Transcript Mendel and Genetics

Intro…GENETICS
MENDEL & MEIOSIS
MENDEL’S LAWS OF HEREDITY
I. WHY MENDEL SUCCEEDED
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Gregor Mendel – father of genetics
1st studies of heredity – the passing of
characteristics to offspring
Genetics – study of heredity
The characteristics passed on called traits
1. MENDEL CHOSE HIS
SUBJECT CAREFULLY
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Used garden peas for a model organism
Have male & female gametes (sex cells)
Male & female same flower
Know what pollination & fertilization mean
He could control the fertilization process
Not many traits to keep track of
2. MENDEL WAS A CAREFUL
RESEARCHER
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USED CAREFULLY CONTROLLED
EXPERIMENTS
STUDIED ONE TRAIT AT A TIME
KEPT DETAILED DATA
II. MENDEL’S MONOHYBRID
CROSSES
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MENDEL STUDIED 7 TRAITS CAREFULLY
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seed shape/color, flower color/position, pod
color/shape, plant height
Mendel crossed plants w/ diff. traits to see
what traits the offspring would have
These offspring are called hybrids –
offspring of parents w/ different traits
A monohybrid cross is one that looks at
only one trait (let’s look at plant height –
tall or short)
A. THE 1ST GENERATION
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Mendel crossed two plants – 1 tall & 1
short
These plants are called the parental
generation (P generation)
The offspring were all called the 1st filial
generation (F1 generation)
All the offspring were tall
B. THE 2ND GENERATION
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Next, Mendel crossed two plants from the
F1 generation
The offspring from this cross are called
the 2nd filial generation (F2 GENERATION)
Mendel found that ¾ of the offspring
were tall & ¼ were short (the short plants
reappeared!!!!!!)
VOCABULARY:
Allele
Genotype
Phenotype
Dominant
Recessive
Trait
Heterozygous
Homozygous
Laws:
Independent
Assortment
Segregation
TO GO ANY FURTHER, WE
MUST UNDERSTAND ALLELES,
DOMINANCE, & SEGREGATION
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Genes – a section of DNA that codes for
one protein
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These genes are what control & produce traits
The genes Mendel studied came in two
forms (tall/short - round/wrinkled
yellow/green…….etc.)
Alternate forms of a gene are called alleles
Alleles are represented by a one or two
letter symbol (e.g. T for tall, t for short)
ALLELES CONT’D
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THESE 2 ALLELS ARE NOW KNOWN TO BE
FOUND ON COPIES OF CHROMOSOMES –
ONE FROM EACH PARENT
THE RULE OF DOMINANCE
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A dominant trait is the trait that will always be
expressed if at least one dominant allele is
present
The dominant allele is always represented by
a capital letter
A recessive trait will only be expressed if both
alleles are recessive
Recessive traits are represented by a lower
case letter
DOMINANCE CONT’D
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LET’S USE TALL & SHORT PEA PLANTS
FOR AN EXAMPLE
WHICH OF THESE WILL SHOW THE
DOMINANT & RECESSIVE TRAIT?
TT
Tt
DOMINANT TRAIT
tt
RECESSIVE TRAIT
THE LAW OF SEGREGATION
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MENDEL ASKED HIMSELF……..”HOW DID
THE RECESSIVE SHORT PLANTS
REAPPEAR IN THE F2 GENERATION?”
HE CONCLUDED THAT EACH TALL PLANT
FROM THE F1 GENERATION CARRIED
TWO ALLELES, 1 DOMINANT TALL ALLELE
& ONE RECESSIVE SHORT ALLELE
SO ALL WERE Tt
SEGREGATION CONT’D
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HE ALSO CONCLUDED THAT ONLY ONE
ALLELE FROM EACH PARENT WENT TO
EACH OFFSPRING
HIS CORRECT HYPOTHESIS WAS THAT
SOMEHOW DURING FERTILIZATION, THE
ALLELES SEPARATED (SEGREGATED) &
COMBINED WITH ANOTHER ALLELE
FROM THE OTHER PARENT
The law of segregation states that during
gamete formation, the alleles separate to
different gametes
F1 GENERATION
TT
FATHER
MOTHER
Tt
T t
Tt
tt
F2 GENERATION
- the law of dominance explained the
heredity of the offspring of the f1
generation
- the law of segregation explained the
heredity of the f2 generation
PUNNETT SQUARE
CROSS T T X Tt
CONT’D
TT X Tt
T
T
T
T
T
T
T
t
T
t
T
t
PHENOTYPES & GENOTYPES
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PHENOTYPE – The Physical appearance – how
an organism looks – the Trait
GENOTYPE – the Allele combination…Aa or AA
or aa…….also Ttyy or ttyy or TTYY
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HOMOZYGOUS – 2 ALLELES SAME
HETEROZYGOUS – 2 ALLELES DIFFERENT
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Like Homo-Sexual…
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Same gender couple
Hetero-Sexual
Different gender couple
ANSWER ON YOUR SHEET
TRAITS = BLUE SKIN & YELLOW SKIN
BB – IS THIS HOMOZYGOUS OR
HETEROZYGOUS?
HOMOZYGOUS
IS BLUE SKIN OR YELLOW SKIN
DOMINANT?
BLUE
MENDEL’S DIHYBRID CROSSES
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MONOHYBRID – MENDEL LOOKED AT
ONE TRAIT
IN HIS DIHYBRID CROSSES – HE LOOKED
AT 2 TRAITS
WANTED TO SEE IF TRAITS ARE
INHERITED TOGETHER OR
INDEPENDENTLY
DIHYBRID CROSS
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TOOK TWO TRUE BREEDING PLANTS FOR
2 DIFFERENT TRAITS (ROUND/WRINKLED
SEEDS ------- YELLOW/GREEN SEEDS)
1ST GENERATION
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WHAT WOULD HAPPEN IF HE CROSSED JUST
TRUE BREEDING ROUND W/ TRUE BREEDING
WRINKLED (ROUND IS DOMINANT)
ALL THE OFFSPRING ARE
ROUND
DIHYBRID CROSS – 1ST
GENERATION CONT’D
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SO WHAT DO YOU THINK HAPPENED
WHEN HE CROSSED TRUE BREEDING
ROUND/YELLOW SEEDS WITH TRUE
BREEDING WRINKLED/GREEN SEEDS
ALL THE F1 WERE ROUND
AND YELLOW
DIHYBRID CROSS – 2ND
GENERATION
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TOOK THE F1 PLANTS AND BRED THEM
TOGETHER (PHENOTYPE WAS
ROUND/YELLOW X ROUND/YELLOW)
2ND GENERATION
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FOUND ROUND/YELLOW
FOUND ROUND/GREEN
FOUND WRINKLED/YELLOW
FOUND WRINKLED/GREEN
( 9 : 3 : 3 : 1 RATIO)
-9
-3
-3
-1
EXPLANATION OF 2ND
GENERATION
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MENDEL CAME UP W/ 2ND LAW – THE
LAW OF INDEPENDENT ASSORTMENT
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Genes for different traits (Pea color, and
flower color) are inherited independently of
each other
Just because you have brown hair, doesn’t
mean you will be short!
DIHYBRID CROSSES
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A LITTLE DIFFERENT
HhGg X HhGg
What are the possible Allele combinations?
USE THE FOIL METHOD
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First, Outer, Inner, Last
FOIL – FIRST, OUTSIDE, INSIDE, LAST
H hGg X HhGg
1. HG
2. Hg
3. hG
4. hg
BOTH PARENTS
ARE THE SAME
NOW LET’S DO A DIHYBRID
CROSS
HhGg X HhGg
HG
Hg
hG
HG
HHGG
HHGg
HhGG
HhGg
Hg
HHGg
HHgg
HhGg
Hhgg
hG
HhGG
HhGg
hhGG
hhGg
hg
HhGg
Hhgg
hhGg
hhgg
hg
WHAT ARE THE PHENOTYPIC
RATIO’S?
HhGg X HhGg
DD:
9
HhGg
Dr:
3
HhGg
Hhgg
rD:
3
HhGg
hhGG
hhGg
rr:
1
Hhgg
hhGg
hhgg
HG
Hg
hG
HG
HHGG
HHGg
HhGG
Hg
HHGg
HHgg
hG
HhGG
hg
HhGg
hg
PROBABILITY
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Does real life follow Punnett Squares??
NO!!!!!! – only shows what will PROBABLY
occur
Like flipping a coin 10 times:
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PROBABILITY says you’ll get heads 50% of
the time.
But you may not … try it.
Certainly over time, with hundreds and
hundreds of flips, YES, you’ll end up with 50%
heads 