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Mendel and Punnet Squares

Gregor Mendel (1822-1884) Father of genetics parentswere________________________________________________________________

______________________________________________________________________________ became an_________________________________________________________________ Work waslargely____________________________________________________________

______________________________________________________________________________

Mendel chose to work with peas, because:1. ___________________________________________________________________________

___________________________________________________________________________2. ___________________________________________________________________________

______________________________________________________________________________________________________________________________________________________

Mendels Experiments Mendel bred a pure-bred (means if two pure-bred individuals are bredtogether, they would only produce offspring with the same characteristics)

__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________ These two individuals were called the

_______________________________________.

The offspring of the parental generation were_______________________________.

- Mendel counted and recorded the numbers and characteristics ofthese offspring.He then bred

_______________________________________________________________.The offspring of the _________________________________________________________

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______________________________________________________________________________- Mendel counted and recorded the numbers and characteristics of

these offspring.

Mendels Results and Conclusions

The F1 generation always showed only one trait____________________________________________________________________________________________________________. The F1 generation must be carrying

________________________________________________________________________________________________________________________. Some individuals in the F2 generation showed the

__________________________________________________________________________________________________________.

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Each individual has two "factors" that determine what external appearancethe offspring will have.

_________________________________________________________________________.

Mendels Laws 1. The Principle of Dominance and Recessiveness - one

_____________________________________________________________________________________________________ 2. Principle of Segregation - the

____________________________________________________________________________________________________________________________ 3. Principle of Independent Assortment -

___________________________________________________________________________________________________________________; another way to look at this is, whether a flower is purple has nothing to do

with the length of the plants stems - each trait is independently inherited.

Modern Genetics Mendel's factors are now called ALLELES. For every trait a person has,

______ alleles determine how that trait is expressed. We use ___________ to denote alleles, since every gene has two alleles, allgenes can be represented by a pair of letters. PP = purple, Pp = purple, pp = white Homozogyous: when the _________________________, the individual is said tobe homozygous, or pure breeding. Letters designating a homozgyousindividual could be capital or lowercase, as long as they are the same. Ex. AA,bb, EE, dd Heterozygous: when the ________________________, in this case theDOMINANT allele is expressed. Ex. Pp, Aa Monohybrid cross = a cross involving one pair of contrasting traits. Ex. Ppx Pp Punnet Square: used to determine the

____________________________________________________________________ given the alleles of the parents Genotype: letters _____________________________ (BB, Pp..etc) Phenotype: _______________________________________ (brown, purple..)

Punnet Squares Used to predict the outcome of a cross. Sample Problem -

*In pea plants (which Gregor Mendel studied), tall pea plants are dominantover short pea plants. Using Punnett Squares, you can predict the genotypesand phenotypes of the offspring of a cross between a homozygous (purebred)tall pea plant and a homozygous (purebred) short pea plant.

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How to solve, Step 1 Designate letters which will represent the genes/traits. Capitalletters represent dominant traits, and lowercase letters representrecessive traits.

T = tall t = short

Step 2 Write down the genotypes (genes) of each parent. These are oftengiven to you or are possible to determine.

TT X tt (tall) (short) - both homozygous (same) or purebred

Step 3 Draw a Punnett square - 4 small squares in the shape of a window.Write the possible gene(s) of one parent across the top and the

gene(s) of the other parent along the side of the Punnett square.

Step 4 Fill in each box of the Punnett square by transferring the letterabove and in front of each box into each appropriate box. As a general

rule, the capital letter goes first and a lowercase letter follows.

Step 5 List the possible genotypes and phenotypes of the offspring forthis cross. The letters inside the boxes indicate probable genotypes (geneticmakeup) of offspring resulting from the cross of these particular parents.

There are 4 boxes, and the genotypic results can be written either asfractions or percents. In this case, all 4 boxes out of the 4 are showing the Ttgenotype. Therefore, each of the offspring has a 4/4 or 100% chance ofshowing the Tt genotype.

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What are the possible genotype(s) of a tall plant?

What are the possible genotype(s) of a short plant?

What would be the phenotype of TT?

What would be the phenotype of tt?

Why is the phenotype of Tt tall and not medium/average?