answer 4

the random, non-directional change in allele between
Purely by chance

Question 5

founder effect

Answer 5

Effect occurs when a small group moves away from its homeland to a totally new area and establishes a population.
chance can cause new group to have: a different allele frequency from the original population, a decreased genetic variation.

Question 6

Bottleneck effect

Answer 6

an event such as a natural disaster Beverly reduces the size of the population.
Chance of survival is by chance and not due to specific trait.

Question 7

speciation steps

Answer 7

Occurs due to variation, isolation and selection leading to two groups becoming so different that they can no longer interbreed.
1. Variation - variation between individuals of a species
2. Isolation - populations of the same species are isolated without gene flow
3. Selection - each population is subjected to different selective agents
4. Speciation - the allele frequency changes until they become so different that the two groups are no longer able to interbreed.

Question 8

Polymerase chain reaction (PCR)

Answer 8

enables small quantities of DNA to be replicated, producing testable amounts to use in analysis techniques.
Mimics the natural process of DNA replication that occurs prior to cell division.
3 steps: denaturing - the two strands of DNA are separated, Annealing - short sections of DNA (primers) are bound to the separated strands, Extension - the short sections of DNA are extended to produce longer strands.
Thermocycling - sequence is repeated 20-30 times

Question 9

denaturation

Answer 9

Enzyme helices separates the two strands of DNA
Temps of 94-96.C are used in PCR to break the hydrogen bonds holding the two strands together
separates strands without disrupting each individual strand.

Question 10

Annealing

Answer 10

Temp decreased to 50-60.C
Allows primers to bind to the single DNA strands
Primers are complementary to either end of the section of DNA to be copied.

Question 11

Extension

Answer 11

A.K.A elongation
Mimics process of DNA replication
Enzyme DNA polymerase used to join new, complementary nucleotides to the sections originating wt the primers.
In PCR, denaturation step usually destroys DNA polymerase, thus Taq polymerase used, doesn’t denature.
Taq’s optimal temp is 68-72.C, extension phase carried out at this temp.

Question 12

Gel electrophoresis

Answer 12

Technique that is able to separate DNA strands based on their lengths.
DNA pieces placed in wells in semi-solid gel that is immersed in solution of an electrolyte.
Electric current passed through the gel, negatively charged DNA moves towards positive electrode. Smaller DNA moves faster thus furthest.
results in pattern of bands, Called DNA fingerprint (DNA profile)

Question 13

Visualising DNA

Answer 13

Ethidium bromide added to gel before it sets
Methylene blue added to gel
DNA probes

Question 14

Comparative genomics

Answer 14

all living things use the same DNA code
Genome sequences of different species are compared.
researchers able to identify regions of similarity and difference.
Provides effective means of studying evolutionary changes among organisms helping to identify genes that are preserved among species.

Question 15

endogenous retrovirus (ERVs)

Answer 15

Viral sequence that has become part of an organisms genome.
store their genetic info as RNA, not DNA.
Enters a cell, copies its RNA genome into DNA through reverse transcription, DNA inserted into the host cell chromosome, and passed onto next generation.
Humans DNA - 8% ERV

Question 16

Reverse transcription

Answer 16

a process where the base sequence in RNA is copied during the synthesis of DNA.

Question 17

Mitochondrial DNA

Answer 17

mtDNA
In the form of small circular molecules
5-10 molecules in each mitochondrion
Has 37 genes: 24 for transfer RNA, 13 for instructions for making some of the enzymes necessary for the reactions of cellular respiration.

Question 18

inheritance of mtDNA

Answer 18

Ovum and sperm contain mitochondria
at insemination, sperm mitochondria destroyed, thus mitochondria inherited from egg

Question 19

Evidence from mitochondrial DNA

Answer 19

mtDNA higher rate of mutation than nuclear DNA.
Scientist able to use the similarity between the mtDNA of any two individuals to provide an estimate of the closeness of their relationship through their maternal ancestors.
Most of value when comparing individuals within a species and for species that are closely related.

Question 20

protein sequences

Answer 20

By comparing the type and sequence of amino acids in similar proteins from different species, degree of similarity can be established.
same species have identical amino acid sequences in their proteins, and those from different species have different AA or are arranged in a diff order.
Degree of difference enables an estimate to be made of the amount of evolution that has taken place since common ancestor.
the longer the time - the greater the number of AA that are different.

Question 21

Ubiquitous proteins

Answer 21

proteins that appear to be in all species
Represented by 1 letter
same function in all species

Question 22

Cytochrome C

Answer 22

Is an ubiquitous protein
contains 104 AA - 37 found in same position in all species.

Question 23

Bioinformatics

Answer 23

the use of computers to describe the molecular components of living things
The more similar the genes of two species, the closer their evolutionary relationship
annotation - identification of genes, needs to be computerised due to length of DNA.

Question 24

Body stature (Inuits)

Answer 24

Long body, short limbs
Small surface area to volume ratio
lose less heat
Have a survival advantage in cold climates
these favourable genes are passed onto the next generation, less favourable died before reproductive age.
Frequency of these alleles increases in population over time.

Question 25

Body stature (Africans)

Answer 25

Short body, long limbs
high surface area to volume ratio
Lose body heat easily (radiation) a survival advantage in hot climates
These favourable genes are passed onto the next generation, less favourable died before reproductive age.
Frequency of these alleles increases in population over time.

Question 26

Sickle-cell anaemia

Answer 26

homozygous - normal RBC’s, Genotype: Hb Hb, phenotype: normal RBC’s, very susceptible to malaria.
Heterozygous (carrier) - Sickle cell trait, Genotype: Hb^s Hb, Phenotype: 1/2 sickled and 1/2 normal, show no ill effects unless O2 levels are low, heterozygous advantage (survival advantage)
Homozygous recessive - SCA, Genotype: Hb^s Hb^s, phenotype: all RBC’s sickle shaped, Very ill + may die early

Question 27

Tay-sachs disease

Answer 27

Homozygous - No TSD, Genotype: TT, Phenotype: normal lipid metabolism, Very susceptible/likely to die from Tuberculosis
Heterozygous - Genotype: Tt, Phenotype: no signs/symptoms, likely to survive and reproduce, ‘Heterozygous advantage’ or ‘selective advantage’, have protection from tuberculosis - an infectious bacterial disease affect lungs/respiratory system.
Homozygous recessive - TSD, Genotype: tt, phenotype: reduced amount of beta-hexosaminidase, very ill and die before reproducing (recessive allele not passed on)

Question 28

Thalassemia a +b

Answer 28

Homozygous normal - genotype: TT, Phenotype: normal HGB in RBC’s, Very susceptible/likely to die from Malaria.
Heterozygous (carrier) - Genotype: Tt, Phenotype: Mildly affected, likely to survive and reproduce, ‘Heterozygous advantage’ have protection from malaria.
Homozygous recessive (a Thalassaemia) - Genotype: tt (no alpha affects B: Thalass major), Phenotype: RBC’s survive only few weeks (severe Anaemia), fatal/die before reproducing - recessive allele no passed on.
Homozygous recessive (B Thalassaemia) - severe but not fatal