Chapter 11 Lesson 3, "How Heredity is Stdid in Humans"

Materials:

• How heredity is studied
• Sumation of lesson worksheet

Objective:

• Students will explain some ways tha scientists study heredity in humans.
• Students will describe DNA and how it replicates.
• Students will explain what a mutation is.
• Students will give exmples of genetic diseases.

Anticipatory Set: *Show the students these five sets of twins and have them guess whether they are idenical twins or not.

What makes identical twins identical? How are fraternal twins different than identical twins? The study of human genetics is much more complicated than fruitflies or peas, why?

1. humans have more chromosomes.
2. humans do not reproduce as quickly.
3. humans can not be used a labatory experiments. (Who was the leader in the 1930s and 1940 who tried this?)

Teacher Input: * In the example of twins at the beginning we dicussed the fact that identical twins have the identical genes, fraternal twins do not. How does this happen. Show a picture of a zygote and remind the students of how the reproductive system works. (Zygote)

Explain the differences between the two types of twins using that zygote example and the pictures from the book on P279 (Zygote, Identical Twins, Fraternal Twins).

The genes of identical twins are the same what do those genes determine? How come identical twins are different in some respects? What else affects the way you develop? (eg. One identical twin dies of lung cancer at 45, the other lives to be 90, Why)

If two identical twins are separated at birth and they live in two totally different parts of the country, one in a rich family and one in a poor family what characteristics will they still have in common? Have the students list the characteristics of the environment that will affect a person: (eg. food, freckles are affected by sunlight, smokers give birth to low weight babies, x-rays, cancers) If there are differences, what would cause them? Is there anything that could have made the two twins look different from one another? What might cause a mutation, or a change in a gene?

Show the students a picture of how DNA replicates.(P281) As you discuss the picture mention these key points:

• All the information that makes you, you, is in your DNA.
• The order of the arrangement of DNA molecules determines what that information is.
• The greater the difference in arrangement the greater the difference in the organisms.
• Each DNA molecule has thousands of genes.
• Each gene is a specific order of bases. (That order determines the trait)
• To duplicate the DNA splits in half and the pairs of bases separate.
• DNA rebuilds into the ladder shape with specific base pairs to form the missing side of the ladder and thus has two identical DNA molecules formed.
• With thousands of these pairings going on sometimes there is a mistake in the order of the pairings.
• The mistake in replicating DNA is a mutation and causes a change in the gene or trait.

Guided Practice: * Describe a genetic disease. Most are caused by a recessive trait. Show the example of how this can affect a population.

Students will look at a pair of grandparents where one of the grandparents has sickle-cell anemia. Then one of the offspring has sickle-cell anemia. Students will trace the disease through four generations. Use this diagram. Use a punnet square at each generation to determine what characteristics the children will have.

Explane how in a smaller gene pool a recessive trait shows up more offen. This is because of inbreeding. Go through laws about marrying cousins. Explain that Hemophilia is also sex-linked. Create a punnett square with a Female carrier and a Male with the disease. In a huge gene pool the population stays healthier. Use an example of hemophilia

Independent Practice: * Students will complete the

• How heredity is studied
• Sumation of lesson worksheet

Check for Understanding: * Students will take the quiz on Lesson 3 "How Heredity is Studied in Humans"

30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).

Alaska Content Standards Addressed in this lesson:

• SCI A-11 Students will understand that similar features are passed on by genes through reproduction (Heredity).
• SCI A-12 Students will distinguish the patterns of similarity and differences in the living world in order to understand the diversity of life and understand the theories that describe the importance of diversity for species and ecosystems.
• SCI A-13 Students will understand the theory of natural selection as an explanation for evidence of changes in life forms over time (Evolution and Natural Selection).
• SCI A-14 Students will understand
  • the interdependence between living things and their environments:,
  • that the living environments consists of individuals, populations, and communities: and
  • that a small change in a portion of an environment may affect the entire environment (Interdependence);

• SCI A-15 Students will use science to understand and describe the local environment (Local Knowledge); and:
• SCI D- 4. evaluate the scientific and social merits of solutions to everyday problems;