th
8
Grade Do Now 11/17/2011
• Essential Question – How can determine the phenotypes for
multiple alleles?
• Objective –
– Identify what controls the inheritance of traits in an
organism
– Explain the relationship between chromosomes and genes.
– Complete dihybrid and Punnett Squares to determine the
traits of a genetic cross.
• Homework – Complete Solving Dihybrid and Complex
Monohybrid Punnett Square Problems 1 – 6 and 8-11
• If you need help, please look at my website under Punnett
Square tutorials for assistance.
• Do Now – Take out your vocabulary words and your
Punnett Square Activity Packet and study it for five
minutes.
YOU ARE HAVING A QUIZ TODAY!!
Finished with your quiz?
• Turn it into your class period bin.
• Pick up Complete Solving Dihybrid and
Complex Monohybrid Punnett Square
Problems pages from the front table and
staple them in order.
• Begin reading pages 330 – 333
• DO NOT TALK UNTIL EVERYONE IS
FINISHED WITH THE QUIZ!
th
8
Grade Do Now 11/18/2011
• Essential Question – How can determine the phenotypes for
multiple alleles?
• Objective –
– Identify what controls the inheritance of traits in an
organism
– Explain the relationship between chromosomes and genes.
– Complete dihybrid and Punnett Squares to determine the
traits of a genetic cross.
• Homework – Complete Solving Dihybrid and Complex
Monohybrid Punnett Square Problems 1 – 6 and 8-11
• If you need help, please look at my website under Punnett
Square tutorials for assistance.
• Do Now –
Do you think it is possible to use a Punnett Square to
determine more than one allele combination?
Gene Interactions
Solving Dihybrid and Complex
Monohybrid Punnett Square
Problems
Monohybrid Crosses
• Up to now we have been doing
monohybrid crosses
R
r
R
RR
Rr
r
Rr
rr
Dihybrid crosses
• A dihybrid cross in involves studying the
inheritance of two traits simultaneously
• Mendel invented the dihybrid cross to
determine if different traits, such as seed
color and seed texture, were inherited
independently or if they were somehow
“linked” to each other
Law of Independent Assortment
• When gametes are formed, the
segregation of one gene pair (the Y’s)
does not affect the segregation of the
other gene pair (the R’s)
Y = yellow
(yellow, round)
y = green
YyRr
R = round
r = wrinkled
yr
YR
Yr
yR
These are the 4 gametes that can be made
from this parent
Solving the Squares
• Cross a green, heterozygous round
parent with a heterozygous yellow,
heterozygous round parent
• yyRr X YyRr
yyRr X YyRr
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
yyRr X YyRr
YR
Yr
yR
yr
yR
YyRR
YyRr
yyRR
yyRr
yr
YyRr
Yyrr
yyRr
yyrr
yR
YyRR
YyRr
yyRR
yyRr
yr
YyRr
Yyrr
yyRr
yyrr
Phenotypes
1
9
2
10
3
11
4
12
5
13
6
14
7
15
8
16
Phenotypes
1
Yellow round
9
Yellow round
2
Yellow round
10
Yellow round
3
Green round
11
Green round
4
Green round
12
Green round
5
Yellow round
13
Yellow round
6
Yellow wrinkled
14
Yellow wrinkled
7
Green round
15
Green round
8
Green wrinkled
16
Green wrinkled
To find the Genotypic Ratio
• Write down all possible allele
combinations.
• Count how many of each combination.
• If you wanted to find the fraction put that
number over 16. (Reduce if necessary)
The Genotypic Ratio =
2 YyRR : 4 YyRr : 2 Yyrr : 2 yyRR : 4 yyRr : 2 yyrr
yyRr X YyRr
YR
Yr
yR
yr
yR
YyRR
YyRr
yyRR
yyRr
yr
YyRr
Yyrr
yyRr
yyrr
yR
YyRR
YyRr
yyRR
yyRr
yr
YyRr
Yyrr
yyRr
yyrr
To Find the Phenotypic Ratio
• Write down all of the possible phenotypic
allele combinations
– For example:
– Yellow and Round
• Count how many of each combination
there is.
The Phenotypic Ratio =
6 Yellow round : 6 green round : 2 yellow wrinkled :
2 green wrinkled