Introduction

We can use DNA and genetics to reconstruct relationships with living and fossil ancestors

It will show how we are related to other primates

It will help us understand diseases and how they are transmitted

The Cell

Prokaryotes are one-celled organisms

Eukaryotes are multi-celled organisms Also have a nucleus and cytoplasm

Types of cells (important!!): Somatic cells: body cells, use mitosis Gametes: sex cells, sperm/egg, use meiosis

DNA Molecule

Think of a cell

Zoom into the middle, in the nucleus

In the nucleus are chromosomes

Inside the chromosomes are bundles of DNA DNA forms sequences or codes that give the

body instructions The complete set of genes in an individual is a

genome

DNA and Chromosomes

Chromosome number is species-specific!

Examples: Camel: 70 Salamander: 24 Apple: 34 Algae: 148 Colobus Monkey: 44 Orangutan: 48 Human 46

Chromosomes

A healthy human has 46 chromosomes, in 23 pairs. Why are they in pairs?

DNA is homoplasmic: every cell in the body has the exact same, complete set of DNA

Mitochrondrial DNA is different and used to trace ancestry. Inherited 100% through mother’s line Heteroplasmic: it can differ within in body

Chromosome Types

Chromosomes are homologous, meaning they are in pairs, with the same information on the same locations

The first 22 (pairs of) chromosomes are autosomes

The 23rd pair are sex chromosomes (XX or XY)

All chromosomes lined up in order is a karyotype

DNA: Blueprint for Life

DNA is the instruction manual for the body

What shape does DNA have?

The sides are made of sugar (deoxyribose) and phosphate

The “rungs” are made of 4 bases: adenine, thymine, cytosine, guanine or A, T, C, G Complementary bases

Specific pairing: A ALWAYS BONDS WITH T C ALWAYS BONDS WITH G

DNA Replication

Cells must make more of themselves Makes identical copies if it is a somatic cell

In order to do this, the FIRST STEP IN CELL DIVISION IS ALWAYS DNA REPLICATION

The bonds between A/T and C/G are broken and the ladder unzips

The lonely letters look for their complementary partner: A for T and C for G

When they attach to free floating letters, they have made two identical ladders and have replicated

Hmmm…

Now, if a cell has 46 chromosomes in it

And we have done DNA replication,

Then that cell will have double the number of chromosomes…it will have 92

Is this normal? How do we get it back to 46?

Mitosis

Somatic cells have all 46 chromosomes. They are diploid in number

To make more, we use mitosis:

After DNA replication, when the cell has 92 chromosomes, it pinches apart and becomes 2 cells, each identical, each with 46 chromosomes

Gametes

Gametes are different

How much genetic information can you pass down to your offspring?

Therefore, gametes have HALF the number of chromosomes: 23. They are haploid in number

Meiosis

Gametes make new cells by meiosis

The first step is still____________________!!!

They now have 92 chromosomes

They divide once (just like mitosis) and have 46

But they MUST DIVIDE A SECOND TIME to end up with 23 chromosomes in each cell (sperm or egg) created

Variation

During meiosis the body can try to add variation

Crossing over and recombination are reshuffling of the genetic material just before division

Sometimes there can be errors Translocations rearrange chromosome

information but can insert or delete information Nondisjunction means that an even number

of chromosomes does not get divided into each cell

Trisomy 21

Nondisjunction can create Trisomy 21, in which 3 chromosomes are created at the 21st spot

This is known as Down Syndrome

Protein Synthesis

DNA is also used in creating proteins, which help in growth, function, and repair of tissues

They are made of amino acids, half of which are made in the body and half of which come from food

Proteins can be structural: responsible for physical features (hair, eye color, bone shape) or regulatory (hormones, enzymes, antibodies)

Protein Synthesis

Has two parts:

I. Part I is Transcription

II. Part II is Translation

Transcription

Begins just like DNA replication

Enzyme splits the bonds of A, T, C, G

BUT, instead of bonding and replicating, one strand bonds in a different way: C bonds with G but A bonds with U (uracil) If a U is involved, it is protein synthesis

The U creates RNA, which is smaller than DNA

mRNA (messenger) is the product formed in this stage

Transcription

The mRNA is small enough to leave the nucleus and go to the ribosome

It carries the message in the form of 3 letter codons Examples: AUG, GCC, AUA, UAC

Translation

In the ribosome, the mRNA codons are met by tRNA (transfer RNA) anticodons that match letters Example: mRNA codons CCG, UAG, CUG tRNA anticodons GGC, AUC, GAC

These matchings “translate” the code until an stop codon makes them stop (like a period in a sentence).

These form amino acids in long chains

The chains keep winding and coiling to form proteins, which have unique 3D shapes

Regulation

Other than Replication and Protein Synthesis, DNA’s function is regulation

These codons start or stop certain functions

DNA has a high degree of stability

Mutations do occur, but the error rate in replication is 1 in 10 billion!

A lot of our DNA is inactive: about 98% of our DNA is not actively doing anything

Blood Type Blood is unique: it has 4 phenotypes but 6

genotypes:

Phenotype Genotype

Type A AA or AO

Type B BB or BO

Type AB AB

Type O OO

Blood Type

You get your blood type from antigens

Antibodies will attack foreign particles, so the letters must match in blood donation or agglutination occurs

A and B are dominant and share dominance: they are codominant

O is recessive (it is neutral and has no antigens)

Blood Type

To donate, letters must match!

Type A can give/receive if it has an A (AA, AO), or O (it is neutral)

Type B can give/receive if it has a B (BB, BO), or O (it is neutral)

Type AB can receive from anyone (AA, BB, AB AB, O is neutral) but can only give to itself

Type O can give to anyone (O is neutral), but can only receive itself

Blood Type

Who is the universal donor?

Who is the universal recipient?

Punnett Square Review

For the trait for ‘handedness’ (right-handed or left-handed), right-handed is dominant

Mother is left-handed and father is homozygous for right-handed. What is the chance their offspring will be left-handed?

Punnett Square

A regular punnett square has the same letter, just uppercase or lowercase; for blood type, this is the only time the square will have different letters

Let’s do a problem with blood type

Sharon just had a baby and doesn’t know who the father is.

Sharon: Type A Guy 1: Type AB

Baby: Type O Guy 2: Type B

Can we say who IS NOT the father?

First, write out the possible genotypes:

Sharon: AA or AO

Guy 1: AB

Guy 2: BB or BO

Baby: OO

Is there anyone who could not be the father?

Yes, Guy 1 because both the mother and the father would have to give the baby an “O”

Using this, what is Sharon’s genotype?

It has to be AO, to give the baby an “O”

Now let’s see if Guy 2 could be the father:

Punnett Square:

Put Sharon’s alleles across the top and Guy 2’s down the side:

A O

B

O

The last box show that there is a chance (1/4 or 25%) that Sharon and Guy 2 gave the baby O alleles, so Guy 2 could be the father

AB BO

AO OO

More Practice

The Punnett Square and the letters you fill in are the genotypes

The end result that we can describe is the phenotype

Example 2:

Red is dominant in rose color

A red rose (homozygous dominant) and a white rose have what chance of producing white roses?

Answer

Homozygous dominant (red) = RR

Homozygous recessive (white) = rr

Rr Rr

Rr Rr

R R

r

r

There is a 0% chance of making white (recessive) roses because each box has at least one dominant (red) R

Questions

Why are there two types of cell divisions (mitosis and meiosis)?

Why does mitosis use DNA and protein synthesis use RNA? How are they different?

What is the difference between a genotype and phenotype?

Who is the universal donor and recipient?