Transcript Mendel’s Peas - rcschools.net

Introduction to Genetics
Heredity and Mendel’s Peas
Mrs. Stewart
Honors Biology
Central Magnet School
Standards:
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
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CLE 3210.4.1 Investigate how genetic
information is encoded in nucleic acids.
CLE 3210.4.2 Describe the relationships
among genes, chromosomes, proteins, and
hereditary traits.
CLE 3210.4.3 Predict the outcome of
monohybrid and dihybrid crosses.
Objectives:

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Differentiate between characteristics
and traits
Analyze Mendal’s principle of
dominance
Predict genotype based on phenotype
Analyze characteristics and traits in
this classroom
Decide with your partner
What is heredity?
Why do family’s look alike?
Heredity & Genetics

Heredity - The transmission of
characteristics from parents to
offspring
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Genetics – the study of heredity

Genes – Segments of DNA that code
for a characteristic
Characteristics vs. Traits

Characteristic – a feature


Example: flower color, hair color, number
of fingers on your hand
Trait – a genetically determined
variant of a characteristic

Example: purple flower color vs white,
having 6 fingers instead of 5
Dogs
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Tell your cats two examples of
characteristics that can be inherited
from human parents to offspring.
Cats

Give your dogs an example of traits
(variations) for the characteristics
he/she listed.
Gregor Mendel (1822-1884)
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“Father of Genetics”
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Austrian Monk
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Studied characteristics & traits in pea plants
 Have only 7 chromosomes
 Can cross pollinate or self pollinate
Flower Reproduction Reminder:
Gregor Mendel’s Peas
•
“Self pollination”Pollen from the plant
fertilizes its own eggs
•
•
Similar to asexual
reproduction.
“True-breeding” produce identical new
plants.
•
“Purebreds”
Mendel’s Peas
•
•
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“Cross-pollination”
Remove male parts
from true breeding
plant, pollinate it
with pollen from a
plant with different
traits.
Produce “hybrids”
•
Genetically
different
Mendel’s Observations
Traits
Characteristics
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Seed shape
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wrinkled or smooth
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Seed color
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yellow or green
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Seed coat color
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white or grey
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Pod shape
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smooth or constricted
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Pod color
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green or yellow
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Flower position
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axial or terminal
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Plant height
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tall or short
Genotype VS. Phenotype
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GENOTYPE: actual combination of alleles
(genes) inherited from parents.
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(One from MOM, and one from DAD.)
Example: Tt, TT or tt
PHENOTYPE: physical
appearance/expression of the trait.

Example: Tall plant or short plant
Alleles
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We use letters to represent the
variations
Capital Letters = Dominant allele
Lowercase letters = recessive allele
Example: T = tall plant, t = short plant
Most genes have two or more variations
(alleles)
Cats and Dogs
(think – pair – share)
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Phenotype
Widows Peak or straight
hair line
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Genotype
Ww, WW or ww
Important Vocabulary Terms

HETEROzygous:
(DIFFERENT)

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HYBRID = offspring of
heterozygous parents
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PUREBRED (truebreeding) = offspring of
homozygous parents –
will produce offspring
identical to parent traits
have different
alleles
Example: Tt
HOMOzygous :
(SAME)

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have the same
alleles.
Example: TT or tt
Generations
•
The parent
generation
•
The first
generation
•
The second
generation
Mendel’s experiments
P – Purebred Tall x
Purebred Short
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F1 – All tall
(hybrids)
F2 – 3:1 ratio tall:short
Tall height “masks” the effects of short height.
Tall is “dominant”; Short is “recessive”.
Principle of Dominance
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some variations are dominant over
others
Dominant traits will mask or hide the
presence of a recessive trait
Recessive traits are hidden/masked by
a dominant allele
Principle of Dominance –
UFC style
Only one can win
•Matt Hughes = Recessive
•BJ Penn = Dominant
Principle of Dominance
Cats And Dogs
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The dominant trait is “gray” fur, and the
recessive trait is “white” fur. Lets use the
following alleles: Gray is G. White is g.
If a bunny is heterozygous gray: Gg
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If a bunny is homozygous white:
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What is the genotype? ______________
What is the genotype? ______________
If a plant is homozygous gray:

gg
GG
What is the genotype? ______________
Principles of Dominance
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Predictable patterns of dominant and
recessive only apply to single gene traits
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Example: ONE gene is responsible for the
type of hairline we have

There are 2 alleles (variations) for this gene

Possible Phenotypes: widow’s peak (W) or
straight hairline (w)
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Possible Genotypes: WW, Ww or ww
Dominance VS. Commonality
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Does “dominant” mean most common?
Not necessarily
Examples:
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Polydactyl – having 6 fingers
Achondroplasia – Dwarfism
O blood type (recessive)
Group Activity
 Inventory
of Traits
Dogs and Cats
Predict you and your partners possible genotypes
for the phenotypes listed in traits activity.
Objectives:




Differentiate between characteristics
and traits
Analyze Mendal’s principle of
dominance
Predict genotype based on phenotype
Analyze characteristics and traits in
this classroom