MENDEL

1
MENDELS LAWS OF HEREDITY
2
Heredity is the passing on of traits from parents
to offspring.
3
Gregor Mendel

• Considered to be the father of Genetics.
• Austrian monk.

4
Mendels Experiments

• Mendel studied pea plants.
• Pea plants reproduce sexually by self pollination.

5
Sexual Reproduction

• Sexual reproduction involves male and female sex
  cells called gametes.
• Female gametes are egg cells and male gametes are
  sperm cells.

6
Fertilization

• During fertilization, gametes joint to form a
  zygote.

7
(No Transcript)
8
Pollination

• The male gamete forms in the pollen grains
• Transfer of pollen grains from male to female
  reproductive organ is called pollination.
• www.trekearth.com/.../photo109591.htm

9
Pea Plants Self Pollinate

• Both sexual organs are located in the same
  flower.
• www.botany.uwc.ac.za/.../pollination1.htm

10
Cross Pollination

• Mendel conducted his experiments by performing
  cross pollination.
• He removed the pollen from one plant and dusted
  it on the ovaries of a plant with different
  traits.

11
Mendels Monohybrid Cross

• A monohybrid cross between two parents that
  differ by one trait.
• Mendel chose tall pea plants that had been tall
  for many generations and crossed them with plants
  that had been short for generations.

12
Results of Monohybrid Cross

• When true tall and true short plants were crossed
  all of the offspring were called the F1
  generation. All plants were tall. The short
  trait seemed to disappear.
• Next, Mendel let the F1 hybrids self pollinate.
  The offspring of this cross are called the F2
  generation. ¾ plants were tall and ¼ plants
  were short.

13
Law of Unit Factor

• Organisms have two genes that control each trait.
  One gene is inherited from the mother, the other
  from the father. The alternative form of these
  genes are called alleles.

14
The Rule of Dominance

• In the F1 generation, Mendel called the trait
  that was observed the dominant and the trait that
  disappeared the recessive trait.

15
Dominant alleles will not allow recessive alleles
to be expressed. Dominant alleles are
represented with capitol letters. Tall allele
T
16
Recessive alleles will only be expressed if no
dominant allele is present. Lower case letters
are used to represent recessive alleles.Short
allele t
17
Phenotypes and Genotypes

• Phenotype the way an organism looks or behaves.
• Genotype The allele combination of an organism
• Homozygous both alleles for a trait are alike
• Heterozygous both alleles for a trait are
  different

18
Examples

• TT homozygous dominant
• tt homozygous recessive
• Tt - heterozygous

19
Dihybrid Crosses

• A cross involving two different traits.
• Mendel crossed homozygous dominant round yellow
  seeds with homozygous recessive wrinkled green
  seeds. All F1 plants had round yellow seeds.
• In the F2 generation the phenotype ratio was 9
  round yellow, 3 round green, 3 wrinkled yellow, 1
  wrinkled green.

20
(No Transcript)
21
Law of Independent Assortment

• Genes for different traits are inherited
  independently of each other.

22
Punnett Square

• Punnett Squares are used to predict the genotype
  of offspring if you know the genotype of the
  parents.
• www.tea.state.tx.us/.../2002/eoc/biology.html

23
In poodles, the trait for brown fur (B) is
dominant to the trait for white fur (b). Predict
the fur color of the offspring if the mother is
homozygous for brown fur and the father has white
fur.
24
Mothers alleles BB
B B
b
b
Fathers alleles bb
25
Mothers alleles BB
B B
b Bb Bb
b Bb Bb
Fathers alleles bb
All children will be heterozygous with brown fur