General Genetics

Mr. Hunter02/07/2011

Biology NotesKennedy High School

Mr. HunterBiology

01/07/13

• OBJECTIVES• SWBAT• Analyze the structure and results of Mendel’s Experiments• Determine the difference between an allele and a gene• Determine the genetic qualities of dominant and recessive

genes

Bell Ringer : What is the difference between a gene and an allele? Pg. 178

Genetic Origins

A. Many of your physical traits resemble those of your parents.

B. Heredity can be defined as the passing of genetic traits from parents to offspring.

C. Before DNA and chromosome structure were discovered genetics was one of the biggest mysteries of science.

Question: Which one of the president’s daughters looks more like their mother?

Gregor Mendel A. Gregor Mendel was a scientist who performed experiments with garden peas. These experiments led to the understanding of heredity.

B. The patterns that he studied within the plants formed the basic foundation for genetics.

C. Genetics is the branch of biology that focuses on heredity.

Question: What type of plants did Mendel experiment on that led to the understanding of heredity?

Experiments of Mendel

A. Mendel observed several traits within his experiments of the pea plants.

B. He recognized that some traits occurred more than others.

C. These traits were soon recognized as being Dominant or Recessive.

Experiments of Mendel

A. A Genetic Cross can be defined as the mating or breeding of two organisms.

B. Garden pea plants that had purple flowers were crossed with those with white flowers.

C. Purple x White = Purple flowers

D. Purple x Purple = Purple and White flowers

Experiments of Mendel

A. Flower color (purple or white)

B. Mating is easily controlled-male and female reproductive structures are in the same flower. Self-fertilization or Cross fertilization can occur.

C. The pea plant is small, grows easily, matures quickly, and produces many offspring.

Question(s): What is the difference between cross fertilization and self-fertilization?

Why did Mendel chose the pea plant for his experiments?

Experiments of Mdendel

A. Monohybrid Cross: A cross that involves one pair of contrasting traits. Mendel’s experiments were initially monohybrid.

B. Ex. Purple flowers x white flowers

C. True Breeding: plants that are allowed to self-fertilize (pollinate) and produce the P generation

D. F1 Generation results from the cross-fertilization (pollination) of the P generation.

E. F2 Generation results from the self-fertilization of the F1 generation.

Ratio Results

• What flower colors were dominant in Mendel’s experiment?

• What flower colors were recessive?• Mendel found the same 3:1 ratio in his experiments• Ratio: Comparison of two numbers that have the same

unit ex. 705/224 and 224/224 or 705:224 = 3:1• Assign. Math Lab pg. 163

Mendel’s Hypotheses

• For each trait inherited, there a two copies of a gene• Alternative forms of a gene are alleles• Alleles can be dominant (D) or recessive (r)• When gametes are formed, alleles separate independently

of each other• Gametes carry one allele for each trait• Fertilization allows the gamete to contribute one allele for

each trait

Allele Types

• Homozygous: Two alleles of a particular gene that code for the same trait are the same. ex YY (dominant yellow color) or yy (recessive yellow color).

• Heterozygous: Two alleles of a particular gene are different for a trait. ex Pp or Yy

Genotype and Phenotype

• Genotype: The set of alleles that an organism has.

• Phenotype: The physical appearance of a trait.

• Ex. If genotype = Pp then phenotype = purple; If pp then phenotype = white

Punnet Square Practice

• To determine the phenotype of an offspring you must first recognize its genotype.

• We have discussed two types of alleles in class, Dominant (B) and Recessive (b)

• We have also discussed Heterozygous (Bb) and Homozygous (BB) or (bb) alleles

• Punnet squares provide a means for determining the phenotypic outcome resulting from the combination of gametes

• The basic construction of a simple punnet square is to the left of this explanation.

Practice Problems

1. Heterozygous dominant x Homozygous recessive

• Hh x hh ( H = white, h = green )

2. homozygous recessive x homozygous recessive

• bb x bb ( B = Black, b = brown)

3. Heterozygous dominant x homozygous dominant

• Tt x TT ( T = tall, t = short )

REVIEW

1. The name of the scientist responsible for forming the foundations of genetics is __________.

2. Why did this scientist chose garden peas to perform his experiments?

3. Heredity can be defined as ________4. Genetics can be defined as _______5. What is difference between dominant

and recessive traits?6. Name four of the characteristics that

Mendel observed in his pea plant experiments. (*the plant traits*)

7. What is the difference between cross fertilization and self-fertilization?

8. Explain the difference between the P, F1 and F2 generations. What type of genetic characteristics can be observed in each one?

9. A gene can be defined as________10. An allele is ___________