What are the Key points?. Mendel Genetics and Punnett Squares Origin of Genetics Steps of a...
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Transcript of What are the Key points?. Mendel Genetics and Punnett Squares Origin of Genetics Steps of a...
![Page 1: What are the Key points?. Mendel Genetics and Punnett Squares Origin of Genetics Steps of a Monohybrid cross Terminology Practice Punnett Squares Determining.](https://reader035.fdocuments.net/reader035/viewer/2022062714/56649d0b5503460f949df846/html5/thumbnails/1.jpg)
What are the Key points?
![Page 2: What are the Key points?. Mendel Genetics and Punnett Squares Origin of Genetics Steps of a Monohybrid cross Terminology Practice Punnett Squares Determining.](https://reader035.fdocuments.net/reader035/viewer/2022062714/56649d0b5503460f949df846/html5/thumbnails/2.jpg)
What are the Key points?
![Page 3: What are the Key points?. Mendel Genetics and Punnett Squares Origin of Genetics Steps of a Monohybrid cross Terminology Practice Punnett Squares Determining.](https://reader035.fdocuments.net/reader035/viewer/2022062714/56649d0b5503460f949df846/html5/thumbnails/3.jpg)
Mendel Genetics and Punnett Squares
Origin of GeneticsSteps of a Monohybrid cross
TerminologyPractice
Punnett SquaresDetermining Unknown
Genotypes
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The Origin of Genetics
• Heredity- the passing of characteristics from parents to offspring
• Genetics- the branch of Biology that focuses on heredity
• Cross- combining traits from two parents by breeding (sexual reproduction)
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The Origin of Genetics• Gregor Mendel
– Austrian monk – Studied theology, science and
mathematics– Noticed patterns in the pea
plants he was growing– Mendel crossed pea plants and
studied the resulting off-spring– Was the first to develop rules
that accurately predict patterns of heredity
– Father of genetics
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The Origin of Genetics
Monohybrid cross- a cross that involved one pair of contrasting traits
Ex. Crossing a white flower with a purple flower.
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Steps of a Monohybrid cross
1. Ensure each variety is true-breeding for a particular characteristic
Ex. A true-breeding purple flower will produce only purple flowers
• These are the 1st two individuals crossed- P generation (parental generation)
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Steps of a Monohybrid Cross
2. Cross-pollinate two P-generation plantsEx. A true breeding purple flower crossed with a true-breeding white flower
• The offspring are called F1 generation (filial generation)
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Steps of a Monohybrid Cross
3. Self-pollinate the F1 generation to create the F2 generation (second filial generation)
– This creates a 3:1 ratio
True breeding
P generation F1 generation
F2 generation
Self pollinate
Self pollinate
Cross
Self pollinate
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Terminology
• Alleles- alternative versions of genes– The gene for hair color can have
multiple alleles (blonde hair allele, brown hair allele, etc)
• Dominant- the expressed (visible) trait
• Recessive- the trait that is not expressed or observable
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Terminology
• Homozygous- when two alleles of a particular gene are the same – (PP), (pp), (RR), (rr), (VV), (vv), etc
• Heterozygous- when two alleles of a particular gene are different– Only the dominant allele is expressed while
the recessive is present, but not expressed– (Pp), (Rr), (Vv), etc
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Terminology• Genotype- the set of alleles an individual
has for a trait– think “genes” and “letters”– (Rr), (RR) or (rr)– (Vv), (VV) or (vv)
• Phenotype- the physical appearance of a trait– Think “face” and “colors”– White, purple, red, blonde, freckles, blue eyes,
etc
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Practice
(assume that P is purple and p is white)
(Pp):What is the genotype?What is the phenotype?Is it homozygous or heterozygous?
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Practice
(assume that P is purple and p is white)
(pp):What is the genotype?What is the phenotype?Is it homozygous or heterozygous?
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Practice
(assume that P is purple and p is white)
(PP):What is the genotype?What is the phenotype?Is it homozygous or heterozygous?
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Punnett Squares
• Punnett square- is a diagram that predicts the outcome of a genetic cross by considering all possible combinations
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Punnet Squares• Ex. Having freckles (F) is dominant to
not having freckles (f). Parent 1 is heterozygous for freckles and Parent 2 is also heterozygousParent 1
Parent 2
F
F F F F
Ff
f
f
f f f
Phenotype ratio?
3:1
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Punnett Squares
Box 1 is homozygous for….Box 2 and 3 is…..Box 4 is….
F
F FF
F
F
f
f
f
f f f
1 2
3 4
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Punnett Squares
• Ex. A homozygous yellow pea plant (Y) is dominant over a homozygous green pea plant (y).
Y Y
y
y
Y
Y
Y
Y
y y
y y
What’s the genotype of all offspring?
What’s the phenotype of all offspring?
Yy
yellowWhat’s the
phenotypic ratio?
4:0
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Determining Unknown Genotypes
• When a phenotype is dominant but the genotype is not known, a test cross is performed.– You cross the unknown genotype
with a homozygous recessive individual
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Determining Unknown Genotypes
What does that mean? You can physically see that the pea plant
is yellow, but you don’t know if they are (YY) or (Yy).
So, you cross the yellow pea plant with a recessive pea plant (yy) that is green.
If the offspring are all yellow the genotype is (YY)
If the offspring are ½ yellow and ½ green the genotype is (Yy)
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Determining Unknown Genotypes
• Doesn’t make sense? Use the Punnett Square and work backwards!
Known, recessive genotype
Unknown genotype
y y
Y
???
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Heterozygous Bb Hybrid
Homozygous BB Pure
Genotype Genetic
Make-up
bb
Phenotype Physical Characteristic
Blond Hair
Mom’s genotype
Dad’s genotype