Ch 11 Continuation of Evolution

Discussion…

Genetic Variation Within Populations

GG Gg gg

• Gene

• Allele

• Genotype

• Phenotype

A section of DNA that codes for a particular protein, physical trait, or function

One of two (or more) different forms of a gene; For example, for the eye color gene, one allele codes for blue eyes, while the other codes for brown. Often, one allele is dominant over the other. Ex: B or b

The combination of alleles for a particular gene; one allele comes from the mother and the other from the father. Ex: BB

The trait that results from the genotype Ex: Blue Eyes

Some Genetics Vocabulary

Genes are made up of complex combinations of the base pairs.

• Some genes code for proteins and enzymes.• Some genes turn other genes on or off. • Large sections of DNA code for NOTHING!

Genes and Chromosomes

A G

TC

Mutations• A mutation is

simply when there is an error in this copying process.

• This happens all the time!

• When the right kind of mutation happens in the right kind of way, the mutated gene becomes part of the gene pool and natural selection continues.

MutationsKeep in mind:Mutations themselves are random “mistakes”, but natural selection is not random! The tiniest genetic change will be favored if it increases an organism’s chances for survival or reproduction, even the slightest bit.

These tiny changes accumulate over the course of millions of years until the descendants have gradually diverged from their ancestors into a new species (or multiple different species).

Carrier Cc Dominant CC Recessive cc

When two carriers mate:

Ratio of Offspring:

Dominant: ¾ 75%

Recessive: ¼25%

Allele

Allele- Variant of a gene

Carrier Bb Dominant BB Recessive bb

When a recessive & carrier mates:

Ratio of Offspring:

Dominant: ½ 50%

Recessive:½ 50%

Gene Flowpg 315

Gene flow: the movement of alleles from one population to another.

Example: Birds of one species can leave their nesting area and fly to a new location. When this occurs alleles are removed from the old gene pool and alleles become part of the new gene pool in the new location.

**Gene flow increases genetic variation**

A lack of gene flow increases the chance that two populations will evolve into different species.

Genetic Drift

Changes in allele frequencies that are due to chance are called genetic drift.

Small populations are more likely to be affected by chance. Due to chance alone some alleles are likely to decrease in frequency and become eliminated. Other alleles are likely to increase in frequency and become fixed.

Bottleneck effect

Bottleneck effect: genetic drift that occurs after an event greatly reduces the size of a population.

Example: Over hunting of seals in the 1800s, reduced the seals to near extinction. Now protected, seal population has grown however it has very little genetic variation. (Certain alleles have been completely lost.)

Founder Effect

Founder Effect: is genetic drift that occurs after a small number of individuals colonize a new area.

Example: Amish in Lancaster – have a high rate of dwarfism

Although dwarfism is actually a rare syndrome found in the human population, there is a high rate in the Amish community because a small number of individuals colonized this area.

Hardy-Weinberg: showed that genotype frequencies in a population stay the same over time as long as certain conditions are met.

Populations that meet these conditions are not evolving & follow the Harding-Weinberg Equilibrium: Very large population – no genetic drift No emigration or immigration- no gene flow No mutations- no new alleles added to gene pool Random mating- no sexual selection No natural Selection- all traits equally aid in survival

Real populations rarely meet all 5 conditions

5 Factors that can lead to evolution

Genetic DriftGene flowMutationSexual SelectionNatural Selection

If one population becomes separated into two isolated groups, given enough time, the two groups will become different species.

Common ancestor of

species A1 and A2.

Two distinct species, no

longer capable of interbreedi

ng.

What did Darwin discover?Galapagos Islands- Speciation

Species ASpecies A1

Species A2

Darwin’s finches

Evidence For Evolution:

II. Homologous Anatomy

Divergent EvolutionRemember, homologous traits are

adaptations that are similar between species because both species share a common ancestor with the adaptation. For example, the following species

In this case, the three species have diverged

from each other for long enough that their wings have gradually

taken on different uses.

Divergent Evolution

all have wings, because they evolved from an earlier bird ancestor with wings.

Bird wing

Bat wing

Evidence For Evolution:

II. Homologous Anatomy

Convergent Evolution

• Not all similarities between species are homologous, however, because not all traits are inherited from a shared ancestor.

• Although both birds and bats use wings to fly, when you look at their anatomy, it’s obvious that their wings are completely different.

• The similarity is not due to common ancestry. Rather, birds and bats have undergone convergent evolution.

Evidence For Evolution:

II. Homologous Anatomy

More ExamplesAnalogy:

Many placental mammal species have corresponding marsupial species, which occupy the same ecological niche on other continents.

Marsupials Placentals

They are not related, however, and their similarities are due to similar environments and ways of life. This is, once again, convergent evolution at work.

All of the placental mammals are more closely related to each other than to any marsupial, and vice versa.