G E N E S 2

How was the Human Genome Mapped?

1. Anonymous donors provided eggs or sperm (haploid genomes) 2. The DNA was isolated from these gametes 3. High quality, rapid sequencings methods allowed small genome fragments to be sequenced. 4. These were arranged in order using overlapping ends to produce a continuous sequence.

Genome

A Genome is the complete set of information in an organism's DNA. It is the sum total of an organisms DNA measured in the number of base pairs contained in a haploid set of chromosomes. This carries the information for all the proteins the organism will ever synthesis. In addition to this it also carries instructions for about 20,000 distinct proteins. Some organelles, such as mitochondria and chloroplasts, contain DNA. This forms part of the genome.

Karyotype

A karyotype is the number and appearance of chromosomes in the nucleus of a eukaryotic cell.

The Knock-Out Mouse

A knock out mouse is a genetically modified mouse in which researchers have inactivated, or knocked out, an existing gene by replacing it or disrupting it with an artificial piece of DNA. They are important animal models for studying the role of genes which have been sequenced but whose functions have not been determined. By causing a specific gene to be inactivate in the mouse, and observing any differences form normal behaviour or physiology, researchers can infer its probable function. Humans share many genes with mice. Consequently, observing the characteristics of knockout mice gives researchers information that can be used to better understand how similar gene may cause or contribute to disease in humans.

DNA strand

A long chain composed of nucleotide subunits.

Complementary Base Pairing

A pairs with T G pairs with C *this happens because of their structures Due to these properties each strand of a DNA molecule contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand.

Monosomies

A zygote that is missing a chromosome is said to have monosomy.

Trisomies

A zygote with 3 copies of a chromosome is said to have trisomy.

Health

All human beings are 99.9 percent identical in their genetic makeup. Differences in the remaining 0.1 percent hold important clues about the causes of diseases. Gaining a better understanding of the interactions between genes and the environment by means of genomics is helping researchers find better ways to improve health and prevent disease. Genomic medicine has already shown benefit in refining diagnoses and guiding therapeutic approaches for many diseases, including cancer. Genetic screening also allows individuals to identify disease or risk factors in their own genomes. Every baby born in Australia is offered screening for about 30 genetic conditions in the Guthrie test, and more than 300 tests for genetic disorders are available through the health care system.

Autosomes

All the chromosomes in a human except from the x and y chromosomes. This includes chromosomes 1-22.

Human Chromosome Number 1

Chromosome 1 is the largest human chromosome, consisting of about 249 million base pairs (bps) and representing approximately 8 percent of the total DNA in cells. Chromosomes 1 likely contains 2,000 and 2,100 genes that provide instruction for making proteins that perform a variety of different roles in the body.

Chromosomes

Chromosomes are thread-like structures found in the nucleus of each cell that DNA is packaged into. Each chromosome is made up of DNA tightly coiled many times around proteins called histones that support its structure. Chromosomes are not visible in the cell's nucleus- not even under a microscope- when the cell is not dividing, However, the DNA that makes up chromosomes becomes more tightly packed during cell division and is then visible under a microscope.

Using Karyotypes to Diagnose Disease

Chromosomes sometimes are incorrectly distributed into the egg or sperm cells during mitosis. When this happens, one cell may get two copies of a chromosome, while the another cell gets none. karyotypes can be used to identify if this has occurred by lining up the chromosomes and identifying if any are missing and if there are any extras.

Comparative Genomics

Comparative genomics is a field of biological research in which genomic features of different organisms are compared. The genomes of a variety of species have now been sequenced and these have been compared with each other or with human genome to help determine the relatedness between species. Comparative genomics is now standard component of the analysis of every new genome sequence.

DNA Replication

DNA carries biological information that must be copied accurately for transmission to the next generation each time a cell divides to form two daughter cells. Because each strand of DNA contains a sequence of nucleotides that is exactly complementary to the nucleotide sequence of its partner strand, each strand can act as a template, or mould, for the synthesis of a new complementary strand.

Information in DNA

DNA encodes information through the order, or sequence, of the nucleotides along each strand. Organisms differ from one another because their respective DNA molecules have different nucleotide sequences and consequently, carry different biological messages.

DNA structure

DNA is made of four type od nucleotides, which are linked into a DNA Strand with a sugar-phosphate backbone from which rthe bases (A,C, G, T) extend. A DNA molecule is composed of two DNA strands held together by relatviely weaker bonds between the paried bases. Because only the base differs in each of the four types of subunits, each polypeptide chain in DNA is analogus to a necklace strung with four types of beads. eg. A,C, T, G The three dimensional sturtcure of DNA known as the double helix arises from the chemical and structural features of its two polynucleotide chains.

Chromatin

Each DNA molecule is coiled tightly around proteins to form a thread called chromatin. The way DNA is packaged into chromatin is a factor in how protein production is controlled. During mitosis, the chromatin condenses to form a chromosome.

Proteins

Genes contain the instructions for producing proteins. The DNA messages must therefore somehow encode proteins. The properties of a protein, which are responsible for its biological function, are determined by its three- dimensional structure, and its structure is determined in turn by the linear sequence of the amino acids of which it is composed. The linear sequence of nucleotides in a gene therefore spell out the linear sequence of amino acids in a protein.

Genetic Expression

Genetic Expression is the process through which a cell translates the nucleotide sequence of a gene into the amino acid sequence of a protein.

Homologous Chromosomes

Homologous chromosomes are pairs of autosomes. Homologous chromosomes have all the same arranged in the same order, but with slight differences in the DNA sequences of the genes.

Human Chromosomes

In humans, each cell normally contains 23 pairs of chromosomes, for a total of 46. Each parent contributes one chromosome to each pair so that offspring get half of their chromosomes from their mother and half from their father.

Nondisjunction

Nondisjunction is the incorrect distribution of chromosomes in a zygote.

Nucleotides

Nucleotides are composed of a five-carbon sugar which are attached to one or more phosphate groups and a nitrogen- containing base. The base is either adenine, cytosine, guanine and thymine.

Identifying Chromosomes

Scientists use three key features to identify which chromosome is which. 1. Size: This is the easiest way to tell chromosomes apart. 2. Banding pattern: the size and location of bands make each chromosome unique. 3. Centromere position: Centromeres appear as a constriction. The position of the centromere varies between the different chromosomes Using these key features, scientists can identify all 46 chromosomes in a human cell.

Sex Chromosomes

Sex chromosomes are the 23rd pair in humans. These chromosomes determine male and females. Females have two copies of the X chromosome while male have one X and one Y.

SRY gene

Sex is determined by the SRY gene, which is responsible for the development of a fetus into a male .

Chromosome Structure

The chromosome consist of two sections or arms which are divided by a central centromere. The short arm of the chromosome is labelled the p arm. The long arm of the chromosome is labelled the q arm. The location of the centromere on each chromosome gives the chromosome its characteristic shape, and can be used to help describe the location of specific genes.

Genetic code

The genetic code is the exact correspondence between the four- latter nucleotide alphabet of DNA and the twenty-letter amino acid alphabet of proteins.

Human Genome Project

The human genome project is an international scientific project with the goal of determining the sequence of chemical base pairs which make up human DNA, and of identifying and mapping all of the genes of the human genome from both a physical (sequence of bases) and a functional (what does the protein encoded by each gene do) standpoint. By mapping the human genome health care providers may be given immense new powers to treat, prevent and cure disease.

Gene Function

The protein encoded by the gene must be identified and studied in order to determine its function. One way to do this is to modify a gene sequence, insert it into an organism and determine the effects of modification. This can help us to understand the normal function of the protein encoded by the gene.

Human X Chromosome

The x chromosome is one of the two sex chromosomes in humans. the x chromosomes is about 155 million bps long. Females have two X chromosomes, while males have only one.

Human y Chromosome

The y chromosome is one of the two sex chromosomes in humans. The y Chromosomes is about 59 million bps long. The y chromosome is present In males, who have one X and one y chromosome. The y chromosome likely contains 50-60 genes that provide instructions for making various proteins. Because only males have a y chromosome, the genes on this chromosome tend to be involved in male sex determination and development.

X inactivation

X inactivation occurs early in embryonic development in females when one of the two X chromosomes is randomly and permanently inactivated in the cells other than eggs cells. X-inactivation ensures that females, like males, have one functional copy of the X chromosome in each body cell. Because X-inactivation is random, in normal females the X chromosome inherited from the mother is active in some cells, and the X chromosome inherited from the father is active in other cells.

Trisomies and Monosomies

if a sperm or egg with too many or too few chromosomes participated in fertilization, it will produce a zygote with too many or too few chromosomes. Most of the time autosomal trisomy and monosomy are lethal because the zygote ends up with too much or too little genetic information. The fetus usually miscarries. But sometimes babies are born with extra or missing autosomes-most commonly one of the smaller chromosomes that have fewer genes. Usually these babies have a genetic disorder, which scientists can diagnose by looking for extra or missing chromosomes in a karyotype. When monosomy or trisomy involves sex chromosomes, individuals usually survive and many are quite healthy.

mtDNA

mtDNA or mitochondrial DNA is DNA found in the mitochondria. Mitochondria have a small amount of their own DNA. Mitochondria are structures within cells that convert the energy from food into a form that cells can use. Each cell contains hundreds to thousands of mitochondria which are located in the fluid that surrounds that nucleus (the cytoplasm). Mitochondrial DNA contains 37 genes, all of which are essential for normal mitochondrial function.