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Objectives:. General: Understand the concepts underlying Mendelian Genetics. Specific: 1. Identify the factors that influence individuality. 2. Describe the experiment of Mendel and explain their importance to the science of heredity. 3. Solve monohybrid crosses. .

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Understand the concepts underlying Mendelian Genetics.


1. Identify the factors that influence individuality.

2. Describe the experiment of Mendel and explain

their importance to the science of heredity.

3. Solve monohybrid crosses.

what s up for today
What’s up for today?
  • Background about Gregor Mendel’s life.
  • Mendel and his experiment.
  • Characteristics of the garden pea.
  • Dominant and Recessive Traits
  • Monohybrid Crosses
gregor mendel 1822 1884
Gregor Mendel(1822-1884)

Responsible for the Laws governing Inheritance of Traits

gregor johann mendel
Gregor Johann Mendel
  • Austrian Monk
  • Studied at the AgustinianMonastary of St. Thomas in Brno
  • Studied the inheritance of traits in pea plants
  • Developed the laws of inheritance
  • Mendel's work was not recognized until the turn of the 20th century
gregor johann mendel1
Gregor Johann Mendel
  • Between 1856 and 1863, Mendel cultivated and tested some 28,000 pea plants
  • He found that the plants' offspring retained traits of the parents
  • Called the “Father of Genetics"
pisum sativum s charateristics
  • Many earlier investigations was done that produced hybrid peas by crossing different varieties.
  • Large number of true-breeding varieties was available.
pisum sativum s charateristics1
  • Pea plants are small and easy to grow and they have relatively short generation.
  • Both the male and female sexual organs are enclosed within the pea flower.
reproduction in flowering plants
Reproduction in Flowering Plants
  • Pollen contains sperm
    • Produced by the stamen
  • Ovary contains eggs
    • Found inside the flower
  • Pollen carries sperm to the eggs for fertilization
    • Self-fertilization can occur in the same flower
    • Cross-fertilization can occur between flowers
steps in mendel s experiment
Steps in Mendel’s Experiment
  • A. Cross-breeding
  • B. Hybrid-breeding
  • C. True-breeding
steps in mendel s experiment1
Steps in Mendel’s Experiment
  • Allowed pea plants of a given variety to produce offspring by self-fertilization for several years. (True-breeding)
  • Performed crosses between varieties exhibiting alternative forms of characters. (cross-breeding)
  • Permitted the hybrid offspring to produce by self fertilization for several generations.
steps in mendel s experiment2
Steps in Mendel’s Experiment
  • True-breeding
  • Cross-breeding
  • Hybrid-breeding



2 B 2

seven characters of pea plant
Seven Characters of Pea Plant
  • Flower color --- Purple (W) or white (w)
  • Seed Color---- Yellow (G) or  Green (g)
  • Seed shape--- Round (W) or Wrinkled (w)
  • Pod Color---  Green (Y) or Yellow (y)
  • Pod Shape--- Inflated(C) or Constricted (c)
  • Flower position--- Axial (T) or Terminal (t)
  • Plant Height--- Tall (D) or Dwarf (d)
expressed and unexpressed
Expressed and Unexpressed
  • Dominant - stronger genes are expressed in the hybrid; represented by a capital letter (R)
  • Recessive - gene that shows up less often in a cross; represented by a lowercase letter (r)
expressed and unexpressed1
Expressed and Unexpressed
  • Homozygous - gene combination involving 2 dominant or 2 recessive genes (e.g. RR or rr);also called pure 
  • Heterozygous - gene combination of one dominant & one recessive allele   (e.g. Rr); also called hybrid

is any observable characteristic or trait of an organism: such as its morphology and development.


isthe genetic makeup of a cell, an organism, or an individual. Represented by letters (WW, YY, Yy, Dd)

  • An alternative form of a gene (one member of a pair) that is located at a specific position on a specific chromosome.
steps in mendel s experiment3
Steps in Mendel’s Experiment
  • True-breeding
  • Cross-breeding
  • Hybrid-breeding
test cross
Test Cross
  • Used to determine if an individual exhibiting a dominant trait is homozygous or heterozygous for that trait.
steps in mendel s experiment4
Steps in Mendel’s Experiment
  • True-breeding
  • Cross-breeding
  • Hybrid-breeding
monohybrid cross
Monohybrid Cross
  • Cross between two individuals having single traits of particular interest.
  • Monohybrid inheritance is the inheritance of a single characteristic.
  • Example:
  • Plant Seed Color (Yellow x Green)
  • Flower Position (Axial x Terminal)

Generation “Gap”

  • Parental P1 Generation= the parental generation in a breeding experiment.
  • F1 generation= the first-generation offspring in a breeding experiment. (1st filial generation)
    • From breeding individuals from the P1 generation
  • F2 generation= the second-generation offspring in a breeding experiment. (2nd filial generation)
    • From breeding individuals from the F1 generation
punnett square
Punnett Square

a diagram that is used to predict an outcome of a particular cross or breeding experiment.

Reginald C. Punnett

f1 generation punnett square
F1 Generation (Punnett Square)



F1 Genotype:Ww

F1 Phenotype: Purple

Ratio:All alike







Trait: Flower Color

W – Purplew – White

Cross: Purple Flower x White Flower

WW x ww

f2 generation
F2 Generation



F2 Genotype:_____

F2 Phenotype: _____

Genotype Ratio: ___

Phenotype Ratio: ___







Trait: Flower Color

Ww– PurpleWw– Purple

Cross: Purple Flower x Purple Flower

Ww x Ww

mendel s postulates
Mendel’s Postulates
      • Genetic characters are controlled “unit factors” that exist in pairs.
    • When two unlike unit factors is responsible for a single trait, one unit factor is dominant and the other is unexpressed.
    • During gamete formation, the paired unit factors separate or segregate.


let s solve the following
Let’s Solve the following
  • In summer squash, white fruit color (Y) is dominant over yellow fruit color (y).  If a squash plant homozygous for white is crossed with a plant homozygous for yellow, what will the phenotypic and genotypic ratios be for:

a. the F1 generation?    

b. the F2 generation?

mendel s law of inheritance
Mendel’s Law of Inheritance

Law of Dominance- States that when pure-breeding plants having contrasting characters are crossed, all the offspring will show only one of the characters. That which appears is the dominant character; that which does not appear is the recessive character.


Principle of Segregation- For any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring.

what is mendelian genetics
What is Mendelian Genetics?

It describes how genes are transmitted from parent to offspring.


Principle of Independent Assortment- Different pairs of alleles are passed to offspring independently of each other.  The result is that new combinations of genes present in neither parent are possible.  For example, a pea plant's inheritance of the ability to produce purple flowers instead of white ones does not make it more likely that it will also inherit the ability to produce yellow pea seeds in contrast to green ones.