genetics and inheritance

Remember back to meiosis. During meioses half of your chromosomes are passed to you through you mother and the other half from your father. In 1866 an Austrian monk, named Gregor Mendel worked on the inheritance of genetics by breeding peas together.

Above is his experiment. Mendel started by crossing a round yellow pea plant (YY) and a wrinkly green pea plant (yy). All of the first generation ended offspring ended up being round and yellow. Mendel then took the first generation offspring and crossed them. What Mendel found was that most of the second generation plants were yellow and around, but a few where wrinkly and green. Mendel continued to do this until he noticed that there was always a 3:1 ration of yellow to green and round to wrinkly.

From this experience Mendel not only was able to better understand inheritance but he was also able to figure out about Dominant and recessive genes. the yellow round plants were Dominant while the wrinkly green plants where recessive. the first generation offsprings had an equal chance to receive either the dominant or recessive trait. One parent passed on the dominant trait while the other passed on the recessive trait, but since one trait was dominant it was the only trait shown.

An organism with two dominant traits are called homozygous dominant, (homo means same). An organism with two recessive traits are known as homozygous recessive and an organism with one dominant trait and one recessive trait are known as heterozygous (heter means different).

In some cases though, both traits can be shown, or neither trait could be shown. This is known at incomplete dominance or co - dominance.

Incomplete dominance - incomplete dominance is when two organism like flowers are crossed (breed) and the offspring ends up having a mixture of both of the parents traits. The picture to the left starts with a homozygous recessive white flower crossed with a homozygous dominant red flower. The first generation ends up all being heterozygous pink flowers. When the two heterozygous pink flowers are crossed the result is a 1:2:1 ratio. 1 homozygous recessive, 2 heterozygous and 1 homozygous dominant traits are inherited by the second generation offspring.

Co-Dominance - results when neither of the traits completely dominants the other trait. So instead of having a dominant and a recessive trait, both traits are equally dominant. The picture the the right is the result of a white flower crossed with a red flower. All of the first generation flowers result in patches of red and white.

How do you know which traits are dominant? Here is a list of dominant vs. recessive traits. Compare your traits with you parent's traits and you can find out which parent you inherited which trait from.

Dominant Recessive

Brown eyes any other color eyes

curly hair staight hair

widows peak normal hairline

dimples & freckles no dimples & freckles

double jointed normal joints

These are just a few, there are many more, but this it just to give you an idea.