1 / 21

6.3 Genetics and Predictions

6.3 Genetics and Predictions. You will be able to:. Explain how probability is used in genetic predictions To construct a Punnett Square for monohybrid and dihybrid crosses To infer genotype by using a testcross. Probability. the measure of how likely an event is.

mikaia
Download Presentation

6.3 Genetics and Predictions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. 6.3 Genetics and Predictions

  2. You will be able to: • Explain how probability is used in genetic predictions • To construct a Punnett Square for monohybrid and dihybrid crosses • To infer genotype by using a testcross

  3. Probability • the measure of how likely an event is. • Measure how likely a species will inherit a trait

  4. Represent probability • Fraction ½ • Percent 50% • Ratio (1:2)

  5. Punnett Square • a simple graphical way of discovering all of the potential combinations of genotypes that can occur in children, given the genotypes of their parents.  • It also shows us the odds of each of the offspring genotypes occurring.

  6. Sample Problems • In pea plants , tall pea plants are dominant over short pea plants. • Using Punnett Squares, you can predict the genotypes and phenotypes of the offspring of a cross between a homozygous (purebred) tall pea plant and a homozygous (purebred) short pea plant.

  7. You begin by drawing a grid Step 1

  8. Designate letters which will represent the genes/traits. Capital letters represent dominant traits lowercase letters represent recessive traits. T = tall t = short Step 2

  9. Write down the genotypes (genes) of each parent. These are often given to you or are possible to determine. TT X tt Step 3

  10. List the genes that each parent can contribute. Parent 1 : T Parent 2: t Step 4

  11. Write the possible gene(s) of one parent across the top The gene(s) of the other parent along the side Step 5

  12. Fill in each box of the Punnett square by transferring the letter above and in front of each box into each appropriate box. As a general rule, the capital letter goes first and a lowercase letter follows. Step 6

  13. Step 7 • List the possible genotypes and phenotypes of the offspring for this cross.

  14. Monohybrid Cross • only one trait is crossed. • A tall pea plant TT is crosses with a short pea plant tt.

  15. Dihybrid Cross • Two traits are crossed. • A tall, green flowered plant is crossed with a short, yellow flowered plant. • TtPp x ttpp

  16. Test Cross • A simple method to confirm the genotype of the F1 hybrid. • F1 hybrid is crossed with the homozygous recessive

  17. Test Cross Example • Tall x Dwarf • Tall Parent = F1 (Tt) • Dwarf Parent = homozygous recessive (tt)

  18. If the F1 tall is heterozygous with (Tt) genotype • and, if Mendel's law of segregation of characters is correct, • then the F1 should produce two types of gametes, (T) and (t) in equal proportion. • The recessive dwarf parent produces only (t) type of gametes. • The resulting test cross progeny should be 50% Tall and 50% Dwarf or in 1:1 ratio as follows

  19. The resulting test cross should be • 50% Tall and 50% Dwarf • 1:1 ratio • 1 tall for every 1 dwarf

More Related