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 H = hard fruit h = soft fruit In This Lesson: Dihybrid Crosses (Lesson 4 of 6)

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 TED: Hortensia Jiménez Díaz – How Mendel’s Pea Plants Helped Us Understand Genetics

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… 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 1.Identify the parent genotypes. – DdHh and DdHh 2.FOIL the genotypes. – First, Outer, Inner, Last – DH, Dh, dH, dh 3.Place one FOIL result across the top, the other down the side of a 4x4 square. 4.Solve as normal.

FOILing How to FOIL: – [First, Outer, Inner, Last] DdHh First Outer Inner Last DH Possible Allele Combinations Dh dH dh

DHDhdHdh DHDDHHDDHhDdHHDdHh DhDDHhDDhhDdHhDdhh dHDdHHDdHhddHHddHh dhDdHhDdhhddHhddhh 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? 9:3 :1

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 DdHH would not work.

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 bt BTBbTt BtBbtt BTBbTt BtBbtt Blue and Short? Question: 8/16 or ½ or 50% Answer:

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 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 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 News: Disney Geneticists Debut New Child Stars

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 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 So, before we get to our closure slide, what does the dihybrid Punnett 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 What are the “headings” for each side of the Punnett Square for the following cross: – HhMM x hhmm Answer: – HM HM hM hM – hm hm hm hm Homework: Pages 99, in your Genetics Worksheets packet