Mendelian Genetics

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Mendelian Genetics Powered By Docstoc
					   Gregory Johann Mendel
• 1822- 1884
• Austrian monk
• Experimented with
  pea plants
• He thought that
  ‘heritable factors’
  (genes) retained their
  generation after
      Terms to Know and Use
• Gene - a heritable feature: i.e. flower color
  coded for on a chromosome
• Trait - variant for a gene: i.e. a purple
  flower, determined by alleles
• Dominant trait - expressed over recessive
  trait when both are present
• Recessive trait - not expressed when the
  dominant trait is present
• Allele - a variation of a gene responsible for
  different traits, often expressed as A or a
• Locus - location of a gene,or allele, on a
• Chromosome - strand of DNA that codes
  for genes
• Haploid - one copy of a chromosome
• Diploid - two copies of a chromosome
• Gamete - a spermatozoa or oocyte (egg)
  cell, they are haploid
• Zygote – diploid, fertilized egg (2N)

• Genotype - the type of alleles on a
  chromosome: genetic makeup

• Phenotype - the physical result of a genotype
  ex. blue eyes

• Hybrid – an organism with two different
Garden Pea Experiments
            • Mendel disagreed with
              the “Blending Theory”
              of inheritance.
            • Started with34 kinds
Dominant Recessive
                          Pea Characteristics

  Trait on the left is dominant. Trait on the right is recessive.
           Mendel Determined that Alleles
             Separate During Meiosis
Parents:                      So, cross purebred smooth peas with
Assume Round is S and the     a plant having the recessive wrinkled
other form is s.              form of the peas and see the result

                  Punnett Square         S                 S
                  used to predict
                 the Genotype of
No Blend            Offspring
   as                   S              Ss                Ss
expected!                            Smooth            Smooth
                        s              Ss                ss
                                     Smooth            Smooth
           Mendel’s Hypotheses
1. There are alternate forms
   of ‘genes’ = alleles

2. For each trait, organisms
   have 2 genes, one from
   mom & one from dad

3. Sperm and egg each
   carry 1 allele/trait
   because alleles separate

4. Dominant alleles mask
   the effects or recessive
Pure Breds
Crosses – have all   Mother contributes:
dominant traits
                     A       or     A

          A          AA           AA

          A          AA           AA
Pure Bred Dominant
 Father breeds with
Pure Bred Recessive
                      Mother contributes:
                      a       or     a

          A           Aa           Aa

          A           Aa           Aa
Purebred Dominant
+ Purebred Recessive

  a Hybrid ----> Aa
       Describing Alleles Properly

• Aa   means the critter is HETEROZYGOUS
  It has two different alleles: A & a
  The critter is not a purebred but a hybrid

• AA or aa means the critter has the same two
 alleles, so it is HOMOZYGOUS
     Mendel's Laws of Inheritance
1. Genes produce traits (characteristics)

2. Law of Segregation alleles are separated during
   meiosis into different eggs/sperm

3. Law of Independent Assortment suggested that
   other alleles do not influence how other alleles
   come together (how they assort) (demonstrated
   with a “dihybrid cross”)

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