Heredity.. An Introduction Unit 5: Seventh Grade http://glencoe.mcgraw-hill.com/sites/007874184x/student_view0/brainpop_movies.html#
Why don’t you look like a rhinoceros? • The answer seems simple --- neither of your parents is a rhinoceros (I assume). • But there is more to this answer than meets the eye. • We look similar to our parents because of heredity.
Heredity • Heredity is the process of passing characteristics or traits, such as eye color, skin, color, hair, color, height, intelligence, etc from parent to offspring. • This happens during reproduction
Passing Along Traits • When people, animals, and plants reproduce, they create new individuals. • These individuals receive traits from both the female and the male parent.
Passing Along Traits • As you may have guessed, the passing of traits from parent to offspring is complicated…. • For example: • Why do I have straight hair while both of my parents have curly hair? • How did my husband and I produce a left-handed child when we are both righties? • How did my two nephews end up with blue eyes when both of their parents have brown eyes?
Apparently we aren’t the only ones who wonder! • About 150 years ago, an Austrian monk named Gregor Mendel started performing important experiments that helped scientists figure out the answers to such questions.
More on Mendel • Gregor Mendel was born in 1822 and grew up on a farm in Austria. • While growing up on the family farm, Mendel observed and learned a lot about flowers and fruit trees. • But it was not until he was working in the monastery’s garden that he began his research on patterns of inheritance
Unraveling the Mystery • Mendel knew that patterns of inheritance were not always clear. • He saw that sometimes a trait that was apparent in one generation (parents) was not present in the next generation (offspring). In the next generation, the trait showed up again. • Mendel wanted to know why
Self-Pollinating Peas • To start unraveling this mystery, Mendel selected to study the inheritance pattern of garden peas.
He actually had good reasons for selecting peas • They grow quickly • They are able to self-pollinate • Plants contain male and female structures and can pollinate themselves. • They will be true breeding plant • All offspring will have the same trait as their parents • They are also able to cross-pollinate • The pollen of one plant can pollinate another plant and carry traits from one plant to another
Characteristics • Mendel only studied one characteristic at a time • A characteristic is a feature that has different forms in a population • For example, hair color is a characteristic • These different forms are called traits. • The different forms of hair color are brown, blond, red, etc. • Mendel used plants that had different traits for each of the characteristics he studied. • Characteristic: seed shape Trait: wrinkled, round • Characteristic: Plant height trait: Tall, short • Characteristic: Flower color Trait: purple, white
Mix and Match • Mendel was careful to use plants that were true breeding for each of the traits he was studying. • By doing this, he would know what to expect if his plants were to cross-pollinate. • He decided to find out what would happen if he bred, or crossed two plants that had different traits of a single characteristic • Example: cross a purple flowered plant with a white flowered plant
Mendel’s First Experiment • In his first experiments, Mendel crossed pea plants to study seven different characteristics. • He used true-bred plants • For example, he crossed plants that had purple flowers with plants that had white flowers. • All of the plants that resulted had purple flowers!
Mendel’s First Experiment • Mendel got similar results for each cross • One trait that was always present in the first generation, such as white flowers, seemed to disappear. • Mendel chose to call the trait that appeared the dominant trait.
Dominant Traits • Dominant traits are the traits that will appear in the offspring if one or both of the parents contributes it. • Examples: • Brown eyes • Dark hair • Dimples • Curly hair • Freckles • Extra digits • Normal hearing
Recessive Traits • Examples: • Grey, green, hazel, blue eyes • Blonde hair • Red hair • Straight hair • No freckles • Normal number of digits • deafness • Because the other trait seemed to recede into the background, Mendel called it the recessive trait. • Recessive traits are traits that must be contributed by both parents in order to appear in the offspring. • Recessive traits can be carried in a person's genes and not appear on that person
Mendel’s Second Experiment • In his second experiment, Mendel allowed the first generation plants to self-pollinate • He found that even when purple flowered plants crossed with white flowered plants, all of the flowers were purple, showing that purple flowers were the dominant trait.
Mendel’s Second Experiment • However, in the second generation, for every three purple flowered plants, there was onewhite flowered plant, showing that the recessive gene was present.
Gone, but not forgotten • In 1865, Mendel published his findings. • But they were not understood or accepted until many years after his death. • Once his research was understood, the door was opened to modern genetics. • Genetic research is one of the fastest changing fields in science today. • http://glencoe.mcgraw-hill.com/sites/007874184x/student_view0/brainpop_movies.html#