Genetics

Genes Gene – is a heritable factor that consist of a length of DNA and influences a specific characteristic Heritable means passed on from parent to offspring Characteristic – refers to genetic traits Eyes, hair color Locus – a specific place on a chromosome where a specific trait occupies

Genes

Alleles Variations or versions of a gene An allele is one specific form of a gene Alleles differ from each other by one or only a few bases If one or more bases (A,C,G, or T) is misplaced or substituted for a different base the result can be dramatic

Mutation A random rare change in genetic material One type of mutation involves a change of the sequences of bases in DNA When this happens the corresponding bases along the mRNA are altered during transcription Thus changing the polypeptide Changing the protein

Mutation A mutation that provides an individual or a species a better chance for survival is considered to be a beneficial mutation. Good chance that it is passed on to the next generation Mutations that cause disease or death are detrimental mutations and are less likely to be passed on to future generations Less likely to pass on because organism will not survive long enough to procreate There are mutations that have no effect When a mutation is successfully passed on from one generation to the next it becomes a new allele

Mutation Base Substitution – the replacement of one base or nucleotide with another Usually causes no change to the protein But sometimes change results in a change that affects protein function Sometime drastically Because several amino acids have more than one codon it makes it possible that a mutation have no effect on a protein

Mutation - Base Substitution Sickle – Cell Disease (AKA – Sickle Cell Anemia) A mutation in the gene that codes for hemoglobin in red blood cells Gives a different shape to the red blood cell Cell takes on a crescent shape like a sickle

Mutation - Base Substitution Sickle Cell In this case one base is substituted for another so the 6th codon in this sequence of hemoglobin GAG becomes GTG The result the amino acid glutamic acid is now valine instead Valine has a different shape causing hemoglobin to take a different shape Symptoms: Weakness, fatigue, and shortness of breath Oxygen cannot be carried efficiently by the irregularly shaped red blood cell Hemoglobin tends to crystallize as well becoming less flexible Red blood cells can get stuck in the capillaries causing blood clots

Mutation - Base Substitution Sickle Cell Although debilitating those who have sickle cell are resistant to malaria Demographically sickle cell is found in those originating in West Africa or the Mediterranean

Genome / Histones Genome – the complete set of genetic materials of an organism, as defined by the order of bases in the DNA Our maps of human chromosomes are still far from complete. There are many sequences we do not know what they do. Complete genomes of some organisms have been worked out: Fruit Fly Drosophila melanogaster The bacteria Escherichia coli Both have been genetically experimented for years

The Human Genome Project Began in the 1990’s (government funded) International cooperation Challenge was to sequence the human genome Was completed in 2003 DNA sequences are entered into a data base and are available to researchers all over the world Scientist are now working on deciphering the code Which genes do what???

The Human Genome Project Sequences are used by scientists: Identify embryonic development Evolutionary relationships with other species For human health; aid in diagnosing, treating, and possibly preventing many ailments allergies diabetes Cancer Production of new medicines

Chromosomes Prokaryotes have one chromosomes consisting of a circular DNA molecule Prokaryotes can reproduce using binary fission (dividing) where as organisms like planta and animals more frequently use sexual reproduction Involving a male and a female Prokaryotes only have one parent SO ONE CHROMOSOME

Prokaryotes Chromosomes Plasmids – small loops of DNA that are extra copies of the genetic material of the organism Not connected to the main bacterial chromosome Plasmid replicate independently of the chromosomal DNA Help the cell adapt to unusual circumstances Can also be found in Archaea Not found in Eukaryotes Can be used for Genetically Modified Organisms (GMO)

Chromosomes The DNA of eukaryotic cells occur as chromosomes Chromatin – strands of DNA, not visible, and proteins called histones This is the form chromosome takes when not dividing Nucleosome – beads that consists of 2 molecules each of four different histones DNA wraps twice around these eight protein molecules DNA is attracted to the histone because DNA is negatively charged and the histones are negatively charged. Between the nucleosomes is a single strand of DNA Usually a 5th type of histone attached to the linking string of DNA near each nucleosome Further wrapping the DNA molecule making it highly condensed

Chromosomes The wrapping or packaging of DNA regulates the transcription process This allows only certain areas of the DNA molecule to be involved in protein synthesis

Multiple Chromosomes Eukaryotic cells have multiple pairs of chromosomes Each have a set of instructions for the cell So in eukaryote species there are different chromosomes that carry different genes

Multiple Chromosomes Homologous Chromosomes – two chromosomes that carry the same genes Two chromosomes is that one came from the father and the other from the mother Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes

Diploid and Haploid Cells Diploid- describes a nucleus that has chromosomes organized into pairs of homologous chromosomes Most humans cells are diploid cells A set of 23 chromosomes 23 from mother 23 from father Haploid – only have a single chromosome from each pair Gametes Human have 23 chromosome The majority of sexual reproducing animal cells are Diploid Exceptions are Male Bee, Wasp, and Ant cells These are haploid

Diploid and Haploid Cells n represents the haploid number and refers to the number of sets of chromosomes that a nucleus can have Human egg have n = 23 Human sperm have n = 23 Zygote – is formed and the two haploid nuclei fuse together matching up their chromosome pairs Humans have 2n = 46

Chromosome Number Generally speaking the number of chromosomes is a feature of particular organisms within a species.

Karyograms and Karyotypes Karyogram – shows the chromosomes of an organism in homologous pairs of decreasing length. Shape depends on position of the centromere Used to show a persons karyotype Karyotype – the specific number and appearance of the chromosomes in his or her cells

Karyograms and Karyotypes How is it obtained? Cells are obtained and grown in a culture The cells are stained and prepared on a glass slide, to see their chromosomes under a light microscope Photomicrograph images are obtained of the chromosomes during a specific phase of cell division called mitotic metaphase. The images are cut out and separated, a process that can be done using scissors or a computer The images of each pair of chromosomes are placed in order by size and the position of their centromeres. Except for the 23 chromosome which can be of different sizes.

Sex Determination 23 pair of chromosomes is the sex chromosome Determines sex The X chromosome is much larger than the Y X has many more genes Human Females have XX Female eggs produce only X chromosomes Human Males XY Male sperm have either an X or a Y Autosomes – chromosomes that do not determine sex Human have 22 pairs of autosomal chromosomes

Autoradiography A technique in which radiation from a substance is captured on photographic film or camera sensor Autoradiograms are exposed to radioactive particles being given off by the substance itself Used in genetics to measure the length of DNA strands

Autoradiography Cairns’ techniques involves injecting radioactive materials into the DNA samples that will expose the film faster. Called radio markers For measuring DNA strands the DNA forming during replication is given a radioactive form of a molecule called Thymidine. Thymidine is a component of a DNA nucleotide Thymine (T) with the pentose sugar (nucleotide) ³H-thymidine (³H radioactive isotope) The radioactive ³H molecule is used as a radio marker to keep track of where those thymidine molecules are Leaves traces of its presence on photographic film

Autoradiography John Cairns used this technique in 1962 Showed a bacterium chromosome is made up of a single circle of DNA Replicated by being unzipped According to Wikipedia he’s still alive