11,12,13

Each one of the conditions required to maintain Hardy-Weinberg equilibrium is violated!

• Are all populations large?– Although many populations are, some are small enough

for random events to change gene frequencies. • This microevolutionary phenomena is called genetic

drift. • Bottleneck Effect:• In this case, disasters such as floods and fires can

drastically reduce the size of the population, leaving by chance, individuals that are not necessarily representative of the original population.

By chance the surviving population is made up mostly of pink

Greater Prairie chicken had major populations removed due to farming. By 1993 only 2 populations totaling 50 birds

remained

• Founder Effect

• This occurs whenever a few individuals colonize a new habitat.

• The founding population is usually small.• Their gene pool may not be representative of the

entire gene pool they left.

• In the Amish, in fact, Ellis-van Creveld syndrome has been traced back to one couple, Samuel King and his wife, who came to the area in 1744. The mutated gene that causes the syndrome was passed along from the Kings and their offspring, and today it is many times more common in the Amish population than in the American population at large.

Description This is a rare autosomal recessive genetic resulting in short stature (average: 3-5'1"), postaxial polydactyly, short arms and legs in relation to the trunk, short ribs and small lungs, and 50-60% of individuals have congenital heart defects. So people with EvC have smaller than average, or absent nails, teeth can be oddly shaped, have very thin enamel and make an appearance far too early (Angus cut his first tooth when he was 7 weeks old), and brittle hair (this is just a name. The hair looks normal but each hair is quite thin). There are other conditions grouped under the term ectodermal dysplasias which affect the sweat glands, but I haven't heard of anyone with EvC having these problems.It is extremely rare for intelligence to be affected but a very small percentage (less than 1%) of babies born with EvC can have structural abnormalities in their brains.The most upsetting aspect of EvC as a parent is finding out that your child has a heart defect. Short stature and pretty unique hands are fine because they don't affect your child's independence and survival, but a heart defect is a huge blow. The majority of children with a common atrium or ASD (atrial septal defect) will be quite happy up until they reach a year or two and then they can have planned surgery which will fix the problem. Recovery can be slower in kids with EvC because of their smaller lungs, but once they get over it they can carry on as normal. Some children deteriorate before this time and need surgery within weeks or months of birth. We were unfortunate in this respect.I did read in a couple of articles on the Internet that between a third to a half of children die in infancy (one article specified the first month of life) due to a combination of heart and lung problems. This is a very scary statistic, and I really didn’t like it, but I guess we have to go by the articles written by those with the most access to the available data. Major breathing difficulties due to small lungs and short ribs can become apparent immediately after birth and sometimes nothing can be done to save the baby. Other children develop problems a few weeks or months down the line because of a combination of heart and lung problems.

Polydactyly

Gene flow occurs• Populations may gain or lose alleles by the

migration or immigration of individuals, seeds, pollen etc.

• For example, a wind storm may blow pollen from an aa population into a population consisting of just AA individuals.

Mutations occur……

• A new mutation that is transmitted in gametes can immediately change a gene pool of a population.

• In fact, rates of one mutation per locus per 105 to 106 gametes is typical for most species.

3 types of selection:Stabilizing, Directional, Disruptive

ch 13 (12,13)

Three modes of natural selection

• Stabilizing Selection• Directional Selection• Disruptive Selection

Stabilizing Directional Disruptive

• Stabilizing selection – Favors the intermediate phenotype out of a range of

phenotypes. – The extremes in variation are selected against. – For example, infants weighing significantly less or more than

7.5 pounds have higher rates of infant mortality. – Selection works against both extremes.– Tends to maintain status quo and reduce variation

• Directional selection – Favors phenotypes at one extreme of the range of variation. – Insecticide resistance is an example. DDT was a widely used

insecticide. After a few years of extensive use, DDT lost its effectiveness on insects. Resistance to DDT is a genetic trait that the presence of DDT in the environment made into a favored trait. Only those insects resistant to DDT survived, leading over time to populations largely resistant to DDT.

• Disruptive selection – favors individuals at both extremes of variation: selection is

against the middle of the curve. – This causes a discontinuity of the variations, causing two or

more morphs or distinct phenotypes. – The African swallowtail butterfly (Papilo dardanus) produces

two distinct morphs, both of which resemble brightly colored but distasteful butterflies of other species. Each morph gains protection from predation although it is in fact quite edible.

So what about sexual selection section 14

• Darwin was the first to investigate the idea that individuals with certain inherited characteristics are more likely than others to obtain mates.

• Sexual selection can result in sexual dimorphism

Sexual selection and sexual differences

• Intrasexual – selection within the same sex. Individuals of one sex are competing for mates of the opposite sex. (Usually this is between males competing for a large group of females…..male deer)

• Intersexual – selection of mate choice. Individuals of one sex (usually females) are choosy in selecting their mates. ….males with the largest or most colorful feather showing

So what’s the purpose of the “choosy female?”

• It appears the females are searching for the males with the “good genes”

• A study was done on a group of tree frogs . Females usually chose the male with the longest mating call

A study was done with one females eggs

• ½ of eggs were fertilized with long calling males

• ½ of eggs were fertilized with short calling males

• Results………………..

The offspring from the long calling males grew bigger, faster and survived better

Pheromones!

The sweaty T –shirt Experiment

• Experiment: sniff test….

• http://www.pbs.org/wgbh/evolution/library/01/6/l_016_08.html

• Result: Women favor the smell of the sweaty T shirts worn by men with immune response genes (IRG) different from their own.

Are Humans Exempt from Natural Selection?

• It has been argued that advances in medicine, sanitation, etc. have removed humans from the rigors of natural selection. There is probably some truth to this, but consider:

– Of all the human eggs that are fertilized, only one-third or so will ever reproduce themselves. The others are eliminated as follows:

• Mortality selection – Some 30% of pregnancies end by spontaneous abortion of

embryos and fetuses. – 5% by stillbirths and infant deaths. – 3% by childhood deaths.

• Sexual selection – Another 20% will survive to adulthood but never marry.

• Fecundity selection – Of those that do marry, 10% will have no children.

http://www.tomchalk.com/evolution.html