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What Is Inheritance
 

What Is Inheritance

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    What Is Inheritance What Is Inheritance Presentation Transcript

    • What is Inheritance?
    • What is it that gives individuals their characteristics?
    • The nucleus of a cell carries all the genetic information. Chromosomes inside the nucleus contain all the genetic information.
    • Chromosome Chromatid Chromatid Centromere
    • Every nucleus in every cell of an organism contains identical copies of these chromosomes. The number of chromosomes present in an organisms’ cells depends on its species. e.g Human Male 46 Chromosomes
    • Fertilisation Recap zygote Gametes Copy diagram Notes
    • Copy and complete the summary
      • Fertilisation is the fusing of a male and female _______ to form a _______.
      • Each gamete has 1 set of _________, so after fertilisation the ______ will contain ___ sets of chromosomes as found in normal body cells.
      Notes
    • Genes
      • A gene is part of a chromosome.
      • Each inherited characteristic is controlled by
      • 2 copies of its gene (one from the mother and
      • one from the father).
      • The 2 copies of the gene for a particular
      • characteristic may be the same or different.
      • Different forms of the same gene are called
      • alleles.
      Notes
    • Will the person be a tongue roller or a non-tongue roller ?
      • Alleles are described as Dominant or Recessive .
      • A dominant allele always shows up in an organisms
      • appearance (masks the recessive allele).
      • A recessive allele only shows up if there are two of
      • them.
      Consider the gene in a human for ability to tongue roll. Allele Tongue roller Allele Non-Tongue roller
    • Activity Daughter Son On your worksheet, label whether each family member has night blindness or normal vision. Trim sheet and stick into your notes. Grandmother Grandfather Grandmother Grandfather Daughter Son Grandson Grandaughter Grandson Grandaughter Night blindness is always masked by normal vision
    • Tongue rolling = Dominant Non-Tongue rolling = Recessive (R) (r) (R) (R) (R) (r) (r) (r) Tongue roller Tongue roller Non-Tongue roller Notes The alleles can be shown as letters. The DOMINANT allele is always in CAPITAL letters. The recessive allele is always the same letter but a small letter.
    • Activity Using the letters: N for normal vision n for night blindness Add the correct letters to your night blindness family tree. For example: Grandmother Grandfather Daughter Son n n n n
    • Two descriptions of an organisms characteristics we need to know are phenotype and genotype.
      • Use the text book page 185 to describe the meaning of an organisms phenotype.
      • Look at the phenotypes example table (Table 21.1). Can you produce a similar table using your own examples.
      Phenotype and Genotype Notes
    • Genotype: The alleles an organism carries for a particular characteristic. e.g RR Rr rr Phenotype is dependant upon genotype and environment ! Notes
    • Hetero zygous and Homo zygous Hetero : difference between two Homo : same as
      • A homozygous organism has two identical alleles of a gene.
      • A heterozygous organism has two different alleles of a gene.
      e.g. Genotype RR or rr TT or tt etc. e.g. Genotype Rr Tt etc. Notes
    • Black hair (B) is the dominant allele. White hair (b) is the recessive allele. Copy and complete using what you have learned. 1 allele for black hair and 1 allele for white hair White Hair bb Black Hair BB 2 Black hair alleles Phenotype Homo/ heterozygous Genotype Alleles carried by guinea pigs Notes
    • This means that the offspring of true breeding black mice are always black and the offspring of true breeding white mice are always white. Animals that always pass on the same characteristics to their offspring from generation to generation are know as True-breeding. True Breeding Notes
    • X P (parents) X F 1 (first generation) F 2 (second generation) Notes Add the names of the generations to your copy of the true breeding, black haired mice.
    • Lets look at this in terms of genotype: Black coat colour is dominant (B) White coat colour is recessive (b) All offspring (F 1 ) BB BB BB Parents x BB BB x Second generation (F 2 ) BB Gametes all B B Gametes all B B Notes
    • What about true breeding for white coated mice? Label the generations on your diagram for the white mice. X X
    • -Draw the cross for the true breeding white mice using the genotypes -Work through exactly as we did for the black mouse Answer All offspring (F 1 ) bb bb bb Parents x bb bb x Second generation (F 2 ) bb Gametes all b b Gametes all b b Notes
    • Another type of cross is when each parent is a true breeding individual, but each has a different phenotype. X P (parents) F 2 (second generation) X F 1 (first generation) Monohybrid Cross Notes
    • Where did the white mouse come from? P bb x BB Bb x Bb Gametes: (F 2 ) Bb BB Bb Bb bb Punnett Square = Gives a ratio of 3 : 1 black white (F 1 ) All Bb BB Bb bb B b B b Gametes all b B B b B b Notes
    • Practice Crosses
      • Pea plants can be tall (T) or dwarf (t).
      • If a true breeding tall plant was crossed with a true breeding tall plant what would the phenotype and genotyope of the F1 and F2 generations be.
      • Pea plants can be tall (T) or dwarf (t).
      • If a true breeding tall plant was crossed with a true breeding dwarf plant what would the phenotype and genotype of the F1 and F2 generations be.
      Practice Crosses
    • Practice Crosses 3. R = red flower r = yellow flower A plant homozygous for red flowers is crossed with a plant that has yellow flowers. - Work through the cross to the F 2 generation.
      • What is the phenotype and genotype of the F 1 .
      • What is the phenotype and genotype ratios of the F 2
    • 4. R = red flower r = yellow flower A plant heterozygous for red flowers is crossed with a plant that has yellow flowers. - Work through the cross to the F 1 generation.
      • What is the phenotype and genotype ratios of the F 1
      Practice Crosses
    • How can we tell if an organism is true breeding ? BB or Bb True breeding Not True breeding A test cross is used to identify the genotype of an individual by crossing it with a homozygous recessive individual… bb If a black coat in mice is dominant (B) it’s genotype could be: Notes
    • All offspring: black Ratio= Black: white 1 : 1 BB or Bb? B B b b Bb Bb Bb Bb B b b b Bb bb Bb bb X BB bb X Bb bb
      • Complete your worksheet for the test cross.
      • Torrance text book page 201: Q’s 2, 3 and 4.
      • Cystic Fibrosis wk sheet
      • Answer the Q’s on your own sheet
      Test Cross Notes
    • Cystic Fibrosis Healthy female Affected female Healthy male Affected male Mhairi Molly Henry Katie Joe Ben Zoe Chloe Sue Chris Erin Tom Doug Polly Steve Rab Jim
    • Sex Determination
      • In human body cells there are 23 pairs of chromosomes (46 chromosomes).
      • 22 pairs of chromosomes carry genetic information for your characteristics.
      • The 23rd pair are sex chromosomes and determine if you are male or female.
    • Types of Sex Chromosomes
      • In humans there are two types of sex chromosomes: X and Y
      Males : X and Y Females : X and X
    • Males X Y Chromosomes Females XX Chromosomes
    • XX X Y Female Female Male X X X Y XX X Y X Y XX Female Male Male Egg Sperm
    • Sex Determination Using page 81 of the Success Guides: -make notes on the sex chromosomes -add your completed cut out of the sex determination diagram. Notes
    • Check Test 1. Describe the term Genotype 2. Describe the term Phenotype 3. What do we mean by a homozygous organism? 4. What do we mean by a heterozygous organism? 1 mark 1 mark 1 mark 1 mark
    • 5. Breeding experiments (crosses) which focus on just one characteristic are called ______ crosses. 6. Organisms which pass on the same characteristics to their offspring over many generations are described as …… 1 mark 1 mark
    • 7. G- Dominant for green seed g- Recessive for yellow seed Consider the following cross: GG x GG
      • Work out:
      • The possible genotypes and phenotypes of the first generation 1 mark
      • The possible genotypes and phenotypes of the second generation 1 mark
    • 8. G- Dominant for green seed g- Recessive for yellow seed Consider the following cross: GG x gg
      • Work out:
      • The possible genotypes and phenotypes of the first generation 1 mark
      • The possible genotypes and phenotypes of the second generation 1 mark
    • Using the example of black and white mice (B- Dominant black allele b recessive white allele)
      • Explain (using crosses) how a test cross is carried out to determine the genotype of an individual showing a dominant characteristic (Black).
      9. 3 marks
    • 10. Which sex chromosomes do males carry? 1 mark 14 Total