Transcript Genetics Introduction 2014

Classical
Genetics
Work of Gregor Mendel (1822-1884)
• In 1843 he entered
Monastery of St. Francis
in Brünn (Brno) now
Czech Republic
• Served as teacher in
church-run school (7th 9th grade):
- Greek
- Math & general science
About 1854
Monastery and Church in Brno
Mendel and Staff of the Augustinian
Monastery c 1865
Mendel
Fr Napp
Matous Klácel,
Mendel’s Experimental Garden
Mendel’s Experiments: Crossed Pea Varieties
with 7 Clearly Distinguishable Traits
Mendel’s First Experiment
• Crossed Pure Tall x Pure Short (Dwarf)
• Predictions: The offspring would be:
A) All tall
B) All short
C) All intermediate
D) Some would be talls and some short
Mendel’s Experiments (1 & 2)
1st Exp:
All offspring (F1)
tall!
1
2nd Exp:
(Bred F1 X F1 and…)
• Results: Ratio of
787 tall to 277
short (3:1)
2
Mendel’s Next (3rd) Experiment
Crossed one of the F1
tall plants with its
dwarf parent:
F1 Tall x Dwarf
Possible Outcomes:
A) All would be tall
B) Mixture of Tall
& Dwarf
• Experimental results —>
50%
50%
Mendel’s Law of Dominance
• These experiments led to an understanding
that one trait can mask (or hide) another
trait.
• The trait that comes through is called
Dominant.
• The trait that is masked is called
Recessive.
Mendel’s Notational System
• Used capital letter to denote what he called the
dominant form of the trait: T = tall
• Used lower case letter to denote what he called
the recessive trait: t = short (dwarf)
• Thus for the Tall and Dwarf crosses:
TT = Original pure-breeding tall parent is called
HOMOZYGOUS Dominant
tt = Original pure-breeding short parent is called
HOMOZYGOUS Recessive
Tt = Hybrid F1 offspring (HETEROZYGOUS)
Dry Erase Review!
•
•
•
•
Let A = dominant and a = recessive
What is the term for AA?
What is the term for Aa?
What is the term for aa?
More Terminology…
• Genotype = The letters assigned to
represent the alleles. (AA, Aa, aa)
• Phenotype = The physical trait of
the allele. (Black, brown)
Dry Erase Review!
• Let A = Angry and a = happy
• Show me... The genotype for
happy.
• Show me…the genotypes for
Angry.
• Show me the phenotype for Aa.
Writing Mendel’s Crosses Using
His Notational System (FOIL)
• How many are tall? How many short?
Tt
Tt
x
/ \
Gametes
T
/ \
t
T
t
Fertilization
TT
Tt
Tt
tt
Mendel’s Law of Segregation
• We can use FOIL to figure out the
genotypic ratio because of
Mendel’s Law of Segregation.
• This Law states that during
Meiosis, the alleles will separate
from each other. (Homologous
pairs separate!)
Dry Erase Review!
• Let A = Angry and a = happy
• Use FOIL method to show a cross
of AA and Aa. List the genotypic
and Phenotypic ratios.
Punnent Square Method
T
t
T
TT
Tt
t
Tt
tt
What is the genotypic ratio for this cross?
Dry Erase Review!
• Let A = Angry and a = happy
• Use Punnent Square method to
show a cross of Aa and aa. List the
genotypic and Phenotypic ratios.
Dry Erase Review!
• Let B = Big and b = small
• Use Punnent Square method to
show a cross of Bb and Bb. List
the genotypic and Phenotypic
ratios.
Tongue Roller
R = Tongue Roller
r = Unable to Roll Tongue
Widow’s Peak
W = Widows Peak
w = Lack of Widow’s
Free Ear Lobe
Attached Ear
Lobe
E = Free Ear Lobe
e = Attached Ear Lobe
Hitchhiker’s Thumb
Hi = Straight Thumb
hi = Hitchhiker’s Thumb
Mid-digital Hair
M = Mid-Digital Hair
m = Absence of Mid-Digital
Hair
Dimples
D = Dimples
d = Absence of Dimples
The Dihybrid Cross
• He asked what the results would be if he
looked at TWO traits at a time
• He chose two different characteristics of
the pea:
1. Seed Coat:
Round (dominant) (R)
Wrinkled (recessive) (r)
2. Seed color:
Yellow (dominant) (Y)
Green (recessive) (y)
Results:
Crossed Two
Double Hybrids
SsYy x SsYy
Pollen
Eggs
Mendel’s Law of Independent
Assortment
• Mendel concluded that during
Meiosis, the chromosomes (and
alleles on them) will sort out
independently of one another.
• In essence, you can have a mix of
dominant and recessive traits!