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Bunny Fur Genetics - Punnett Square & Dihybrid Cross

This text explains how to use Punnett squares to determine offspring genotypes and probabilities in a dihybrid cross for bunny fur color and length. It also discusses sex-linked traits and pedigrees.

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Bunny Fur Genetics - Punnett Square & Dihybrid Cross

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  1. Warm- Up Brown fur (B)is dominant to white fur (b) in a Type of bunny. Draw a Punnett square to show a cross between a homozygous recessive male and a heterozygous female. • What genotype(s) in the offspring will code for brown fur? • What is the probability that their bunnies will have white fur?

  2. What is a Dihybrid Cross? • “Di” means two • In a dihybrid cross • Two parents are mated (hybrid) • We examine two traits (di) A dihybrid cross is used to determine the possible offspring of two parents based on two traits.

  3. c. In this example: • Tail length is indicated by S for short tail or s for long tail. • Coat color is indicated by B for brown coat or b for white coat while

  4. Mendel worked with Pea Plants

  5. Let’s Try a Problem ▬► Consider this cross Pea Plants can have these traits Round (R) Wrinkled (r) Yellow (Y) Green (y)

  6. He found these traits in Pea Plants

  7. Steps to solving Dihybrid problems Copy the Problem • A pea plant that is heterozygous for round, yellow seeds is self fertilized, do a Punnett Square to solve.

  8. Copy the Steps Step 1: Determine the parental genotypes Heterozygous= Round= ___ yellow=___seeds Combine=______________

  9. Step 2: Determine the gametes. Use FOIL method {First, Outer, Inner, Last} RrYy RY, Ry, rY, ry (parent 1) and RY, Ry, rY, ry(parent 2)

  10. Step 3: Put gametes on Punnett Square

  11. Sex Linked Trait Examples • Hemophilia A (Factor VIII deficiency) • Red/Green color blindness • Male-pattern baldness* • Duchenne Muscular Dystrophy (DMD)

  12. Chromosomes • The sex chromosomes are the 23rd pair of chromosomes. • The other 22 pairs of chromosomes are called autosomes. • Traits or diseases can be either sex-linked or autosomal

  13. What are Pedigrees? • Pedigrees • chart • show how a trait is passed down over several generations • Can show autosomal or sex-linked traits b. Pedigrees look like family trees

  14. Example

  15. What are the Sex chromosomes? • The 23rd pair of chromosomes determine your sex. • There are two different sex chromosomes: X and Y • Females have the chromosomes XX • Males have the chromosomes XY • Where do we get the first X chromosome from?

  16. What are Sex-Linked Traits? a. Certain traits are called sex-linked because the traits are determined by genes on the X and Y chromosomes (the sex chromosomes). b. Most sex-linked traits are only found on the X chromosome.

  17. What are the Sex chromosomes? c. Genetic diseases or mutations are carried on the X chromosome. • Females are more likely to be carriers because they have two X chromosomes • Males are more likely to inherit genetic diseases because they only have one X chromosome • Example: Red/Green Colorblindness occurs in 1 out of 10 males in the US and 1 out of 100 females in the US.

  18. Look at Chromosome Chart

  19. Warm Up Yellow seed color (Y) is dominant to green seed color (y), and round seeds (R) are dominant to wrinkled seeds (r). A plant that is homozygous for green, wrinkled seeds is crossed with a heterozygous yellow and round plant. Draw the dihybrid cross. What’s the probability that they will produce plants with yellow, wrinkled seeds?

  20. Agenda • Objectives: SWBAT: Identify the sex chromosomes in humans and recognize inheritance patterns that are sex-linked, using a pedigree or scenario • Pedigrees • Complete Practice Sheet • White Board Practice (If there’s time) • Exit Ticket • Gather materials for Quiz

  21. Examine a Pedigree

  22. Pedigree Worksheet

  23. Put together packet • Phenotype Study • Genetics Review 1 • Reading guide 6.3 • Punnett Squares- Crosses involving one trait • Bill Nye Video Questions • Punnett Square Worksheet • Human Chromosomes • Bikini Bottom Genetics (I still have those that were turned in)

  24. Warm Up • What’s the phenotype of person #3? • What’s the genotype of person # 4? • Who are the children of person’s 1 and 2?

  25. Agenda • White Board Review • Turn in packets • Quiz • Video

  26. Draw the symbol for carrier female

  27. In bunnies, brown fur (B) is dominant to white fur (b) and short fur (S) is dominant to long fur (s). • What would be the genotype of a heterozygous brown bunny with short fur? 2. What about a homozygous white bunny with short fur?

  28. If brown fur is dominant to white fur and short fur is dominant to long fur, what’s the probability that the offspring will be brown with short fur?

  29. Write the genotype of a male with hemophilia (which is caused by a recessive gene on the X chromosome)

  30. A heterozygous tall plant is crossed with a short plant. The tall gene is dominant to the short gene in plants. What’s the probability that the offspring will be tall?

  31. What percent of the offspring are homozygous recessive?

  32. If the dominant fur color is gray and the recessive fur color is black, what’s the probability of the offspring having gray fur?

  33. In certain breeds of dogs, deafness is due to a recessive allele (d) of a particular gene, and normal hearing is due to its dominant allele (D). What percentage of the offspring of a normal heterozygous (Dd) dog and a deaf dog (dd) would be expected to have normal hearing?

  34. The following genotypes were found in a male cat and a female cat: BbSs(male) bbSS(female) Which one of the following choices is true of the phenotype of offspring from these parents? • All offspring will have black fur. • All offspring will have white fur. • All offspring will have long-haired fur. • All offspring will have short-haired fur.

  35. Hemophilia is a sex-linked recessive disease. If a woman has a genotype XRXrdoes she have hemophilia?

  36. If a man is XrY does he have hemophilia?

  37. A woman is XRXrand a man is XrY, what’s the probability that their children will have hemophilia?

  38. A man with a widow’s peak marries a woman with a straight hairline. Use the letter “H” • If one of his parents had a widow’s peak and the other did not, what is his genotype? • What’s the probability that they will have children with a widow’s peak?

  39. A pregnant couple wants to know if their child will have curly hair. Having curly hair is a dominant trait. The mother has the prettiest curls and so do her parents. The father however, has straight hair. What’s the probability that their child will have curly hair?

  40. Autosomal or sex-linked disorder?

  41. Autosomal or sex-linked disorder?

  42. Clean up White Boards • Turn in your markers and white boards • Spread yourselves out around the classroom for the quiz

  43. Cracking the code • http://www.pbs.org/wgbh/nova/body/cracking-the-code-of-life.html

  44. Warm Up • What are some traits that can be passed down in a family? • Are all traits inherited the same way? Explain what you think in complete sentences.

  45. Agenda • Objectives: SWBAT Define and distinguish between different modes of inheritance. • Look at different scenarios of inheritance • Worksheet • DNA Cracking the Code Video

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