CHAPTER 11 NOTES – GENETICS



UNIT 8 NOTES – GENETICS

I. History of Genetics

A. Gregor Mendel

1. Austrian Monk

2. Trained in math and science at the University of Vienna

3. Worked in the monastery and taught at a local high school

4. Was in charge of the garden at the monastery

5. Performed experiments with ordinary garden peas

II. Mendel’s Observations

A. Knew that pea plants reproduced sexually (sperm and egg cells)

B. Had several stocks of pea plants that were true-breeding

1. True-breeding plants are pure bred for their traits

2. True-breeding plants will produce offspring identical to themselves if allowed to self-pollinate

C. Mendel wanted to cross different strains of the true-breeding peas to see the results in the offspring

III. Mendel’s Experiments

A. Mendel took pollen from one plant (which contains sperm cells) and cross-pollinated another plant’s female structure

B. Mendel expected to see a blending/mixture of the two parents’ traits in the offspring, but that was not the case

1. Tall plant X Short plant resulted in all tall offspring

2. Round seeds X Wrinkled seeds resulted in all round seed offspring

3. Green pods X Yellow pods resulted in all green pod offspring

4. Yellow seeds X Green seeds resulted in all yellow seed offspring

C. From these results Mendel came to two conclusions:

1. Inheritance is determined by factors that are passed from one generation to the next (these factors are called genes)

a. Genes can be expressed in different forms, like tall and short or green pods and yellow pods

b. These different forms of a gene for a specific trait are called alleles

2. Some alleles are dominant and some alleles are recessive

a. Dominant alleles will block out the appearance of recessive alleles

b. An organism with a dominant allele will always exhibit that form of the trait

c. An organism with a recessive allele will exhibit that form of the trait only when the dominant allele for that is not present

d. This is known as Mendel’s Principle of Dominance

IV. An example of one of Mendel’s genetic experiments

A. Mendel crossed a Tall pea plant X a Short pea plant

1. These original plants are the parents or the “P” generation

B. The “P” generation cross resulted in all Tall pea plant offspring

1. These offspring are called the “F1” generation, or first filial generation

a. Mendel now knew that the allele for Tall was dominant to the allele for Short

b. Mendel wondered what happened to the allele for short; had it simply disappeared or was it still present?

C. To answer that question, Mendel crossed two F1 generation plants in order to observe the results

1. The resulting offspring were called the “F2” generation, or the second filial generation

2. In the F2 generation the recessive allele once again showed up!

a. Roughly 75% of the F2 generation were Tall pea plants

b. Roughly 25% of the F2 generation were Short pea plants

c. The only way that the recessive allele can once again be exhibited in F2 generation plants is for the alleles to separate or segregrate at some point.

D. Law of Segregation

1. States that during meiosis (when gametes/sex cells are produced), alleles will segregrate from each other so that each gamete/sex cell will carry only one copy of each gene.

V. Genetics and Probability

A. The principles of probability can be used to explain the results of genetic crosses.

B. Coin Flip Activity

1. Get into groups of two

2. Materials needed: two coins, pencil/pen, paper

3. Procedure for first activity:

a. make two columns with the headings of “HEADS” and “TAILS”

b. one person flips a coin 50 times, calling out whether it lands on heads or tails each time

c. other person records tally marks of the 50 coin flips

d. record totals for your group and for the class as a whole

e. results should be approximately 50% heads and 50% tails

4. Procedure for second activity:

a. make three columns with the heading of “2 HEADS,” “2 TAILS,” and “1 HEAD & 1 TAIL”

b. one person flips both coins 50 times, calling out the results of the flip each time

c. other person records tally marks of the 50 coin flips

d. record totals for your group and for the class as a whole

e. discuss the results of the coin flips in general

f. make two columns with the headings “DOMINANT” and “RECESSIVE”

g. discuss the results of the coin flip using the principle of dominance; have the head side of the coin represent the dominant allele and the tail side of the coin represent the recessive allele

VI. Punnett Squares

A. a Punnett square is a genetic tool used to predict the possible offspring from two parents

B. Genotype – the actual genetic makeup of an organism (not visible when you look at an organisms)

C. Phenotype – the visible trait you can see when you look at an organism (like tall, short, green, yellow, etc.

D. Homozygous Genotype– both alleles for a gene are the same; either both are dominant (TT) or both are recessive (tt)

E. Heterozygous Genotype – the two alleles for a gene are different (Tt)

***WORK SOME PRACTICE GENETIC CROSSES WITH ONE TRAIT USING THE PRINCIPLE OF DOMINANCE, THEN HAVE TWO ASSIGNMENTS FOR GRADES***

VII. Two-trait crosses and Independent Assortment

***WORK SOME PRACTICE GENETIC CROSSES WITH TWO TRAITS USING THE PRINCIPLE OF DOMINANCE, THEN HAVE TWO ASSIGNMENTS FOR GRADES***

VIII. Principle of Incomplete Dominance

A. Sometimes traits are controlled by two alleles that are not dominant or recessive to each other – this means that whenever a heterozygous genotype is present in an organism, a blending of the two traits will appear in the phenotype. EX: Red Rose (RR) crossed with a White Rose (WW) will result in a Pink Rose (RW)

***WORK SOME PRACTICE GENETIC CROSSES WITH ONE AND TWO TRAITS USING THE PRINCIPLES OF INCOMPLETE DOMINANCE, THEN HAVE AN ASSIGNMENT FOR A GRADE***

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