Biology last SAC

CLOCK IN

Genotype vs phenotype

genotype:

• pair of alleles that determine a characteristic

phenotype:

• Appearance of the characteristic resulting from a genotypes interaction with the environment

Discontinuous variation vs continuous variation

Discontinuous:

When only one gene is involved and results in only a small number of discrete phenotypes.

coloumn graph

Continuous:

phenotype of a particular gene has a RANGE of phenotypes, not just one or two.

Scatterplot / trendline

Polygenic

traits that show continuous variation are controlled by multiple genes

e.g: height

Gene pool

The range of genes and their alleles present in an interbreeding population

• must have the potential to be passed on to the next generation

Equation for Allele frequency

2x(num of target homozygotes) +(num of heterozygotes)

——————————————————————— x 100

2x(total num of individuals)

• btw, homozygotes with the trait will have 2 copies of the allele, heterozygotes only got 1

• homozygotes: MM or mm

• heterozygotes: Mm

How can allele frequencies within a gene pool change?

• Mutations

• Environmental pressures

What are 2 mutagens that cause induced mutations?

• Gamma rays

• UV light

Most mutations are detected and repaired by enzymes.

If they cannot be repaired, they fall into categories. What are these categories?

1. Neutral mutations

   1. Has no effect on survival

2. Beneficial mutations

   1. Increase the likelihood of survival

3. Harmful mutations

   1. Decrease the likelihood of survival

What happens if a mutation occurs on the germ line? (in sperm and egg cells)

• the mutation can be passed on to future generations

• if it occurs in a somantic cell, the mutation will only affect the individual (will not be passed on)

what are the 2 types of mutations?

1. Gene mutations

   1. Permanent change in the base sequence of DNA

2. Chromosomal mutations

   1. Changes in the structure of chromosomes

What are point mutations?

Mutations in genes involving the addition, deletion or alteration of a single base (hence point)

What are substitution mutations, and what do they do?

A substitution mutation is when one base is substituted for another base in a particular gene

They can cause:

1. Missense mutations, which cause a different amino acid to be coded into the polypeptide. Consequently, the resultant protein is a completely different shape and no longer functions

2. Silent Mutations - no change in amino acid, because of degeneracy (still codes for the same amino acid). e.g: CCA codes for glycine. Any change in its last base does nothing; degenerate

3. Nonsense Mutations - the substitution mutation creates a STOP codon. Therefore, wherever the mutation occured, the polypeptide chain is stopped and a partial protein is created, where it has no function.

What 2 types of Missense mutation are there?

1. Conservative

   1. The amino acid replaced has similar chemical properties to the original and has little to no effect on the function of the polypeptide made

2. Non-conservative

   1. Different chemical properties, unlikely to carry out original function.

What is a frameshift mutation?

• When a base is inserted or deleted.

• shifts the series of codons by one base

• creates a different amino acid sequence

What are the 2 types of frameshift mutation, and what do they do?

1. Insertion

   1. extra base is added

   2. affects the protein production from the point of insertion

2. Deletion

   1. base is left out of the DNA sequence

   2. affects everything from the point of the mutation

What is a block mutation?

Mutations that affect large portions of chromosomes, typically multiple genes

What are the 5 types of Block Mutation?

1. Duplication

   1. Replication of a section of the chromosome, resulting in multiple copies of the gene

2. Deletion

   1. removal of sections. often lethal

3. Inversion

   1. two or more bases copied the wrong way around, hence different amino acid

4. Insertion

   1. one section of the chromosome breaks off, and attaches to a different chromosome, leads to trisomy (3 sets of chromosomes instead of 2)

5. Translocation

   1. Whole chromosomes or a segment is exchanged with another chromosome or segment. can cause cancer.

What is a karyotype and what is karyotyping?

• A karyotype is a prepared set of human chromosomes (e.g: 23 homologous series )

• Karyotyping is used to detect genetic chromosomal abnormalities.

  • e.g: in fetuses before birth, so that parents can make an informed choice.

What is aneuploidy? And what is a polyploidy?

Aneuploidy:

the presence of an abnormal number of chromosomes, either extra or missing.

Polyploidy:

When three or more sets of chromosomes

Natural vs artificial selection?

Natural:

• When selection of survival of an individual is achieved by the natural environment

Artificial:

• When humans choose which individuals mate and therefore produce offspring through artificial means (selective breeding)

remember:

selection does not generate variation, it acts on the variation that already exists in the population

What are the 6 things for the theory of modern evolution?

1. Variation

   1. varying genotypic combinations, which is inheritable.

   2. generated by mutations, meiosis, sexual reproduction, and gene flow

2. Reproduction

   1. leads to genetically similar offspring (identical for asexual)

3. Struggle for survival

   1. the number of potential offspring that parents can produce is always larger than the number that survive or the environment can support.

   2. only the fittest or individuals that are most adapted will survive long enough to reproduce

4. Environmental selection pressures

   1. individuals that compete successfully for resources will leave a much larger proportion of offspring.

   2. as environments change over time, those organisms with characteristics that suit the environment are most likely to survive and produce offspring

5. Chance effects

6. Divergence and speciation

   1. isolation leads to divergence of species.

What are the 4 things that cause variation (called morphs):

1. Mutations

   1. These produce genotypic and hence phenotypic differences between individuals

2. Meiosis

   1. This occurs through genetic recombination (independent assortment and crossing over)

3. Sexual reproduction

   1. fusion of gametes from two individuals

4. Gene flow

   1. genetic exchange resulting from the movement of individuals from one population to another.

What are the key stages of natural selection (when asked “natural selection“)

1. Genetic variation

   1. differing genes in population

2. Overproduction

   1. produce more offspting than the environment can support (survival of the fittest)

3. Struggle to survive

   1. Selection pressures

4. Successful reproduction

   1. organisms with helpful traits live the longest.

5. Change in allelic frequency

What is an example of natural selection?

The Australian Blowfly

1. The major method of control was via insecticides, such as dieldrin

2. However, the evolution of insecticide resistance decreased the effectiveness of the insecticide. (RR = reistant, rr = highly sensitive, Rr = intermediary between the two)

theres also antibiotic resistance in bacteria.

• Decreases genetic diversity

Darwin’s Finches (natural selection)

• finches on neighbouring islands were closely related, yet seperate species

• each island had differing survivial pressures

• The finches adapted to suit their own islands, eventually becoming different species

• This is called adaptive radiation

• Their beaks differed from species to species, to adapt to the food available on their island (larger beaks = tougher barriers to get through)

What is gene flow?

Movement of genes of alleles from one population to another through interbreeding. Leads to variation.

• Increases genetic diversity

Genetic Drift

the change in frequency of alleles from generation to generation by chance alone.

can lead to either the founder effect or the bottleneck effect.

• Decreases genetic diversity

What is the founder effect?

• the name given to a population which started with one or very few members

• genetic pool is very small

• variation is limited to the alleles that came from the original members of the population

• e.g: isolation on an island or smth like that

• Decreases genetic diversity

What is the bottleneck effect?

• When there is a severe reduction in population size through intense natural selection or disaster

• variation can be decreased significantly with the loss of some alleles

• Inbreeding severely decreases variation and makes offspring vulnerable to disease or environmental change

• Decreases genetic diversity

What is selective breeding?

(also called artificial selection)

A form of selection where humans actively choose which traits should be passed onto offspring.

2 examples of selective breeding?

• dairy cattle bred to produce more milk

• Crops - bred to produce higher-quality food

what are the 4 steps of selective breeding?

1. Determine the desired trait

2. interbreed parents who show that desired trait

3. select offspring with the best form of the trait, and interbreed them

4. Continue this process until the population reliably reproduces the desired trait

What are 2 detrimental effects of selective breeding?

1. Reducing resistance to environmental change

   1. Less genetic variation, then less alleles available to survive if there is a change to the environment

2. Reduces biodiversity

   1. Selective bred species replaced natural varieties.

What is a consequence of rapid genetic change

Antibiotic resistance in bacteria

• means the bacteria can survive in the presence of an antibiotic

can be caused by:

1. doctors over-prescribing antibiotics - more opportunities for bacteria to mutate

2. Increased use of antibiotics in livestock farmings - resistant bacteria can be passed on to humans.

Impression fossils

• When the fossil forms and hard parts leach out and leave a cast or space left behind

Mineralised fossils

• When minerals fill up the cast that is formed, and hardens

Trace fossils

• Preserved evidence of an animal’s activity, behaviour without containing parts of the organism

• e.g: footsteps

Mummified organisms (fossil)

• organisms that have been trapped in a substance under conditions that reduce decay

• e.g: Insects trapped in amber

What is the process of fossilization?

1. Organism dies and is buried quickly by sediments in an undisturbed area

2. Oxygen is excluded

3. The weight of sediment layers squeeze out water, increasing pressure and temperature

4. Hard parts leech out leaving a cast or space in the sediment, which is filled with minerals and hardened

5. If the space is not filled, an impression fossil is left behind

6. If the space is filled later with foreign material, a cast is formed

7. The filled space is a mould of the organism

8. The sediment is buried by many layers. Pressure and temperature is exerted to form rock

What is relative dating?

• dating the absolute age of rock layers above and below the layer containing the fossil

• Depends on stratification (the formation of layers in sedimentary rocks)

  • just extra info to know:

    • Principle of faunal succession: higher rocks = younger

What are index fossils?

• Index fossils are fossils that have already been dated.

• they give evidence of the relative age of fossils from different locations

What is absolute dating / radiometric dating?

• dating a fossil directly to determine its absolute age

• based on the principle that radioactive elements decay at a constant rate

What is Radiocarbon dating?

• Calculating the amount of decay of ¹⁴C based on its half life

• When an organism dies, its ¹⁴C disintegrates to ¹⁴N

• The half life of ¹⁴C is approx 5700 ± 40

• the amount of ¹⁴C is measured and compared to the amount of ¹²C in the rock

• limited to samples not older than 50 000 years old

What is potassium/argon dating?

• used to date fossils up to billion of years old

• ⁴⁰K has a much longer lifespan than ¹⁴C

• ⁴⁰K is released from volanic rocks and decays into the gas ⁴⁰Ar

• the proportion of ⁴⁰K and ⁴⁰Ar are compared to calculate the age of the volcanic rock

• decay curve is the same as radiocarbon dating, but the x axis / time frame is much longer