Biology for Kids
Mendel and Inheritance
What is heredity?
Heredity is when certain traits are passed from the parents to the children. Traits are characteristics such as eye color, height, and athletic ability. Heredity is passed through genes in the DNA molecule. In biology the study of heredity is called genetics.
Scientist Gregor Mendel (1822 - 1884) is considered the father of the science of genetics. Through experimentation he found that certain traits were inherited following specific patterns.
Gregor studied inheritance by experimenting with peas in his garden. Peas work as an excellent test subject as they can self-pollinate, cross fertilize, and have several traits that only have two forms. This enabled Mendel to easily control his experiments and reduced the possibility of the outcomes to something he could record and manage.
Gregor studied seven traits of the pea plant: seed color, seed shape, flower position, flower color, pod shape, pod color, and the stem length. There were three major steps to Mendel's experiments:
1. First he produced a parent generation of true-breeding plants. He made these by self-fertilizing the plants until he knew they bred true to the seven traits. For example, the purple flowering plants always produced seeds that made purple flowers. He called these plants the P generation (for parent).
2. Next, he produced a second generation of plants (F1) by breeding two different true-breeding P plants.
3. He then produced a third generation of plants (F2) by self-pollinating two F1 generation plants that had the same traits.
Mendel found some incredible results from his experiments.
Mendel found that the F1 generation all produced the same trait. Even though the two parents had different traits, the offspring always had the same trait. For example, if he bred a P plant with a purple flower with a P plant with a white flower, all of the offspring (F1) plants would have purple flowers. This is because the purple flower is the dominate trait.
These results can be shown in a diagram called a Punnett square. The dominate gene is shown with a capital letter and the recessive gene with a lower case letter. Here the purple is the dominant gene shown with a "P" and the white is the recessive gene shown with a "w."
You can go to this page to learn more about inheritance patterns and Punnett Squares.
In the F2 generation he found that 75% of the flowers were purple and 25% were white. Even though both parents had purple flowers, 25% of the offspring had white flowers. This turned out to be because of a recessive gene or trait was present in both parents.
Here is the Punnett square showing that 25% of the offspring had two "w" genes causing them to have white flowers:
Homozygous and Heterozygous
When two of the genes are the same (like with "PP" or "ww" above) they are called homozygous. When they are different (like with "Pw") they are called Heterozygous.
Interesting Facts about Mendel and Inheritance
- Mendel's work was rejected by his fellow scientists while he was alive. It wasn't until later that his work was rediscovered and confirmed through further experimentation.
- Mendel was a monk and performed his experiments in the monastery garden. His experimentation largely ended when he was promoted to abbot.
- Mendel also ran experiments with honey bees, but found them much more difficult to experiment with.
- The idea that an offspring receives one unit of inheritance from each parent is the called the "theory of segregation."
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