Topic 3

• chromosome


  A threadlike, gene-carrying structure found in the nucleus. Each chromosome consists of one very long DNA molecule and associated proteins.
• difference between dna in eukaryotes and prokaryotes

  Prokaryotic- one chromosome, ring shaped, in cytoplasm, made of dna

  Eukaryotic- many chromosomes, made of dna, in strands, in nuclei
• what is sickle cell anemia

  The hemoglobin molecule, resulting in crescent shaped RBCs which have a difficult passing through blood vessels. Occurs from a base substitution mutation where valine is produced instead of glutamine.
• how to determine sex by karyogram


  x is longer than y. if it is xx, it is female, if it is xy, then it is
• describe first phase of meiosis

  Interphase (s-phase)

  In the S-phase of the interphase before meiosis begins, DNA replication takes place.

  Chromosomes are replicated and these copies are attached to each other at the centromere.

  The attached chromosome and its copy are known as sister chromatids.

  
  

  Prophase I

  DNA supercoils and chromosomes condense

  -nuclear membrane dissolves

  - centrioles migrate to the poles of the cell.

  - Crossing-over between chrimosomes can take place. This results in recombination of alleles and is a source of genetic variation in gametes

  Metaphase I

  -bivalents line up at the equator

  - Random orientation occurs - each bivalent aligns independently and hence the daughter nuclei get a different mix of chromosomes.

  This is a significant source of genetic variation: there are 2n possible orientations in metaphase I and II. That is 223 in humans - or 8,388,068 different combinations in gametes!

  
  

  Anaphase I

  - Homologous pairs are separated and pulled to opposing poles.

  Spindle fibres contract

  - This is the reduction division - the bivalent is split and half the chromosomes move towards each pole.

  
  

  Telophase I

  Cytokinesis

  New nuclei membrane forms

  Chromosomes decondense
• how does down syndrome occur

  3 copies of chromosomes on chromosome 21
• genome size


  The amount of DNA contained in one copy of a genome
• difference of karyotype and karyogram

  A karyogram is A diagram or photograph of the chromosomes present in a nucleus (of a eukaryote cell) arranged in homologous pairs of decreasing length

  A karyotype is A property of the cell described by the number and type of chromosomes present in the nucleus (of a eukaryote cell)
• Explain why meiosis is described as a reduction division.


  because it reduces the number of chromosomes from 46 chromosomes or 2n to 23 chromosomes or n (n describes a single chromosome set).
• why does crossing over occur

  to create diversity, bigger allele pool
• Disjunction


  the separation of homologous pairs of chromosomes following meiotic synapsis
• Compare and constrast between the outcomes of non-disjunction in anaphase I with anaphase II

  -both spiral and use endoflagellum to cause diseas
• Chorionic Villus Sampling


  sampling of placental tissues for prenatal diagnosis of potential genetic defects
• Amniocentesis


  A technique of prenatal diagnosis in which amniotic fluid, obtained by aspiration from a needle inserted into the uterus, is analyzed to detect certain genetic and congenital defects in the fetus.
• chromatid


  one of two identical "sister" parts of a duplicated chromosome
• symptoms of sickle cell anemia

  Causes blood to sickle so it is unable to carry as much oxygen to the cells of the body and can get stuck in vessels. Pain in the hands, feet, anemia, fatigue, yellowing of skin and eyes, rediced life span
• advantages in technology that made human genome project possible

  ¥ Biotechnology techniques such as PCR are used to prepare samples: the DNA needs to be copied to prepare a sufficiently large pure samples to sequence

  ¥ Computers automate the sequencing process

  ¥ Fluorescent labeling techniques enable all four nucleotides to be analysed together

  ¥ Lasers are used to fluoresce the dye markers

  ¥ Digital camera technology reads the dye markers

  Computers are used to assemble the base sequence
• John Cairn


  grew bacteria in media containing radioactive nucleotides, isolated the dna, and placed it on a electron-microscope grid covered with photographic emulsion
• chromosome


  made of DNA and protein; contains genes; structural units that are made up of DNA and proteins; by coiling DNA around proteins many times, large amount of information can be stored inside nucleus

  
• genes


  heritable factors that control specific characteristics; various specific forms of a gene (ex: 2 forms of gene that influences height=tall or short); different alleles are due to a slight variation in the base sequence;

  
  

  multiple alleles: more than 2 alleles for one gene (ex: blood type), occupy same locus on one chromosome
• alleles


  different forms of a specific gene
• gene locus


  specific position of a gene on a chromosome
• What do all individuals of a species carry?

  same genes at same loci on same chromosome
• human body cell (somatic cells)

  have 46 chromosomes
• human sex cells (gametes)

  have 23 chromosomes
• members of a species have...

  same number of chromosomes each with same genes in sane gene loci (number of chromosomes varies between species)
• mutations


  new alleles are formed by mutation--> random changes, base substitution (change in one base in sequence of a gene which may or may not change amino acid sequence), neutral or harmful, can be lethal, mutations in somatic cells are not passed on but mutations in gametes are
• Sickle cell disease


  single base substitution leads to production of valine instead of glutamine; leads to production of abnormal red blood cells
• gene mutations (gene wrongly expressed)


  mutation is a permanent change in the base sequence of DNA; it is cumulative effects of millions of mutations and natural selection that have allowed all organisms to evolve from simpler ancestors; not all mutations cause disease;
• mutations more likely to occur when....

  exposed to mutagens like radiation and some chemicals
• malaria


  parasitic disease caused by a plasmodium cell; cannot infect sickle cells so people with sickle cell trait are resistant to malaria (sickle cell more prevalent in areas where malaria is endemic=natural selection)
• genome


  whole of the genetic information of an organism; humans: all DNA in nucleus & mitochondria; plant: all DNA in nucleus, mitochondria, & chloroplast; prokaryotes: smaller circular DNA & plasmids
• human genome project


  23,000 protein encoding genes; highly repetitive sequences (satellite DNA) important to gene expression
• bacterial chromosomes


  circular DNA molecule consisting of one chromosome (not associated with proteins, one copy of each gene)
• plasmids


  some prokaryotes contain them; extra DNA molecules (small and circular), not associated with proteins, not needed for basic life functions, multiple copies may be present, not always passed on in cell division, can be transferred from one cell to another (transformation)
• plasmid used in bacterial transformation

  
• eukaryote chromosomes


  linear DNA associated with histone proteins; different chromosomes carry different genes (different in size & location of centromere, 23 types of chromosomes in human cells, each chromosome can carry thousands of genes); homologous chromosomes (carry same gene sequences, but not necessarily same alleles, allows for interbreeding, 1 from mom & 1 from dad)

  
• sister chromatids


  exact replicas

  
• haploid


  one chromosome of each type, humans=23, ex: gametes, end result of meiosis (4 haploid cells)
• diploid


  pairs of homologous chromosomes-2 copies of every gene; humans 26 chromosomes, ex: somatic cells, end result of mitosis (2 genetically identical diploid cells)