Co Dominance– When both alleles in a heterozygous individuals are shown in its phenotype.
For example RW sows red and white colors on a flower Alleles have equal effects on the
Incomplete dominance – When an intermediate allele is shown. Ie// RW shows pink color on
Pleiotropic: When one single gene affects more than one other effect on the body
phenotypically. Example, sickle cell disease can cause heart failure and also fatigue and impaired
mental function. So one allele has an effect on many other processes.
H ARDY W EINBERG E QUILIBRIUM
Hard Weinberg equilibrium is when genetic variation in a population will remain constant
from one generation to the next when there is no factors that disturb it.
1. No mutations occur
2. No migration
3. Very large population size
4. All genotypes survive and reproduce equally as well
5. Random mating
This is point of genetic equilibrium: this is when no change in allele or genotype frequencies
are occurring in succeeding generations. This is a null model and a reference point for evaluating
circumstance in which evolution can occur.
DNA in nucleus, alleles gets transcribed into RNA and leaves nucleus. Goes to ribosomes and go
to ER. They get translated on ER (RNA to protein) and packaged into vesicles. Go to Golgi
apparatus. Then the proteins are sent from vesicles to the membrane.
Melanin (black and red melanin). Melanin is produced by melanocytes. It is packed into
melanosomes. They export the melanin to keratinocytes, which give hair and skin their colors.
Brown is a mixture of red and black melanin. GENE PRODUCT is W-MC1R (brown allele) which sits in the membrane (membrane product).
It AMP levels are high, it makes black melanin. In hormone response, when AMP levels are low,
RED melanin is produced.
The B allele code for MC1R is always high (AMP
levels always high is on all the time).
The black allele is always on so it is DOMINANT.
The dominant alleles never inhibits the recessive one,
the allele that is on all the time is the dominant and it
is determining the phenotype.
In a population with no fitness, the starting allele frequencies will be maintained, doesn’t matter
what is dominant and what is isn’t (WHE)
Punnet Square for POPULATIONs
Top and left are percentages.
Allele Frequencies: frequency of individual alleles
Gene pool: all alleles of individuals in a single population
Population: a group of sexually interbreeding individuals
Deme: a local group of sexually interbreeding individuals in which gene pool is distinct. There
an be many demes within ONE population of species. Once we know allele frequency in population (through HWE), then we plug values of p and q
values into HW equation. If the value is 1, then these are the expected ratios.
Selection: not all genotypes have equal fitness. Some genotypes may be more likely to produce
phenotypes that cause the pigs to be eaten. These have low fitness.
Average Absolute fitness (W); for example 8 offspring per lifetime
Average Relative Fitness (w): relative to other genotypes, how better is this fitness. Is it
average and higher than average. (w). Most important one.
Fittest genotype has a w=1, so all others are w=W/W max
When selection is happening, we have to know the dominance of alleles. Dominant
(favourable) will never outcompete recessive.
If we have a beneficial recessive allele, it will take a long time to get established. The
recessive can OUTCOMPETE dominant deleterious allele over time.
Batesian Mimicry: A palatable species (one that can be eaten) mimics another member of the
same species that is not palatable. It mimics the dangerous warning code that predators are
Mullerian Mimicry: 2 unrelated species that are BOTH dangerous, mimic the same warning
code even though they are completely different from each other.
Genetic Load: extent to which population moves away from optimal genetic constitution.
Different Types of Selection: Selection of single locus
Most traits are not governed by a single locus, they are more continuous distribution.
Stabilizing Selection: intermediate have much better fitness. Ie// medium sized birds have highest
Directional: selection in favour of extreme phenotypes ie// large birds are most favoured and
selected. Not all populations experience directional in the SAME direction. They can vary over
time. Disruptive Selection: Individuals at both extremes are selectively favoured so they have the
Frequency – Dependent Selection ( the fitness of geneotypes relies on frequency of it)
NEGATIVE FREQUENCY DEPENDENCE (being rare)
Advantage of being rare
Ie// predators who form search images of prey. If there is a lot of grey squirrels, then
hawks form a search image of grey squirrels. So the rare squirrel (white squirrel) will be
POSITIVE FREQUENCY DEPENDENCE (BEING COMMON)
When predators learn which warning to avoid. Warning coloration for example. This lets
the predator know its better to avoid eating the individual.
Why aren’t all living things perfectly adapted to their environment?\
Environment is always changing and natural selection cant predict future
Selection doesn’t always choose the best alleles, what if these alleles aren’t even present
Limited by dominance relationships
TRADE OFF ; good in one reason but negative effect for another reason
Genetic Drift: random unpredictable changes in allele frequencies. Not selection. Very strong in
small populations They can oppose selection. If selection is trying to get a deleterious allele out,
genetic drift can bring it back.
How does drift affect variation within a population: decrease, causes one allele go to
Mutation: mutation is not directed towards the need of the organism.
Most mutations have neutral effects of fitness, but the ones that due affect fitness are
harmful. Most mutations oppose selection, but some may be material for adaptation.
Gene Flow (migration): movement of alleles between populations.
Can introduce new alleles
Can oppose selection (selection-migration balance) – prevents population from being
perfectly adapted to the environment. Ie// a black rat living in black mountain moves to
white mountain with white rats. Ruins fitness of the white rats.
Hardy- Weinberg assumes random mating - But mating