Biology Unit 2

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  • Created by: slr674
  • Created on: 20-11-14 18:21
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  • Biology Unit 2
    • New Species
      • Speciation is formation of NEW species
      • Could become separated geographically
        • e.g. Move to different islands, the environment between them changes, so can't cross it
        • Natural selection takes place
          • = different variations of characteristics favoured
          • characteristics of population change
            • Characteristics so different, individuals from different populations can't interbreed, even if were in same area
              • = DIFFERENT species!
    • Extinction
      • All individuals of a species dies out
      • CAUSES
        • Disease
        • Competitors e.g. take food/resources
        • New predators
        • Catastrophic event
          • e.g. asteroid or massive volcano erruption
        • Changes to environment over millions of years
          • organisms cannot adapt fast enough
          • GEOLOGICAL TIME
    • Fossils
      • remains from organisms from many years ago, found in rocks
      • Formation
        • Dead organisms decay
          • 1.Hard parts don't decay easily, so fossilise
            • e.g. teeth and bones
          • 2.Conditions don't allow decay e.g. not enough oxygen
            • Soft tissues also fossilise e.g. leaf, muscle tissue, animals with no hard parts
          • 3.Parts of organisms replaced by other materials as decay
        • traces of organisms fossilise in special conditions
          • e.g. footprints as casts in mud
      • age figured out by age of rock, can show how much organisms changed over millions of years
      • record not completed because...
        • 1.they only form in special conditions
        • 2.many early life forms had soft bodies, so left few traces
        • 3.geological changes in rock = destroys fossils
    • Embryo screening
      • people who think they have allele from inherited disorder can have embryo screened at early stage of pregnancy
      • Issues
        • Economic
          • may cost parents extra money to support child with disorder
          • would child need lot of hospital treatment/drugs?
        • Social
          • who will care for child if parents can't?
          • If needs lots of care, is it fair on other children in family?
        • Ethical
          • embryo has same right to life as person
          • Screening carries small risk of damaging embryo - should risk be taken?
    • Family trees
      • Can inherit allele for a disorder
      • Cystic Fibrosis disorder affects cell membranes, makes mucus stickier than normal
      • F = dominant allele and f = recessive allele
      • Ff are CARRIERS
      • ff is cystic fibrosis
      • FF doesn't have it, can't pass it on
      • Caused by RECESSIVE allele
    • Punnet squares
      • Polydactyly= condition of having more than 5 toes or five fingers
      • DD=polydactyly
      • Dd=polodactyly
      • dd=normal
      • Caused by DOMINANT allele
    • Mendel's work
      • studied inheritance of many characteristics in pea plants
      • 1.published work =1865 2. died=1884 3. later work by other geneticists linked Mendel's "inherited factors" to genes and chromosomes
      • 1.spent several years producing PURE-BREEDING plants
        • produced same characteristics every time when bred with each other
        • 2. made the crosses by hand, so could be certain which parents produce offspring
          • 3.repeated each test 100s of times

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