Transcript bio 11 genetics sep 15

16.1 Genes and Variations
The connection between heredity and evolution
Darwin did not know about Mendel’s findings
This left 2 big gaps in his thinking:
He didn’t know how traits were passed on
He didn’t understand why everyone and everything was different
Evolutionary biologists in 1930 made this connection
Natural selection and genes
Natural selection focuses on inheritable traits
Traits are determined by the inheritance of genes (dominant or recessive versions)
People inherit different versions which lead to variety
Some organisms inherit better versions of the trait than something else-why they survive
Organisms are typically Bb for traits
Gene Pool and Relative Frequency
Gene pool-made up of all the genes, including all the different alleles, that are in a population
Relative Frequency-number of times an allele occurs in a gene pool compared with the number of times
other alleles for the same gene occur
Out of 50 alleles, 20 are dominant and 30 are recessive.
Evolution is any change in the relative frequency of alleles in a population
If the relative freq. of the B in the mouse population changed over time to 30%, the population is evolving.
Why are organisms genetically different?
Mutations-change in the DNA base pairs
Caused by DNA replication errors or radiation/chemicals
No effect, increase or decrease fitness
Gene Shuffling-occurs during meiosis
Crossing over
Combining of different alleles during sexual reproduction
Limitations: does not change the relative frequency of alleles in a population
Single Gene and Polygenic traits
The number of genes that control a trait determine the # of phenotypes
Single gene trait-one gene controls a trait
Widow’s peak/attached vs unattached earlobes
Phenotypic ratios are determined by frequency of alleles and whether alleles
are dominant or recessive
Polygenic traits
Traits controlled by more than one gene
Height
Bell shaped curve shows how many organisms have a certain phenotype
The two extreme ends have low values and most organisms fall in the middle
range
Normal distribution
16.2 Evolution as Genetic Change
Genetics of Evolution-How does evolution work on
polygenic and single gene inheritance
Single gene trait-controlled by one gene
Natural selection changes the allele frequency and evolution takes place
Polygenic traits are affected in 3 ways
Directional, stabilizing, disruptive
Directional Selection
When individuals at one end of the curve have a higher fitness than the
middle
Example: finches
Thicker beaks can feed more easily on harder thicker shelled seeds
A food shortage may cause the supply of small and medium sized seeds to
decline
Birds that have larger beaks will survive because they have higher fitness
Stabilizing selection
When individuals near the center have higher fitness than individuals at either
end
Human babies
Smaller babies are less likely to be healthy
Larger babies have difficult being born
Average babies have the best chance
Disruptive Selection
When individuals at the upper and lower ends have the highest fitness
Birds with big and small beaks are more fit
Genetic Drift
Random change in allele frequency (number of times you see a certain
letter for a gene) that occur in small populations
Individuals carry a particular allele may leave more descendants than other
individuals, just by chance.
Over time, chance can cause an allele to become common in a population
Founder Effect
A situation in which allele frequencies change as a result of the migration of
a small subgroup of a population
Fruit flies on Hawaiian Islands
All descended from the same mainland, but different habitats on different
islands now have allele frequencies that are different from the original
Hardy-Weinberg principle
Explains when no change takes place over time
Allele frequency in a population will remain constant unless one or more factors cause those
frequencies to change
The situation in which allele frequency stays the same is called genetic equilibrium
5 conditions
Random mating
Population is large
No mutations
No natural selection
No migration
Link between antibiotics and evolution
Antibiotics are used to kill bacteria.
Many disease causing bacteria are evolving a resistance to antibiotics
How did this happen?
One or two bacteria have a genetic mutation which allows it to be unaffected by
bacteria; reproduction happens and eventually all bacteria have this resistance
Could this be a problem?
16.3 Ideas
Speciation-forming a new species
Reproductive isolation can make it happen
Cannot breed with their own kind and produce fertile offspring
3 ways: behavioral, geographic, temporal
Behavioral isolation
Individuals are able to reproduce but have different reproductive strategies
Can be important since it prevents one species from mating with another
Cheetahs have a certain mating behavior that does not allow them to mate
with other cats like lions and leopards
Eastern and western meadowlark have different calling songs even though
they are in the same area
Geographic Isolation
Barriers separate mating
The Colorado River split and separated two types of squirrels
Abert squirrel and Kaibab squirrel are very similar but have different fur colors
Temporal Isolation
Species reproduce at different times
Orchid species in the rainforest
Rana aurora - breeds January - March
Rana boylii - breeds late March - May
Unique about Darwin’s birds
They were all finches; he thought they were robins, warbler, and blackbirds
Assumptions:
Differences in beak size and shape produce different fitness that made
natural selection take place
There must be enough heritable variation
Tests for variation and findings
They caught individual birds
Recorded which lived and which died
Recorded anatomical characteristics (bell shaped curve)
Found there was tons of diversity amongst inheritable traits
How and when do finches specialize
During rainy season, food is plentiful so they are NOT picky
When it is drier and food is scarce, they are pickier
Changes in food supply can make it take place rapidly
Directional selection
Turn to page 408
Hypothesis A suggests that Lake 1 and 2 are not related
Hypothesis B suggests they are related
Hypothesis A
Ways speciation occurs
Founding of a new population
Finches from South American mainland arrived
Geographic Isolation
Flew to a different island
Changes in the gene pool
Reproductive isolation
Like finches with same beak size
Ecological competition
Limitations
No formation of a new species
Why care about evolution?
Understand things change and help us to respond to these changes