Genetics

Potential benefits associated with genetic modification of crops

- Higher crop yield (more production = more money) - crop yield is a debatable benefit - Less or no pesticides used because already resistant to harmful pests - Can use pest resistant crops or modified crops in areas where water availability is limited - Crops last longer or don't spoil during storage - Varieties of crops lacking certain allergens or toxins

Arguments Against Therapeutic Cloning

- Involves the creation and destruction of human embryos (at what point do we afford the right to life?) - Embryonic stem cells are capable of continued division and may develop into cancerous cells and cause tumors - More embryos are generally produced than are needed, so excess embryos are killed - With additional cost and effort, alternative technologies may fulfill similar roles

Potential risks associated with genetic modification of crops

- Long term effects on humans are unknown - Cross-pollination could occur when seeds from the GM crop pollinate neighboring farmer's crops - Cross-pollination could occur with wild species giving them a competitive advantage. This could allow these plants to outcompete and eliminate other plants (decrease biodiversity). - Patent protection (exclusive rights) given to companies that develop new types of seeds using genetic engineering. They could charge large amounts of money for seeds and the people that need them the most in the 3rd world countries couldn't afford to grow these crops. - Some people or livestock might have allergic reactions to certain proteins produced by transferred genes - Use of GMO crops that contain a toxin to kill a pest can lead to resistance to the toxin in the target pest

Arguments for Therapeutic Cloning

- May be used to cure serious diseases or disabilities with cell therapy (replacing bad cells with good ones) - Stem cells can be taken from embryos that have stopped developing and would have died anyway (e.g. abortions) - Cells are taken at a stage when the embryo has no nervous system and can arguably feel no pain

What happens if both alleles are dominant

- Share codominance (be expressed equally in the phenotype) - Share incomplete dominance (neither is fully expressed in the phenotype, resulting in blending) - Demonstrate a dominance order (e.g. allele A > allele B > allele C)

Two examples of current uses of genetically modified crops

1. Engineering crops to extend shelf life of fresh produce Tomatoes have been engineered to have an extended keeping quality by switching off the gene for ripening and thus delaying the natural process of softening of fruit 2. Engineering of crops to provide protection from insects Maize crops have been engineered to be toxic to the corn borer by introducing a toxin gene from a bacterium

Gene mutation

A change in the nucleotide sequence of a section of DNA coding for a particular feature

Clones

A clone is a group of genetically identical organisms or a group of cells derived from a single parent cell Organisms that reproduce asexually, produce genetically identical offspring Identical twins in humans are also clones

Karyotype

A karyotype is a visual profile of all the chromosomes in a cell - The chromosomes are arranged into homologous pairs and displayed according to their structural characteristics

Radiation and mutagenic chemicals

A mutation is a random change to the base sequence of a gene Both radiation and certain chemicals can cause genetic diseases and cancer - Radiation can cause mutations if it has enough energy to chemical change one's DNA. Eg. UV radiation and x-rays - Certain chemical substances can all cause chemical change in DNA and are therefore considered mutagenic. Eg. Nitrosamines (an important group of mutagens found in tobacco)

Non-disjunction

A non-disjunction is an error in meiosis, where the chromosome pairs fail to split during cell division. Non-disjunction can occur in: - Anaphase I where the homologous pairs fail to split - Anaphase II, where the sister chromatids fail to split. The result of this error is too many chromosomes in a gamete cell or too few chromosomes in the final gamete cell. One of the gamete cells could have 22 chromosomes and one could have 24 chromosomes. The resulting zygote will therefore have 47 or 45 chromosomes. An example of a non-disjunction is Down syndrome.

Male sex determination

A specific gene only on the Y chromosome called the SRY gene codes for a protein called the testis-determining factor (TDF). The TDF is a DNA-binding protein or regulatory protein that is responsible for the initiation of male sex determination in humans

Dominant allele

An allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state. The dominant allele masks the recessive in the heterozygous state.

Recessive allele

An allele that only has an effect on the phenotype when present in the homozygous state.

Carrier

An individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele

Female carriers of X-linked recessive alleles

An individual with a recessive allele for a disease condition that is masked by a normal dominant allele is said to be a carrier Carriers are heterozygous and can potentially pass the trait on to the next generation, but do not suffer from the defective condition themselves Females can be carriers for X-linked recessive conditions because they have two X chromosomes - males (XY) cannot be carriers Because a male only inherits an X chromosome from his mother, his chances of inheriting the disease condition from a carrier mother is greater

Female sex-linked genes

As human females have two X chromosomes (and therefore two alleles for any given X-linked gene), they can be either homozygous or heterozygous Males only have one X chromosome (and therefore only one allele) and are hemizygous

Assexual reproduction in animals

Asexual reproduction in animals is less common than sexual reproduction. For example, it can happen in: sea anemones and starfish

Cloning animals at the embryonic stage

At the very early embryo stage, cells are still pluripotent (meaning they can become any type of tissue) These cells can be separated artificially in a laboratory in order to create more than one of the same organism The separated pluripotent cells can then be inserted into the uterus of a surrogate mother or mothers in order to produce genetically identical offspring The separation of cells has to happen early in development, preferably the 8 cell stage

DNA Profiling - Paternity Testing

Children inherit half of their alleles from each parent and thus should possess a combination of their parents alleles Scientists can take a blood sample which contains a father's DNA and a blood sample from a child which contains the child's DNA. They can then run a gel electrophoresis to compare the banding patterns between the father and the child.

Chromosome number

Chromosome number is a characteristic feature of that species. Chromosome number does not indicate how complicated an organism might be Organisms with different numbers of chromosomes would unlikely be able to interbreed Chromosome number tends to remain unchanged over millions of years of evolution; however, sometimes through evolution chromosomes can fuse together or split to change the number of chromosomes an organism contains

Synthesis

Chromosomes are replicated in the synthesis (S) phase during interphase This means that each chromosome will have an attached identical copy before meiosis occurs These are called sister chromatids

(10) Meiosis II - Telophase II

Chromosomes arrive at opposite poles. Nuclear envelope begins to develop around each of the four haploid cells. Chromosomes begin to unwind to form chromatin. Cytokinesis occurs and cells are split apart.

(6) Meiosis I - Telophase I

Chromosomes begin to uncoil and nuclear membrane reforms. Spindle fibers and microtubules break down and disintegrate. Chromosome number reduces from 2n (diploid) to n (haploid), however each chromatid still has the replicated sister chromatid still attached (not homologous pairs anymore). Cytokinesis occurs and the cell splits into two separate cells. No more replication is needed.

(7) Meiosis II - Prophase II

Chromosomes condense again and become visible. Spindle fibers again form. Nuclear membrane disintegrates again.

(8) Meiosis II - Metaphase II

Chromosomes line up along the equator. Centromeres contain two kinetochores that attach to spindle fibers from the centrosomes at each pole. Resembles metaphase from mitosis.

Inheritance of colour blindness and haemophilia

Colour blindness and haemophilia are both examples of X-linked recessive conditions The gene loci for these conditions are found on the X chromosome (they are not present of the Y chromosome) As males only have one allele for this gene they cannot be a carrier for the condition This means they have a higher frequency of being recessive and expressing the trait Males will always inherit an X-linked recessive condition from their mother Females will only inherit an X-linked recessive condition if they receive a recessive allele from both parents

(2) Meiosis I - Recombination (Prophase I)

Crossing over occurs between non-sister chromatids of a particular chromosome. Chiasmata are points where two homologous non-sister chromatids exchange genetic material during crossing over in meiosis. Chromosomes intertwine and break at the exact same positions in non-sister chromatids. Segments of the adjacent homologues are exchanged during crossing over, therefore the two sister chromatids are no longer identical and creates new combinations of genes This creates variation in the offspring regardless of random orientation.

Cystic Fibrosis

Cystic fibrosis is a autosomal recessive disease caused by an allele of the CFTR gene on chromosome 7 C = functioning CFTR gene c = CFTR gene with mutation Cc = Cystic fibrosis carrier cc = Cystic fibrosis sufferer Mutations in the CFTR gene disrupt the function of the chloride channels, preventing them from regulating the flow of chloride ions and water across cell membranes. As a result, cells that line the passageways of the lungs, pancreas, and other organs produce mucus that is unusually thick and sticky. This mucus clogs the airways and various ducts, causing the characteristic signs and symptoms of cystic fibrosis

DNA Profiling - Forensic Investigation

DNA profiling can also be used in criminal investigations where a small sample of blood, semen, hair or other cells where DNA is present is collected. PCR can be applied to these small samples of DNA to amplify the DNA into millions of copies to create enough DNA to be analyzed for the investigation. DNA is cut into fragments that are separated through gel electrophoresis and DNA profiling, the DNA sample can be compared to a suspect's DNA to prove if they are innocent or guilty.

DNA Profiling - Ancestral Relationships

DNA profiling can also be used to support ancestral relationships between organisms for evolutionary studies.

DNA Profiling

DNA profiling is a technique by which individuals are identified on the basis of their respective DNA profiles in comparison to an unknown sample of DNA.

Diploid nuclei

Diploid nuclei have two copies of each type of chromosome. One chromosome comes from the mother and one from the father. Haploid gametes (sperm and egg) fuse during sexual reproduction which produces zygote with a diploid nucleus This cell will then divide by mitosis to produce numerous cells, all with a diploid nucleus Each nucleus has two copies of each gene, accept the sex chromosomes

Dominant and recessive alleles

Dominant alleles mask the effects of recessive alleles and are expressed in the phenotype For example, if B is dominant for brown hair color and little b is recessive for blonde hair colour, an individual that is BB (homozygous dominant) will have brown hair. If the individual has the genotype Bb (heterozygous), they will also have brown hair, as the dominant B is masking the expression of b If the individual has the genotype bb (homozygous recessive), that person will have blonde hair

How does non-disjunction cause downs syndrome

Down syndrome occurs when chromosome 21 fails to separate, and one of the gametes ends up with an extra chromosome 21. Therefore, a child that receives that gamete with an extra chromosome 21 will have 47 chromosomes in every cell. Down syndrome is also called Trisomy 21. Some Down syndrome symptoms include impairment in cognitive ability and physical growth, hearing loss, oversized tongue, shorter limbs and social difficulties.

Gene position on chromosomes

Each gene occupies a specific location or position on a chromosome called a locus Since there are only 46 chromosomes in a human diploid cell (23 pairs in females including two X chromosomes and 23 pairs including X and a Y chromosome in males). Each chromosome contains many different genes often linked in groups

Histone proteins

Eukaryotic chromosomes are linear and are made up of DNA and histone proteins. Histones are globular shaped protein in which the DNA is wrapped around. DNA wrapped around 8 histone proteins is called a nucleosome. The DNA wraps twice around the histone protein core. Another histone protein is attached to the outside of the DNA strand. This helps maintain the colloidal structure of the nucleosome. DNA, because of its negative charge is attracted to the positive charge on the amino acids of the histone proteins.

Eukaryotic chromosomes

Eukaryotic chromosomes are linear chromosomes that vary in length and in position of the centromere that holds the sister chromatids together In humans there are 23 types of chromosomes. The 23rd pair are the sex chromosomes. Males have an X and a Y chromosome and females have two X chromosomes Each chromosome carries a specific sequence of genes along the linear DNA molecule. All eukaryotic species contain at least two different chromosomes, but most contain more than two

Gametes

Gametes which are sex cells such as sperm and eggs Gametes contain one set of chromosomes or one chromosome of each type and are therefore haploid (n) Since they have only one chromosome of each type, gametes also only contain one allele of each gene The specific allele depends upon if that particular chromosome came from the mother or father and if crossing over occurred during prophase 1 Together the two gametes form a zygote

Gel electrophoresis

Gel electrophoresis is a technique which is used to separate fragments of DNA according to size Before gel electrophoresis takes place, enzymes are used to cut DNA into fragments of various lengths and different charges. Samples of fragmented DNA are placed in the wells of an agarose gel The gel is placed in a buffering solution and an electrical current is passed across the gel (positive on one side and negative on the other). DNA, being negatively charged (due to phosphate), moves to the positive terminus (anode) Smaller fragments are less impeded by the gel matrix and move faster through the gel The fragments are thus separated according to size

Gene transfer - DNA Extraction

Gene transfer is taking one gene from an organism and inserting it into another organism. DNA Extraction - Plasmids are small circles of DNA found in bacteria cells. A plasmid is removed from a bacterial cell. A gene of interest is removed from an organism's genome. The gene of interest and plasmid are both amplified using PCR technology.

Genetic modification

Genetic modification is carried out by gene transfer between species. A gene produces a certain polypeptide in an organism. Since the genetic code is universal, when a gene is removed from one species and transferred to another the sequence of amino acids in the polypeptide produced remains unchanged. Gene modification has been used to introduce new characteristics to certain animal species.

Genotype and phenotype

Genotype: The allele combination of an organism Phenotype: The characteristics of an organism (determined by a combination of genotype and environmental factors)

Haploid nuclei

Haploid nuclei have one copy of each chromosome or one full set of the chromosomes in that particular species eg. Human 23 chromosomes These are called gametes, which are sperm and egg Human sperm and eggs each contain 23 chromosomes

Homologous chromosome

Homologous chromosomes are chromosomes that share: - The same structural features (e.g. same size, same banding pattern, same centromere position) - The same genes at the same loci positions (while genes are the same, alleles may be different)

Homologous chromosomes

Homologous chromosomes are chromosomes within each cell that carry the same genes One chromosome came from an individual's mother and one from the father They have the same shape and size These chromosomes pair up during meiosis Even though these chromosomes carry the same genes, they could have different alleles

Homozygous and heterozygous

Homozygous - when a person has two of the same allele Heterozygous - when a person has two different alleles

Homozygous and heterozygous alleles

Homozygous: having two identical alleles of a gene. Heterozygous: having two different alleles of a gene.

Huntington's disease

Humans have two copies of the Huntingtin gene (HTT), which codes for the protein Huntingtin (Htt) Huntington's disease is dominantly inherited. Meaning only one bad copy of the gene from either the mother or father will result in Huntington's disease. Children of people affected with the disease have a 50% chance of getting that allele from an affected parent. If both parents have Huntington's disease, offspring have a 75% chance of being affected by the disease. Huntington's disease is a neurodegenerative genetic disorder that affects muscle coordination and leads to mental decline and behavioral symptoms

Pedigree charts

In a pedigree chart, males are represented as squares and females as circles If the square or circle is filled in black, the individual is affected by the condition Some pedigree's represent a carrier with a half filled in circle or square (males are only carriers for autosomal diseases). If it is not filled in, you have to figure out if the individual is a carrier from the inheritance pattern. Mating between two individuals is represented by a horizontal line Children are represented by a vertical line between two parents.

Karyotyping

In karyotyping, chromosomes are arranged in pairs according to their size and structure with the largest at chromosome pair 1 and the smallest at chromosome 22. Chromosomes are stained during mitosis (generally in metaphase) in order to see the chromosomes, and a micrograph is taken of the stained chromosomes This stained image of the chromosomes is called a Karyogram The 23rd pair are the sex chromosomes. Females have two X chromosomes and males have one X chromosome and one Y chromosome.

Disjunction

In meiosis I, homologous chromosomes split, but the centromeres do not divide since the sister chromatids do not separate One chromosome from each pair separate and migrate towards separate poles. This separation is called a disjunction. This halves the chromosome number of each cell and is therefore called reduction division. The two new cells formed after the first division are haploid (n)

Meiosis II

In meiosis II, the haploid chromosomes in the two cells (each have 2 chromatids because replication occurs before meiosis takes place) divide to form four haploid cells each with one set of chromosomes This is called reduction division because the chromosome number is halved This results in the formation of four genetically distinct haploid daughter cells

Meiosis I

In the first division the diploid nucleus 2n, which consists of homologous pairs of chromosomes (half maternal and half paternal chromosomes), divides to form two haploid cells (n). These cells after the first division are considered haploid because the homologous pairs of the nucleus are separated into the two new cells.

Genetic diseases

Many genetic diseases are caused by recessive alleles contained on autosomal chromosomes (any chromosomes that do not determine sex 1-22) Therefore, the disease would only be expressed if an individual has two recessive alleles (i.e. aa) If an individual has one of the dominant alleles (i.e. Aa), they will not show symptoms of the disease. These people are known as carriers. They can pass this allele on to their offspring If the other parent is also a carrier then their offspring have a 25% chance of getting the disease A small number of diseases are co-dominant, such as sickle cell anemia which was studied in 3.1 HAHA - do not have sickle cell anemia, HAHS - mild anemia, HSHS - severe anemia An example of a recessive genetic disease is cystic fibrosis and a dominant disease is Huntington's Disease

Genetic variation

Meiosis is the formation of gametes that produce offspring that are genetically different than their parents. The two main ways variation is created in the offspring is through crossing-over and through random orientation of the chromosomes.

Meiosis

Meiosis is the process in which the diploid (2n) nucleus divides to form four haploid (n) nuclei Meiosis has two divisions called Meiosis I and Meiosis II

Punnett grid

Monohybrid inheritance is the inheritance of a single gene. The trait coded for by the gene is controlled by different forms of the gene called alleles. A Punnett square or grid is a tool used to solve genetic problems.

Cloning adult animals

Once cells start to differentiate and embryos develop into a fetus and eventually an adult cloning becomes much more difficult Therapeutic cloning is an example of cloning using differentiated cells This type of cloning can be used to create a specific tissue or organ Cloning using differentiated cells can also be used to reproduce organisms like dolly the sheep. This is done through somatic-cell nuclear transfer.

Allele

One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the same gene.

Other types of non-disjunctions

Other types of non-disjunctions are trisomy 18 (Edwards Syndrome - many of these fetuses die before birth), trisomy 13 (Patau's syndrome - causes multiple and complex organ defects and highly effects normal development).

Polymerase chain reaction (PCR)

PCR is a way of producing large quantites of a specific target sequence of DNA E.g. crime scene samples of blood, semen, tissue, hair, etc. PCR occurs in a thermal cycler and involves a repeat procedure of 3 steps: 1. Denaturation: DNA sample is heated to separate it into two strands 2. Annealing: DNA primers attach to opposite ends of the target sequence 3. Elongation: A heat-tolerant DNA polymerase (Taq) copies the strands One cycle of PCR yields two identical copies of the DNA sequence

Co-dominant alleles

Pairs of alleles that both affect the phenotype when present in a heterozygote.

Assexual reproduction in plants

Plants use a variety of natural methods of cloning involving stems, roots, leaves or bulbs. Eg. Strawberry plants grow horizontal stems called runners that grow roots into the soil. These small plants develop into independent cloned strawberry plants Underground stems called tubers in potatoes can form new potato plants which are clones of the original parent potato plant

Prokaryote plasmid

Plasmids are small separate (usually circular) DNA molecules located in some prokaryotic cells Plasmids are also naked (not associated with proteins) and are not needed for daily life processes in the cell. The genes in plasmids are often associated with antibiotic resistant and can be transferred from one bacterial cell to another. Plasmids are readily used by scientists to artificially transfer genes from one species to another (ie. Gene for human insulin)

Use of karyotyping

Pre-natal karyotyping is often used to: - Determine the gender of an unborn child (via identification of sex chromosomes) - Test for chromosomal abnormalities (e.g. aneuploidies resulting from non-disjunction) - Amniocentesis - Chorionic Villus Sampling

Prokaryote chromosomes

Prokaryotes have one chromosome consisting of a circular DNA molecule The DNA in a prokaryote is called the nucleoid region which is circular DNA - which, unlike eukaryotes, is not associated with any histone proteins There is one copy of each gene in the nucleoid except when the cell and its DNA are replicating

Define sex linkage

Sex linkage refers to when a gene controlling a characteristic is found on a sex chromosome (and so we associate the trait with a predominant gender)

Cause of Sickle Cell Anaemia

Sickle cell is caused by a base-substitution when the adenine base in GAG is replaced by a thymine base, changing the triplet to GTG on the 6th codon for the beta chain of haemoglobin. During transcription GTG changes to CAC instead of CTC. The normal triplet when translated (GAG) codes for the amino acid glutamic acid. When the base substitution occurs, the amino acid that is translated (GUG) is now valine. Since valine has a different shape and charge than glutamic acid, the resulting polypeptide's shape and structure changes. As a result, hemoglobin's shape will change, as does the shape of the red blood cell (forms a sickle shape - half-moon).

Somatic Cell Nuclear Transfer (SCNT)

Somatic cell removed from the donor and cultured (removed from the udder in Dolly). Unfertilized egg is removed from another sheep and its nucleus is removed. The unfertilized egg is fused with the cultured somatic cell using an electric current. The embryo created now contains all the genetic information from only the first sheep. The embryo divides by mitosis "in vitro" until it reaches the blastocyst stage (hollow ball of about 16 cells). Next, the blastocyst is transferred and embedded into the womb of a third surrogate sheep. The cloned embryo will continue to grow, until a baby lamb is born that is genetically identical to the first sheep that donated the somatic cell.

(5) Meiosis I - Anaphase I

Spindle fibers attached to part of the homologous pairs, shorten and pull the homologous pairs apart. The chiasmata also break down and separate. One chromosome of each pair move to opposite poles of the cell.

(9) Meiosis II - Anaphase II

Spindle fibers pull apart the centromeres and sister chromatids are pulled towards the opposite poles. At this point the chromatids are considered chromosomes again.

Test Cross

Testing a suspected heterozygote by crossing it with a known homozygous recessive

How sex chromosomes control gender

The 23rd pair of chromosomes are sex chromosomes and determine gender Females are XX - they possess two X chromosomes Males are XY - they posses one X chromosome and a much shorter Y chromosome The Y chromosome contains the genes for developing male sex characteristic - hence the father is always responsible for determining gender If the male sperm contains the X chromosome the growing embryo will develop into a girl If the male sperm contains a Y chromosome the growing embryo will develop into a boy In all cases the female egg will contain an X chromosome (as the mother is XX)

ABO blood groups

The ABO gene has three alleles: IA, IB and i IA and IB are codominant, wherease i is recessive

Human Genome Project (HGP)

The Human Genome Project (HGP) was an international cooperative venture established to sequence the 3 billion base pairs (~25,000 genes) in the human genome The outcomes of this project include: Mapping - We now know the number, location and basic sequence of human genes Ancestry - It will give us improved insight into the origins, evolution and historical migratory patterns of humans Medicine - With the discovery of new proteins and their functions, we can develop improved treatments (pharmacogenetics and rational drug design) Screening - This has allowed for the production of specific gene probes to detect sufferers and carriers of genetic disease conditions

Sex determination

The X and Y chromosome determine the sex of an individual The X chromosome is quite large in comparison to the Y chromosome and has a centromere that is located near the centre or middle of the chromosome The Y chromosome is relatively small with its centromere located near the end of the chromosome All other chromosomes are called autosomes and do not affect the sex of an individual The X chromosome has many genes located on it essential to human development, while the Y chromosome has a small number of genes (some of these are shared with the X chromosome). The rest of the genes on the Y chromosome are only necessary for male development

Some genes are present on the X chromosome and absent from the shorter Y chromosome

The Y chromosome is much shorter than the X chromosome and contains only a few genes (hairy ears gene) The X chromosome is much longer and contains several genes (red-green colour blindness) not present on the Y chromosome In human females, only one of the X chromosomes remains active throughout life

Gene

The basic unit of heredity or a heritable factor that controls a specific characteristic. DNA consists of the base pairs adenine, guanine, cytosine and thymine The number of genes in an organism's genome does not indicate how complicated an organism is

Amniocentesis

The cells obtained by amniocentesis come from the embryo and not the mother, allowing doctors to analyze the DNA genome of the embryo. Amniocentesis procedure involves the extraction of a small amount of amniotic fluid (contains fetal tissues) with a needle, from the amnion or amniotic sac surrounding a developing fetus. The fetal DNA is examined for genetic abnormalities through karyotyping.

Chorionic Villus Sampling

The cells obtained by chorionic villus sampling come from the embryo and not the mother, allowing doctors to analyze the DNA genome of the embryo. Chorionic villus sampling involves removing a sample of the chorionic villus (placental tissue) to test for genetic abnormalities through karyotyping. CVS can be carried out 8-12 weeks into the pregnancy.

When genes are transferred between species

The genetic code is universal, meaning that for every living organism the same codons code for the same amino acids (there are a few rare exceptions) This means that the genetic information from one organism could be translated by another

(3) Meiosis I - Metaphase I

The homologous chromosome pairs line up along the cell's equator (metaphase plate). Bivalents (homologous pairs) that come from the mother or the father line up randomly on either side of the cell equator, independently of the other homologous pairs. Each bivalent has a special protein structure called a kinetochore where spindle fibers attach during division to pull the chromosomes apart. These kinetochores are attached to spindle fibers that are attached to the opposite poles.

Consequences of Sickle Cell Anaemia

The insoluble haemoglobin cannot effectively carry oxygen, causing individual to feel constantly tired The sickle cells may accumulate in the capillaries and form clots, blocking blood supply to vital organs and causing a myriad of health problems Also causes anaemia

(1) Meiosis I - Prophase I

The nuclear membrane begins to break down and disintegrate. The replicated chromosomes begin to condense and become visible. Homologous chromosomes synapse (pair up) to form bivalents. Spindle microtubules begin to form.

Locus

The particular position on homologous chromosomes of a gene

Gene transfer - Digestion and Ligation

The plasmid is cut - may generate short sequence overhangs ("sticky ends") that allow the the two DNA constructs to fit together. The gene of interest and plasmid are spliced together by DNA ligase creating a recombinant plasmid

Gene transfer - Transfection and Expressio

The recombinant plasmid is inserted into the desired host cells. The cells will hopefully produce the desired trait encoded by the gene of interest (expression). The product may need to subsequently be isolated from the host and purified

Genome

The whole of the genetic information of an organism In humans, the genome consists of 46 chromosomes plus the mitochondrial DNA In plants, the genome also consists of chloroplast DNA on top of their chromosomes and mitochondrial DNA Prokaryotes have a circular chromosome and plasmids in their genome

Multiple alleles

There can be two or more alleles of a specific gene depending on the gene (if there are more than two alleles = multiple alleles) Eg. The gene that influences human blood type has three different alleles that code for blood types A, B and O.

Human Genome Project

What they found: Most of the genome does not code for proteins (originally labeled "junk DNA"). Some of these regions consist of areas that can affect gene expression or are highly repetitive sequences called satellite DNA. Scientists can now also predict which sequences do code for protein (approximately 21000-23000 sequences)

(4) Meiosis I - Random variation

When homologues line up along the equatorial plate in metaphase I, the orientation of each pair is random The maternal or paternal homologue can orient towards either pole They are attached to a different spindle fibre, randomly attaching them to either pole The orientation of how one set of chromosomes lines up has no effect on the other bivalents This means the number of combinations that can occur in the gamete is 2n (n=number of chromosome pairs). Therefore, in a female or male gamete there can be 223 or 8,388,608 different possible combinations. The same number of possible combinations in the other gamete will combine with to form a zygote (random fertilization) Means that the genetic variation possibilities in the offspring is immeasurable

Zygotes

When the gametes (n) fuse to form a zygote (2n), two copies of each gene exist in the diploid zygote The zygote may contain two of the same allele AA or aa or two different alleles such as Aa