Name:                  Robin L. Lewis

Subject:               Biology I-Genetics

Period:                 2^nd

Approximate Time:       50 minutes

Objectives:

The student will…

1. Apply genetic principles to sex-linkage inheritance problems.

Materials:

Dry erase markers, erasers, white board, notebook paper

Set:

Yesterday, we reviewed incomplete dominance, co dominance and multiple alleles. Today, I want you to think about 3 things that seem to go together in life.  For example, peas and cornbread; apples and oranges.  Review student responses.  In genetics, there are some genes that seem to go together; rather, they seem to be inherited together.  We call these genes linked genes.  On the board write: linked genes- genes inherited together.

Procedures:

1. Bellwork: Review homework from yesterday.  Have students check their responses and ask questions about ones they didn’t understand.
2. Set.
3. Linked genes.
   1. Get them when two genes are close on the same chromosome. Ex. Ever noticed that people with red hair usually have freckles.
   2. Was first noted by Thomas Morgan, a scientist

                                         i.    Studied a fruit fly- Drosophilia.

                                        ii.    Saw that the fly body color and wing size were inherited together.

4. Sex-Linked: Not only are genes inherited together on regular chromosomes, they are also linked on sex chromosomes.
   1. Gametes-sex cells

                                         i.    Female=XX

                                        ii.    Male=XY

1.    Show cross between a man and woman and possible sex outcomes for their children.

2. X chromosome

                                         i.    Bigger, therefore has more chromosomes

                                        ii.    More defects.

3. X-linked

                                         i.    Inheritance pattern: Mother to son.  Father to daughter.

                                        ii.    Usually males are more affected.  Let’s see why this is true.

4. Y-linked

                                         i.    Father to son.  Why?

5. Color-blindness-Explain red/green.

                                         i.    Write genotypes and phenotypes on the board for each case: B= normal; b= color blind

                                        ii.    Carrier

6. Examples

                                         i.    Woman w/ normal vision marries a man w/ normal vision.  Will their children have normal vision?

1.    Have to break it down into girls and boys.

                                        ii.    Hemophilia-recessive on X.  Man has it, marries a woman who is a carrier.  Chance their first born will have it? (50%)

                                       iii.    Can a mother whose father and husband are color blind have an affected daughter?  Son?

Closure:

Today we applied genetic principles to sex-linkage inheritance problems.  We discussed how why genes are linked and we looked at problems conserning linked genes.  Let’s review.  Ask questions about linked genes.  Tomorrow we will further look in to heritance by looking a pedigree that shows how traits are passed down in a family.  Tonight for homework, practice monohybrid crosses concerning sex-linked, codominance and incomplete dominance.

Assessment/Evaluation:

1. The teacher will gauge student responses (M) to practice problems and questions about sex-linked genes (D).
2. Formally, the teacher will give a quiz (M) on sex-linked genes, incomplete dominance, complete dominance, codominance, and multiple alleles problems (C).  This quiz will be graded (M) and recorded in the gradebook (D).

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