6.1

• Genes


  Regions along the DNA molecule that code for proteins and ultimately determine what you look like and how your cells in your body function
• Alleles


  Different versions to alternative forms of the same gene. In many cases they cause slight differences in the characteristics of an individual.
• Genome


  The complete set of DNA of an organism. It is sufficient to build and maintain that organism. Each nucleated cell in the body contains the same set of gene material.
• In humans, a copy of the entire genome consists of more than 3 billion DNA base pairs
• The genome includes both coding regions (genes) and non-coding DNA, probably present in the nucleus, mitochondrion or chloroplast for plants.
• Structure of DNA


  • DNA is double stranded, with one strand being complementary to the other. This is due to base pairing between nitrogen bases of each strand.
  • Complementary base pairing occurs such that: A pairs with T (vice versa), G pairs with C (vice versa).
• The double helix


  The end of the polynucleotide strand can be labelled as 5' (five prime) and 3' (prime). The number indicates: A free phosphate on the five carbon of the ribose ring, A free hydroxyl group on the three carbon of the ribose ring. The two complementary strands are said to be antiparallel. One strand runs 5' to 3' and the other strand runs 3' to '5.
• Genes


  The basic physical and functional unit of heredity. Genes are made up of DNA. Some genes act as instructions to make molecules called protein.
• Central dogma


  The central dogma of molecular biology explains the flow of genetic information within a biological system.
• The study of genomes is known as genomics, and the most powerful tool for genomics is sequencing technology.
• Determining gene function


  Knowing the genome sequencing enables us to determine the function of genes. We can compare a gene of unknown function to a gene of known function in another species (to determine its function). We can study the effects of mutations by comparing normal versions of the gene to an abnormal version of a gene (one that causes disease).
• Chromosomes


  • Thread-like structures located inside the nucleus of animal and plant cells. Each chromosome is made of protein (histone) and a single molecule of deoxyribonucleic acid (DNA). Chromosomes can be seen through a microscope when the nucleus dissolves during cell division.
• Haploid


  Refers to one set of chromosomes (n). In humans, (n) = 23 chromosomes. Only gametes (sperm and ova) are haploid.
• Diploid


  Refers to pair of chromosomes (2n), having one from each parent. In humans, (2n) = 46 chromosomes. Only somatic (body) cells are diploid.
• Chromosomes


  • Linear in eukaryotes, Circular in prokaryotes. The number of chromosomes is constant in each species. Each chromosomes carries a unique set of genes. Chromosomes are passed on to daughter cells during mitosis and to germ cells during meiosis.
• Chromosomal coiling and structure

  The DNA is wound and histones forming a nucleosome. The DNA is then coiled and super coiled to form the chromosome structure we see during mitosis.
• Chromosome structure


  • Each chromosome (linear) consists of: Centromere, Chromosome arms. The centromere rarely in the exact middle and hence the short arm.
• Chromosomes can vary in size: Chromosome 1 (longest) has 200 genes, The Y chromosome (shortest) has only just over 200 genes.
• Homologous chromosomes


  Chromosomes that contains the same genes at the same location (loci), are usually in pairs in diploid cells, and pair up during metaphase 1 in meiosis. Alleles can be different.
• Chromatids


  Are identical DNA molecules, Formed during S phase in the cell cycle, Contain identical alleles.
• Types of chromosomes


  • Autosomes
  • X chromosomes
  • Y chromosomes
• Sex determination


  Male gives X and Y chromosomes, Female gives X and X chromosomes, Gender is determined by male.
• Other species may have different chromosomes: Birds, butterfly and strawberries have Z and W chromosomes.
• Polyploidy


  More than 2 sets of chromosomes in a genome. E.g., 3n, 4n, 6n... Can occur through errors in meiosis or through mitosis producing somatic polyploidy cells.
• In humans, polyploidy zygotes don't survive.
• Polyploidy plants are more common than in animals because many can also survive through asexual reproduction. E.g., a 3n plant is typically sterile or has low fertility but can survive through vegetative reproduction.
• Colchicine can be used to artificially introduce polyploidy to plants.
• Mitochondrial and chloroplast chromosomes

  Circular rather than linear. Mitochondrial DNA (mtDNA) contains the code for the proteins that make up the mitochondria. Chloroplast DNA (cpDNA) contains about 100 genes which code for the proteins involved in photosynthesis.
• Karyotypes are used for identifying chromosomal abnormalities.