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Genetics

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Cassandra Battram

on 10 April 2013

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Transcript of Genetics

Genetics Punnett Squares! DNA Fingerprinting 2.4 Mutations What are mutations? Mitosis and Meiosis Inside our DNA 2.3 DNA - Base Pairs What is a base pair? 2.2 Inheritance The Jim Twins - Nature vs. Nurture... Banana DNA What you'll be doing today: REVIEW 2.5 Genetic Technologies A way of determining the outcome of SEX! Today you will be extracting DNA from a banana!
Work in your Quad-Pods to determine the order of the procedure, (ask Ms. Battram to check it before moving on!!!) then go bananas!
Once you've finished the lab, answer the analysis questions and hand it in (one per group) so that you don't have any homework!! :) •There are 4 possible nitrogen bases of a nucleotide
•THEY ALWAYS OCCUR IN PAIRS because the shapes of the bases fit together
• They are:
–Guanine (G)
–Cytosine (C)
–Adenine (A)
–Thymine (T) This Chapter... Deoyribonucleic acid = DNA Double helix (Watson and Crick, 1953); sugar phosphate backbone
Made up of nucleotides; a nucleotide has three parts:
1) Deoxyribose sugar
2) Phosphate
3) One of 4 nitrogen bases How does all of our
DNA fit into a cell? DNA is very LONG, 2 metres in EVERY cell!

In order to fit in the nucleus DNA is very THIN
and COMPACT:
compacted even further as a twisted helix that takes up less space
Wound around HISTONES - these are proteins that act like a SPOOL DNA Replication Why do we have DNA? FOR PROTEIN SYNTHESIS!! BEFORE a cell can divide to make a new cell, DNA must be REPLICATED! Here is the 4 step process:

1) The 2 complimentary strands of DNA UNTWIST, base pair BONDS BREAK apart, and STRANDS SEPARATE like a ZIPPER
(This process is controlled and aided by protein enzymes)

2) Freefloating bases in the nucleus attach to the newly exposed bases on the strand

3) This creates 2 NEW DNA molecules, each with 1 STRAND ORIGINAL and 1 newly created strand

4) Then, the newly paired strands coil back into a DOUBLE HELIX DNA is the blueprint for every part of you!! Protein Synthesis PROTEINS are chain-like molecules composed of amino acids
AMINO ACIDS are the individual links in the protein chain
There are 20 amino acids

The DNA GENETIC CODE (order of the nitrogen bases G,C,A,T) determines the triplet CODONS (three nitrogen bases)
Each codon CODES for a specific amino acid


· There are 64 different possible combinations of the 4 nitrogen bases even though only 20 amino acids exist (p.113)
· Multiple nitrogen base combinations code for each amino acid
· Some codes start or stop the creation of a protein

PROTEINS ARE ESSENTIAL for the body's functioning
Made up of one or more amino acid chains
Can bend and form unique shapes that allows the protein to function...
ie. hemoglobin – shape allows it to hold O2 and CO2 inside it LET'S TRY IT! A CHANGE in the SEQUENCE of NITROGEN BASES along DNA
Can occur naturally or from exposure to a MUTAGEN (ie. UV light, radiation)
If a mutagen leads to the formation of cancerous cells, it is considered a CARCINOGEN
Carried forward every time DNA replicates, so change will affect that cell forever
Cells can repair minor DNA "typos"
Some can cause the gene to stop working or to work differently, sometimes genes still function normally - when???
Responsible for GENETIC VARIATION within species
SOMETIMES A MUTATION IS BENEFICIAL = EVOLUTION Types of Mutations: 1. POINT MUTATION
One single nucleotide is substituted for another during replication
Alteration in Amino Acid chain can now possibly affect protein functioning

Original DNA strand: ...ATG GGA GTT CA...
Original AA: Met Gly Val

Mutated DNA strand: ...CTG GGA GTT CA...
Affected AA: Leu Gly Val What happens if a
mutation occurs? Most mutations are corrected by repair enzymes that clip out incorrect nucleotide and insert correct one
Substitution can be disastrous if incorrect mutation changes protein so it cannot perform its function (MISSENCE mutation) Examples:
Sickle cell anemia hemoglobin misshaped and caused red blood cell to twist/misshape into a sickle affecting iron and oxygen carrying capabilities
PKU (phenylketonuria ) change in aa sequence of an enzyme so that it can't carry out the chemical reaction phenylpyruvic acid accumulates in brain cells and impairs the development of the fetal brain
Hemophilia defective protein causes a problem in blood clotting original DNA strand: ...ATG GGA GTT CA...
original AA: Met Gly Val

deletion: A
mutated DNA strand: ...TGG GAG TTC A...
affected AA: Try Gly Phe

addition: C
mutated DNA strand: ...ACT GGG AGT TCA...
affected AA: Thr Gly Ser 2. FRAMESHIFT MUTATION
Deletion OR addition of a nucleotide during DNA replication
Causes CODON to SHIFT and be read differently An individual's DNA is like a finger print, no 2 people's are alike (except for identical twins/triplets) thus DNA can be used to match individuals to biological remains (Like on CSI!)

To see a ‘fingerprint’:
Scientists take a sample of DNA and cut it into small pieces (fragments)
These are placed in an electrophoresis gel and allowed to move through
Different weights of DNA will move through the gel at different speeds, leaving distinctive bands of DNA behind Medicines and Gene Therapy Gene therapy uses a vector (virus) to repair/replace defective genes in the treatment and possible cure of genetic diseases

Scientists have taken advantage of how viruses deliver their genes when they infect cells
Disease causing genes of the virus are removed and the therapeutic gene is spliced into viral DNA
Patients are infected with many of the altered viruses
Each virus injects the recombinant DNA (with therapeutic gene) into patient's cell to allow cell to produce the missing or defective protein

Examples:
CF and the cold virus (adenovirus)
"Bubble Baby" child had no ADA enzyme and so no immune system (SCID) cured by gene therapy Transgenics Gene(s) from one species transferred and spliced into DNA of another species - It is FASTER than selective breeding

Result:
A genetically modified organism (GMO)

Details:
Restriction endonucleases cut DNA at specific locations, removing a specific gene that can be spliced into a different piece of DNA, resulting in a strand of recombinant DNA

Potential:
genetic material put into different organism to be used to produce proteins that can be harvested and used for a variety of purposes
· bacteria with a human gene for producing insulin
· organisms produce their own pesticides
· pigs with human genes for successful organ transplants Controversy with GMO's Ethically – harm to existing animals, reasoning behind, unknown effects, who oversees it?

Economically – can be quick, cheap, effective, but what about it if gets out of control in ecosystem
ex: A pesticide producing corn plant was discovered to be killing monarch butterfly caterpillars!

Some people worry about our new found ability to combine different diseases into one, to set it loose on the world (bioweapons) Bacterial Resistance Beneficial mutations in bacteria often cause them to become resistant to treatment from antibiotics
These bacteria will then survive, reproduce and create more antibiotic resistant bacteria
Bacteria can actually reproduce every 20 minutes in some types, so adaptation to their environment and selection for beneficial mutations is fast

Bacteria also have the ability to suck up pieces of free DNA from the environment and add them to their own DNA strand = TRANSFORMATION

A PLASMID is a self-replicating piece of DNA that can be transferred between bacteria, allowing it to share genes on the plasmids between bacteria http://www.pbs.org/wgbh/nova/education/body/create-dna-fingerprint.html CHROMOSOMES are the genetic material inside the nuclei of your cells that hold your DNA!
The number of chromosomes in a cell's nucleus depends on the species
More complex organisms tend to have several chromosomes
Humans have 46 chromosomes - 23 pairs, one copy from each parent 2n What is a chromosome? CHROMOSOMES are long, thin strands coiled at regular intervals around protein molecules for protection

They are best seen/photographed when the cell is dividing and producing an identical copy of itself (Mitosis)

Chromosomes contain GENES
A GENE is a section of DNA that CODES for a particular protein to be made, in between genes there is a lot of JUNK DNA that doesn't code for anything

Chromosomes are paired, so that:
· A backup copy exists
· Each is unique and different from the other half of the pair - THIS ALLOWS FOR GENETIC DIVERSITY!!! Human Karyotype Chromosomes are normally a big mess of spaghetti like strands in the
nucleus of every one of your cells
A KARYOTYPE allows us to separate the chromosomes into their pairs, then examine them for abnormalities
amniocentesis: prenatal test done to look at karyotype of unborn child

There are 3 ways to match up the pairs of chromosomes:
1) LENGTH – usually arranged from longest to shortest, where #1 is the
longest
2) BANDING PATTERN – when DNA is stained, some parts of the chromosome become darker than others, and it looks like stripes
3) CENTROMERES – the very tightly wrapped part, that dips in, (like a waist), where the two chromosomes join up can be anywhere along chromosome The last two chromosomes in a karyotype are the sex chromosomes
In human’s, XX is a female, and XY is a male Mitosis/Meiosis How do these chromosomes replicate? Cells must be able to make more copies of themselves to:
· Repair damage and replace dead cells
· Grow and develop
· Reproduce

Two processes vital to cell reproduction:
1) MITOSIS – for autosomal (normal body cells) to duplicate themselves (2n)
2) MEIOSIS – for sex cells/gametes SPERM and EGG cells) to be created with HALF of the total DNA Mitosis (Mi - two- sis) OVERVIEW: cell gets larger, DNA doubles, cell splits into two cells each identical to what you started with Meiosis (Me-one-sis) OVERVIEW:sexual reproduction 2 stage cell division that produces gametes with half the number of chromosomes than the original cell DIPLOID cells have pairs of HOMOLOGOUS CHROMOSOME PAIRS
of chromosomes that MATCH in length, centromere position, and banding pattern
One chromosome from the pair is inherited from mother, other from father
· Autosomal cells must replicate DNA before dividing
· After cells divide, 2 identical daughter cells are produced 1. Pair of homologous chromosomes separate in the cell
2. Each strand of DNA replicates itself
(humans: now there are 46 pairs = 92 chromosomes)
3. All pairs line up along the center of the cell (alignment)
4. Pairs are pulled apart at their centromeres and individuals chromosomes are separated to the edges of the cell
5. Cell now divides down the middle into daughter cells and the single chromosomes can pair up with their homologous chromosome again (each cell now has 23 pairs = 46 total chromosomes) · GAMETES (sperm and egg sex cells) combine to make new/unique offspring
· Homologous chromosomes pair up and exchange DNA segments (CROSSING OVER)
· Chromosomes ALIGN and SEPARATE and 2 daughter cells are produced
· A 2nd cell division occurs resulting in 4 cells = gametes
· Gametes are HAPLOID cells because they have HALF the number of chromosomes since there was not another replication before the 2nd cell division 1. Begins like mitosis homologous chromosomes splitting apart, and each chromosome replicating
2. Each new pair lines up beside its pair and crossing over occurs
3. Cell divides, creating 2 new cells that each have a unique pair of chromosomes (these new cells are diploid 2n )
4. Each chromosome lines up in the middle, and the cell divides its DNA again, creating 2 new cells that now each only have 1 copy of the chromosome (haploid 1n)
5. Now there are 4 cells, each with 1 strand of DNA inside Mitosis vs. Meiosis Fertilization · Chromosomes in a male gamete (sperm) join with chromosomes in a female gamete (egg)
· Fused cell now contains 2 sets of chromosomes (like those in autosomal cells)
· With 2 sets of chromosomes, the fertilized egg now grows and develops by mitosis MAKES 4 HAPLOID CELLS MAKES 2 DIPLOID CELLS Early Ideas of Inheritance 17th/18th century: PREFORMATION - the belief that all body parts are already formed at the beginning of development and just grow from small to large
19th century: DARWIN'S THEORY of EVOLUTION - he realized that organisms best suited to their environment survived and passed on their characteristics to their offspring...but, he couldn't explain HOW they got passed on
1860s: GREGOR MENDEL (monk) - Was the first to carefully study and record inheritance patterns in pea plants. He is therefore considered to be the "father of genetics"
He used SELECTIVE BREEDING OF PEA PLANTS to find out more... Mendel's Peas... Pea plants were good test subjects because:
Grow in large numbers
Easy to grow
Reproduction can be manipulated by cross-pollinating (transfer pollen from one plant to another)
Can self-pollinate (transfer pollen from one plat to female part of same plant or plant with same genetic makeup)
Several traits in pea plants easy to recognize and only come in 2 distinctive forms:
* purple/white flowers
* round/wrinkled seeds
* yellow/green seeds Mendel’s Techniques:
Mathematical/quantitative
Spent years ensuring true breeding (pure) traits in the pea plants
Prevented self pollination/fertilization
New zygotes = seeds
Planted, grew and observed the traits

Parents are always called the parental generation or P
Offspring are called the first filial generation or F1
If you allow F1 to self pollinate (fertilize) the resulting peas in the pod are called the F2 generation Mendel concluded:
1. Inheritance of traits must be determined by factors (genes)
2. Individuals randomly inherit 1 gene from each parent
3. Genes are independently passed to the offspring
4. Some genes are more (dominant) than others and may mask a less powerful (recessive) gene, but it can still be passed onto the offspring Inheritance... It was believed that parents pass on ‘heritable factors’ to their offspring (no blending of information)

Our ancestors and scientists had no knowledge of DNA, chromosome, or genes, and so you can imagine that it would seem impossible to understand how TRAITS or CHARACTERISTICS get passed on!

Terminology of Inheritance: YOU NEED TO KNOW THESE, I PROMISE!
Acquired trait: traits acquired during a person's lifetime because of experiences, education, upbringing

Inherited trait: traits genetically passed on from one generation to the next

Allele: alternative form of a gene responsible for a trait

Genotype: 2 letter code (alleles) for a trait

Phenotype: how the trait will physically appear Advantages to Sex Each offspring is unique – 1 cell with 1 pair of chromosome creates 4 gametes with unique DNA (crossing over)
When combined with any of the other 4 gametes from the other sex, you could end up with 16 unique possible combinations of DNA
If you consider all 23 chromosomes and the possibility for crossing over and recombination, the number of unique possible gene combinations is over 70 trillion
Truly we are UNIQUE....no one else has our DNA or ever will! Humans controlling Sex = Selective Breeding... Recall the "Belgian Blue" HUGE cow from the video last week.!

Humans have been selectively breeding food organisms for 10’s of thousands of years
Wheat is oldest known selectively bred food product – we have been breeding wheat for larger and larger grains and higher yield for 10 – 20, 000 years
We look for traits we like, and choose those organisms that have it to be bred to other organisms who also have the trait.
Then, from the offspring we choose those with the trait and continue to breed for it.
This process has given us wheat, corn, dairy cattle, apples, oranges, etc. 1. There are alternative forms for genes called alleles.
For each trait, you inherit 2 alleles, one from each parent
2. Principle of Dominance – 1 allele can mask/dominate the other allele – the trait is represented by a letter and the alleles by upper/lower case letters
ie. green seed color: G=dominant, g=recessive
3. Law of Segregation – during the creation of sex cells, alleles of genes separate and move into different sex cells
(1 copy of each allele – only 23 chromosomes in each sex cell)
4. Law of Independent Assortment – genes will sort independently of one another into different sex cells... Principles of Heredity – Mendel’s Laws Tomorrow, we will predict the outcomes of sex! Punnett Square: a table using alleles of parents to predict all possible outcomes resulting from gamete fertilization

1. Draw a square and label each row and column with alleles of each gamete.
2. Complete the square with the possible offspring genotypes.
3. Determine fractions/percentages of offspring of each genotype this is the probability of an individual offspring having a particular genotype.


3/4 offspring (75%) green seeds
1/4 offspring (25%) yellow seeds


Probability = # of chances of an event
-----------------------------------------
# of possible combinations Genotypes Homozygous = 2 copies of same allele
ie. GG or gg

Heterozygous = 1 dominant 1 recessive allele
ie. Gg IN THIS CASE, YOU ARE A CARRIER OF THE RECESSIVE ALLELE BUT DO NOT EXPRESS IT!

Note: the only way you can see the recessive form of the trait is the organism would have to be homozygous for the recessive allele
ie. gg = yellow seeds Other Mechanisms of Inheritance Not all traits are controlled by one gene or only have 2
alleles for a gene...

Examples:
Hair color is controlled by more than 1 pair of genes
Blood type is a trait with more than 2 possible alleles

Sexlinked inheritance: traits not directly related to sexual characteristics, coded by genes located on sex chromosomes (ie. hemophilia)

Autosomal inheritance: traits controlled by genes found on the 22 pairs of autosomal chromosomes

Genetic Diseases are passed on in the same way: a mutation in a gene is being passed down from parent to offspring

Recall, an individual can be a CARRIER and possess a form of the
gene that results in the disease but does not have any symptoms of that diseases it will however be passed along to their offspring Blood Types 3 forms (alleles) of the blood type gene, represented by A, B, O
These 3 alleles can produce 4 phenotypes (phenotype is observed in terms of the type and presence of antigens on the surface of the blood cell)
A and B alleles are dominant over O allele, but neither A nor B is dominant over the other and instead exhibit codominance (both allele products are expressed at the same time) resulting in the AB phenotype
O allele is recessive and does not produce antigens and can be masked by A and B alleles. (to express O blood type, individual must be homozygous for O allele (OO) Sex-Linked Traits 1)COLOUR BLINDNESS!
X and Y chromosomes determine gender but also carry other genes

Example:
Colourblindness is an X chromosome, sexlinked
trait (the allele is not carried on the Y chromosome)

Possible genotypes are XN and Xn:
Colourblind male = XnY
Full colour vision male: XNY
Full colour vision female carrier: XNXn
Colourblind female: XnXn 2) HEMOPHILIA
Hemophila A and B - Both caused by mutation producing blood-clotting proteins
Found on X chromosome

People bleed for longer time internal bleeding is a risk

Sexlinked recessive inheritance located on X chromosome
Hemophilia A affects 1/10000
Hemophilia B affects 1/50000
More common in males Sex-Linked Traits Continued Autosomal Diseases Cystic Fibrosis
Thick, sticky mucus in the lungs and digestive tract builds up, making it difficult to breathe and digest food
Prone to lung infections because can't clear bacteria from lungs
Autosomal recessive
Gene located on chromosome 7
1/2500 children born affected 1/25 are carriers Huntington Disease
Brain cells die in particular regions
Results in continual reduction in ability to control
movement and emotions, make decisions, memory
Appears between 30 45 yrs
Autosomal dominant inheritance
Gene is on chromosome 4
1/10000 affected Pedigree Charts Pedrigree: a set of standard symbols used a a tool to trace a particular genetic trait genetic family tree

Circles=females, squares=males
Offspring are listed in birth order (numbers)
Roman numerals symbolize generations
Shading indicates person has the condition
Half shading indicates a carrier
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