chapter 4 definitions

• Allele


  One of various versions of the same gene (at the same locus) distinguished by small differences in the DNA sequence
• Aneuploidy


  Describes a genome that varies from the conventional genome through the loss or addition of one or a few chromosomes
• Apoptosis


  A programmed series of events that leads to cell death as a result of the dismantling of the internal contents of the cell by various enzymes, including caspases
• Behaviour


  Responses and reactions of an organism in particular situations
• Beneficial mutation


  A mutation that increases an organism’s chances of survival and reproduction
• Chiasma


  The point of contact between two (non-sister) chromatids belonging to a set of maternal and paternal homologous chromosomes where crossing over may occur
• Chromatin


  The complex of proteins and DNA found in eukaryotic non-dividing cells
• Cloning vector


  In cloning, the vector is the DNA molecule that is used to carry the cloned piece of DNA
• Codon


  A set of three consecutive nucleotides found in a DNA or an mRNA molecule; it carries a code for a specific amino acid
• Crossing over

  An event during meiosis, in which homologous chromosomes (non-sister chromatids) exchange alleles (genetic segments) with one another
• Deleterious mutation


  A mutation that decreases an organism’s chances of survival and reproduction
• Deletion mutation


  A mutation in which one or more nucleotide pairs have been lost from a segment of DNA
• Diploid (2n)


  Describes a cell or organism that has a genome that contains two copies of each chromosome, represented by 2n
• Double-strand break


  A mutation involving breaks in the sugar–phosphate backbones of both DNA strands at the same nucleotide pair, resulting in the complete breakage of a chromosome
• Expressed


  Describes a gene that has been read, transcribed and translated into a protein
• Fertilisation


  The union of haploid male and female gametes during sexual reproduction to produce a diploid zygote; the random union of gametes is known as random fertilisation
• Frameshift mutation

  A mutation that changes the reading frame used in translation, during polypeptide synthesis
• Gamete


  A sex cell; it can be a male or female sex cell and has a haploid number of chromosomes
• Gene


  A unit of heredity that transmits information from one generation to the next; a segment of DNA that codes for a polypeptide
• Genetic code


  The way that the four nitrogenous bases of DNA (adenine, thymine, guanine and cytosine) are ordered and contain information to direct the creation of specific proteins
• Genome


  All of the genetic material contained in an organism or a cell; it includes the chromosomes within the nucleus and the DNA in mitochondria and chloroplasts
• Genotype


  The specific combination of alleles for each gene locus that belongs to an individual or cell
• Germline cell


  The cell line in eukaryotic organisms from which the gametes are derived
• Haploid (n)

  Describes a cell or organism that has a genome that contains one copy of each chromosome; represented by n
• Heredity


  The study of inheritance; the genetic transmission of characteristics from one generation to another
• Homologous chromosome

  A pair of chromosomes that have the same size and shape; they have genes at the same locations; one is maternal and one is paternal
• Horizontal gene transfer


  The process by which genetic material from one organism becomes incorporated into the genome of another organism
• Independent assortment


  The random orientation of maternal and paternal homologous chromosomes at the equator during metaphase I; the orientation of each homologous pair is randomly to one side or the other, and each pair is unaffected by the orientation of any other homologous pair
• Insertion mutation


  A mutation in which one or more nucleotide pairs have been added to a segment of DNA
• Intraspecific variation


  Differences between individuals of the same species
• Karyotype


  A display that presents the number and appearance of the chromosomes of an organism
• Karyotype


  A display that presents the number and appearance of the chromosomes of an organism or cell as observed at metaphase
• Meiosis

  Involves two rounds of cell division, but only one round of DNA replication; during meiosis, the chromosome number of a cell is halved
• Missense mutation


  A gene mutation that results in one amino acid being replaced by another amino acid in the encoded protein
• Monoploid (1n)

  Describes a cell or organism that has a functional genome consisting of one copy of each chromosome, represented by 1n
• Monosomy


  The condition in which somatic cells of an organism are missing one copy of a particular chromosome
• Mutagen


  An agent capable of inducing mutations
• Mutant

  A cell or organism that bears a mutation
• Mutation


  A permanent change in the DNA sequence of a gene; a source of new alleles in a population’s gene pool; the process of generating a mutation
• Mutation rate


  The number of changes per gene copy in a population over a period of time