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Genetics
Living Environment
Genetics• Genetics is the study of inheritance
patterns.
• Your genetic inheritance are on the chromosomes you got from mom’s egg and dad’s sperm during fertilization.
• Each chromosome contains genes which code for your physical traits.
A Little History…• Gregor Mendel, an Austrian monk, grew
pea plants.
• He was a scientist too, and he systematically kept track of how pea plants inherited their traits.
• He found a few interesting things…
What Mendel Found• He found that for each physical trait, also
called the phenotype, there were TWOdifferent versions of the gene.
• An allele is the same gene, but a different version; Mendel found that each gene had two alleles.
• He also found that one allele is dominant,and the other is recessive.
Dominant vs. Recessive• A dominant allele is one that whose
phenotype will ALWAYS be expressed if you have the dominant allele. (shown as a CAPITAL LETTER)
• A recessive allele’s trait will only be expressed IF both copies of this gene are recessive.(shown as a lower case letter)
• If a pea plant has as their two genes TT or Tt, then the pea plant will be tall; if the pea plant has tt, then the plant will be short.
Dominant vs. Recessive• Genotype: The combination of alleles that
an organism has, for example, TT or Tt or tt.
• If a pea plant’s genotype is TT or Tt, the plant will have a phenotype (physical trait) of tall.
• If a pea plant’s genotype is tt, the phenotype will be short.
If only it were that simple
• It’s not though…
• As it turns out, plenty of organisms have more than just two alleles for each gene, and some genes are dependent on other genes to work, and some even need certain environmental triggers
• It’d take another 100 years before we figured out where genes were located…
DNA• DNA is where genetic information is
stored.
• Each chromosome is a single DNAmolecule.
• DNA and RNA are both made from nucleotides.
• Nucleotides are the monomers for nucleic acids.
Shape of DNA• Nucleotides come in four
basic types: Adenine (A), Guanine (G), Thymine (T), Cytosine (C)
• Each DNA molecule is made of two long strands of nucleotides that are connected in the middle to form a double helix shape.
The Shape is Important
• In order for DNA to have the shape it does, the nucleotides have to match up in a certain way.
• A T
• T A
• C G
• GC
• This gives the DNA its double helix shape.
Base Pairs
Watson and Crick and…Franklin• So, it turns out that genes are stored on
nucleic acid molecules called DNA– DeoxyriboNucleic Acid
• The two scientists who discovered the shape of DNA were James Watson and Francis Crick.– They used cardboard models to figure out the
shape after looking at X-rays taken by Rosalind Franklin
Why is the Shape Important?
• As Watson and Crick noted, the shapeshows how the DNA molecule is replicated.
• The center, where the nucleotides are joined, unzips and an enzyme copies each side of the DNA.
• This is called replication.
DNA Replication• Remember how before Prophase and
Prophase I the chromosomes replicate?• Here’s how they do it:• The DNA strand unwinds and an enzyme
called DNA polymerase copies the DNA on both sides
• Every time the enzyme encounters an A, it matches the A with a T and vice versa
• Every time the enzyme encounters a G, it matches the G with a C, and vice versa
• It happens very very fast!
Replication Video
DNA as a Protein Map
• DNA codes for your traits right?
• Well, kinda.
• It actually codes for proteins
• The proteins are either used for structureor are enzymes
• These proteins then either are your traits, or cause your traits to be built
DNA Codes for Protein
• Remember the base pairs?
• A,T,C,G
• Think of them as the letters in the protein code
• When making protein, your cell looks at the sequence of those bases, three at a time, to figure out what protein to make
• What are proteins made out of?
DNA Protein
• Every three bases on a strand of DNA codes for an amino acid.
• A gene is the number of base pairs which code for a single protein. – Exon-a gene, or DNA that codes for a protein– Intron-A non-coding part of DNA that may
have other uses
• Since proteins can be thousands of amino acids long, the number of bases in a gene can be HUGE
• You have 3 billion base pairs in your DNA
DNA to RNA
• But wait…the DNA never leaves the nucleus right?
• Which organelle makes proteins?
• So, how does the information get from the nucleus to the ribosome?
• RNA- RiboNucleic Acid
• Made of the same bases as DNA, except instead of T, it uses Uracil, or U
RNA-Transcription
• Transcription is the process that forms messenger RNA, or mRNA.
• The gene to be copied is transcribed, or copied, into RNA.
• Its copied the same way that DNA is copied, except that everywhere there is an A, a U is pasted into the mRNA molecule instead of a T.
• So if the DNA gene is ATGGCCT the mRNA strand is UACCGGA.
Transcription
• RNA polymerase starts at a location on the DNA known as a promoter
• A promoter is a place with a special sequence of base pairs that acts as a starting point for the enzyme that makes mRNA (messenger RNA)
• The RNA polymerase makes a single strand of complimentary RNA to the gene the enzyme is copying
Transcription
Translation• The mRNA moves out of the nucleus and
finds the nearest ribosome
• The mRNA is then translated using tRNA(transfer RNA) into an amino acid chain (protein).
• Each three base pairs is called a codon, and codes for a specific amino acid.
Translation
• So the mRNA is translated into tRNA, which would read exactly like the original DNA.
• The tRNA is then used by the ribosome to make a sequence of amino acids, called a protein!
• This is how the ribosomes know what proteins they should make and when they should make those proteins.
Translation Video
Protein Synthesis
• The proteins made in this way are often enzymes, which cause certain chemicalreactions to happen, or are used for structure inside the body.
• This is how DNA codes for your body’s structure and function
Mutations
• Sometimes, a mistake is made when copying the DNA.
• This mistake is called a mutation.• If the mutation results in a different protein
being produced, one of two things could happen– The new protein doesn’t work like the old one,
and the organism dies (most often happens)– The new protein works better than the old one,
and the organism has an advantage (rarely happens)
Genetic Variation• Mutation is the cause of genetic variation
• Remember, mutation is a mistake in the copying of DNA.
• Its very rare that a mutation is beneficial
• This is important for evolution
Genetic Engineering
• When humans purposely change the genetic sequence of a species, it’s called genetic engineering.
• Turns out, we’ve been doing it for over 10,000 years.
Selective Breeding
• Selective Breeding is when humans make sure two parents with desirable traits mate, and then makes sure that those same traits keep being paired together.
Hybridization• Hybridization is crossing two organisms
that are from different species in order to create an organism with desirable traits.
• Hybrids are infertile
X
Modern Genetic Engineering
• Focuses on changing DNA rather than on breeding of organisms
• Has given rise to the science of molecular biology
• Uses various tools to manipulate DNA
Tools for Genetic Engineering
• When scientists want to take a certain gene, they use an enzyme, call a restriction enzyme, to cut just that specific piece of DNA out
Recombinant DNA
• Recombinant DNA is DNA that is made from two different DNA molecules
• E.g. insulin gene from humans inserted into bacteria
Making Copies of DNA• DNA Polymerase Chain Reaction is the
process by which DNA is copied in a test tube.
• Basically, scientists throw the DNA, bases, DNA polymerase into a bath, and let it go for several hours.
• The DNA polymerase copies the DNA over and over and over and over and over again.
Comparing DNA
• Gel electrophoresis is the main method for comparing samples of DNA.
• In gel electrophoresis, DNA samples are placed inside a gel pack at one end.
• Electricity is run through the gel pack, and that electricity pushes the samples at different rates, depending on the size of the sample.
• The samples that are the same size go the same distance.
GMO’s• Transgenic organisms- Organism that
have genes from another organism inserted into their genome.
– E.g. 52% of soybeans are transgenic; they have genes which help to resist the cold, 25% of corn has genes which help to make it make more pest-resistant
