Science semester 1 Biology

• Bases in DNA


  • adenine
  • thymine
  • cytosine
  • guanine
• Complementary base pairing


  • guanine and cytosine
  • adenine and thymine
• The bases always join onto the sugar in the nucleotide, never the phosphate
• Hydrogen bonds


  Weak bonds that join the bases
• Sex chromosomes


  2 of the chromosomes inherited from the parents that determine sex
• Autosomes


  The other 44 chromosomes that determine other characteristics of the person
• Some traits don't have a phenotype such as colour blindness because you can't see it on a person like you can with eye colour
• Some genes don't have a dominant allele, if two different alleles are present then the offspring is a mixture of the two
• More common for males to have sex linked diseases because the y chromosome doesn't possess any matching alleles
• Y chromosome


  • Only contains information relevant to male features eg. Body hair
  • Smaller than other chromosomes
• Fertilisation


  Gametes join together to create a zygote
• Interphase


  The DNA replication has occurred, and the chromosomes are not yet visible.
• Prophase


  The chromosomes become visible, and the two chromatids are joined at the centromere.
• Metaphase


  The chromosomes line up along the equator of the cell, preparing to divide.
• Anaphase


  The chromosomes split, and the chromatids move to the poles of the cell.
• Telophase


  The cell begins to split in half, and the chromatids are now completely separate chromosomes.
• Daughter Cells


  Once fully split, there are now two daughter cells with separate chromosomes.
• Mitosis is the process in which chromosomes replicate to produce exactly the same number of chromosomes in the next generation of cells 
• Meiosis is the process in which chromosomes replicate, but each cell produced has only half the original number of chromosomes. It only occurs in reproductive organs
• Process of meiosis

  1.     the DNA replicates itself, the same as mitosis 

  2.     the cell divides into 2 daughter cells 

  3.     the two daughter cells divide creating 4 daughter cells each with half the required chromosomes needed in a diploid cell
• DNA


  Deoxyribonucleic acid
• Nucleotide


  Made up of sugar, phosphate, and base
• Complementary base pairing


  • Adenine and Thymine always pair
  • Cytosine and Guanine always pair
• Sex linked inheritance


  Y chromosome doesn't carry a gene to express, several sex-linked diseases are caused by recessive genes on the x chromosome, which makes them more common in males than females
• Simple Human Inheritance


  Characteristics are under the control of a single gene
• Homologous pair


  Same type of chromosome (corresponding chromosome one from the father, one from the mother)
• Diploid number


  The number of chromosomes in normal cells (46 in humans)
• Haploid number


  The number of chromosomes that gametes have which is half of what is needed to create a human. In humans the haploid number is 23
• Bases


  • Adenine
  • Thymine
  • Cytosine
  • Guanine
• Bases


  • Form the rungs of the DNA
  • Each has a pair that they always match with, eg: g and c, T and a
• Hydrogen bond


  Weak chemical bonds that connect the bases to each other
• Covalent bond


  Stronger than hydrogen bonds and connects the nucleotides to each other
• Chromosome


  Made of DNA and protein, are long threadlike structures found in the nucleus of most cells
• Chromatid


  One of two sides of the chromosome pair, joined at the centromere
• Centromere


  The place where two sister chromosomes are joined
• Replication


  1. The process of copying DNA

  2. A cell makes a new copy of each chromosome

  3. Now that it has twice as many chromosomes as it should have, its ready to divide
• Division


  The process of cells dividing and creating new cells to make up an organism
• Gamete


  The sex cells (sperm and eggs), undergo meiosis, are known as haploid cells, have half the number of chromosomes as regular cells
• Autosomes


  • 44 of the 46 chromosomes in human cells, they determine characteristics
• Sex cells


  • 2 of the 46 cells in humans, they determine the sex of the person