06/03/2014

1

Biological Psychology

DNA, Genetics & Evolution

Is this what makes you human?

06/03/2014

2

Chromosomes

Each chromosome is a double stranded molecule of deoxyribonucleic acid (DNA).

The structure of the molecule was described in 1953 by James Watson and Francis Crick.

06/03/2014

3

DNA

The two strands are held together by nucleotide bases which are attracted to each other.

So that:

Adenine links to Thymine

Guanine links to Cytosine

06/03/2014

4

So what are genes?

Genes are sequences of nucleotide bases.

Imagine a simple alphabet made up of only 4 letters

A, T, C, G

Genes are words made up of sequences of these bases

Interesting Facts

It has been estimated that the human genome (the total complement of all 23 pairs of chromosomes) contains over 3,000 million base pairs (A-T, C-G).

To enable over 3,000 million base pairs to exist, each cell in the body contains about 6 feet of DNA crammed into a nucleus that is 0.005mm in diameter.

It is estimated that our 23 pairs of chromosomes contain around 30,000 genes.

This is the amount of information required to build a human being from a single egg and to maintain it through life.

06/03/2014

5

The Importance of DNA

Genes provide a code to make amino acids.

Amino acids are the building blocks of proteins.

Our genes can only make 20 different amino acids.

All our proteins are made from these 20 amino acids

DNA and Proteins

So:

The instructions for making proteins are stored on chromosomes locked away in the cells nucleus.

However, protein manufacture does not take place in the nucleus, but in the surrounding cytoplasm. How?

06/03/2014

6

The Answer

Thanks to another nucleic acid ribonucleic acid (RNA).

Similar to DNA, but it exists as a single strand, enabling it to move in and out of the nucleus.

Has the base URACIL instead of thymine.

The Process

MESSENGER RNA (mRNA) transports the DNAs instructions from the nucleus to the cytoplasm.

The genes are translated into amino acids.

Each amino acid is added to a lengthening strand.

When the length of the mRNA is finally translated, the completed protein is released.

06/03/2014

7

Why are proteins important?

They are vital constituents of all living things.

A typical mammalian cell may have as many as 10,000 different proteins, each with its own unique role.

One of the most important roles of proteins is as enzymes

Where do we get our DNA from?

DNA is passed on from parent to child.

But you do not get all your parents DNA, you get half from you mother and half from your father.

This allows you to have different combinations of genes than your siblings.

This allow for variation between and within species.

06/03/2014

8

Human Reproduction

Humans have 23 matched pairs of chromosomes in the nucleus of all cells with one exception

The Egg and Sperm Cells

DIPLOID CELLS

46 chromosomes (most cells in the body)

HAPLOID CELLS

23 chromosomes (the egg in the female, sperm in the male)

Human Reproduction

Diploid cells replicate by a process called MITOSIS

Mitosis generates a complete copy of the cells genetic information

All new cells contain copies of all 23 matched pairs of chromosomes.

06/03/2014

9

Human Reproduction

Haploid cells (sperm and egg) are created by a process celled MEIOSIS

Only half the number of chromosomes

1 of each rather than 2 are assigned to each cell

The chromosome are randomly assigned to each gamete

Human Reproduction

When the sperm fertilises an egg, chromosomes from the mother pair up with the relevant partner chromosome from the father.

Therefore the resulting offspring inherits half its genetic information from its mother and half from its father.

06/03/2014

10

Human Reproduction

Why is this important?

VARIATION

New gene combinations are constantly produced.

No two individuals are the same.

Is this always true?

Genes and Chromosomes

Genes are located on CHROMOSOMES, which are present in the nucleus of every cell.

Chromosomes occur in matched pairs.

The 2 genes (alleles) that control each trait are situated at the same locus on each chromosome of a particular pair.

Each species has a characteristic number of pairs of chromosomes in each of its body cells.

How many pairs of chromosomes do humans have?

06/03/2014

11

A bit more variation

Variation is further promoted by the phenomenon of crossing over.

This occurs during meiosis.

06/03/2014

12

Mendel 1822-1884

Published his work in 1866.

In his revolutionary work, he did not deal with variation, but rather consistent traits.

He showed that traits can be passed from Grandparent to offspring, bypassing the parental generation.

He showed that traits were carried through something other than blood as had been assumed.

We will consider the work of Mendel in the seminar

Charles Darwin

Not a natural Biologist.

Not a natural academic.

But now known as the founder of modern day biology.

06/03/2014

13

Pre-Darwinian Thought 19th Century Britain

Creationism was accepted unchallenged by the general public

However, much of the evidence Darwin used to develop his theory was known

Geologists and Palaeontologists had evidence that life had existed on Earth for a long time AND that it had changed over time.

Members of a species look similar to each other when compared to another species.

BUT when compared to each other, there are differences between members of a species.

Theory of Inheritance of Acquired Traits

Jean-Baptiste Lamarck (1744-1829)

Suggested that the giraffes neck grow because the muscles in the parent stretch as it reached for food and that this trait was passed on to the offspring.

This is now disregarded as we know that only sperm and egg cells can pass on information.

06/03/2014

14

Charles Darwin (1809 1882)

Darwin returned from his world trip on the Beagle in 1837

By 1838 he had developed his theory of Evolution

Alfred Russell Wallace independently developed the same theory

In 1859 Darwin published his book On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life. Known As Origins of the Species

Darwins Theory

Evolution decent with modification

Evolution has occurred by branching so that different species share common ancestral species.

Natural Selection

The main mechanism of evolution. This is where random changes to an individual occur. Those which are beneficial will be passed on to the next generation.

06/03/2014

15

Natural Selection Members of a species vary greatly in their structure,

physiology and behaviour, traits that are associated with survival are more likely to be passed onto the next generation. Therefore natural selection leads to the evolution of species which are better able to surviving and reproducing in their particular environment.

The Reaction Caricature in Hornet taken from

http://en.wikipedia.org/wiki/Charles_Darwin

Is evolution universally accepted now?

Do YOU accept the theory of evolution?

Have you examined the evidence for evolution?

http://news.bbc.co.uk/1/hi/education/7612152.

stm

http://news.bbc.co.uk/1/hi/education/7619670.stm

06/03/2014

16

1. Darwins Evidence

He documented the evolution of fossil records through progressive geological layers

2. Darwins Evidence Taken from Carlson (2001) Physiology of Behaviour

06/03/2014

17

3. Darwins Evidence

Darwin argued that if dogs and horses could be bred to produce offspring with desirable characteristics, then why could this not happen naturally.

NATURAL SELECTION

Further Evidence

Science has moved on since Darwin. Can you think of any other ways of testing the theory of evolution?

Remember Darwin did not know about how information was passed on from parents to offspring. He had not seen the work of Mendel.

06/03/2014

18

Example of Natural Selection The Case of the disappearing (white) English Peppered

Moth

KEY FACTS

The English Peppered Moth (Biston Betularia) is whitish with black speckles on its wings.

They are camouflaged on speckled lichen on trees.

A genetic mutation can cause some moths to be all black, these are said to be melanistic.

Melanistic moths not camouflaged on lichen.

1800s Industrial Revolution.

Lichens sensitive to air pollution and die.

Black soot turns trees black

Example of Natural Selection And the White Moths Disappeared.

What has caused this mysterious disappearance? The white moths, no longer have an advantage and are being eaten.

The Black moths have an advantage and are not been eaten, so are able to reproduce and pass on the mutation.

There were however white moths in the countryside.

In the 20th Century The Clean Air acts, changed the environment again.

The white moths re-appear

06/03/2014

19

Survival of the Fittest The individual best suited to their

environment will survive to pass on these genes to the next generation.

This is a phrase coined by Herbert Spencer and was used to justify Social Darwinism.

Human Evolution: A big brain? Adult human brain weighs between 1200g and

1400g

Adult elephant brain weighs between 5,000g and 8,000g

Brain Body Ratio Humans 2.33%

Elephant 0.2%

Shrew 3.33%

06/03/2014

20

Human Evolution

Kingdom Animal

Phylum Chordate

Class Mammal

Order Primate

Family Hominid

Genus Homo

Species Sapiens

The Ape who Evolved to be Human

What key factors separate humans and apes?

06/03/2014

21

Human Evolution

From Kenyon http://www.flyfishingdevon.co.uk/salmon/

Evolutionary Psychology

Explains human behaviour in terms of evolution.

Darwin himself believed that human behaviour could be explained in terms of evolution.

06/03/2014

22

Whose Genes?

From Kenyon http://www.flyfishingdevon.co.uk/salmon/

Evolution Facts Evolution is not a straight line

Evolution does not progress to preordained perfection

Humans are the last surviving species of a family that has existed for a very short time

Evolution can be rapid

Fewer than 1% of known species are in existence

Not all existing behaviours or structures are adaptive

06/03/2014

23

Conclusion

Darwin developed his theory of evolution to explain the diversity that he saw around him

DNA was identified by Watson and Crick in the 1950s

Traits are passed from one generation to the next by genes located on chromosomes

We now understand that many human traits involve many genes (Polygenic)

And genes often provide just a predisposition to a condition or trait.