Reproduction

• Types of reproduction


  • Sexual
  • Asexual
• Organisms that reproduce sexually

  • Most animals
  • Plants
• Organisms that reproduce asexually

  • Bacteria
  • Some plants and animals
• Fusion of gametes in sexual reproduction

  Yes (in animals egg and sperm, in plants ova and pollen)
• Offspring in sexual reproduction


  No as the offspring will inherit characteristics from both parents so will show variation
• Offspring in asexual reproduction

  Yes, known as clones so no genetic variation (more likely to suffer from a mutation or not be adapted to a change in the environment)
• Type of cell division in sexual reproduction

  Meiosis (this halves the number of chromosomes in the gametes)

  
• Type of cell division in asexual reproduction

  Mitosis (also referred to as binary fission in bacteria)

  
• Sexual Reproduction


  1. Requires a male and female

  2. Both produce gametes

  3. Gametes are produced by meiosis

  4. Gametes have half the genetic information of a body cell

  5. During meiosis, the genetic information is mixed so each of the gametes has different genetic material

  6. This leads to variety in offspring

  7. When both gametes meet, the nuclei from each fuse together

  8. This makes the first cell of the new organism called the zygote

  9. In the plants, the zygote is a seed

  10. In animals, the zygote divides by meiosis into a balls of cells called an embryo

  11. In meiosis, all of the cells are genetically identical
• Asexual Reproduction


  1. Only involves one parent

  2. Cells divide by mitosis

  3. No fusion of gametes so there is no mixing of genetic information

  4. No variation in offspring

  5. Gives rise to genetically identical offspring known as clones

  6. Genetic material is identical to parent and to each other

  7. Only mitosis is involved

  
• Advantages of asexual reproduction

  • 1 parent so less time and energy to find a mate
  • Faster
  • Produces larger numbers of identical offspring
• Disadvantages of asexual reproduction

  • If conditions change, organisms may not survive due to all being identical
• Advantages of sexual reproduction

  • Produces variation in offspring
• Disadvantages of sexual reproduction

  • 2 parents required so more time and energy is spent on finding a mate
  • Slower
• Meiosis


  • A type of cell division that produces gametes (sperm and egg cells)
  • Meiosis only occurs in the gonads (sex organs / testes and ovaries)
  • Meiosis produces variation as each gamete has a random mix of chromosomes from the parent
  • It is called the reduction division because the chromosome number is halved
  • Fertilisation restores the full number of chromosomes

  
• Fertilisation


  1. More variation is added when fertilisation takes place

  2. Each sex cell has a single set of chromeosomes

  3. When 2 sex cells join, the single new cell formed has a full set of chromosomes

  4. In humans, the egg cell has 23 chromosomes and so does the sperm

  5. When they join together, they produce a single new body cell with 46 chromosomes in 23 pairs

  6. The combination of genes on the chromosomes of every newly fertilised egg is unique

  7. Once fertilisation is complete, the unique new cell begins to divide by mitosis to form a new individual

  8. The number of cells increases rapidly

  9. As the embryo develops, the cells differentiate to form different tissues, organs and organ systems

  
• Variation in asexual reproduction

  • The offspring are produced as a result of mitosis from the parent cells
  • They contain exactly the same chromosomes and genes as the parent cells

  
• Variation in sexual reproduction

  The gametes are produced by meiosis in the sex organs of the parents
• Spore


  Microscopic biological particles that allow fungi to be reproduced
• Hyphae


  A long, branching filamentous structure of a fungus
• Pollen


  Plant male gamete
• Runner


  A stem like growth extending from a parent plant's growing point
• Gametocyte

  A cell that divides by meiosis to form gametes
• Asexual reproduction in fungi

  1. Toadstools and puffballs full of spores

  2. Moulds that rot food also reproduce this way

  3. Made up of hyphae that form structures we see

  4. They produce spores by mitosis so they are identical and only contain half the number of chromosomes
• Sexual reproduction in fungi

  1. 2 hyphae from different fungi join and nuclei fuse so new hyphae has 2 sets of chromosomes

  2. Undergoes meiosis to make haploid spores, each with one set of chromosomes

  3. Some spores may produce fungi better adapted to conditions
• Sexual reproduction in plants

  1. Flowers contain sex organs

  2. Pollen and egg cells produced using meiosis

  3. Pollen from one flower must reach female parts of other - pollination

  4. Once pollen has fused with egg cell, seeds are formed

  5. Process introduces variation and enables plants to survive as conditions change through natural selection
• Asexual reproduction in plants

  1. New plants grow following mitosis

  2. Means that new plants are formed even if flowers are destroyed by weather or eaten

  3. However no variation is introduced
• Reproduction in Malaria Parasites

  1. Parasites reproduce differently in different stages of their life

  2. Malarial parasites spend part of their life in body of female mosquito and part in the blood of humans

  3. Asexual - in human liver ad blood cells

  4. Sexual - When mosquito take their blood meal, the drop in temp between human and mosquito triggers sexual reproduction

  5. 20 mins until sexuals forms develop, burst out of blood cells and meet to form zygotes with 2 sets of chromosomes

  6. These zygotes undergo meiosis to produce new asexual parasites that will infect a new human host

  7. Show lots of variation
• DNA

  • Stands for deoxyribonucleic acid
  • Is a polymer
  • Long strands of DNA twist and spiral to form a double helix structure
  • Genes are small sections of this DNA
  • This is where genetics information is stored
  • Each chromosome contains thousands of genes joined together
  • Each gene codes of a particular sequence of amino acids to make a specific protein
  • These proteins include enzymes that control cell chemistry

  
• Genome

  • The entire genetic material of the organism
  • Human genome contains over 2 billion base pairs and 21000 genes
  • The HGP took place from 1990-2003 with the aim of reading the human genome
  • Scientists are still currently sequencing genomes of thousands of different people so we can gather as much information about DNA as we can
  • We are also sequencing the genomes of other species as it allows us to see relationships between organisms and identify causes of diseases caused by pathogens so a treatment can be found

  
• DNA structure

  • Found in nucleus and controls protein synthesis
  • Long strands of DNA are made up of alternating sugar and phosphate sections
  • Make up the backbone of the molecule
  • Attached to each sugar is a base, represented by A, C, T or G
  • Combination of sugar, phosphate and base is a nucleotide
  • Dna polymer is made of repeating nucleotide units
  • Unit is grouped into threes and each group of three bases code for a particular amino acid
  • Each gene is made up hundreds of thousands of these bases
  • Order of these bases controls the order in which the amino acids are assembled to produce a protein
  • Change or mutation in a single group of bases can be enough to change or disrupt the whole protein structure
  • A always pairs with T
  • C always pairs with G
• Gene Expression

  • Refers to when a gene codes for protein
  • Lots of DNA in cells that does not code for proteins
  • Non-coding DNA is involved in determining if genes make a protein

  
• Mutation


  • Mutation is a change in a gene or chromosome
  • It is a rare, random change in the genetic material and it can be inherited
• Genotype

  The alleles that are present
• Phenotype


  The physical characteristic of an individual
• Dominant

  Allele will always be expressed (shown) even if one is present
• Recessive


  Allele only expressed if both alleles are recessive as otherwise the dominant allele masks the recessive one
• Homozygous

  An individual with the same alleles
• Heterozygous


  An individual with different alleles
• Polydactyly

  Genetic disorder caused by a dominant allele, resulting in extra digits (fingers or toes)