Often, fish that live in caves for many generations are found blind, unlike similar fish living in the open. 1.How did the fish become blind?(Guidance: If you lock people in a

cave for years, will their children be born blind??) 2. ….

Cave Dweller Fish (Blind)

Cave 1 Cave 2

100 km

An Experiment:

X

Seeing!

1. How did the fish become blind?

2. Why did only distant cave dwellers give seeing offspring?

X

blind

X

blind

Chasing a Gazelle in Tanzania

Cheetahs are the fastest land animal on earth. It’s a great hunter. It is relatively immune to common infections. Yet, they are endangered to extinction. What could be the reason?

Cheetah’s adaptations for speed

Sickle Cell anemia – continue jigsaw reading.

Turn in homework (sickle cell anemia II).

Gene pool: The total collection of alleles in the population.Allele frequency: The fraction of one allele out of the gene pool.Example: If all of the individuals are heterozygote Aa, what is the allele frequency of A and a?

1. How do we know they are going extinct?2. What evidence is there for genetic uniformity?3. What are the ideas regarding the historical events that lead to the cheetah’s situation?4. Why is genetic variation important for survival?

At least two items for each:

“Cheetah Extinction”

1) For each part:-List at least TWO important or interesting facts.

- How does the text explain, genetically, why cheetahs might go extinct.

The text is divided into four parts, each part per one group member to read.

Together, write the answers to the following questions on the group paper:

What is the purpose of the 3rd paragraph in context of the article? To….A. suggest that humans caused

cheetah’s extinction.B. reject the idea that humans

caused the cheetah’s extinction.C. compare famous people and their

effect on cheetahs.D. Portray the life of humans and

cheetahs in the past.

Cheetahs are the fastest land animal on earth. It’s a great hunter. It is relatively immune to common infections. Yet, they are endangered to extinction. What could be the reason?

Cheetah’s adaptations for speed

Journal 2: “Cheetah Extinction”

For your part:1) List at least TWO important or interesting facts. 2) How does the text explain, genetically, why cheetahs might go extinct.

The text is divided into four parts, each part per one group member to read.

original population

new population

Chance

survivors

1. Describe the bottleneck effect. What is the principle (general idea)?

2. If the balls were variations of genes – what is happening to the population?

repr

oduc

tion

?

GENETIC DRIFT

Bottle Neck Effect: few survivors.Founders Effect: few that separated

* A change in the frequency of an allele due to random sampling

* Typically, starts from a very small, isolated population.

For example:

1) Bottle neck effect: After a natural disaster. A few “lucky ones” survive, not necessarily the most adapted.

Example: Cheetahs2) Founder Effect: A small group

separates and migrates to a new place.

Example: Rafting on logs.

Founder Effect: A type of genetic drift

Natural Selection Genetic Drift

Better Adapted survive

‘Lucky’ survive adapted or not adapted

Future adaptations can build up gradually

Future Adaptations need to ‘catch up’ rapidly.

So, how does genetic diversity build up?

Genetic Diversity: How does it form? A. Mutations:

New DNA sequences- Very slowly accumulatingB. Mixing genes – recombination:Depends on sexual reproduction- Varieties of eggs and sperm in

meiosis- Various combinations of mating.- No new genes are formed – only

mixed!

Sexual reproduction creates diversity in the population.In which steps in the reproduction cycle are genes ‘shuffled?’ Explain.Meiosis – segregation of alleles.

Selection of gametes for the zygote.

Meiosis - crossing over.

Choice of a mate.

4N 2N

4N

N

N

2N

2N

N+N

The Sexual Life Cycle

New generation

Zygote

Gam

etes

Body cells

***

Gene pool: The total collection of alleles in the population.

Allele frequency: The fraction of one allele out of the gene pool.

Example: If all of the individuals are heterozygote Aa, what is the allele frequency of A and a?

Sickle Cell Anemia

Sickle cellNormal cell

Sickle Cells blocking the blood vessel

malaria

gc1 sickle cell

malaria

malaria

Fy0 allele

1) Why is sickle cell anemia still around, despite natural selection?

2) What would happen over time to the frequency of an allele for a serious disorder that is dominant? Explain.

Suppose there are two deadly genetic disorders – one carried by a dominant allele,

B-disorder b-normalone carried by a recessive allele.

H- normal, h-disorder

Which disorder do you expect will disappear faster from the population by natural selection, B or h? Explain.

Quiz: Genetic Variation and Extinction

1) How did the cheetahs lose genetic diversity?

2) Why does lack of genetic diversity risk the existence of the cheetah species?

3) What is the main difference between genetic drift and natural selection?

Write in complete sentences. You do not need to copy the questions.

Some recessive disorders, such as Tay Sachs, sickle cell anemia and Cystic fibrosis, shorten the life of the affected individuals.

What would you expect would happen to the frequency of these alleles in the population over time? Explain.

Deer’s antlers (horns): They help it compete for a mate, yet may get in the way when running through thick woods, or feed in dense brush.Will the future deer still have antlers? Explain.

+ -

Organisms that survive are well adapted to their environment. Therefore, why do they need to maintain genetic diversity in their populations?

In what conditions is a mutation not a source of genetic variation? (Hint: location in the body, effect on protein..)

Previous Giraffe Neck Lengths

If the trees that the Giraffes eat have evolved to be taller, what would this graph look like today? Draw and explain your answer.

Short Medium Long% o

f in

div

idu

als

% o

f in

div

idu

als

Today’s Giraffe Neck Lengths

The giraffes with longer necks would have a greater chance to compete on the taller trees, and became the majority.

Short Medium Long