Inheritance

• Sexual reproduction starts with the gametes (created by meiosis) which fuse to form a zygote which divide by meiosis to form an embryo. The mixture of DNA cause genetic variation
• the gametes in a human are egg and sperm but in a plant, they are egg and pollen
• asexual reproduction has only one parent and is when an ordinary cell divides. there is no mixing of chromosomes so the offspring are genetically identical to the parent
• advantages of sexual reproduction


  • if the environment changes, the variation means the offspring could survive
  • can be selectively bred to get desirable qualities
• disadvantage of sexual reproduction


  • slower as requires finding a mate
• advantage of asexual reproduction


  • faster so its useful when conditions are favourable
• disadvantage of asexual reproduction


  • since they are identical, they could all die if conditions are unfavourable
• meiosis is the process of making gametes
• normal cells are diploid so they have 46 chromosomes
• gametes are haploid so they have 23 chromosomes
• meiosis takes place in reproductive organs which is testes in males and ovaries in females
• stages of mitosis


  1. all chromosomes copy and pair up
  2. cell divides into 2 diploid cells
  3. these divide again to form 4 genetically different haploid cells with different alleles
• chromosomes are found in the nucleus and contain DNA which have inherited features
• DNA consists of two strands which are polymers and is in a double helix structure
• DNA is a polymer of molecules called nucleotides
• Nucleotides consist of a phosphate, deoxyribose sugar and a base
• there are 4 bases: A,T,C,G
• the DNA strands are complimentary and the bases pair on the opposite sides. A always links to T and C always links to G
• Genes are a small section of DNA on a chromosome. each gene encodes for a specific series of amino acids to make a specific protein
• Genomes are the entire genetic material of an organism
• scientists have discovered the whole genome of a human which has advantages such as:


  • linking diseases with genes
  • Understand and treat inherited diseases like cystic fibrosis
  • Trace human ancestry