The Norwood Science Center

Human Body

Grade 5

TITLE: GENETICS OF EYE COLOR

PURPOSE: How is eye color passed on from parents to offspring?

MATERIALS: (per student)

Notebook

Pencil

Punnett Square Worksheet

(per teacher)

Overheads reviewing Intro to Genetics lesson and Punnett Square worksheet

PROCEDURE:

01. Allow students 5 minutes to review their notes from the Introduction to Genetics lesson presented during their last Science Center visit.

02. Using overheads (see attached) students are presented with a series of statements in Jeopardy Game fashion. Their task is to prepare a question that correctly addresses the statement. This step serves as a reinforcement of the previous lesson and an introduction to the current lesson.

03. Review with students the following previously presented concepts from the Intro to Genetics lesson:

§ Genes contain a set of directions for a trait.

§ Genes appear in pairs – one passed on from each parent.

§ There are two types of genes – Dominant and recessive.

§ Dominant genes carry a trait that always appears if inherited.

§ Recessive genes carry a trait that will be masked over if paired with a Dominant gene.

§ Upper case letters are used for Dominant traits while lower case letters are used for recessive traits.

04. Having Freckles is a Dominant trait and is designated with the upper case letter “F.” Not having Freckles is a recessive trait and is designated with the lower case letter “f.”

05. Provide the class with the following chart on the board:

Gene Pair
Individual #1 / FF
Individual #2 / Ff
Individual #3 / ff

Individual #1 will have Freckles since they are completely Dominant for the trait. Individual #2 will also have Freckles since the Dominant “F” gene will mask over the recessive “f” gene. Individual #3 will not have Freckles since they are completely recessive for the trait and do not possess the Dominant gene for Freckles.

06. Write the following terms and definitions on the board:

§ Genotype – the type of genes you have

§ Phenotype – the trait shown or displayed based on your genotype

07. Display the following chart on the board and ask students to complete the missing information:

Genotype / Phenotype
Individual #1 / FF = Dominant/Dominant / Freckles
Individual #2 / ? / ?
Individual #3 / ? / ?

Solution:

Genotype / Phenotype
Individual #1 / FF = Dominant/Dominant / Freckles
Individual #2 / Ff = Dominant/recessive / Freckles
Individual #3 / Ff = recessive/recessive / no Freckles

08. Distribute a copy of the Punnett Square worksheet to each student.

09. The Punnett Squares will be used to determine the four possible outcomes of gene pairs of offspring based on the gene pairs of the parents. The trait discussed will be eye color –specifically the Dominant eye color Brown (B) and the recessive eye color blue (b).

10. Using the first Punnett Square, have students write in the following gene pairs of parents who genotype is Dominant/Dominant and phenotype is brown eyes:

11. Offspring receive one gene from each parent. If the offspring received one Brown eye gene from one parent and another Brown eye gene from the other parent, one resulting gene pair for the offspring would be BB as indicated below.

12. Completion of the Punnett Square and calculation of the occurrences of the four types of gene pairs would indicate the following possibilities for offspring of two parents completely Dominant for Brown eyes:

All the offspring will be completely Dominant for Brown eyes.

12. In the next Punnett Square, students are instructed to write in the following genotypes for parents and are guided through the process of completing the sections of the Punnett Square and the calculating of the occurrences of the four types of gene pairs.

CONCLUSION:

01. Ask the class, could two brown-eyed parents have a blue eye child? From their data, they will notice that there is a 25% chance of two brown-eyed parents having a blue-eyed child as long as both parents carry the recessive gene for blue eyes and pass that gene along to their offspring.

02. It should be clear from their Punnett Square calculations that in order for a recessive trait to appear, the gene pair for that individual must be completely recessive. If the Dominant gene did occur, it would mask over the recessive trait and not allow it to be displayed.

Genetics of Eye Color Gr. 5 07 Page 2 of 4