Day 11 October 14th Chapters 7 and 8

Second exam, posted!

Chapter 7: Mendelian Inheritance

Family resemblance: how traits are inherited

Lectures by Mark Manteuffel, St. Louis Community College; Clicker Questions by Kristen Curran, University of Wisconsin-Whitewater

(note the hand position of each twin)

Where do we begin and our parents end?

Selective Breeding: Observing Heredity

Observations are easy – figuring out how is hard!!!

Are any human traits determined by a single

gene? Traits that are determined by

the instructions a person carries at one gene are called single-

gene traits.9,000 human traits

Other traits, such as height, hair color, and eye color, are a bit trickier.

Sexist view of science?

True-Breeding

7.4 Segregation: you’ve got two copies of each gene but put only one copy in each sperm or egg.

A dominant trait masks the effect of a recessive trait.

7.5 Observing an individual’s phenotype is not sufficient for determining its genotype.

Phenotypes and Genotypes

The outward appearance of an individual is called their phenotype.

Underlying the phenotype is the genotype. • This is an organism’s genetic

composition.

Surprise???

How do we analyze and predict the outcome of crosses?

Assign symbols to represent the different variants of a gene.

Generally we use an uppercase letter for the dominant allele and lowercase for the recessive allele.

If we don’t know which of the two possible genotypes the pigmented individual is, we can write A_, where the “_” is a placeholder for the unknown second allele, whose identity we aren’t certain of.

Probability has a central role in genetics for two reasons: The first is a consequence of

segregation.

The second reason is that fertilization, too, is a chance event.

7.6 Chance is important in genetics.

Probabilities Any gamete produced by an individual

heterozygous for a trait has a 50% probability of carrying the dominant allele and a 50% probability of carrying the recessive allele.

Probabilities

If a male is heterozygous for albinism (Aa) and a female is homozygous for albinism (aa), what is the probability that their child will be homozygous for albinism (aa)?

Analyzing Which Individuals Manifest the Trait and Which Do Not

Why do breeders value “pedigreed” horses and

dogs so much?

7.10 What’s your blood type?

Some genes may have more than two alleles.

It can be O, A, B, or AB

Multiple Allelism

in which a single gene has more than two alleles

each individual still carries only two alleles

Inheritance of the ABO Blood Groups

A, B, and O alleles

The A and B alleles are both completely dominant to O.

The A and B alleles are codominant to each other.

Individuals can be one of four different blood types: A, B, AB, and O.

Why are people with type O blood considered “universal donors”? Why are those with type AB considered “universal acceptors”?

7.11 Multi-gene Traits

How are continuously varying traits such as height influenced

by genes?Old wives’ tales suggest a couple of ways for predicting height: if the baby is a boy, they say to add five inches to the mothers’ height and average that with the father’s height. Or if it is a girl, subtract five inches from the father’s height and average that with the mother’s height. Alternatively, the lore says to just take the child’s height at two years and double it.

Polygenic Trait

A trait that is influenced by many different genes

Mind-blowingly complicated!!!

Additive Effects

what happens when the effects of alleles from multiple genes all

contribute to the ultimate phenotype

The Tall Gene – hormones and

bone length and growth factors – oh

my!

Why might computer nerds be more likely to have autistic children?

•Autism involves 10 or 20 different genes!•Unusual abilities of perception, analytical skills, and focus. This idea—called the “geek theory of autism”

7.12 Pleiotropy: How can one gene influence multiple traits?

What is the benefit of “almost” having sickle cell disease?

The SRY Gene “Sex-determining Region on the Y-

chromosome”

Causes fetal gonads to develop as testes shortly after fertilization.

Following the gonads’ secretion of testosterone, other developmental changes also occur.

7.13 Why are more men than women color-blind? Sex-linked traits differ in their

patterns of expression in males and females.

If a man is color-blind, did he inherit this condition

from his mother, his father, or both parents?

men only get one chance to inherit the normal version of the gene

Chapter 8: Evolution and Natural Selection

Darwin’s dangerous idea: evolution by natural selection

Lectures by Mark Manteuffel, St. Louis Community College ; Clicker Questions by Kristen Curran, University of Wisconsin-Whitewater

Evolution in Action

8.1 We can see evolution occur right before us. Therefore, evolution is a scientific process.

Could you breed fruit flies who could live longer than 20 hours on average?

Populations are studied

When these eggs hatch, do you think the flies in this new generation will live longer than 20 hours without food?

Make a prediction: A population of fruit flies was starved until 80% of the flies were dead. The remaining flies were fed and offspring were produced. What do you expect to see in the next generation if you repeat the starvation experiment?

1. More flies will be alive after 20 hours.

2. Fewer flies will be alive after 20 hours.

3. Fruit flies fed after 80% of the population is dead will lay more eggs.

4. No change in the average number of fruit flies that were alive after 20 hours.

Make a prediction: A population of fruit flies was starved until 80% of the flies were dead. The remaining flies were fed and offspring were produced. What do you expect to see in the next generation if you repeat the starvation experiment?

1. More flies will be alive after 20 hours.

2. Fewer flies will be alive after 20 hours.

3. Fruit flies fed after 80% of the population is dead will lay more eggs.

4. No change in the average number of fruit flies that were alive after 20 hours.

After 60 generations the average starvation resistance of fruit flies was 160 hours! What has happened to this population of fruit flies?

1. They are genetically identical to the original population.

2. The are genetically different from the original population.

After 60 generations the average starvation resistance of fruit flies was 160 hours! What has happened to this population of fruit flies?

1. They are genetically identical to the original population.

2. The are genetically different from the original population.

What happened? Evolution

• a genetic change in the population

Natural selection• the consequence of certain individual

organisms in a population being born with characteristics that enable them to survive better and reproduce more than the offspring of other individuals in the population

Does evolution occur?

The answer is an unambiguous: YES.

We can watch it happen in the lab whenever we want.

Recall from our discussion of the scientific method that for an experiment’s results to be valid, they must be reproducible.

Experiments in Evolution

Dogs? Rabbits?

In Nature -

Why are camels a successful species?

Evolution

How does evolution occur?

What types of changes can evolution cause in a population?

Five primary lines of evidence

Evolution by natural selection

Darwin’s Journey to an Idea

8.2 Before Darwin, most people believed that all species had been created separately and were unchanging.

Button started the debate by suggesting the Earth had to be at least 75,000 years old!

Jean-Baptiste Lamarck

Biologist, early 1800s

Living species might change over time.

(Was wrong about the mechanism - he thought that change came about through the use or disuse of features)

Charles Lyell

Geologist

1830 book Principles of Geology• Geological forces had shaped the earth and

were continuing to do so.

Gradual but constant change

This idea that the physical features of the earth were constantly changing would most closely parallel Darwin’s idea that the living species of the earth, too, were gradually—but constantly—changing.

We know the Earth is constantly changing

• Fossils of shells have been found high in the Andes Mountains

• Forest fires wipe out entire species of plants and animals.

• Rivers flow, and carve out rock, creating two distinct shores, where different species live.

• Lakes dry up, killing all marine life inside.• Pollution and Toxic spills kill organisms.• Volcanoes.• Humans are changing the earth.

In the 1790s, Georges Cuvier began to explore the bottoms of coal and slate mines and found fossils

Why were fossils such a problem for people at that time?

• This was highly troubling for people at the time.

http://www.bspcn.com/2009/04/03/11-extinct-animals-that-have-been-photographed-alive/

Extinction

• five mass extinctions on earth, and four in the last 3.5 billion years - many species have disappeared in a relatively short period of geological time.

• The "Great Dying" about 250 million years ago,

which is estimated to have killed 90% of species existing at the time.

• Most extinctions have occurred naturally, without human intervention: it is estimated that 99.9% of all species that have ever existed are now extinct.