reproduction

• Deoxyribonucleic acid - DNA is a polymer that is found in the nucleus of all cells
• the chromosomes in the 23rd pair are known as sex chromosomes
• chromosomes only have an 'X' shape when the DNA has been duplicated ready for cell division. The rest of the time, they will look more like like an 'l' shape

  
• A small section of DNA that codes for a specific protein - gene
• DNA can code for proteins by coding for the sequence in which amino acids are joined together
• The entire set of genetic material in an organism - Genome
• Terms related to genes

  • Allele
  • Dominant
  • Recessive
  • Homozygous
  • Heterozygous
  • Genotype
  • Phenotype
• Gene

  A segment of DNA that codes for a particular type of protein
• Allele

  Different versions of the same gene
• Homozygous


  Having two of the same alleles for a gene
• Heterozygous


  Having two different alleles for a gene
• Dominant allele


  The allele that gets expressed when present, regardless of the other allele
• Recessive allele


  The allele that only gets expressed when two copies are present (homozygous recessive)
• Genotype

  The entire collection of alleles an organism has
• Phenotype

  The characteristics an organism develops based on its genotype
• Characteristics are often determined by multiple interacting genes, not just a single gene
• The only way to have a recessive trait expressed is if an organism is homozygous for the recessive allele
• Organisms with different genotypes can have the same phenotype, and organisms with the same genotype can have different phenotypes
• where are the chromosomes?

  nucleus

  
• Alleles are the different versions of a particular gene
• 1. One definition describes a genotype as: 'an individual's collection of genes'.
  2. But the more common definition in this course is: 'the two alleles present for a particular gene'. 
  3. In either case, the term genotype refers to the specific genes or allele that an individual has.
• Sexual reproduction

  Involves the fusion of male and female gametes (fertilization), resulting in offspring that contain a mixture of their parents' genes and are genetically different
• Gametes


  Cells like sperm and eggs in animals, or pollen and eggs in flowering plants, that only have half the normal genetic material (chromosomes)
• Meiosis

  The process by which gametes are produced, with each gamete containing half the normal genetic material
• Sexual reproduction does not necessarily involve sex or intercourse, but rather the fusion of male and female gametes
• Asexual reproduction

  Takes place with only one parent and does not involve the fusion of gametes, resulting in offspring that are genetically identical clones of the parent
• Mitosis


  The process by which eukaryotic organisms like plants, fungi, and some animals reproduce asexually
• Binary fission

  The process by which prokaryotic organisms like bacteria reproduce asexually
• Most animals rely on sexual reproduction, while bacteria all reproduce asexually
• Some organisms, like plants, can reproduce through both sexual and asexual means
• Sperm and egg cells are haploid cells and only have 23 chromosomes. When a sperm fertilises the egg though, they form a diploid cell that has 46 chromosomes.
• When bacteria reproduce asexually - binary fission: the process by which a single cell divides to produce two identical daughter cells
• Gametes


  Sex cells like sperm cells and egg cells that only contain half the genetic material of a normal cell (haploid)
• Diploid cells


  Cells that have two sets of genetic information, one from each parent
• Meiosis

  1. Replication of DNA

  2. Chromosomes line up in pairs

  3. Chromosomes pulled apart and cell splits in two

  4. Cell splits in two again resulting in four genetically unique cells
• Chromosomes

  • Contain genetic information
  • Humans have 23 different types of chromosomes
  • Each chromosome has two copies, one from the mother and one from the father
• The left-to-right order of the chromosome pairs is random during meiosis
• The four cells produced by meiosis are all genetically unique
• Sperm and egg fuse during fertilization

  They form a diploid cell that can divide by mitosis to form an embryo, fetus and fully grown organism
• Genetic diagram

  Shows the different combinations of alleles that can be obtained from two parents