DNA - year 10 topic 1

• Adenine, thymine, cytosine, guanine


  3 bases in DNA
• 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 connect the bases to each other
• Chromosomes inherited from parents


  • 2 sex chromosomes
  • 44 autosomes
• 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
• 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 and are smaller than other chromosomes
• Gametes join together in fertilisation to create a zygote
• Hydrogen bonds join the bases to each other
• Mitosis


  1. Interphase

  2. Prophase

  3. Metaphase

  4. Anaphase

  5. Telophase

  6. Daughter cells
• Meiosis


  1. DNA replicates

  2. Cell divides into 2 daughter cells

  3. 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


  Where the 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


  Where 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 and guanine. They each have 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 and are formed by sharing electrons
• 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


  The process of copying DNA. Where a cell makes a new copy of each chromosome, 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
• Mitosis


  The process of cells dividing to create two daughter cells, the chromosomes in the cell replicate themselves and then divide to create two new cells with the same amount of chromosomes as the parent cell
• Meiosis


  Occurs in haploid cells (gametes), produces cells that half the number of chromosomes than regular cells
• Karyotypes


  A chart of all the chromosomes in a diploid cell ( not sperm or egg), arranged in homologous pairs in order of size, centromere position and banding pattern, sex chromosomes are at the end
• Allele


  An alternate form of a gene
• Recessive gene


  An allele which can be masked by another allele, can only be expressed when two copies are present, is always written with the lower case
• Dominant gene


  The dominant allele is always written with an upper case, will always be expressed because it can't be masked by another allele
• Homozygous


  If an individual has two copies of the same alleles, prefix "homo' means 'same'
• Heterozygous


  An individual has two different alleles of a gene, prefix 'hetero' means 'other'
• Incomplete dominance


  When both alleles aren't dominant, eg. Red and white flower making a pink flower