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In This Lesson: Dihybrid Crosses (Lesson 4 of 6). Today is Friday (!), December 13 th (!) , 2013. Pre-Class (notebooks): CHALLENGE: Diagram the following dihybrid cross in your notebooks: Hint: You’ll need a 4x4 grid. DdHh x DdHh D = dark flowers d = light flowers

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today is friday december 13 th 2013

In This Lesson:

Dihybrid Crosses

(Lesson 4 of 6)

Today is Friday (!),December 13th (!), 2013

Pre-Class (notebooks):

CHALLENGE:

Diagram the following dihybrid cross in your notebooks:

Hint: You’ll need a 4x4 grid.

DdHhxDdHh

D = dark flowers

d = light flowers

H = hard fruit

h = soft fruit

today s agenda
Today’s Agenda
  • DIHYBRID PUNNETT SQUARES
    • Which includes probably the most colorful slide you’ll see in my class…
  • Where is this in my book?
    • Academic: P. 270 and following…
    • Honors: P. 158 and following…
the lead in
The Lead-In
  • TED: Hortensia Jiménez Díaz – How Mendel’s Pea Plants Helped Us Understand Genetics
dihybrid practice
Dihybrid Practice
  • It’s time for some practice using ExploreLearning!
  • This Gizmo is called Mouse Genetics (Two Traits).
  • There is an accompanying Quia quiz.
  • [Log-in Instructions]
first of all
First of all…
  • What is a dihybrid cross?
    • Remember, a monohybrid cross is a cross that analyzes only one trait.
      • Example: Mom with blue eyes, Dad with green eyes, child with ___ eyes?
    • A dihybrid cross is a cross that analyzes two traits.
      • Example: Mom with blue eyes and blonde hair, Dad with green eyes and brown hair, child with ___ hair and ___ eyes?
  • Now let’s solve our pre-class.
solving dihybrid crosses
Solving Dihybrid Crosses
  • Identify the parent genotypes.
    • DdHhand DdHh
  • FOIL the genotypes.
    • First, Outer, Inner, Last
    • DH, Dh, dH, dh
    • DH, Dh, dH, dh
  • Place one FOIL result across the top, the other down the side of a 4x4 square.
  • Solve as normal.
foiling
FOILing
  • How to FOIL:
    • [First, Outer, Inner, Last]

Possible Allele Combinations

DdHh

DH

Dh

dH

Outer

First

Last

Inner

dh

DdHh

ddhh x ddhh

:1

9

:3

:3

DdHh x DdHh

Which plants will have the dominant phenotype for both traits?

Which plants will have the dominant phenotype for flowers but recessive for fruit?

Which plants will have the dominant phenotype for fruit but recessive for flowers?

Which plants will have the recessive phenotype for both traits?

shortcuts
Shortcuts
  • When you cross two heterozygous individuals in a monohybrid cross, you get a 3:1 phenotype ratio.
  • When you cross two completely heterozygous individuals in a dihybrid cross, you get a 9:3:3:1 phenotype ratio.
    • 9 = Individuals that are dominant/dominant.
    • 3 = Individuals that are dominant/recessive.
    • 3 = Individuals that are recessive/dominant.
    • 1 = Individuals that are recessive/recessive.
  • Important:
    • It only works like this if you have two completely heterozygous individuals.
    • In other words, a cross of DdHh x DdHHwould not work.
dihybrid practice problem
Dihybrid Practice Problem
  • In pea plants, B is dominant for blue flowers and b is recessive for white flowers.
  • In pea plants, T is dominant for tall stems and t is recessive for short stems.
  • What is the likelihood of getting a short, blue-flowered plant from the following cross:
    • BBTt and bbtt
bbtt x bbtt

Question:

Answer:

BBTtxbbtt

Blue and Short?

8/16 or ½ or 50%

dihybrid practice problems
Dihybrid Practice Problems
  • Imagine that a man that can tongue-roll (T) marries a woman that can tongue-roll.
  • In addition, he has phantom fingers (F) and so does she.
  • They have a child.
  • What is the probability that their child is a tongue-roller without phantom fingers?
    • Cross is TtFf x TtFf
  • 3/16
dihybrid practice problems1
Dihybrid Practice Problems
  • Imagine that a man that can tongue-roll (T) marries a woman that cannot tongue-roll (t).
  • In addition, he has phantom fingers (F) while she does not (f).
  • They have a child.
  • What is the probability that their child is a non-tongue-roller with phantom fingers?
    • Cross is TtFf x ttff
  • 4/16 or ¼ or 25% or 1:3
dihybrid practice problems2
Dihybrid Practice Problems
  • Imagine that a man that can tongue-roll (T) marries a woman that cannot tongue-roll (t).
  • In addition, he has phantom fingers (F) while she does not (f).
  • They have a child.
  • What is the probability that their child is a non-tongue-roller with phantom fingers?
    • Cross is TtFF x ttff
  • 8/16 or ½ or 50% or 1:1
brief break
Brief Break
  • News: Disney Geneticists Debut New Child Stars
dihybrid practice problems3
Dihybrid Practice Problems
  • In certain flowers, “tall” is the dominant trait for height and “short” is recessive. Green flowers are dominant, yellow are recessive.
  • Imagine that a flower heterozygous for height and flower color is crossed with a flower also heterozygous for height and flower color.
  • They have flower children.
  • What is the probability that their first offspring is both tall and green?
    • Cross is TtGg x TtGg
  • 9/16
dihybrid practice problems4
Dihybrid Practice Problems
  • In certain flowers, “tall” is the dominant trait for height and “short” is recessive. Green flowers are dominant, yellow are recessive.
  • Imagine that a flower homozygous dominant for height and homozygous recessive for flower color is crossed with a flower heterozygous for height and flower color.
  • They have flower children.
  • What is the probability that their first offspring is both tall and green?
    • Cross is TTgg x TtGg
  • 8/16 or ½ or 50% or 1:1
the big picture
The Big Picture
  • So, before we get to our closure slide, what does the dihybridPunnett Square tell us about alleles in general?
  • It illustrates Mendel’s Law of Independent Assortment.
    • This is the idea that during meiosis, alleles separate mostly at random and come together independently in the finished gametes.
    • For example, alleles for “detached earlobes” and “hitchhiker thumb” are not inherited together.
      • Remember crossing over (synapsis)?
closure and homework
Closure and Homework
  • What are the “headings” for each side of the Punnett Square for the following cross:
    • HhMMxhhmm
  • Answer:
    • HM HM hMhM
    • hmhmhmhm
  • Homework: Pages 99, 156-157 in your Genetics Worksheets packet