chapter 2 definitions

• Allele


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


  The process by which a single parent produces offspring and that does not involve fusion of gametes; a process that usually results in identical offspring
• Autosome


  A chromosome that is not a sex chromosome
• Binary fission

  The division of a cell into two cells without mitosis; a prokaryotic cell undergoes binary fission to form two identical daughter cells; a form of asexual reproduction
• Bivalent

  A structure (visible in a cell during prophase I of meiosis) made up of two homologous chromosomes joined together
• Cell cycle

  An ordered sequence of events in the life of a cell from when it was formed from a parent cell until its own division
• Cell division


  The splitting of a cell into two new functioning cells
• Cell plate


  The structure produced by dividing plant cells in the place where the new cell wall is forming
• Centriole


  A minute rod-shaped organelle present in many resting cells, just outside the nuclear membrane that helps make the spindle fibres for cell division; a centrosome contains two centrioles; it is usually absent in plants
• Centromere


  The waist-like constriction in a chromosome where the spindle fibres attach; it enables the movement of chromosomes during cell division
• Centrosome


  An organelle containing a pair of centrioles; it duplicates during cell division, while the DNA is duplicating, and the two centrosomes then separate to opposite poles of the dividing cell; it produces the spindle during cell mitosis and meiosis, and one of the centrosomes goes into each daughter cell
• Chromatid


  Daughter strand of a duplicated chromosome that is joined to another chromatid by a centromere
• Chromatin


  An organised, loosely coiled complex of DNA and its proteins that is found in eukaryotic non-dividing cells; it is more compact than the DNA of prokaryotes; chromatin supercoils to become the chromosomes observable during eukaryotic cell division
• Chromosome

  A structure composed of DNA and protein that contains linear arrays of genes carrying genetic information; prokaryotes generally have one circular chromosome, whereas eukaryotes have a number of linear chromosomes
• Cleavage


  The division of the cytoplasm in an animal cell
• Cleavage furrow


  A shallow, ring-like depression that forms on the surface of an animal cell undergoing cytokinesis as contractile microfilaments pull the cell membrane inward; it defines where the cytoplasm will be divided to make two cells
• Crossing over


  The exchange of genetic material between maternal and paternal homologous chromosomes (of non-sister chromatids) that occurs during the first step of meiosis (prophase I)
• Cytokinesis


  The division of the cytoplasm immediately after mitosis, meiosis I or meiosis II to create two separate daughter cells
• Differentiation

  The process during development whereby newly formed cells become more specialised as they mature; an example of cell differentiation is the development of root tip cells of plants into phloem, xylem, and root hairs; during the process of differentiation, cells gain specialised structures and functions
• Diploid (2n)


  Describes a cell or organism that has a genome that contains two copies of each chromosome; the diploid number of chromosomes is represented by 2n
• DNA (deoxyribonucleic acid)


  The information-containing molecule present in all living things that contains the instructions, written in a chemical code, for the production of proteins by the cell; the information it contains is sufficient for the making and maintaining of the organism; in addition, DNA is the genetic material that passes this information on to the next generation
• Eukaryotic cell


  A complex cell containing membrane-bound organelles, including a nucleus
• Fertilisation


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


  A male or female reproductive cell; one of each type combine at fertilisation; in humans, the gametes are ova and sperm cells; in flowering plants, pollen grains contain male gametes and ovules contain female gametes
• Gene


  A unit of heredity that transmits information from one generation to the next; a segment of DNA that codes for a p
• Human gametes

  • Ova
  • Sperm cells
• Flowering plant gametes

  • Pollen grains
  • Ovules
• Gene


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


  Refers to the mechanisms and patterns of inheritance; relating to the transmission of coded chemical instructions from one generation to the next
• 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
• Germline cell


  A specialised sex cell that gives rise to gametes; early in an embryo’s development, its germline cells specialise into male or female germ cells
• Haploid (n)

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


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


  One of the non-identical chromosomes that pairs up at meiosis (e.g. the X and Y chromosomes in male humans)
• Histone


  A protein around which DNA winds in eukaryotic cells to form a nucleosome
• Homologous chromosomes

  A pair of chromosomes of the same size and shape and that has the same genes at the same locations
• Interphase


  The stage between nuclear divisions that involves metabolic activity, growth, and duplication of chromosomes
• Karyotype


  A display of the number and appearance of the chromosomes of an organism or cell as observed at metaphase
• Locus (plural loci)


  The position a gene occupies on a chromosome