1. 5-2-18 Mendel and His Peas cont.

2. Do Now: Take out your homework
Do Now: Take out your homework. Complete the following in your science notebook
Read “Mendel’s Cross-Pollination” and examine Figure 2. Understand that Mendel physically controlled which plants were pollinated in order to learn how inheritance of traits worked.
Answer the following questions
Why did Mendel perform cross-pollination experiments (instead of just allowing the plants to self-pollinate)?
Why was it important for Mendel to use a large number of plants for each cross?
3. Why was it important for Mendel to use true-breeding plants in his experiments?

3. Rally Robin: Discuss the following questions with your shoulder partner. Partner A shares first while Partner B listens; then switch roles.
Why did Mendel perform cross-pollination experiments (instead of just allowing the plants to self-pollinate)?
Answer: Mendel used cross-pollination to determine which crosses produced which traits.
Why was it important for Mendel to use a large number of plants for each cross?
Answer: Testing many plants produced more data and made Mendel’s conclusions more reliable. If his sample had been smaller, small differences could have led him to unsupportable conclusions.
Why was it important for Mendel to use true-breeding plants in his experiments?
Answer: He needed to have plants that bred with predictable traits to know if cross-breeding had an effect on the next generation of plants.

4. HW Review: Key Concept Builder – Why did Mendel conduct cross-pollination experiments?
1. E heredity 2. I genetics 3. A self-pollination 4. F cross-pollination 5. C pollen carriers 6. H observable traits 7. G true-breeding plant 8. D stamen 9. B pistil 1. reproduce, traits 2. (in either order) self-pollination, cross-pollination 3. true-breeding 4. color, length 5. cross-breeding, hybrid 6. first, second

5. EQ: What did Mendel conclude about inherited traits
EQ: What did Mendel conclude about inherited traits? EQ: How do dominant and recessive traits interact?

6. Mendel’s Experimental Methods
Mendel began his experiments with plants that were true-breeding for the trait he would test.
When a true-breeding plant self-pollinates, it always produces offspring with traits that match the parent.
Ex: when a true-breeding pea plant with wrinkled seeds self-pollinates, it only produces plants with wrinkled seeds.
Self-pollination
All offspring also have wrinkled peas
True-breeding (wrinkled peas)

7. Mendel’s Results
Once Mendel had enough true-breeding plants for a trait he wanted to test, he cross-pollinated selected plants.

8. First-Generation Crosses
Hybrids: Plants that come from true-breeding parent plants with different forms of the same trait.

9. Mendel’s Results: Second-Generation (Hybrid) Crosses
Mendel also cross- pollinated hybrid plants.
He observed that offspring of hybrid crosses always showed traits in a 3:1 ratio.
Turn & Talk: Are the results of the two crosses the same? Explain.
Yes, the flowers are arranged differently in the image, but the numbers of purple and white flowers are the same, a 3:1 ratio.

10. Mendel’s Results
Mendel recorded traits of offspring from many hybrid crosses.
He observed that the offspring of hybrid crosses always showed traits in a 3:1 ratio
A ratio is a comparison of two numbers or quantities by division. For example, the ratio comparing 6,022 yellow seeds to 2,001 green seeds can be written as 6,022 to 2,001 or 6,002 : 2,001 or 6,022 2,001
To simplify the ratio, divide the first number by the second number.

11. Mendel’s Conclusions
Mendel concluded that two factors, one from each sperm and one from each egg, control each inherited trait.
Remember that when Mendel cross-pollinated a true-breeding plant with purple flowers and a true-breeding plant with white flowers, the hybrid offspring had only purple flowers.
Mendel hypothesized that the hybrid offspring had one genetic factor for purple flowers and one genetic factor for white flowers. But why were there no white flowers?

12. Mendel’s Conclusions
Mendel hypothesized that the purple factor is the only factor expressed because it blocks the white factor.
Dominant trait: a genetic factor that blocks another genetic factor.
Rasgo dominante: factor genetico que bloquera otro factor genetico.
A dominant trait is observed when offspring have either one or two dominant factors.
In this example, “R” represents a dominant factor and “r” represents a recessive factor. The dominant trait is being Unaffected by a disease. The recessive trait is being Affected by a disease.

13. Mendel’s Conclusions
Recessive trait: a genetic factor that is blocked by the presence of a dominant factor.
Rasgo recesivo: factor genetico boqueado por la presencia de un factor dominante.
A recessive trait, such as white pea flowers, is observed only when two recessive genetic factors are present in offspring.
In this example, “R” represents a dominant factor and “r” represents a recessive factor. The dominant trait is being Unaffected by a disease. The recessive trait is being Affected by a disease.

14. Rally Robin
With your shoulder partner, take turns naming the dominant traits of pea plants observed by Mendel. Partner A starts.
Dominant traits of pea plants include purple flowers, axial flowers, yellow seeds, round seeds, smooth pods, green pods, and long stems
With your shoulder partner, take turns naming the recessive traits of pea plants observed by Mendel. Partner B starts.
Recessive traits of pea plants include white flowers, terminal flowers, green seeds, wrinkled seeds, bumpy pods, yellow pods, and short stems
Mendel observed that about 75% of plants had the dominant form of each trait and 25% of plants had the recessive form of each trait.

15. Homework: Key Concept Builder – What did Mendel conclude about inherited traits? How do dominant and recessive factors interact?
Use the online textbook, your notes, and the PowerPoint to answer the questions.