Genetics

Standard Level Biology: Genetics Chromosomes are bundles of long strands of DNA. Eukaryotes that reproduce sexually need at least 2 chromosomes (always come in pairs). Humans have 46 chromosomes - 23 pairs.Prokaryotes only have 1 strand of DNA with no association to proteins (as the eukaryotic DNA strands are wound around proteins to tighten the bundles into chromosomes). A gene is the heritable character that controls specific characteristics. There are approximately 30,000 genes possessed by one human.An allele is a specific form of gene, as there may be more than one form of a specific gene that determines a different form of the same characteristic.Mutations occur randomly through a rare change of genetic material. Mutation may occur if a nucleotide's base-pairs are changed during DNA replication or through accidental incorrect coding during translation.The consequences of base substitution mutation may be unnoticed or may offer a different phenotype. Sickle cell anemia for example occurs when base-pairs in the gene that codes for haemoglobin are altered, causing a sickle shape instead of the pinched red blood cell (making the cell not as flexible and causing easy fatigue and slower blood flow). In this case an amino acid in the polypeptide chain creating the haemoglobin is switched, altering the shape and hence resulting in the alteration of the blood cell's shape. People with this condition are immune to Malaria.Meiosis is the division of sex cells. Meiosis undergoes the same process as mitosis, however during metaphase the replicated DNA does not connect to the microtubules in order to split the chromatids, instead the mitotic spindles will attach themselves to the centromeres of chromatids to pull homologous pairs away from one another. Resulting in anaphase pulling chromatid pairs away from the equator of the cell not the chromosomes themselves. The metaphase of meiosis is significant for genetic variation due to cross-overs between the homologous pairs occurring - mixing paternal and maternal DNA before being separated. During telophase the cell divides with full chromatids indside and cytokinesis splits the cell membranes. It is then prophase II, metaphase II and anaphase II that split the (now genetically unique) chromatid sisters. Telophase II forms new nuclear envelopes around the genetic information and cytokinesis splits the two cells into 4.Meiosis will result in 4 gametes (unfertilized sex cells).

Down's Syndrome is the symptom of a chromosome's inability to separate during either the first or second stage of cell division, resulting in an extra chromosome of the 21st homologous pair. This event is called non-disjunction. The risk of this syndrome increases as the mother's age passes over 35 years.Karyotypes are the photographic representation of chromosomes arranged according to a format. Cells are stained and prepared on a glass slide to see their chromosomes under a light microscope. Then photomicrograph images are taken of the chromosomes during mitotic metaphase. The images are cut out and arranged according to size and position of the centromere in order to find the homologous pairs.In order to obtain an unborn baby's karyotypes amniocentesis may be undergone during which a hypodermic needle will collect amniotic fluid from the fetus. Otherwise cells are taken from tissue samples from the placenta's villus projections on the cell-wall.

Theoretical GeneticsGregor Mendel used artificial pollination in order to test the genetic probability of certain phenotypes.Genotypes are the symbolic representation of alleles to represent the recessive versus dominant or co-dominant traits of a gene.Phenotypes are the visual characteristics of a genotype.A Dominant Allele is the allele whose phenotype will be expressed no matter the allele combination (hetero or homozygous).A Recessive Allele is the allele whose phenotype will only be expressed if it the alleles are homozygous, otherwise it will only be genetically carried where as the dominant allele will be expressed.Co-Dominant alleles are pars of alleles that both affect the phenotype when present in heterozygotic alleles.The Locus is the location of a gene on a homologous pairs of chromosomes.Homozygous is having two identical alleles of a gene.Heterozygous is having two different alleles of a gene.A Carrier is someone who carries a phenotype recessively that does not affect them, however may affect their offspring.A Test Cross is when a suspected hetezygote is crossed with a known homologous recessive in order to see the outcome of the offspring which may explain if it is heterozygotic or homozygotic.A punnett grid may be constructed in order to understand the possibility of offspring receiving certain phenotypes of particular alleles.

In particular cases there may be three alleles present of the same gene - blood types for example. There are four possible phenotypes of bloodtypes; A, B, AB and O (offering six different genotypes). Bloodtype may consist of the following genotypes; IA IA, IA i = phenotype AIB IB, IB i = phenotype BIA IB = phenotype ABii = phenotype OThe last homologous pair of chrosomes (23rd) determines the sex of an individual. The X chromosome contains more genes than the Y and is therefore larger. Females can only supply a gamete with an X chromosome where the sperm may contain either an X or a Y chromosome. This makes the chances of female and male offspring 50%. (The Punnett Grid will include the genotypes XX and XY). A genetic trait whose locus is on the X chromosome is sex-linked. Color Blindness and Haemophilia are two sex-linked traits. These traits are often recessive however there are several dominant sex-linked traits. The recessive nature makes the probability of offspring being affected less compared to those who are not affected (or might be carrying the allele), however this is mostly dependent on the sex of the offspring. Considering a sex-linked trait is recessive:XB XB = non affected femaleXB Xb = non affected female (carrier)Xb Xb = affected femaleXB Y = non affected maleXb Y = affected male

Carriers can only be females as they are the only possible heterozygous pairing. This means that the individual is not affected however they may pass the trait on to future generations - who may either express it or also be carriers.Pedigree charts are used to represent a the genetic hereditary material passed through a family's generations in terms of recessive and dominant (even carried) alleles.Genetic Engineering and biotechnology can be used in order to obtain treatments and vaccines for diseases as well as offering DNA evidence for crime investigations or parental testing.Is it ethically acceptable to manipulate nature through this application of genetics?Since DNA is a universal coding system for all organisms it offers a large ray of applicable properties.Polymerase Chain Reaction is the process of copying a small strand of DNA into millions of copies - supplying enough DNA for laboratory analysis of limited genetic resources (smears left on crime scenes).Gel Electrophoresis is the process of chopping up DNA into fragments with the help of enzymes, then placed into wells in a gel fluid (aligned on one end). The gel is then exposed to an electric current (positive on one side and negative on the other). The largest and heaviest (least charged) particles do not move easily through the gel and get stuck close to the wells, the smallest and most charged particles pass through the gel to the other side. This then leaves a pattern on the gel. DNA profiling can be used with Gel Eletrophoresis as the aim is to identify similarities between the original DNA and a potential match. After both DNA samples have gone through the process they may be compared, if the patterns are similar the samples most likely originate from a relatives, if they are identical it is most likely the same person. During parental testing the mother's and father's DNA patterns should combine to make up the original DNA.DNA profiling may also be used in order to identify genetic similarities between species and observe for any relations. This method may reinforce previous evidences of evolution.The human genome project was an international cooperative initiative taken up in 1990 that lasted up until 2003. Its aim was to sequence the entire human genome. Today the project has continued into deciphering genes and what particular genes code for which phenotypes. This project would be able to aid in finding the source of hereditary diseases through a assortation of genetic libraries. The genome project could also help cure diseases by looking into healthy people or people immune to certain antigens. Finding specific genes that control specific protein synthesis of molecules that may cure diseases and then replicating it in a laboratory is one method. Genetic makeup can also be scrutinized with the genome project through comparing and understanding ancestries of ethnic groups and geographic locations of groups.

Gene transfer is the use of one organism's genetic material in order to alter and improve another organism's. Because DNA is universal it is possible to alter the genetic makeup of individuals. Genetic engineering is often seen in foods such as vegetables in order to make it more sustainable in cold temperatures or against pests. This kind of genetic information may be found in arctic fish or bacteria able to kill pests. Enzymes known as endonucleases cut the DNA of the donor organism at specified points. Then the DNA fragment is pasted with DNA ligase which recognizes the base-pairs meant to be bonded together, attaching them. GM (genetically modified) foods can also have unwanted genes taken out of them and sometimes replaced. Flavr Savr tomatoes were sold in the US in 1994, meant to rot at a slower rate. Other vegetables have a higher salinity resistance, making them easier to farm. These are called transgenic plants.Cloning involves a host-cell (Yeast or the bacteria E. coli are common candidates) where the gene meant to be copied is transferred into a DNA plasmid of E. Coli. The gene transfer method is used on the plasmid (for this process the plasmid must first be removed from the bacteria's interior). E. coli then expresses this gene and synthesizes whatever polypeptide chain the gene codes for. Cloning is used when creating insulin for diabetics which was in the past extracted from animal carcasses.Transgenic animals also exist (don't really get why they're so special?). Sheep may produce milk with certain factors beneficial to us as we lack the genes necessary, that have been cloned in a sheep's host body.The benefits of Genetically modified organisms are almost limitless as we could improve our immune-systems and ability to withstand diseases and alter unwanted hereditary illnesses, as well as creating foods that are healthier and less likely to be eaten by pests or rot while also being friendlier to the environment (no need for pesticides), faster crops may aid in areas suffering from famine.The negative factors include long-term effects on ecosystems if plants with advantagous characteristics overpopulate and cause a disruption in its community, potentially leading to less biodiversity and endangering animals (if it is a plant capable of resisting predators with toxins while also very nutritious for human consumption), allergies could arise to the GM foods, it could also put economic pressure on the world if independent/private companies profit too much from the GM foods compared to smaller industries, allowing for a monopoly. Clones are either a group of identical organisms or the offspring of a single parent. Reproductive cloning is the use of a donor cell's nucleus in a host's unfertilized egg with a removed nucleus. The two are fused with electricity and become a blastocyst which is then inserted in a surrogate mother. Hence the operation is still the making of an entire individual through differentiated cells. Therapeutic cloning is the use of a stem cell in order to copy cells, without needing an entire organism. This process uses stem cells from embryonic extraction which includes ending the growth of an embryo. There are ethical concerns regarding this due to the natural purpose of embryos only being to reproduce life where as it is being used for the creation and cloning of cells in order to grow new organs for therapeutic purposes.