2 Main Jobs of the Nucleus:





Body Cell Sex Cell
2 of each kind of chromosome 1 of each kind of chromosome
2 times as many chromosome sas sex cells 1/2 as many chromosomes as body cells
Human Body Cell = 46 chromosomes Human Sex Cell = 23 chromosomes













Examples of traits: Eye color, hair color, shape of body parts (ears), chemical processes (some diseases)



Sex Cell Chromosome Body Cell Chromosome
has 1 copy of a gene for each trait Has 2 copies of a gene for each trait
1 copy  comes from your _____________ (egg)
1 copy comes from your _____________ (sperm)







Dominant & Recessives Genes

Dominant Genes:



Recessive Genes:



Pure Dominant:



Pure Recessive:












Predicting Phenotypes of Offspring (Punnett Squares)

The likely percentage of offspring that will display certain phenotypes can be estimated using a tool called a Punnett Square

Example:   Attached earlobes are Dominant to Free  Earlobes (Recessive)

 A mother that is Pure Dominant (AA) for attached earlobes marries a man that is Pure Recessive for free earlobes (aa).  What percentage of their offspring will be likely to have attached earlobes?










Now…consider that BOTH parents are Heterozygous, with attached earlobes (Aa) and (Aa). Predict the offspring below:









Expected Results – The results you EXPECT to see from a Punnett Square cross.

 Using a Punnett Square, predict the probability of offspring phenotypes based on the parents’ genotypes.

 Cleft Chin is Dominant (Ii) (II)
Smooth Chin is Recessive (ii)

 Mother is Heterozygous (Ii), Father is Pure Recessive (ii):









Observed Results – The ACTUAL results you observe from a real cross.

         DO NOT always match expected results.

        The ______________ the sample size (more results) observed, the more _______________________________________________________________



Example: Flipping a coin:

50% chance of heads, 50% chance of tails.

        Flip a few times –

        Flip many (100) times –


Gregor Mendel



Mendel’s Work:


Complete Dominance - The dominant gene completely hides the recessive gene.

 Example trait: Height




















Incomplete Dominance – “Blending” of traits.


Example Trait: Flower Color of Pea Plant.




















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