Often Mendelian genetics refers to basic genetics that use Punnett Squares and statistics to predict the phenotypes of offspring. Modern Genetics usually refers to our modern-day understanding of how DNA and genes control the expression of traits. During Mendel's time, biologists did not know about DNA and genes.


Punnett Square Flash Game

DNA From the Beginning

MGHE Drosophila Simulation

Chapter 11.1 - Gregor Mendel

Mendel's Law of Segregation (MONOHYBRID CROSS)

As Viewed by Modern Genetics

Task: Show the P, F1 and F2 generations of a true-breeding round seeded plant crossed with a true breeding wrinkle-seeded plant.
(Click to see Answer)

The Punnett Square


One Trait Test Cross


Mendel's Law of Independent Assortment


Dihybrid Cross: RrYy x RrYy

TIP: In any cross that is dihybrid (AaBb x AaBb) you will always get a 9:3:3:1 ratio, if you memorize this, you can save the trouble of doing a giant square!


A Mathematical Alternative (LAWS OF PROBABILITY)

A punnet square is not needed to determine the ratios of genotypes and phenotypes. Simple statistics and math can save you the trouble of filling out a square.

In a monohybrid cross Pp x Pp, each parent produced P gametes and p gametes

If you wanted to determine how many of the offspring are pp: x =

Example 2:

H is dominate for long hair (h = short) and B is dominate for black eyes (b = red eyes). If the parents are...

HhBb x hhBb

How many off the offspring will be short haired and red eyed?

Task: Use mathematical analysis to determine the number of short haired, black eyed offspring from the cross above.


Used to determine the genotype of an "unknown" by crossing it with an individual that is homozygous recessive for both traits.

In flies (Long wings is dominant to short wings, Gray body is dominant to black)

A L __ G ___ is test crossed.

The offspring are 1:1:1:1 --> What is the genotype of the unknown parent?
If the offspring are half long winged & gray, and half long winged and black --> What is the genotype of the unknown parent?