Download 5-1 Mendel`s Work I. Mendel`s Experiments 1. Heredity

5-1 Mendel’s Work
I.
Mendel’s Experiments
1. Heredity- the passing of physical characteristics from parents to
offspring.
2. Trait- Each different form of a characteristic, such as height or seed
color.
3. Today Mendel’s discoveries form the foundation of genetics.
4. Genetics- the scientific study of heredity.
5. Fertilization- a new organism begins to form when egg and sperm
join through a process called pollination.
6. Before pollination can occur pollen must reach the pistol of the
flower.
A. Crossing Pea Plants
1. Mendel decided to cross Purebred plants with contrasting traits.
(Tall and Short plants)
2. Purebred- the offspring of many generations that have the same
trait. Purebred short pea plants always come from shore parent
plants.
B. The F1 Offspring
1. Mendel crossed purebred tall plants with purebred short plants.
2. Even though one of the parent plants were short, none of the
offspring were short. It seemed as if the short trait was “lost”.
C. The F2 Offspring
1. When the plants from F1 generation were full grown Mendel allowed
them to self pollinate and the offspring were a mix of tall and short.
2. About ¾ of the plants were tall and ¼ were short.
D. Experiments with Other Traits
II.
1. In all of Mendel’s crosses, only one form of the trait appeared in the
F1 generation. However, in the F2 generation, the “lost” form of the
trait always reappeared in about ¼ of the plants.
Dominant and Recessive Alleles
1. The factors that control each trait exist in pairs, the female
contributes one factor, while the male contributes the other.
A. Genes and Alleles
1. Today scientist use the word gene for the factors that control the
traits
2. Alleles-the different forms of a gene.
3. An organisms traits are determined by the alleles it inherits from its
parents. Some alleles are dominant, while others are recessive.
4. Dominant Allele- the one whose trait always shows up in the
organisms when the allele is present.
5. Recessive Allele- is hidden whenever the dominant allele is present.
6. A trait controlled by a recessive allele will only show up if the
organism does not have the dominant allele.
B. Alleles in Mendel’s Crosses
1. Hybrid- organism that has two different alleles for a trait.
2. In hybrid alleles the offspring will have the trait of the dominant
allele.
3. The offspring will only carry the trait of the recessive allele if both
alleles are recessive.
C. Symbols for Alleles
1. Geneticists use letters to represent alleles. A dominant allele is
represented with a capital letter, whereas a recessive allele is
represented by a lowercase letter.
TT: (dominant/dominant), Tt:(dominant/recessive), or
tt:(recessive/recessive).
D. Significance of Mendel’s Contribution
1. Before Mendel’s most people thought that genetic information
could be blended to produce new traits.
2. Mendel is often called the Father of Genetics.