inheritance, variation and evolution

• what is sexual reproduction?

  the fusion of male and female gametes
• what is sexual reproduction in animals?

  sperm and egg cells
• what is sexual reproduction in flowering plants?

  pollen and egg cells
• how is variation produced in offspring?

  sexual reproduction
• how many chromosomes do each gamete contain?

  23
• what is asexual reproduction?


  production of new individuals that are identical to their parents; does not involve the fusion of gametes
• how many parents does asexual reproduction have?

  one
• what cell division is involved in sexual reproduction?


  meiosis
• what is meiosis?


  cell division that forms four daughter cells with half the number of chromosomes as the parent cell
• what cell division in used in asexual reproduction?

  mitosis
• what are runners?


  long shoots from plants, such as strawberries, that are used for asexual reproduction, which touch the ground and grow a new plant
• what is a gamete?


  a specialised sex cell formed by meiosis
• what is DNA?


  nucleic acid molecules that contain genetic information and make up chromosomes
• what are chromosomes?


  long molecules found in the nucleus of all cells; made from DNA
• what is a gene?

  part of a chromosome, made of DNA, which codes for a protein
• what is a genome?

  all the genetic material found in an organism or a species
• the formation of gametes involves what cell division?


  meiosis
• what happens in meiosis?

  :

  1. copies of the genetic information are made
  2. the cell divides twice to form four gametes, each with a single set of chromosomes
  3. all gametes re genetically different from eachother
• why is meiosis important?

  it halves the number of chromosomes in gametes, this means that fertilisation can restore the full number of chromosomes
• what are the six stages in meiosis?

  stages:

  1. cells with two pairs of chromosomes (diploid cell)
  2. each chromosome replicates itself
  3. chromosomes part company and move to opposite poles
  4. cell divides for the first time
  5. the copies now separate and the second cell division takes place
  6. four haploid cells (gametes) each with half the number of chromosomes as the parent cell
• what is an allele?


  an alternative form of a particular gene
• what is a genotype?

  the combination of alleles for a particular gene, e.g. BB, Bb or bb
• what is a phenotype?


  the physical expression of the genotype (the trait shown)
• what is a dominant allele?

  an allele that only needs to be present once in order to be expressed
• what is a recessive allele?


  an allele that will only be expressed if there are two present
• what is a homozygous genotype?


  carrying two copies of the same allele for a gene e.g. BB or bb
• what is a heterozygous genotype?

  carrying two different alleles for a gene e.g Bb
• what is monohybrid inheritance?

  the pattern of inheritance shown when a characteristic is controlled by a single gene
• what is cystic fibrosis?

  a genetic condition that causes a build-up of mucus in the lungs
• cystic fibrosis is a disorder of what?

  cell membranes
• what is cystic fibrosis controlled by?

  a single gene that has two recessive alleles for defective cell membrane
• what is polydactyly?


  a genetic disorder caused by a dominant allele, where affected people have extra fingers or toes
• what is polydactyly caused by?


  a dominant allele
• how can we tell if someone will inherit a disorder?

  embryo screening
• what is embryo screening?

  embryos are tested to see if they have inherited disorders
• what are some issues with embryo screening?


  issues:

  • expensive
  • large number of embryos are created but only a small number implanted, meaning some are destroyed
• what are sex chromosomes?

  a pair of chromosomes that determine the sex of organisms
• what sex chromosomes do males have?

  XY
• what are the sex chromosomes of females?

  XX
• what is variation?


  differences between individuals of the same species