Mendelian Genetics and Basic Inheritance by Cy1lRA3S


									By: Mr Knox
 History of Inheritance
 Who was Gregor Mendel?
 What did he do?
 Mendel’s Laws of Inheritance
 Compare to Modern Genetics
 Simple Dominance
 Punnett Squares
    Chapter   8

History of Inheritance
 During Mendel’s era 1822-1884
 Blending Theory
 Inherited traits came from a blend of both Parents.
  Long hair + short hair = medium hair.
 The nature of these factors of inheritance were not
  known,... until Mendel.
Gregor Mendel
            Austrian Monk-
            Father of Genetics
            Worked mainly with
             Pea Plants
            Worked for 6-7 years!
    What Did Mendel Do?
 Worked with the Pea
  Plant. Pisum
 Pea Plant Self
  Pollinates, has closed
  reproductive system.
 Let Self Pollinate to
  make Pure Lines for a
   Chapter   8

Mendel’s Studies of Traits
                     Mendel’s Breeding
   What did Mendel Do?
 Mated plants with
  known traits
 Evaluated results,
  based on math, came
 up with Laws of
Mendelian Traits- (Genes) Fig. in
 Trait:                    Dominant     Recessive
                          Expression:   Expression
   1. Form of ripe seed Smooth          Wrinkle
   2. Color of seed albumen Yellow      Green
   3. Color of seed coat Grey           White
   4. Form of ripe pods Inflated        Constricted
   5. Color of unripe pods Green        Yellow
   6. Position of flowers Axial         Terminal
   7. Length of stem      Tall          Dwarf
 Traits = Genes, form of gene called allele
 2 Traits/genes, one from male and one from
  female needed for gene expression.
 For pea color gene G=dominant, g = recessive
  G and g are alleles for Pea color gene.
 Dominant- only needs 1 of the 2 genes for the
  characteristic to be expressed. GG or Gg
 Recessive- “hidden trait” in which both genes must
  be the same form to be expressed. gg

Comparing Dominant and

Recessive Traits
 Genotype- actual genetic make up of
 GG- homozygous dominant- both genes are
 Gg- heterozygous - two different genes or
 gg- homozygous recessive- both alleles are
 Phenotype- what the offspring appears to be.
 GG, Gg - are both YELLOW
 gg- is green

 Genotype will determine your phenotype
Sample Experiment
 Mendel bred pure lines for a trait, example
  YELLOW PEAS and green peas.
 YELLOW = GG, green = gg, pure lines
      P1 x P1 or YELLOW x green
 P = parents
 F1 = first filial or “family” =
  offspring (kids)
 F1 are called hybrids,
  results of crossing or
  mating of two different
 All F1 offspring were
                  GG- Meiosis- (genes on chromosomes)

              G      G

gg       Gg         Gg
         Gg         Gg
   Punnet’s Square
 The Punnett’s Square
  below explains simple
 GG x gg= all YELLOW
 Yellow is dominant to
                            G G
 G and g are egg and
  sperm, from Meiosis     g Gg Gg
 Gg are zygotes or       g Gg Gg
  offspring from
   F1 x F1 or YELLOW x YELLOW
 Mendel then
  crossed F1 with F1
 Ratio of offspring
  or F2 came out 3 to
 YELLOW to green
  Mendel crossed
   two YELLOW peas
  Some offspring
   were green.
                           G g
  This showed that
                         G GG Gg
   some traits were
                         g Gg gg
   hidden or recessive
Three Steps of Mendel’s Experiments
Punnett Square
 Shows the PROBABLE outcome/ratio not
 the actual!
   Ratios for P x P
 The phenotype
  ratio of crossing
                           G    G
  pure YELLOW GG         g Gg   Gg
  with pure green gg     g Gg   Gg
  would be
 All Yellow or 4 to 0
 Genotype ratio is
  also all Gg
  Ratios for F1 x F1
 Genotype ratio
  would be                 G g
 1 GG                   G GG Gg
 2 Gg
 1 gg
                         g Gg gg
 1:2:1
 Phenotype ratios for
  crossing Gg x Gg are
 3 YELLOW : 1 green
Chapter   8
Mendel’s Crosses and Results
What are the possible parents
genotype or genetic make up?
Genotype and Phenotype
 Genotype determines what you “look” like or
  your Phenotype.
 Based on what you look like, you may not
  know what your actual genetic make up is.
 A seed that is YELLOW could be either GG
  or Gg.
 However a green recessive will be gg
 If known phenotype YELLOW but unknown
  genotype then you mate with a recessive for
  trait- gg.
 Someone tell me how you can tell the
  genotype is GG or Gg????
 Offspring will be exhibit recessive trait if Gg.
Mendel’s Laws of Inheritance
 Keep in mind, Mendel did not know of
 Chromosomes or Genes
 Dominant or Recessive
 Meiosis
 Laws he derived were based on MATH and
Laws of Inheritance
 Law of Dominance- one trait is “seen” while
 the other is “hidden”
Laws of Inheritance
 Law of Segregation (meiosis)- parents
 transmit “factors” (genes) to offspring in
 pairs, one from each parent.
    Chapter   8

Mendel’s Factors
Laws of Inheritance
 Law of Independent Assortment- each trait
 is independent from each other, meaning
 pea color did not effect tallness, etc...
Testing for Genotype
 In order to determine the actual genetic
  make up of the Parent, the offspring are
  examined after the Parents are crossed.
 The ratio of offspring can determine the
  genotype of the Parent.
 Mendel used this method.

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