Transcript Heredity Chapter 5-1

DO NOW:
4/14
Can you roll your tongue? Do you have a widow’s
peak? Are your earlobes attached or do they dangle?
Objectives:
1. Explain the relationship between traits and heredity.
2. Describe the experiments of Gregor Mendel.
3. Differentiate between dominant and recessive traits.
Who was Gregor Mendel?

 Gregor Mendel was born in 1822 in Heinzendorf,
Austria.
 At age 21, Mendel entered a monastery.
 Performed many scientific experiments in the
monastery garden.
 Mendel discovered the principles of heredity, the
passing of traits from parents to offspring.
Unraveling the Mystery

 Mendel used garden pea plants for his experiments.
 Self-Pollinating Peas have both male and female
reproductive structures. So, pollen from one flower
can fertilize the ovule of the same flower.
 Pea plants also grow quickly, allowing him to produce
many generations within a short time span.
 When a true-breeding plant self pollinates, all of the
offspring will have the same trait as the parent.
Unraveling the Mystery

 Pea plants can also crosspollinate.
 Pollen from one plant
fertilizes the ovule of a
flower on a different plant.
 The image shows crosspollination and selfpollination.
Unraveling the Mystery,
continued

 Characteristics
 Mendel studied only one
pea characteristic at a time.
 A characteristic is a feature
that has different forms in a
population. (Ex. Eye color)
 Different forms of a
characteristic are called
traits. (Ex. Brown and Blue)
Unraveling the Mystery,
continued

 Mix and Match
 Mendel was careful to
use plants that were true
breeding for each of the
traits he was studying.
 This allowed him to
know what to expect if
his plants were to selfpollinate.
Mendel’s First
Experiments

 Mendel crossed pea plants to study seven different
characteristics.
 He noticed that one trait was always present in the first
generation, and the other trait seemed to disappear.
 Mendel called the trait that appeared the dominant trait.
 The trait that seemed to fade into the background was
called the recessive trait.
Mendel’s Second Experiments

 To find out more about
recessive traits, Mendel
allowed the first-generation
plants to self-pollinate.
 In each case some of the
second-generation plants had
the recessive trait.
Mendel’s Second Experiments,
continued

 Ratios in Mendel’s Experiments
 The recessive trait did not show
up as often as the dominant trait.
 Mendel decided to figure out the
ratio of dominant traits to
recessive traits.
Mendel’s Second
Experiments, continued

 In all cases
the ratio was
about 3:1
dominant :
recessive.
Mendel’s Second
Experiments, continued

 Gregor Mendel – Gone But Not Forgotten
 Mendel realized that his results could be explained
only if each plant had two sets of instructions for each
characteristic.
 Mendel’s work opened the door to modern genetics.
DO NOW:
4/15
Why did Mendel decide to use pea plants to further
his understanding of heredity?
Objectives:
1. Explain the relationship between traits and heredity.
2. Describe the experiments of Gregor Mendel.
3. Differentiate between dominant and recessive traits.