Transcript Heredity - Madison County Schools

Heredity
2012-2013
Your Physical Appearance
• Heredity is the passing of
traits from parents to an
offspring.
• Gregor Mendel was the
first scientist to
successfully study
inheritance
• He is the “Father of
Genetics”
Why Pea Plants?
• Mendel use Garden Pea Plants for his
research because:
– They grow quickly
– They naturally self-pollinate
Mendel’s Success
• Mendel was successful with his pea
plant research because:
– he studied one trait at a time!
(independent variable)
– He had studied statistics
*A trait is a distinct phenotypic characteristic
that may be inherited
Pea Plant Traits
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Flower Color
Flower Position
Seed Color
Seed Shape
Pod Shape
Pod Color
Plant Height
The Experiment
• Mendel began by taking pure trait
plants and cross-pollinating them
• He did this by hand, not with bees!
The Experiment Part I
(Example 1)
Plant height
Mendel crossed a Tall parent plant with a short
parent plant:
Tall
TT
parent 1
x
short
=
x
tt
=
x
parent 1
=
All Tall
Tt
First Filial (F1)
The Experiment Part I
(Example 2)
Flower Color
Mendel crossed a Purple parent plant with a white
parent plant:
Purple
PP
parent 1
x
white
=
x
pp
=
x
parent 1
=
All Purple
Pp
First Filial (F1)
The Experiment Part II
• He wondered why one trait disappeared
when he crossed the two pure plants
• He decided to allow the new F1 plants
to naturally self-pollinate and here is
what he found……..
Example 1- Plant Height
F1 Tall plants
self-pollinate and
produce:
75% Tall Plants
25% short plants
Example 2 - Flower Color
F1 Purple Flower
color plants
self-pollinate and
produce:
75% Purple flowers
25% white flowers
Mendel’s Conclusion
• The Principle of Dominance and
Recessiveness states that one trait is
more likely to occur than the other.
– Dominant is a trait that is most likely to
occur
– Recessive is a trait that is usually hidden
in the first generation, but may reappear
later
Probability
• The chance or possibility that a certain
outcome will occur. Usually written as:
– Fractions
– Decimals
Let’s Learn a New Language..
Genotype- the genetic
make-up of an
organism (TT, Tt, tt)
Phenotype- the
physical appearance
of an organim (Tall,
short, Purple, white)
Dominant- more likely
to occur (The tall
plants or the purple
flowers)
Recessive- less likely
to occur (The short
plants or the white
flowers)
Let’s Learn a New Language..
• Homozygous- when both alleles are the
SAME
– Homozygous Dominant: TT, PP, WW
– Homozygous Recessive: tt, pp, ww
• Heterozygous- when each allele is
DIFFERENT
– Tt, Pp, Ww
Let’s Learn a New Language..
• An Allele is an alternate form of a gene;
one part of a pair
• A Gene is composed of two alleles, one
from each parent
Allele +
T(mom) +
Allele =
t(dad) =
Gene
Tt(child)
Punnett Squares
• Developed by
Rudolph Punnett to
make genetics
easier for us to
understand
Genetics Example 1
In garden pea plants, tall plants are dominant (T)
and short plants are recessive (t). A pea plant
that is homozygous dominant for height is crossed
with one that is homozygous recessive for plant
height.
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Draw a Punnett square to represent the problem.
What are the possible genotypes?
What are the possible phenotypes?
What is the probability of each genotype?
What is the probability of each phenotype?
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Genotypes
Phenotypes
Probability of genotypes
Probability of phenotypes
Genetics Example 2
In garden pea plants, purple flower color (P) is
dominant over white flower color (p). A pea plant
that is homozygous recesive for flower color is
crossed with one that is heterozygous for flower
color.
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Draw a Punnett square to represent the problem.
What are the possible genotypes?
What are the possible phenotypes?
What is the probability of each genotype?
What is the probability of each phenotype?
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Genotypes
Phenotypes
Probability of genotypes
Probability of phenotypes
Genetics Examples
In garden pea plants, yellow seeds (Y) are
dominant and green seeds (y) are recessive.
What offspring would result if two heterozygous
plants were crossed?
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•
•
Draw a Punnett square to represent the problem.
What are the possible genotypes?
What are the possible phenotypes?
What is the probability of each genotype?
What is the probability of each phenotype?
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•
•
•
Genotypes
Phenotypes
Probability of genotypes
Probability of phenotypes
More Genetics
Incomplete Dominance
• Sometimes one trait is not
completely dominant over
the other
– The same letter allele is used
– Red x White = Pink
RR x R’R’ = RR’
• This results with a combined
genotype
– Snap dragons
Codominance
• Sometimes both traits
are equally dominant
– Different letter alleles
are used
– Black x White =
Checkered
BB
x
WW =
BW
• This results in both
traits being expressed
– Checkered Chickens
Alternate forms of Genetics
• Gregor Mendel studied simple genetic
inheritance:
– Offspring were either dominant or
recessive
• But not all traits are simple!!
Thomas Hunt Morgan
• Studied Fruit Flies
• Discovered
– Gender inheritance
– Other traits associated with
gender
Gender
• Gender is always
determined by
the male
QuickTime™ and a
decompressor
are needed to see this picture.
Sex-linked Traits
• Some traits are only located on the “X”
chromosome
• Since Males only have one “x”
chromosome, they are more likely to
show the trait than a female with two “x”
chromosomes
Sex-linked Traits
• Colorblindness
• Hemophilia
• Muscular
dystrophy
Other Types of Inheritance
Insert chart here
Meiosis
• Meiosis is the formation of gametes in
sexually reproducing organisms
– Sperm (male)
– Egg (female)
Benefits of Meiosis
• Forms gametes (sex cells)
• Allows for genetic variation
• Reduces the number of chromosomes by half
– Human body cells 46 chromosome
– Human sex cells 23 chromosome
• Allows the chromosome number of any
organism to remain consistent
Haploid vs Diploid
• Haploid cells contain 1 set of
chromosomes (23 total in humans)
– Sperm
– Egg
• Diploid cells contain 2 sets of
chromosomes (46 total in humans)
– One set from mom
– One set from dad
Meiosis
Male vs Female Meiosis
Karyotype
• A karyotype is a picture of someone’s
chromosomes
Male Karyotype
Female Karyotype
What do you think?
Genetic Disorders
• Genetic disorders are caused by
mutations in DNA
– Mutations that occur spontaneously
– Congenital ( people are born with them)
– Unable to cure
– Can occur in children even when parents
do not have them (recessive traits)
Genetic Counselors
• Genetic counselors are available for people
who fear passing genetic disorders to their
offspring
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Cystic fibrosis
Sickle-cell anemia
Huntington’s disease
Down’s syndrome
Many others
• They begin with making a pedigree to observe
the family history of traits
Pedigree
• A pedigree is
a map of a
family genetic
history
Genetics in Action
Selective Breeding
Genetic Engineering
Genetics Terminology
• Purebred organisms result from
crossing two organims with similar traits
• Hybrids are produced when two
organisms with different traits are
combined
Purebred
• Advantages
– Predictable outcome
Example:
Dog breeds
Lab x Lab = Lab
LL x LL = LL
• Disadvantages
– Undesirable traits
are possible
– A lack of genetic
variation will result
Hybrids
• Advantages
– Variety of traits may
appear
– Can encourage
desirable traits to
occur
Example:
kiwi x strawberry =
kiwiberry
• Disadvantage
– Unpredictable
outcomes are likely
Selective Breeding
• Selective breeding involves the crossing of
organisms with desired traits to maximize
their potential
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Fruits
Vegetables
Flowers
Livestock
Insulin
Genetic Engineering
• A faster form of selective breeding
• Genetic engineering is when genetic
information is changed within the DNA
of an organism