During the process of meiosis, independent assortment and crossing over (recombination) can occur. This results in genetic variation in the offspring of sexually reproducing individuals

◦ Describe what happens during independent assortment

◦ Explain how crossing over (recombination) can contribute to the genetic variation that results from sexual reproduction. You may wish to draw a diagram.

◦ Genetic variation can be a results from mutation. Explain the results of mutation sin somatic and gametic cells

Exam question(2008)

EVOLUTIONMAH – Year 12

What is the gene pool? Where does the variation originally come

from? What is gene flow?

DO NOW

Summary

...process by which new species of plants and animals develop from earlier forms

...is the change in the gene pool of a population over periods of time and occurs whenever the frequency of alleles in the gene pool changes

... is the change in the inherited traits of a population of organisms through successive generations

Evolution Intro

Homerman

What is the gene pool?

Is the total number of genes and alleles present within a population at a given point in time

Gene Pools and Allele Frequencies

Allele Frequency Frequency of allele = Occurrence of that

allele Total number of alleles

Take two bits of paper either a pink/green (or beans)

We will use this to show how allele frequencies can change

Frequency of allele = Occurrence of that allele Total number of alleles

Sickle Cell and Malaria Simulation

Simulation

Gene Pools and Allele Frequency

Gene Pool 1

Gene Pool 2

GEOGRAPHICAL BARRIERS THAT AFFECT GENE FLOW

GENE FLOW: Genes are exchanged with other gene pools as individuals move between them. This is a source of new genetic variation and tends to reduce differences between populations due to natural selection or genetic drift

IMIGRATION AND EMIGRATION

VARIATION IN GENE POOL DUE TO MUTATIONS AND RECOMBINATION

Factors Favouring Gene Pool Stability

Factors Favouring Gene Pool Change

Large Population Small Population

Random Mating Assortative mating (like and like)

No gene flow Gene Flow (immigration and emigration)

No Mutation Mutations

No Natural Selection Natural Selection

Gene Pool Change

Evolution, Alleles, and Gene Pools Variation within a gene pool comes from

mutation or recombination

Changes in allele frequencies proceed EVOLUTION

Changes in allele frequency come from immigration and emigration (gene flow), genetic drift (CHANCE), natural selection, sexual selection

Crossing Over

Gene Migration Is the introduction or loss of alleles into or out of a

population

Immigration: when individuals migrate INTO a population they bring new alleles into the gene pool

Emigration: When individuals migrate OUT OF a population they remove some of the alleles from the gene pool

New alleles introduced into a gene pool INCREASE S THE GENETIC VARIATION of a population more likely to survive changes in the environment

Genetic Drift ...is the change in allele frequency in a gene

pool in a small population by CHANCE alone

e.g. The death of an individual carrying a rare allele will make the frequency of that allele less or removed all together

Special cases: Founder and Bottleneck

Founder Effect...occurs when a few individuals migrate from a

larger population to establish a new population in a new area

Consequence: The colonising population may evolve differently from that of the parent population

In some cases: it may be possible for certain alleles to be missing altogether from the individuals in the isolated population.

Polydactyly Fingers

Polydactyly -- extra fingers or sometimes toes -- is one symptom of Ellis-van Creveld syndrome. The syndrome is commonly found among the Old Order Amish of Pennsylvania, a population that experiences the "founder effect."

Why?? Genetically inherited diseases like Ellis-van

Creveld are more concentrated among the Amish because they marry within their own community.

This prevents new genetic variation from entering the population.

Children are therefore more likely to inherit two copies of the particular recessive genes that lead to genetic disease.

Huntington’s is a neurodegenerative genetic disorder that affects muscle coordination and leads to cognitive decline and dementia

The Afrikaner population of Dutch settlers in South Africa is descended mainly from a few colonists.

Today, the Afrikaner population has an unusually high frequency of the gene that causes Huntington’s disease, because those original Dutch colonists just happened to carry that gene with unusually high frequency.

This effect is easy to recognize in genetic diseases, but of course, the frequencies of all sorts of genes are affected by founder events.

Founder and Huntington’s

Milk A1/A2 Protein

Another example

Bottleneck Effect...occurs when a population is reduced to low numbers

by predation, disease, periods of climate change, or catastrophe (selection pressures of natural disasters)

The populations recover after being squeezed through a ‘bottleneck’ of low numbers

Results in some alleles being above normal number or lost altogether (loss of genetic variation)

Pg. 105 Biozone

Northern elephant seals have reduced genetic variation probably because of a population bottleneck humans inflicted on them in the 1890s.

Hunting reduced their population size to as few as 20 individuals at the end of the 19th century.

Example of Bottleneck

Their population has since rebounded to over 30,000—but their genes still carry the marks of this bottleneck: they have much less genetic variation than a population of southern elephant seals that was not so intensely hunted.

Example of Bottleneck

Non-random Mating Nearby mating lead to inbreeding (song) The ultimate of inbreeding is self-

fertilisation (occurs in plants)

InbreedingResults in homozygous alleles – heterozygous

advantage lostChance of unfavourable recessive genes turning

up in the offspring is enhanced – humans have strict rules against incest

Natural Selection...is the environment selecting FOR or AGAINST

certain PHENOTYPESphenotypes: structure, metabolism, behaviour, physiology

environment factors: predators, competition, disease, lack of food, light, water, climate factors

..possess adaptations such as ability to avoid predators or to compete strongly for food

BEAN EXPERIMENT

Natural Selection...can act on phenotypes in different ways

that will either maintain or change the genotypes present in a species

Population Size

Is just a fancy name for speciation by geographic isolation

Speciation: The formation of new and distinct species in the course of evolution

Allopatric speciation

In this mode of speciation, something extrinsic to the organisms prevents two or more groups from mating with each other regularly, eventually causing that lineage to speciate.

Isolation might occur because of great distance or a physical barrier, such as a desert or river.

Allopatric speciation

In order for a speciation even to be considered “allopatric,” gene flow between the soon-to-be species must be greatly reduced—but it doesn’t have to be reduced completely to zero.

Allopatric speciation (cont)

A single randomly mating species is widely distributed through a geographical region.

Quite suddenly, a natural barrier forms, dividing the species into two separate groups.

Over the succeeding generations, either through selection or random events, the two populations come to differ.

When the barrier is removed, the populations are now so different that there is no reproduction between them: they have become two distinct species

Steps Involved:

Geographic patterns: If allopatric speciation happens, we’d predict that populations of the same species in different geographic locations would be genetically different. There are abundant observations suggesting that this is often true.

For example, many species exhibit regional “varieties” that are slightly different genetically and in appearance, as in the case of the Northern Spotted Owl and the Mexican Spotted Owl.

Example:

On the Galapagos islands Charles Darwin noticed a large variety of finches which differed in beak shape and overall size.

WHY WOULD INDIVIDUALS ON THE SAME ISLAND OR NEARBY ISLANDS HAVE

DIFFERERNT BEAK SHAPES AND SIZES?

Question?

On the Galapagos islands Charles Darwin noticed a large variety of finches which differed in beak shape and overall size.

WHY WOULD INDIVIDUALS ON THE SAME ISLAND OR NEARBY ISLANDS HAVE

DIFFERERNT BEAK SHAPES AND SIZES?

THIS IS ADAPTIVE RADIATION AND NATURAL SELECTION AT WORK

Question?

This is where species all deriving from a common ancestor have over time successfully adapted to their environment via natural selection.

The development of many different forms from an originally homogeneous group of organisms as they fill different ecological niches

Adaptive radiation (defined…)

This is where species all deriving from a common ancestor have over time successfully adapted to their environment via natural selection

Finches managed to occupy the Galapagos islands, over 600 miles away from their original location. They occupied an ecological niche with little competition.

As the population began to flourish in these advantageous conditions, intraspecific competition became a factor, and resources on the islands were squeezed and could not sustain the population of the finches for long.

Due to the mechanisms of natural selection, and changes in the gene pool, the finches became more adapted to the environment.

As competition grew, the finches managed to find new ecological niches, that would present less competition and allow them, and their genome to be continued.

The finches adapted to take advantage of the various food sources available on the island, which were being used by other species. Over the long term, the original finch species may have disappeared, but by diversifying, would stand a better chance of survival.

All in all, the finches had adapted to their environment via natural selection, which in turn, has allowed the species to survive in the longer term, the prime directive of any species.

Example: Finches

Adaptive Radiation

Patterns of Evolution

Divergent evolution is the process of two or more related species becoming more and more dissimilar.

Example: The red fox and the kit fox provide and example of two species that have undergone divergent evolution. The red fox lives in mixed farmlands and forests, where its red color helps it blend in with surrounding trees. The kit fox lives on the plains and in the deserts, where its sandy color helps conceal it from prey and predators. The ears of the kit fox are larger than those of the red fox. The kit fox's large ears are an adaptation to its desert environment. The enlarged surface area of its ears helps the fox get rid of excess body heat. Similarities in structure indicate that the red fox and the kit fox had a common ancestor. As they adapted to different environments, the appearance of the two species diverged.

Divergent Evolution

Divergent Evolution

Related Species

Related Species

Different Environment

s

Less Alike

Convergent evolution - unrelated species become more and more similar in appearance as they adapt to the same kind of environment.

Example: unrelated types of plants that have adapted to desert environments. The Cactus which grows in the American desert has similar resemblances to the euphorbia, which grows in the African deserts. Both have fleshy stems armed with spines. These adaptations help the plants store water and ward off predators.

Convergent Evolution

Convergent Bird and bat wings are analogous—that is,

they have separate evolutionary origins, but are superficially similar because they evolved to serve the same function. Analogies are the result of convergent evolution.

Convergent EvolutionUnrelated Species

Similar Environment

s

Unrelated Species

More Alike