inheritance, variation and evolution

• mitosis:

  • 2 cells are produced
  • growth and repair
  • genetically identical cells
• meiosis:

  • produces haploid ( non identical sex cells)
  • produces gametes (sex cells )
• sexual reproduction:

  • fusion of the nuclei of two gametes to form a zygote
  • production of offspring that are genetically different from each other
• gametes are sex cells
• gametes of animals : egg and sperm
• gametes of flowering plants: pollen and egg cells
• formation of gametes involves meiosis
• asexual reproduction:

  • no sex cells or fertilisation
  • only one parent so no no fusion of gametes
  • offspring are genetically identical to parent and each other
  • only mitosis
• in meiosis:

  • cells in reproductive organs divide by meiosis
  • haploid cells have half the number of chromosomes compared to diploid
• process of meiosis:

  • copies of the genetic material are made
  • cell divides twice
  • four genetically different haploid daughter cells formed each with a single set of chromosomes
  • all gametes are genetically different from each other
• gametes join at fertilisation to restore the number of chromosomes
• the new cell divides by mitosis. the number of cells increases as the embryo develops cells differentiate
• advantages of sexual reproduction:

  • produces variation in the offspring
  • gives a survival advantage if the environment changes by natural selection
  • can be sped up by humans in selective breeding
• the disadvantages of sexual reproduction:

  • requires two parents
  • requires time and energy
  • prevents favourable genes from passing to the next generation
  • produces fewer offspring than asexual
• advantages of asexual reproduction:

  • one parent required
  • more time and energy efficient as do not need to find a mate
  • many identical offspring can be produced when conditions are favourable
• disadvantages of asexual reproduction:

  • no diversity
  • prone to extinction
  • cannot adapt to new environmental changes
• some organisms reproduce sexually and asexually:

  • malarial parasites
  • fungi
  • plants such as strawberry runners or bulb division in daffodils
• fungi reproduce asexually by spores byt sexually by variation
• Malarial parasites reproduce asexually in the human host, but sexually in the mosquito
• Many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils.
• the genome is the entire set of genetic material in an organism
• The genetic material in the nucleus of a cell is composed of a chemical called DNA.
• DNA is a polymer made up of two strands forming a double helix
• The DNA is contained in structures called chromosomes.
• DNA: deoxyribonucleic acid
• a chromosome is a long strand of DNA wrapped around proteins
• a gene is a small section of DNA on a chromosome.
• Each gene codes for a particular sequence of amino acids, to make a specific protein.
• The whole human genome has now been studied and this will have great importance for medicine in the future.
• Human Genome Project (2003):

  • improves our understanding of the genes linked with different types of disease
  • understanding and treatment of inherited disorders
  • study human migration
• DNA is a polymer made up from four different nucleotide
• each nucleotide consists of:

  • common sugar
  • phosphate group
  • one of the four bases attached to the sugar
• DNA consists of four bases:

  • A - adenine
  • C - cytosine
  • G - guanine
  • T - thymine
• a sequence of three bases is the code of a particular amino acid
• the order of bases controls the order in which amino acids are assembled to produce a particular protein
• the long strands of DNA consist of alternating sugar and phosphate sections.
• attached to each sugar is one of the four bases
• the DNA polymer is made up of repeating nucleotides units
• in the complementary strand:

  • a C is linked with a G
  • a A is linked with a T
• proteins are synthesis on ribosomes according to a template