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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?