Transcript Mendel`s Theories

Early Belief about Inheritance
• Blending Theory
• Children were a mixture of both parents
• But, if this were true over time what would
we see?
• A reduction in variety of traits.
GREGOR MENDEL 1822-1884
• The monk who worked with?
MENDEL’S GOAL
• EXPLAIN the PATTERN of HEREDITY
from PARENT to OFFSPRING
WHY PEA PLANTS?
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EASY TO GROW
REPRODUCE IN A SHORT TIME
GET RESULTS QUICKLY
ONLY 7 TRAITS
EACH TRAIT ONLY HAS 2 FORMS
MALE & FEMALE PARTS on flowers allow for
– SELF-FERTILIZATION OR MENDEL could
CROSS FERTILIZE them
HOW MENDEL CROSS FERTILIZED
FLOWERS & THEIR PARTS
MENDEL’S FIRST TRAIT
EXPERIMENT- Flower Color
• We use a punnett square to
show the results:
• Two purebred parents are
crossed
• One parent has PP it has
purple flowers
• The other has pp white flowers
• A dominant trait is a capital
letter P
• A recessive trait is a small
letter p
• The offspring are all purple.
Because they have one
dominant gene P. Even
though they have a p gene.
White recessive
offspring
Purple
Dominant
How to fill & label a punnett
cross
alleles
Phenotype
Purple flower
• The letters pp or PP are called
ALLELES.
Phenotype
white flower
• Each parent CONTRIBUTES
one ALLELE to their offspring
• Therefor there are 2 ALLELES
for each TRAIT, one from
each parent
• The alleles are genes. So we
call the combination of alleles,
genotype, think Genes
Genotypes of
• When we look at the physical
4 offspring
characteristics the genotype
are ?___
creates this is called a
What is the
phenotype of
phenotype, think
offspring?___
Physical. Purple, white
flowers
http://nortonbooks.com/college/biology/animations/ch10p02.htm
How to do a punnett square
http://www.zerobio.com/videos/monohybrid.html
MENDEL’S OBSERVATIONS OF
OF 1ST PURE-BRED CROSS
• THE PARENT’s generation uses the code P.
• They are PUREBRED plants. They had 2 genes that
were both represented by the same letters, either PP for
purple flowers or pp for white flower color.
• We also call purebreds Homozygous for a trait. Two
letters that are the same- PP or pp.
• THE OFFSPRING generation uses the code F-1
• In this example the offspring are Hybrids or
Heterozygous, Pp. They have 2 genes, one dominant
and one recessive. Because the offspring have one
dominant gene P they have purple flowers.
If someone believed in the Blending Hypothesis
they would have predicted that the offspring of a
purple and white flower …
• LIGHT PURPLE
• But they were not. Mendel therefore
called the purple color a Dominant trait.
MENDEL’S OBSERVATIONS OF 1ST
PURE-BRED CROSS
• ALL OFFSPRING had DOMINANT, purple flowers
• None had the white flowers, or Recessive trait.
MENDEL’S 2ND EXPERIMENT
SELF-FERTILIZATION CROSS
• He bred the F-1GENERATION
• Remember the F-1 were HYBRIDS, Pp
– They had two genes, one dominant and one
recessive.
• But Mendel did not realize this. He only saw that
they had purple flowers. So he expected to
see?
• All purple offspring when they were bred with
each other
F-2 RESULTS
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However, he had SOME PURPLE & also some White
flowered plants appear
HOW WAS THIS POSSIBLE?!
THE RECESSIVE TRAIT was always there in the genes
of the flowers.
To get a white flower two recessive genes had to come
together in an offspring to show up. pp
The phenotype ratio of offspring he had by flower color
was 3:1 Three purple to one white.
The genotype ratio he got was 1 PP, 2Pp, 1 pp
it is written at 1:2:1
Mendel’s 2nd Experiment
Ratios
Mendel’s 1st exp.
Mendel’s 2nd
experiment
Crosses
purebreds
Crosses
hybrids
DI-HYBRID CROSSES
http://www.siskiyous.edu/class/bio1/genetics/dihybrid_v2.html
MENDEL’S HYPOTHESIS
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Mendel’s Theories
1. EACH TRAIT IS
CONTROLLED BY A FACTOR…
2. MANY FACTORS HAVE 2
FORMS
3. ONE IS DOMINANT OVER
ANOTHER
4. EACH PARENT
CONTRIBUTES 1 FACTOR
5. FACTORS SEPARATE WHEN
GAMETES FORM, & JOIN TO
MAKE A PAIR for a ZYGOTE
6. SOME TRAITS DISAPPEAR
IN A GENERATION, THEN
REAPPEAR.
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What we know About Genetics
A factor is a GENE
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A gene has two copies
(chromosomes)
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DOMINANT/RECESSIVE
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1 GENE
MEIOSIS and Fertilization
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A PARENT can have a Recessive
TRAIT & not EXPRESS it
physically & can pass it onto their
child
INDEPENDENT ASSORTMENT
• http://bcs.whfreeman.com/thelifewire/conte
nt/chp10/1002001.html
PROBABILITY
http://nortonbooks.com/college/biology/animations/ch10a05.htm
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• ABILITY TO PREDICT FUTURE EVENT
PREDICT THE FREQUENCY OF OFFSPRING TRAITS
EXAMPLE A COIN TOSS
WHAT are the CHANCES of GETTING HEADS with 1
COIN?
½, one side is heads, the other is tails
WHAT are the CHANCES of getting HEADS with 2
COINS?
½ x ½ =?
¼!
TEST CROSS
• When you are not sure what the GENOTYPE is for a
dominant trait, example a black dog
– It can be HOMOZYGOUS BB or HETEROZYGOUS
Bb
• You would breed the dominant trait organism with a
HOMOZYGOUS RECESSIVE bb mate since they have
no dominant genes
• This mate can only give recessive genes to the offspring
• This is what a breeder would do to determine if the
dominant organism’s phenotype is homozygous or
heterozygous
TEST CROSS
Cross your dominant organism w/a recessive organism
Example 1
HOMOZYGOUS
genotype
Example 2
HETEROZYGOUS
genotype
t
All offspring are
heterozygous then the
unknown parent must be a
purebred, or homozygous
dominant
2 offspring are
heterozygous, 2 are
recessive. Therefore, the
parent is not a purebred.