Chapter Seven

• Deoxyribonucleic acid (DNA)


  A double-stranded nucleic acid chain made up of nucleotides. DNA carries the instructions for proteins which are required for cell and organism survival
• Nucleic acid


  The class of macromolecules that includes DNA and RNA. All nucleic acids are polymers made out of nucleotide monomers
• Nucleotide


  The monomer unit of nucleic acids. Made up of a nitrogen-containing base, a sugar molecule (ribose in RNA and deoxyribose in DNA), and a phosphate group
• Gene


  A section of DNA that carries the code to make a protein
• Genome


  The complete set of DNA contained within an organism's chromosomes
• Locus (pl. loci)


  The fixed position on a chromosome where a particular gene is located
• Inheritance


  The genetic transmission of traits from parent to offspring
• Phenotype


  The observable trait of an individual
• Haploid


  Describes a single set of chromosomes (n)
• Allele


  Alternate forms of a gene
• Histone protein


  Highly basic proteins that associate with DNA inside the nucleus and help it condense into a chromosome allowing it to fit inside the nucleus
• Chromosome


  The structure made of protein and nucleic acids that carries genetic information
• Somatic cell


  Any cell that is not a reproductive cell (such as sperm and egg cells). Somatic cells are diploid (2n), meaning they contain two sets of chromosomes – one inherited from each parent
• Chromatid


  One half of a replicated chromosome. Prior to cell division, chromosomes are duplicated and two copies join together at their centromeres (joined chromatids are known as sister chromatids)
• Homologous chromosomes


  A pair of chromosomes of similar length, gene position, and centromere location. One of the pair is inherited from the mother (maternal chromosome) and the other from the father (paternal chromosome)
• Homologue


  A homologous chromosome
• Karyotype


  A visual representation of an individual's entire genome organised into homologous pairs
• Autosome


  Any chromosome (1–22) in humans that is not a sex chromosome
• Sex chromosome


  A chromosome responsible for determining the biological sex of an organism. In humans, sex chromosomes can be either an X or Y chromosome
• Aneuploidy


  When a cell or organism varies in the usual number of chromosomes in its genome by the addition or loss of a chromosome
• Polyploidy


  When an organism contains additional sets of chromosomes in its genome
• Monosomy


  A genetic abnormality where an organism has one missing chromosome
• Trisomy


  A genetic abnormality where an organism has one extra chromosome
• Tetrasomy


  A genetic abnormality where an organism has two extra chromosomes
• Meiosis


  A specialised form of cell division used to produce gametes in sexually reproducing organisms
• Gametes


  Reproductive cells that arise from germline cells and contain half the genetic material (n) of a somatic cell. The gametes in animals are sperm and egg cells
• Zygote


  The diploid cell formed by the combination of two haploid gamete cells
• Germline cell


  Cells that are involved in the generation of gametes in eukaryotes
• Gonads


  The organs that produce gametes from germline cells. In humans these are the testes (male) and ovaries (female)
• Metaphase plate


  The equator of a dividing cell where chromosomes will line up during metaphase
• Microtubules


  Long tube-like fibre proteins that form part of the cytoskeleton of a eukaryotic cell and help give the cell its structure. Microtubules are used for a variety of cell movements, including transport of cell organelles and the movement of chromosomes during cell division
• Cytokinesis


  The division of the cytoplasm and formation of two daughter cells
• Crossing over


  The exchange of genetic material between non-sister chromatids during prophase I of meiosis, resulting in new combinations of alleles in daughter cells
• Chiasma


  The point/location of overlap between two non-sister chromatids
• Independent assortment


  The random orientation of homologous chromosomes along the metaphase plate during metaphase I
• Diploid


  Having two sets (2n) of each chromosome, one from each parent
• Homozygous


  Having identical alleles for the same gene on homologous chromosomes
• Heterozygous


  Having different alleles for the same gene on homologous chromosomes
• Dominant allele


  The variant of a gene that masks the effect of a recessive allele of the same gene on a homologous chromosome
• Recessive allele


  The variant of a gene that is masked by a dominant allele on a homologous chromosome