Often, fish that live in caves for many generations are found blind, unlike similar fish living in t...
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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 2. Cave Dweller Fish (Blind). Cave 1. X. X.

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1. How did the fish become blind?

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1 how did the fish become blind

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. ….


1 how did the fish become blind

Cave 2

Cave Dweller Fish (Blind)

Cave 1

X

X

blind

blind

X

Seeing!

100 km

An Experiment:

  • How did the fish become blind?

  • Why did only distant cave dwellers give seeing offspring?


1 how did the fish become blind

Chasing a Gazelle in Tanzania


1 how did the fish become blind

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?


1 how did the fish become blind

Cheetah’s adaptations for speed


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Sickle Cell anemia – continue jigsaw reading.

Turn in homework (sickle cell anemia II).


1 how did the fish become blind

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 did the fish become blind

At least two items for each:

  • 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?


1 how did the fish become blind

“Cheetah Extinction”

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

  • 1) For each part:

  • List at least TWO important or interesting facts.

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

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


1 how did the fish become blind

  • What is the purpose of the 3rd paragraph in context of the article? To….

  • suggest that humans caused cheetah’s extinction.

  • reject the idea that humans caused the cheetah’s extinction.

  • compare famous people and their effect on cheetahs.

  • Portray the life of humans and cheetahs in the past.


1 how did the fish become blind

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?


1 how did the fish become blind

Cheetah’s adaptations for speed


1 how did the fish become blind

Journal 2: “Cheetah Extinction”

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

For your part:

1) List at least TWO important or interesting facts.

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


1 how did the fish become blind

Chance survivors

original population

new population


1 how did the fish become blind

reproduction

?

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

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


1 how did the fish become blind

GENETIC DRIFT

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

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

For example:

Bottle Neck Effect: few survivors.

Founders Effect: few that separated


1 how did the fish become blind

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

Example: Cheetahs

2)Founder Effect: A small group separates and migrates to a new place.

Example: Rafting on logs.


1 how did the fish become blind

Founder Effect: A type of genetic drift


1 how did the fish become blind

Natural Selection

Genetic Drift

‘Lucky’ survive adapted or not adapted

Better Adapted survive

Future Adaptations need to ‘catch up’ rapidly.

Future adaptations can build up gradually


1 how did the fish become blind

So, how does genetic diversity build up?


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Genetic Diversity: How does it form?

  • Mutations:

  • New DNA sequences

  • Very slowly accumulating

  • B. 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!


1 how did the fish become blind

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.


1 how did the fish become blind

*

*

*

Body cells

2N

4N

2N

4N

The Sexual

Life Cycle

New generation

N

2N

Gametes

N+N

Zygote

N


1 how did the fish become blind

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 did the fish become blind

Sickle Cell Anemia

Sickle cell

Normal cell


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Sickle Cells blocking the blood vessel


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malaria


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gc1 sickle cell

malaria


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Fy0 allele

malaria


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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.


1 how did the fish become blind

Suppose there are two deadly genetic disorders –

one carried by a dominant allele,

B-disorderb-normal

one 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.


1 how did the fish become blind

Quiz: Genetic Variation and Extinction

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

  • How did the cheetahs lose genetic diversity?

  • 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?


1 how did the fish become blind

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.


1 how did the fish become blind

+

-

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.


1 how did the fish become blind

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


1 how did the fish become blind

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


1 how did the fish become blind

Previous Giraffe Neck Lengths

% of individuals

Short

Medium

Long

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


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Today’s Giraffe Neck Lengths

% of individuals

Short

Medium

Long

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


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