Genetic Diversity Flashcards by G Smith

Charles Darwin

Published the “origin of species” in 1859

Natural Selection: Survival of the fittest→ adaptability

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Gregor Mendel (1866)

1st person to explain how traits are passed to offspring
Father of Genetics
Invisible factors determine what an offspring would look like.
Alleles

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Allele

a trait that you get from your parents.

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Fredrich Miescher

1869: he identified the “nuclein” which we call deoxyribonucleic aide.
Tried to isolate proteins found in white blood cells, but accidentally purified the DNA in cells.
It had different properties and a high concentration of phosphorus, so he realized he had discovered a new substance.

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Oswald Avery

1944: he realized that DNA was the molecule that transferred information from parents→ offspring.
By now, it was known that genes were units of heredity, and they could be passed on, but it was unknown how.

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Phoebus Levene

1929: he identified components of DNA molecule: ACGT→ nucleic bases, as well as, sugar-ribose and phosphate.

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Erwin Chargaff

1950: he researched DNA and found out that it is all the same nucleic acids.
Made Chargaff’s Rules
In any double-stranded DNA molecule:
A number of Guanine nucleotides= number of Cytosine.
A number of Adenine nucleotides= number of Thymine nucleotides.
The composition is different in each species→ ratio.

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Rosalind Franklin

1952: used crystallography to examine DNA.
Took pictures and determined
Dimensions of a strand of DNA
That phosphates were on the outside of the DNA structure.

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James Watson and Francis Crick

1953: Watson and Crick used Rosalind’s pictures to determine the structure of DNA.
Made the double helix model.
Showed that DNA was made up of two complementary strands.
Showed the G bonds with C and A bonds with T on opposite strands.

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DNA Replication- Watson and Crick

Watson and Crick hypothesized that when DNA replicates, it does so in a semiconservative manner.
Semiconservative means that when DNA replicates, each new strand will have one strand from the original molecule.
Was tested in the Meselso-Stahl experiment.
Fed bacteria with two different isotopes of nitrogen (N14 and N15) then they replicated the DNA in N14 solution and observed the results.

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DNA Sequencing

1990: Human Genome Project began.
An international effort which began in the US to sequence the entire human genome.
2003: the project was complete.
It was determined that the human genome is made up of 2.85 billion nucleotides.
20,000-25,000 protein-encoding genes were present in the genome.

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Cloning

1996: first animal clone was born.

Cell from a 6-year-old sheep was used.

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The Present

We are able to identify dangerous genes in a developing embryo or full grown adult.
Knowing what diseases your embryo might have can have many effects.
The knowledge that your baby could have a certain genetic disorder can cause you to have an abortion.
Spotting diseases early could allow for pre-emptive treatment that can cure or treat the child.

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The Future

Method of removing and replacing certain genes within an adult organism.
Could cure cancer and genetic diseases.
If you have a specific genetic disease, a virus containing the correct gene could be injected into you, and edit your DNA to remove defective gene and replace with a healthy version of it.

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Nucleotides

DNA is made of 4 different nucleotides which are either purines U2 (2 rings) (adenine and guanine) or pyrimidines (1 ring) (cytosine and thymine).
Purines always hydrogen bond to pyrimidines.
Nucleotides form rings of DNA ladder
Purines will always bound to a pyrimidine
Hydrogen will be attracted to nitrogen and oxygen, but if you have two hydrogens together, they will repel.

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A single strand of DNA

Each strand has two ends
A 5’ (pronounced five prime) end and a 3’ (3 prime)
The 5’ end has a phosphate as the start of the strand.
The 3’ end has a hydroxyl (-OH) group (part of the ribose sugar) as the last part of the strand.
When DNA is replicated, new nucleotides are added in the 5’ to 3’ direction
Nucleotides form a bond with a ribose sugar
The backbone is held together by phosphodiester bonds between phosphate and sugar.

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Packaging 2 meters of DNA in a cell

DNA is a very long molecule, that requires it to be condensed to store it more efficiently.
The double strand wraps itself around proteins called histones.
These histone DNA complexes coil like a phone cord
Which then coils again and again.
During mitosis, the DNA is completely condensed in each chromosome.
After mitosis, the DNA unravels slightly.

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Genes

Majority of DNA doesn’t contain useful information.
The useful parts that contain instructions for assembling proteins are found in genes.
Genes are sporadically along the chromosome.
Large stretches of non-coding DNA between genes
This non-coding DNA can tell proteins where to find genes.

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Ribonucleic Acid (RNA)

RNA is another type of genetic material
RNA is very similar to DNA with a few exceptions.
The nucleotide thymine is replaced with uracil (which still bonds to adenine)
RNA is single-stranded instead of double-stranded
The ribose sugar in the backbone is missing a hydroxyl.

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RNA’s Function

RNA is created as a complementary strand to DNA.
RNA leaves the nucleus where it combines with ribosomes and amino acids to form proteins.
RIbosomes read RNA 3 nucleotides at a time.
3 nucleotides are called a codon
Every codon corresponds to a specific amino acid
There are 20 different amino acids
Amino acids form long chains that fold to become proteins.
DNA to RNA to Proteins= all life based on this.

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Mitosis

Mitosis is the process of a cell dividing.
4 stages resulting in 2 new clone cells.
Stages: Interphase, Prophase, Metaphase, Telophase, Cytokinesis. (Ian Pass Me Another Tequila Cup)

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Meiosis

Produces 4 haploid cells after 2 cycles of cell division.
These cells do not contain identical DNA of the parent cell.
Humans have 23 pairs of chromosomes.

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Preparing for Meiosis

By the end of cells interphase, it has successfully replicated its DNA, so each chromosome contains identical strands of DNA called sister chromatids.
These chromosomes pair up with their homologous chromosomes (matching chromosome containing the same genes). The pair is called a Tetrad (tetrad means 4, and there are 4 chromatids in a tetrad(.
Pairing process called synapsis when crossover occurs.
Crossover= when chromatid overlaps + exchange segments of DNA.

Meiosis 1: Prophase 1

Chromosomes condense and synapsis and crossover occurs.

Spindle fibres extend out of centrioles and attach to each chromosomes’ centimetre.

Meiosis 1: Metaphase 1:

Spindle fibres move homologous pairs into a line down the centre of the cell
Each chromosome pair is attached to opposite poles of the cell.

Meiosis 1: Anaphase 1:

One of each homologous pair of chromosomes is pulled to opposite ends of the cell.
There are 23 chromosomes on each side of cell now.

Meiosis 1: Telophase 1:

Spindle fibres attach and cell split into two new haploid cells.

Meiosis 11: Prophase 11

Each pair of sister chromatids condense and new spindle fibres attach to each sister chromatid.

Meiosis 11: Metaphase 11:

Sister chromatids line up down the middle of the cell.

Meiosis 11: Anaphase 11:

Sister chromatids are ripped apart and are taken to each side of the cell.

Meiosis 11: Telophase 11 and Cytokinesis:

Chromatids start to uncondensed and then nuclear membrane starts to form around DNA.
4 haploid cells that are not identical to their parent cell.

Genetic Diversity:

There are a few ways meiosis provides genetic diversity from the parent.
Crossover between paternal and maternal copies of DNA exchanges genes so physical strands are not identical.
Separating chromosomes causes some maternal and paternal DNA in each haploid cell.

Sperm and Eggs

When spermatogenesis (sperm from meiosis) produces 4 healthy sperm cells, oogenesis (produces eggs from meiosis) only ends up creating on viable egg out of 4 new cells.
During telophase 1 and 11, one of the cells will get the majority of cell contents with DNA and others will die, turning in to the polar body.
Allows one egg to have more nutrients.

Errors in Meiosis

Occasionally chromosomes will not split evenly between two cells –> Non-disjunction

What does non-disjunction result in?

Trisomy: three sets of chromosomes in cell→ Down Syndrome
Monosomy: one chromosome in a set→ Turner Syndrome

What do mistakes in meiosis do?

Cause evolution
A small percent are beneficial to the organism
Most cause death
Small number provide an advantage.

What can go wrong in meiosis?

When DNA is replicated before mitosis and meiosis, the cell can make errors.
Errors= mutation
Proof-reader proteins try to fix errors.
If proof-reader misses errors, the mutation will stick around.

Point Mutations→ 3 types

Base pair substitution: One nucleotide is switched for another.
Insertion: Extra nucleotide is added.
Deletion: Nucleotide is removed from DNA

What are the effects of point mutations?

Silent mutations, missense, nonsense, and readthrough mutations

Silent Mutation

Occurs when mutation results in a different codon, but same amino acid.
No effects on protein synthesis or the cell.

Missense

Changes codon and results in a different acid being added to the protein.
Effects range depends on what original and current amino acids are.
If the small amino acid is substituted for a large, it can cause the protein to fold improperly.

Nonsense

When mutation changes codon into a “stop codon.”
Result in shorter amino acid change.
Most of the time, this will completely destroy how the protein functions.
Causes serious harm to a cell.

Readthrough Mutation

Mutation changes stop into regular codon.
Results in a much larger amino acid chain.
Will usually destroy the function of the protein.
Very severe effects on the cell.

Genes

a segment of DNA that corresponds to a specific protein.
Depending on protein, there are different traits.
Every gene has different variations.
Gene variation: Allele
Every human has 2 copies of gene → mother and father.
Locus: where on the chromosome the gene is.

Allele

There are some mismatches.
Represented with capital and lowercase letters.
Alleles you have are the genotype.
The trait that you observe is your phenotype.

Dominant and Recessive Genes

With 2 alleles, one of them is more likely expressed→ Dominant allele; other is recessive.
For dominant to be expressed, only one copy is needed.
For recessive to be expressed, only one copy is needed.
Recessive alleles need both to be recessive.
SS= Straight→ homozygous dominant
Ss= Straight→ heterozygous
ss= Curly→ homozygous recessive

Gregor Mendel and Mendalian Genetics

Discovered patterns from breeding peas with different alleles.
He decided to breed a dominant round pea plant with a recessive wrinkled pea plant→ and all were round.
Discovered that there are two copies of every gene.

Punnett Squares

Method of determining the probability of offsprings genotype after mating.

Dihybrid Crosses

When 2 traits are shown at once.
Each column and row represents possible alleles/.
Since each parent has to pass on 1 of each allele, there are 4 combinations.
RS
Rs
rS
rs

Incomplete Dominance

Not all genes are dominant or recessive.
When both alleles are expressed partially at the same time.
Results in blended phenotypes.
No dominant or recessive gene.
Colour of roses: Red= CR White= CW

Codominance

In codominance, both alleles are expressed fully.

Mixed phenotype

X Linked Traits

Females 23rd chromosome= XX Males= XY

Means that if there is a trait found on the X chromosome, males are more likely to get it.

Karyotyping

Karyotyping: a process in which geneticists can analyze a cell’s chromosomes.
Can only be seen when a cell is condensed.
This can help identify criminals.

How DNA is Cut

A restriction enzyme is a protein that cuts DNA at specific sequences.

Two Types of Restriction Enzymes

Sticky and Blunt

These are used to identify suspects using DNA gel electrophoresis.

Agarose Gel Electrophoresis

Method of separating small pieces of DNA in a gel
DNA is placed at one end and current is applied.
Negatively charged DNA is moved.
Smaller pieces move faster.

Pedigrees

Type of family tree that shows the phenotype of its family members,
Circles represent females.
Squares represent males.
When the shape is filled in, it has the traits.
When mating, a line is drawn between the two.
These can determine likely genotypes of family members.
Roman numerals number the generations

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Genetic Diversity Flashcards

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