Review

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Review

• Monohybrid Dihybrid Crosses

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DOMINANT/RECESSIVE
Dominant

• _____________ allele is represented by a
  ____________ letter.(usually the first letter of
  the trait)
• ____________ allele is represented by the SAME
• _________________ letter.
• EX Tall ______
• Short ______

capital
Recessive
lower-case
T
t
NOT S for short
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HOMOZYGOUSHETEROZYGOUS

• When both alleles in the pair are the _______,
  the organism is _______________ or
  __________
• EX ____ or ___
• When both alleles in the pair are _____________,
  the organism is
• _________________ or _____________
• Ex ____

SAME
HOMOZYGOUS PURE
TT tt
DIFFERENT
HETEROZYGOUS HYBRID
Tt
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PHENOTYPE/GENOTYPE

• The ________________ of an organism is its
  _____________
• The ____________of an organism is
• its _____________

genetic makeup
GENOTYPE
appearance
PHENOTYPE
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MAKING A CROSS for only a __________ trait
____________________
ONE GENE
MONOHYBRID CROSS

• A Punnett square for a MONOHYBRID CROSS looks
  like this

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PUNNETT SQUARES

• are used to show possible offspring from a cross
  between 2 parents

_______________ go at top and on left
side Boxes show _______________________________
Parent alleles
T T


T t
possible offspring combinations
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STEPS FOR MAKING CROSSES
Figure out parent alleles Choose
Punnett size Put in
parent gametes Fill in offspring
combinations probabilities
phenotypes
genotypes
1. ___________ what _________________ are 2.
________correct__________ square __________ 3.
______ possible_______________________ 4. ______
boxes with _____________________ 5. Determine
____________of_____________
____________
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IN PEA PLANTS

• Tall is dominant over short
• TALL ____
• SHORT ____

T
t
LETS MAKE A CROSS! PURE TALL PURE
SHORT
X
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PURE TALL parentWhat are the parent alleles?

• T T _________

HOMOZYGOUS
?
?
What gametes can it make?
T
T
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PURE SHORT parent What are the parent alleles?

• t t _________

HOMOZYGOUS
?
?
What gametes can it make?
t
t
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ALL

• _____ of the offspring
• ____
• ___/4
• will be

T t
T t
100
4
T t
T t
Tt
TALL
GENOTYPE _____ PHENOTYPE _______
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HYBRID TALL parent What are the parent alleles?

• T t _________

HETEROZYGOUS
?
?
What gametes can it make?
T
t
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T
t

• GENOTYPES
• ¼ _____
• ½ _____
• ¼ _____

TT
T
T t
T T
Tt
tt
T t
t t
t
75
3/4
TALL
PHENOTYPES ____ or ____ _________
____ or ____ _________
1/4
SHORT
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PRACTICE MAKING GAMETES for a MONOHYBRID CROSS
R
Tall ____ Round seeds ___ Short
____ Wrinkled seeds ___
T
t
r
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What are the possible gametes?

• Homozygous Tall parent
• What gametes can it produce?

T T
?
?
T
T
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What are the possible gametes?

• PURE wrinkled parent
• What gametes can it produce?

rr
?
?
r
r
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What are the possible gametes?

• Heterozygous Round parent
• What gametes can it produce?

R r
?
?
R
r
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What are the possible gametes?

• Hybrid Tall parent
• What gametes can it produce?

Tt
?
?
T
t
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DIHYBRID CROSSES

• (2 traits)

http//mac122.icu.ac.jp/BIOBK/BioBookgenintro.html
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• Mendel also asked the question?
• Does the gene that determines if a seed
• is round or wrinkled have anything to
• do with the gene for seed shape?
• Must a seed that is yellow
• also be round?

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MAKING A CROSS with ___________________________
____________
TWO gene traits
DIHYBRID CROSS

• A Punnett square for a DIHYBRID CROSS looks like
  this

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Figure 11-10 Independent Assortment in Peas
Section 11-3
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LETS MAKE A DIHYBRID CROSS

• HOMOZYGOUS
• YELLOW ROUND

HOMOZYGOUS GREEN WRINKLED
rryy
RRYY
1. ___________ what _________________ are 2.
________correct__________ square __________ 3.
______ possible_______________________ 4. ______
boxes with _____________________ 5. Determine
____________of_____________
____________
Figure out parent alleles Choose
Punnett size Put in
parent gametes Fill in offspring
combinations probabilities
phenotypes
genotypes
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• LAW OF __________________________
• the factors are distributed to gametes
  independently of other factors

INDEPENDENT ASSORTMENT
Image modified from http//anthro.palomar.edu/me
ndel/mendel_1.htm
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PRACTICE MAKING GAMETES
WHAT ARE THE POSSIBLE GAMETES THIS PARENT CAN
MAKE?

HOMOZYGOUS ROUND YELLOW
Each gamete shouldget one of each kindof gene
R R Y Y
R Y
R Y
R Y
R Y
___________ ____________ _____________
_____________
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PRACTICE MAKING GAMETES
WHAT ARE THE POSSIBLE GAMETES THIS PARENT CAN
MAKE?

Each gamete shouldget one of each kindof gene
HOMOZYGOUS WRINKLED GREEN
r r y y
r y
r y
r y
r y
___________ ____________ _____________
_____________
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PRACTICE MAKING GAMETES
WHAT ARE THE POSSIBLE GAMETES THIS PARENT CAN
MAKE?

HETEROZYGOUSROUND YELLOW
Each gamete shouldget one of each kindof gene
R r Y y
R Y
r y
r Y
R y
___________ ____________ _____________
_____________
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RrYy RrYy RrYy RrYy RrYy RrYy RrYy
RrYy RrYy RrYy RrYy RrYy RrYy
RrYy RrYy RrYy
RrYy
100 of offspring _______ genotype
_______________________ phenotype
ROUND YELLOW
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MAKE ANOTHER CROSS
HETEROZYGOUSROUND YELLOW
HETEROZYGOUSROUND YELLOW
X
R r Y y
R r Y y
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POSSIBLE PARENT GAMETES?
RY
Ry
ry
ry
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____ Round Yellow ____ Round
green ____ Wrinkled
yellow ____ wrinkled green
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RRYY RRYy RrYY RrYy RRYy RRyy RrYy
RryyRrYY RrYy rrYY rrYy RrYy Rryy
rrYy rryy
3
3
1
heterozygous dihybrid
Sign of a ______________________ cross is
a _____________ ratio in offspring.

9331
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9
____ ____________ TRAIT 1 ____________ TRAIT
2 ____ ____________ TRAIT 1
_____________ TRAIT 2 ____ ____________ TRAIT
1 _____________ TRAIT 2 ____ ____________
TRAIT 1 _____________ TRAIT 2
dominant dominant
3
dominant recessive
3
recessive dominant
1
recessive recessive
__________ratio is a clue that its a
____________________________cross
9331
HETEROZYGOUS TWO gene

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PRACTICE MAKING GAMETESfor DIHYBRID CROSSES
http//www.emc.maricopa.edu/faculty/farabee/BIOBK/
BioBookTOC.html
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What are the possible gametes?
R R T T

• pure round pure tall __________
• ____ ____ _____ ______
• What gametes can it produce?

?
?
?
?
R T
R T
R T
R T
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What are the possible gametes?
T t R R

• Heterozygous Tall __________
• pure round
• ____ ____ _____ ______
• What gametes can it produce?

?
?
?
?
T R
T R
t R
t R
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What are the possible gametes?
T t r r

• Hybrid tall __________
• pure wrinkled
• ____ ____ _____ ______
• What gametes can it produce?

?
?
?
?
T r
T r
t r
t r
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What are the possible gametes?
T t R r

• Heterozygous tall __________
• hybrid round
• ____ ____ _____ ______
• What gametes can it produce?

?
?
?
?
T R
T r
t r
t R
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The Law of Dominance In a cross of parents that
are pure for contrasting traits, only one form of
the trait will appear in the next generation. 
Offspring that are hybrid for a trait will have
only the dominant trait in the phenotype. The
Law of Segregation During the formation of
gametes (eggs or sperm), the two alleles
responsible for a trait separate from each
other.  Alleles for a trait are then "recombined"
at fertilization, producing the genotype for the
traits of the offspring. The Law of Independent
Assortment Alleles for different traits are
distributed to sex cells ( offspring)
independently of one another.
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MENDEL'S GENETIC LAWS Summary
LAW PARENT CROSS OFFSPRING
DOMINANCE TT x tt tall x short 100 Tt tall
SEGREGATION Tt x Tt tall x tall 75 tall 25 short
INDEPENDENT ASSORTMENT RrGg x RrGg round green x round green 9/16 round seeds green pods 3/16 round seeds yellow pods 3/16 wrinkled seeds green pods 1/16 wrinkled seeds yellow pods