Warm- Up # 4
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What is a dominant trait?
What is a recessive trait?
Is “Bb” genotype or phenotype?
Is black hair genotype or phenotype?
Which of these is heterozygous:
A. TT
B. Tt
C. tt
Learning Target
1/31
• I can determine the genotype and phenotype
of a monohybrid cross using a Punnett Square
Vocab Review
• Genotype - the genetic make-up of an
organism
HH: homozygous dominant
Hh: heterozygous dominant
hh: homozygous recessive
• Phenotype: the way an organism looks or
behaves based on the genotype (trait)
Examples: left-handed, brown eyes, long nose
CH 11 Punnett
Squares Notes
Mendel’s Law of Segregation
Alleles separate during
meiosis
Rr
R
R
Sperm
r
r
Sperm
Mendel’s Law of
Independent Assortment
An individual can give lots of
combinations of alleles
RrGg
RG
Rg
rG
rg
Punnett Squares
• Punnett Square - a tool used to predict the
genotype of an organism’s offspring
Bb
Female
Bb
Male
Example Punnett Square
• Trait: Body Color
dominant = green body (G)
recessive = blue body (g)
Parent #1: Gg
Parent #2: Gg
G
g
G
GG
Gg
g
Gg
gg
Example Punnett Square
G
g
G
g
GG
Gg
Gg
gg
dominant = green body (G)
recessive = blue body (h)
• Possible Offspring Genotypes:
1 GG
25%
2 Gg
50%
1 gg
25%
Possible Offspring
Phenotypes:
3 green body 75%
1 blue body
25%
Practice Problem #1
• Trait: Human Eye Color
dominant = brown eyes (B)
recessive = blue eyes (b)
Parent #1: BB
Parent #2: Bb
B
B
B
BB
BB
b
Bb
Bb
Practice Problem #1
B
B
B
BB
BB
b
Bb
Bb
• Possible Offspring Genotypes:
2 BB
50%
2 Bb
50%
Possible Offspring Phenotypes:
4 brown eyes 100%
0 blue eyes
0%
Practice Problem #2
• In many animals black fur
is dominant (B) and
brown fur is recessive (b).
• Complete the Punnett
b
Square for
Female dog-Bb
Male dog- bb
b
B
b
Bb
bb
Bb
bb
Practice Problem #2
B
b
b
Bb
bb
b
Bb
bb
• Possible genotypes:
2 Bb
50%
2 bb
50%
• Possible phenotypes:
2 Black fur dog 50%
2 Brown fur dog 50%
Practice Problem #3
• In people right-handed
is dominant (R)
and left-handed is
recessive (r)
• Complete the Punnett
Square for:
Heterozygous parent
Homozygous recessive
parent
R
r
r
Rr
rr
r
Rr
rr
Practice Problem #3
R
r
r
Rr
rr
r
Rr
rr
• Possible genotypes:
2 Rr
50%
2 rr
50%
• Possible phenotypes:
2 Right-handed 50%
2 Left-handed 50%
Monohybrid cross
• Homozygous dominant + homozygous recessive
• Example: BB x bb, HH x hh
B
B
b
Bb
Bb
b
Bb
Bb