Genes L8 Flashcards
What is microevolution?
- Changes -> gene pool -> organism -> overtime
What is a gene pool?
- All alleles of all genes -> all individuals -> population.
- Represents genetic variation -> population
What are alleles?
- Different forms/types of gene -> polymorphisms.
Mutation
What is the term polymorphic used to describe?
- Gene locus with more than one allele
What is macroevolution?
• Macroevolution: - Large scale evolution - Evolution across major animal groups Above species level Eg. Phyla, Order, Phyla etc. - Speciation
Contrast microevolution & macroevolution.
• Macroevolution: - Large scale evolution - Evolution across major animal groups Above species level Eg. Phyla, Order, Phyla etc. - Speciation
• Microevolution:
- Evolution within species or population
- Microevolution & Chance -> macroevolution.
What results in macroevolution occurring?
- Microevolution & Chance -> macroevolution.
Requirements for evolution by natural selection?
- Varying reproductive successes
- Genetic variation -> (Differences between individuals)
What is evolution?
• Evolution -> changes -> genetic structure -> population/species -> over time.
Describe what population genetics is.
• Population genetics
- Study of genetic changes -> evolution.
- Study of microevolution
>Darwin’s theory -> evolution by natural selection
> Mendel’s theory -> inheritance
- Modern synthesis / neo-Darwinism
What can population genetics be used to investigate in terms of human pathogens?
Evolving human pathogens
Human evolution in response to pathogens
Use of population genetics in investigating evolving human pathogens?
Evolving human pathogens: - Bacteria -> Antibiotic resistance Eg. MRSA - Viruses -> Anti-viral drug resistance Eg. HIV - Emerging pathogens Eg. Ebola, influenza viruses
Use of population genetics in investigating human evolution in retaliation to pathogens?
Human evolution -> pathogens:
- Resistance
- > blood-bourne parasites Eg. Malaria parasites, Plamodium sp.
Use of population genetics in wild populations?
• Uses of population genetics in wild populations:
- Range/quantity & distribution -> genetic diversity
- Response -> population -> change
Describe the gene locus model & what is is used for.
• Single gene locus model - Used to study gene pool - Diploid organisms >Single gene >> 2 alternative alleles i) R -> dominant ii) r -> recessive - 3 genotypes RR -> Homozygous Rr -> Heterozygous rr -> Homozygous >> 2 phenotypes RR & Rr -> red flower rr -> white flowers
What is a genotype?
• Genotype:
- The genetic composition of an organism determining a particular characteristic (phenotype).
What is a phenotype?
• Phenotype:
- Observable characteristics of an organism as a result of interaction between it’s genotype & their environment.
What is measured in the gene pool? Describe how both of these are calculated.
- Allele/Allelic frequency:
(Number of particular type of allele)/(Total number of alleles) - Genotype/Genotypic frequency:
(Number of individuals with one particular genotype)/(Total number of all individuals)
Describe the Hardy-Weinburg equilibrium.
• Hardy-Weinburg equilibrium: - Allele & genotype frequencies reach an equilibrium over time & remain unchanged. - p2 + 2pq +q2 = 1 Genotype frequency: f(RR) + f(Rr) + f(rr) =1 Allele frequencies -> p & q >> p + q = 1 Conditions: Large population size Random reproduction No migration of populations No selection No mutation
Equation of genotypic frequency for H-W eqm?
- p2 + 2pq +q2 = 1
Genotype frequency: f(RR) + f(Rr) + f(rr) =1
Equation of allelic frequency for H-W eqm?
Allele frequencies -> p & q
|»_space; p + q = 1
What is the definition of the H-W principle and what are it’s conditions?
- Allele & genotype frequencies reach an equilibrium over time & remain unchanged. Conditions: Large population size Random reproduction No migration of populations No selection No mutation
Calculate the allelic frequency for both allele types from a population of 100 in which 40-> homozygous dominant
50-> heterozygous & 10-> homozygous recessive.
- F(A1A1) = 40/100 = 0.4
- F(A1A2) = 50/100 = 0.5
- F(A2A2) = 10/100 = 0.1
- Allele frequency A1 = (No. of A1 alleles)/(Total no. of alleles)
[2(40) + 50]/200 = 130/200 = 0.65
Allele frequency: If 100 genotypes – 2 alleles per genotype -> 200.
Dominant alleles -> Homozygous dominant -> A1A1
-> 2 dominant alleles per homozygous dominant genotype
Heterozygous -> A1A2 -> 1 dominant allele per heterozygous.
Homozygous recessive -> A2A2 -> No dominant alleles per genotype
» No. of alleles = 2(No. of homozygous dominant genotype) + 1(No. heterozygous genotype)
- Allele frequency A2 = (No. of A2 alleles)/(Total no. of alleles)
[50 + 2(10)]/200 = 70/200 = 0.35.
Recessive alleles -> homozygous recessive -> A2A2
->2 recessive alleles per homozygous recessive genotype
Heterozygous -> A1A2 => 1 recessive allele per heterozygous genotype
Homozygous dominant -> A1A1 -> No dominant alleles per genotype
»_space; No. of recessive alleles = 2(No. of homozygous recessive genotype) +
1(No. of heterozygous genotype)
• If 70% of population of has dominant (R) allele, calculate the genotype frequencies of the population.
p+q=1
p=0.7 -> q=1-0.7 -> 0.3
Genotype frequencies: f(RR) + f(Rr) + f(rr) = 1
p2= (0.7)2 -> q2= (0.3)2
(0.7)2 + 2pq + (0.3)2 = 1
2pq = 1 -0.58 -> 0.42
pq= 0.42/2 -> 0.21
p2 = homozygous dominant (RR)
> (0.7)2 ->0.45
q2 = homozygous recessive (rr)
> (0.3)2 -> 0.09
2pq = heterozygous (Rr)
> 2(0.7)(0.3) = 0.42What test do you use to find if observed & expected values of H-W test are significant?
Chi-squared
• All patients with cystic fibrosis have a recessive mutation -> homozygous for allele. 1/2500 are affected. Assuming population at H-W eqm, what is the expected frequency of individuals who are heterozygous for the disease causing allele?
- q = sqrt(0.0004) -> 0.02
- p = 1-0.02 -> 0.98
- p2 + 2pq + q2 = 1
- 2pq -> 2(0.98)(0.02) -> 0.0392
Name the factors affecting allele & genotype frequencies.
Genetic drift
Non-random reproduction
Migration
Selection
Describe how genetic drift can affect allele & genotype frequencies.
- Genetic drift -> low population
Change -> allele frequencies -> chance events
i) Founder effect:
Small no. of individuals -> start new population
ii) Bottleneck:
No. of breeding individuals -> reduced -> chance event
Describe how non-random reproduction can affect allele & genotype frequencies.
Sexual selection Assortative mating i) Positive Mate -> unrelated partners -> similar phenotype >>Decreases heterozygosity >>Increases homozygosity Eg. Inbreeding Inbreeding depression: Reduced fitness -> expression of harmful, recessive alleles. ii) Negative Mate -> unrelated partners -> different phenotype >>Increases heterozygosity >>Decreases homozygosity
Describe how Selection can affect allele & genotype frequencies.
Natural selection Acts on phenotyoes -> gene pool i) Stabilising ii) Directional iii) Disruptive
Describe how - Migration/Gene flow can affect allele & genotype frequencies.
Transfer of alleles -> between diff populations
»_space;If gene flow prevented -> speciation possible
»_space;Helps maintain genetic variation
What is a factor required for natural selection?
• Natural selection requires heritable genetic variation.
Name the methods in which genetic variation can be preserved.
Balancing selection
Clinical variation
Diploidy
Neutral alleles
Describe how balancing selection can preserve genetic variation.
Balancing selection
» Heterozygote advantage
Higher fitness than either homozygote
Eg. Sickle-cell anemia
»Frequency dependent selection
Allele selected against -> high frequency
Allele selected for -> low frequency
Eg. Scale-eating fish
»Left & right mouthed predators
Left -> attack back right flank
Right -> attack back left flank
-»If high no. right mouthed
– Prey expecting to be attacked -> left flank
– Less likely to predict attack -> right flank
– Left mouthed have advantage -> incr. no. of left-mouthed individuals.
-»Low no. right mouthed
–High no left mouthed -> expect attack on right flank
– Incr. success of right mouthed -> pop. Incr.
Describe how clinical variation can preserve genetic variation.
Clinal variation
|»_space;Different selective pressures -> across geographic range -> population
Describe how diploidy can preserve genetic variation.
Diploidy:
If deleterious (harmful) allele recessive -> selection can only act on homozygous recessive genotype
»Remaining deleterious alleles -> hidden -> heterozygotes -> not expressed.
Describe how neutral alleles can preserve genetic variation.
Neutral alleles:
Nucleotide differences -> don’t effect fitness of organisms
>Synonymous mutations
»_space;Don’t alter amino acid seq.
>Non-synonymous mutations
»_space;Alter amino acids seq.
Most nucleotide differences -> sections of genome -> don’t encode proteins.
What is the sexual selection theory?
• Sexual selection theory:
- Males would want to mate with the max. number of possible females
What is the sexual conflict theory?
• Sexual conflict theory:
- Sexual selection theory of males conflicts with females desire to mate with fittest males only.
What is polyandry?
• Polyandry:
- Female has more than one male mate.
What is polygyny?
• Polygyny:
- Male has more than one female mate.
Give an example of a case study demonstrating how population genetics can be used.
• Population genetics case study: Cheetahs
- 1900: >100,000 -> 2014: ~10,000.
- 2 population bottlenecks:
100,000 yrs -> migration -> N. America – Africa
11-13,000 yrs -> Pleistocene mammal extinction
- Poor sperm quality, low fecundity & high susceptibility to infection.
- Solitary females -> large range: >800km2
- Male coalitions (2-3 brothers) -> small territories: 40km2
- Solitary males (floaters) -> large range
- Males only associate -> females -> mating
No parental care
- DNA samples -> paternity testing
43% litters -> fathered by more than one male
>Often outside females range
Example of polyandry
