genetics and evolution

Question 1

what are the 7 mechanism of evolution?

Answer 1

1. natural selection
2. mutations
3. random genetic drift
4. founder effect
5. migration
6. barriers to gene flow
7. genetic diseases

Question 2

what are the types of chromosomal mutations?(5)

Answer 2

• Deletion- when part of a chromosome is lost
• Duplication - A section of chromosome occurs twice- part of a cromatid (copied chromosome) breaks off and joins onto the wrong chromosome.
• Inversion - a piece of chromosome breaks from the middle of a chromosome but when it reattaches its the wrong way.
• Translocation - part of a chromosome breaks off and joins the wrong chromosome.
• Non-disjunction/Aneuploidy - when the eggs and sperm are formed sometimes chromatid pairs do not move to seperate cells. Instead one cell receives both chromatids and will have an extra chromosome, whilst the other cell is one chromosome short. Trisomy 21 (down syndrome)

Question 3

what is natural selection?

Answer 3

refers to natures balance- certain species are more likely to survive if they have specific characteristics (survival advantage)
3 main keys- variation, birth rate and natures balance
eg, caterpillars- green are more likely to survive over a neon
-must be a struggle for existence to ensure the more suited species can survive and pass on the better characteristics
-examples in humans: body stature depending on the area you live in, eg eskimos are short, and carry more fat- this poses a survival advantage for the conditions they live in- whereas there are long-limbed, tall, thin Africans that have a survival advantage in Africa.

Question 4

what is random genetic drift?

Answer 4

-an allele that is rare in large populations may randomly become frequent in small populations.
-can only happen in small populations
Eg, Australian aborigines on Bentinck island, all have an allele for 1B (blood type B), whereas mainland has blood type 1A and 1B. Due to Mornington island aborigines hopping to the mainland thousands of years ago and the bentinck islanders not.
-allele frequency changes for no ‘real’ reason which means there’s no survival advantage.

Question 5

what is the founder effect?

Answer 5

• occurs during the founding/establishing of a new colony
• small group —> the small isolated group leaving the mainland are not representative of the whole populations dominant gene frequencies.
• eg, those leaving a country to colonise an island may not be representative of the dominant allele frequencies.
• eg in 1775, typhoon in Micronesia wiped out majority of population, amongst the survivors was a man who had a rare form of total colourblindness, now 5% of the population is colourblind opposed to the 0.0033% the rest of the world experiences.

Question 6

what is migration

Answer 6

EMIGRATION (exit) when a population leaves an area, IMMIGRATION when people enter a new area.

• when a population loses or gains new variations in a population then there will be a frequency change.
• when china started to trade in 16th century- dominant Chinese blood group was Rh+, however European immigrants came and brought Rh- blood type alleles.

Question 7

what is barriers to gene flow?

Answer 7

There are 2 main types of barrier to gene flow
GEOGRAPHICAL BARRIERS; Oceans, mountains, deserts, rivers
SOCIO-CULTURAL BARRIERS; Language (for example the Basque population), religion (jewish-orthodox)
-these populations are isolated, stopping the inter-mingling between populations resulting in barriers to gene flow.
-jewish orthodox and the dunkers, can’t marry outside of faith group
-economic status, social position, educational background.

Question 8

what are genetic diseases?

Answer 8

TAY-SACHS DISEASE (prominent in Ashkenazi-jewish populations meaning it is lethal-recessive and effects population genome.)
-missing enzyme which stops the metabolising of fats
-in rest of pop, affects 1 in every 500,000, in ak jews its 1 in every 2,500.
-survival advantage however, is that it provides resistance over TB if a person is a carrier (this was helpful for the ghettos).
SICKLE-CELL ANAEMIA
-tay sachs occurs when a mutated gene replaces the normal gene that breaks down lipids via an enzyme (protein coded by normal gene)
-provides resistance against malaria. prominent in tropical African regions
THALASSAEMIA
-around the Mediterranean, cousin marriages were once common, now there is a higher presence of thalassaemia in these pops

Question 9

what are the 6 pieces of evidence for evolution?

Answer 9

1. comparative studies of embryology
2. comparative studies of anatomy (vestigial organs)
3. comparative studies of anatomy (homologous organs)
4. comparative studies of DNA
5. comparative studies of proteins
6. fossils

Question 10

what is comparative study of embryology?

Answer 10

• each organism (birds, mammals, amphibians, fish, humans) starts of with similar characteristics that include;
• fish like gills
• a tail
• similar brain development
• 2 chambered heart

Question 11

what is the comparative study of anatomy (vestigial organs)

Answer 11

refers to organs found in an organism that no longer serve a function suggesting they once would have been used by a common ancestor.

• eg appendix (digest greens)
• abdominal muscles- 6 pack (used to hold innards in when we were not bipedal beings)

Question 12

what is the comparative study of anatomy (homologous organs)

Answer 12

-when looking at a species fo organisms (horse, whale, bat, frog, human, lion etc) we all have the same bone structure in our fore arms suggesting a common ancestor

Question 13

what is the comparative study of biochemistry (DNA)

Answer 13

proves evolution as all organisms on earth share the same genetic coding (sugar phosphate, A+T, C+G)

Question 14

what is the comparative study of biochemistry (proteins)

Answer 14

there are 20 different amino acids, they form in sequences to code for proteins. When comparing humans and chimps, these sequences are identical but point mutations will occur as species differ.

Question 15

fossil evidence for evolution & overall limitations

Answer 15

Dating Fossils ———>
-there are 2 main types of dating technique.
Relative dating, eg index fossils (pollen grains), fluorine analysis and stratigraphy,
Absolute dating, eg potassium argon, radiocarbon dating and dendrochronology (tree rings)
LIMITATIONS:
-organisms need to be left for a long time undisturbed
-must be prescience of hard body parts
-some are buried too deep to be found or have been destroyed by human activity.

Question 16

describe the three ways to date fossils (relative dating techniques)

Answer 16

INDEX FOSSILS

• have to be widespread
• have to exist for just a short period of time (100-1000 year)
• an example is pollen grains- when comparing core samples of rock layers- you can line up the index fossils along them to indicate which species came first

STRATIGRAPHY/CORRELATION OF ROCK STRATA
-looking at the layers of rocks and what is in it- fossils found in rock layers closer to the earths surface are more recent.
limiting factors: earth movement can change direction of compositions, all samples must come from the same area

FLUORINE ANALYSIS
-groundwater contains fluoride ions
-petrification occurs when bone materials are replaced by minerals containing fluoride- we can compare the age of species depending on how much ppm of flouride they contain
limiting factors; has to be used in the same area as different places have different fluoride groundwater concentrations.

Question 17

describe the three ways to date fossils (absolute dating techniques)

Answer 17

RADIO CARBON DATING

• the earth is continually bombarded by cosmic rays- the outer layer of nitrogen is changed into radioactive carbon due to this
• the half life of radioactive carbon is 5,730 years (time taken for half of it to turn back into nitrogen) meaning radioactive carbon concs in the atmosphere are constant,
• due to food chains every living thing contains radioactive carbon to the ratio of 1:10^12
• we can measure the amount of radio active carbon in an organism through mass, ratio and radiation amounts.
• limiting factors: after 60,000 years, not enough 14^C to measure- meaning a fossil must be younger than this
• can only measure living organisms part of a food chain

POTASSIUM ARGON DATING

• only happens within volcanic areas
• constant state of argon and potassium is 40^K (100%) and 40^Ar (0%)
• half life cycle of 1.3 billion years, once rock settles, it takes 1.3 billion years for half of the argon and half of the potassium to be even.
• we can judge the organisms trapped BETWEEN layers of molten rock based on this dating technique b y comparing the layers of rock it is trapped between
• limiting factors: no living organisms can be dated within the rock, fossils have to be older than 100,000 years due to the large half life cycle

DENDROCHRONOLOGY

• tree rings = 1 ring = 1 year
• the thickness of each ring varies on the weather patterns etc
• certain rings can be used as marker rings, we can use these as referrals to timber used in ancient human structures to give an exact year.
• core samples are taken out

Question 18

what are mutagens? what do they do? (4 CAUSES)

Answer 18

substances or processes that can accelerate the development of mutations

1. CHEMICALS: formaldehyde, mustard gas, antibiotics
2. IRRIDATION: x-rays, UV rays, gamma rays
3. TEMPERATURE: for sperm development, optimum temp is a couple degrees below body temp (no tights whities)
4. SPONTANEOUS

Question 19

how can genes become mutated?

Answer 19

• point mutations ( a change in just one base), could alter a protein, have no effect at all or prevent the whole protein form being produced.
• just one missing protein from a gene can have huge effects- for instance ALBANISM as a result of one missing protein that codes for melanin.

Question 20

what are lethal recessives?

Answer 20

most gene mutations produce a lethal recessive allele as they prevent the gene from coding that specific protein, therefor if a person carrying a lethal recessive allele mates with another person carrying a lethal recessive allele they can cause the death of embryo or foetus.
-Tay Sachs disease causes death in early childhood because of this (stops the metabolising of fats causing a buildup)

Question 21

what is speciation? (4 steps)

Answer 21

refers to making 2 different species from a population that was once in a common gene pool.

1. variations: a population must exist with variations, sharing a common gene pool
2. isolation: the population is halved by a barrier- no more interbreeding meaning there are now 2 separate gene pools.
3. selection: must be selection pressures (natural selection) occurring to both of the seperate populations, this brings a change in gene frequencies, leading to the eventual evolution of a new subspecies.
4. speciation: over time, the changes in gene frequencies will be enough to prevent fertile interbreeding, meaning there are now 2 seperate sub species.

Question 22

what is mitochondrial DNA?

Answer 22

• passed on from mothers
• scientists can look at the mtDNA between any two species and see how close they are through their maternal ancestors, eg if they have very similar or identical mtDNA, they are considered closely related.