TITLE:  Introduction to Genetics
Presented to grade level 7

GOALS
The purpose of this lesson is to give the students an introduction to the field of genetics, focusing on the history of the science of genetics with an emphasis on Mendelian genetics. The lesson also includes an overview of the terms used in the field of genetics.
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SPECIFIC OBJECTIVES

• An understanding of who Gregor Mendel was and his significance to the science of genetics.
• An understanding of Mendel's pea plant experiment and its consequences.
• An understanding of the difference between dominant and recessive genes and their relationship to incomplete dominance.
• An understanding of the inheritance of genes, including the laws of segregation and independent assortment.
• Understanding the difference between pure-breds and hybrids.

BACKGROUND
1. Mendel's Pea experiment.
Why did Mendel choose pea plants?  Pea plants grow and reproduce quickly.  They have a wide variety of different traits, and were easy to breed and cross-pollinate.

What did Mendel do?  First, he tranferred pollen from flowers on short-stemmed plants to the stigmas of flowers on other short-stemmed plants and found out that all the offspring were short-stemmed.  Mendel called these plants true-breeding plants, plants that always produce offspring with the same traits as their parents.  When he crossed tall-stemmed plants with other tall-temmed plants, he found that both tall and short plants resulted.

What were Mendel's conclusions?  Mendel realized that each plant must contain two factors for a particular trait.  He called these factors genes.  Alternative forms of a gene (tall and short) are now called alleles. When he crossed two true-breeding plants with opposite traits (for example tall with short), the offspring showed only one of the traits, which Mendel called the dominant trait.   He called the weaker trait which did not appear in those offspring recessive.

How are the genes inherited?  Mendel realized that each parent could only contribute one of the factors (genes) to the plant in the offspring generation, so the offspring in the first filial generation would get one factor from the female parent and one from the male parent.  The two gene types contributed by a single parent separate into the sex cells according to Mendel's Law of Segregation.  Each gene pair for a trait is inherited independently of the gene pairs for other traits. For example, when a tall plant with yellow seeds forms its sex cells, the genes for stem length separate independently from the genes for seed color. This is referred to as Independent Assortment.

2. Important Terms.
 

Trait	The characteristics of an organism.
Genetics	The study of heredity, or the passing on of traits from an organism to its offspring.
True-breeding	Organisms that always produce offspring with the same traits as their parents.
P generation	The parental generation
F1 generation	The first filial generation; the result of crossing two members of the P generation
F2 generation	The second filial generation; the result of crossing two members of the F1 generation
Genes	The units of heredity
Phenotype	The physical appearance of a trait
Dominant allele	An alternative gene form that is "stronger", and controls the phenotype despite the presence of a recessive allele.  Represented with a capital letter, for instance T for tall.
Recessive allele	An alternative gene form that is "weaker" and that usually does not influence the phenotype in the presence of a dominant allele.  Represented by a lower case letter, for instance t for short.
Pure-bred	Organisms that have two of the same allele (TT or tt).
Hybrid	Organism with a mix of alleles from different pure-bred types (Tt).
Law of segregation	When the parent plant forms sex cells (sperm or eggs), the parent's gene pairs separate, so a parent's sex cell will carry only one allele for a particular trait.
Law of independent   assortment	Each gene pair for a trait is inherited independently of the gene pairs for all other traits.
Incomplete dominance	Each allele modifies the phenotype to some degree, producing a blended trait.

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SOLs COVERED

LS 13

The student will investigate and understand that organisms reproduce and transmit genetic information to new generations. The key concepts included with this lesson are: the characteristics that can and cannot be inherited, and the historical contributions and significance of discoveries related to genetics.

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DEMONSTRATIONS AND EXHIBITS
Materials needed:  Red and blue paper and a blue or red filter (or cellophane)

1. Complete and Incomplete Dominance.

• Hold one sheet of paper in front of the other, pointing out that only one color is viewed.
• Hold a blue filter over a piece of red paper (or red filter over blue paper).  The students will observe that the paper now looks purple.  Similar to incomplete dominance, the color traits have blended.

INTERACTIVE EXERCISES
Materials needed: Dominant and Recessive Traits Worksheet

1. Dominant and Recessive Traits.

• Student break up into groups of two and works on the Dominant and Recessive Traits Worksheet.  After they are completed, discuss the class findings as a whole.  The main goal of the activity is to encoruage interaction among the students as well as to give an introduction to dominant and recessive traits.

INTERESTING EXAMPLES

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OTHER RESOURCES
 

Literature	.
Local Places to Visit	.
Related Web Sites	Mendel's Paper on plant hybridization (English) Mendel and Mendelian Genetics

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