Transcript Phenotype - mrmitchellbiowiki

The Central Dogma!
DNA – double helix
•
DNA coils to form a
chromosome
• You receive 1 set of
chromosome from mom &
one from dad
• Chromosomes have areas
that code for a gene
• 1 gene = 1 protein
Number of Genes on
Chromosomes
Introduction to Genetics
Chapter 9
Section 1 – Mendel’s Legacy
Section 2 – Genetic Crosses
Mendel’s Legacy
Gregor Mendel was a priest in the mid 19th
Century.
Studied different pea plants
Father of GENETICS – the scientific study of
heredity
What is heredity?-passing down of physical
characteristics from parent to offspring
Mendel’s Experiments
Self pollinated
Developed a method of cross pollination
P generation, F1 generation, F2 generation
TRAITS: plant height, flower position, pod
color, pod appearance, seed texture, seed
color, flower color
The Outcome of Mendel’s Work
In all of Mendel’s experiments
First generation ONLY produced one form of
the trait (i.e. tall)
Second generation the “lost” form the trait
reappeared in about ¼ of the plants
Mendel’s Findings TODAY
Factors that control the traits are called GENES.
Alleles – contrasting forms of a gene
i.e. Tall vs. Short; round vs. wrinkled
Inherited from parents
Dominant Allele – trait always shows up when the
allele is present
Recessive Allele – “masked” or hidden by the
dominant trait
TERMS TO KNOW
Phenotype – the physical characteristic displayed by
the organism (PHYSICAL = PHENOTYPE)
Genotype – the actual combination of alleles held by
the organism (GENOTYPE = GENES)
Genotype = Rr
Phenotype = Red
Mendel concluded that the paired “factors” or alleles
separate when making reproductive cells
This means that each gamete only gets one copy of
each allele
When fertilized, the offspring would have 2 copies
Law of Segregation
Alleles are segregated or separated during the
formation of gametes.
Mendel also observed that dominant traits do not
always appear together.
Mendel concluded that these factors are not
connected
Law of Independent Assortment
“Factors” or alleles for different characteristics
are distributed to gametes independently
Explain this in YOUR words
Representing Alleles
Use letters to represent alleles
Use the same letter for one trait (T for height)
Capital letter for dominant (T = Tall)
Lowercase letter for recessive letter (t = short)
Purebred
Short
Parent
T
T
t
Tt
Tt
t
Tt
Tt
Purebred
Tall
Parent
Hybrid
Offspring
Genetic Crosses
What is the chance that a coin will land on
heads?
Probability – a number that describes how
likely it is that an event will occur.
Interdependence of Events
If you toss a coin once
and then toss again, the
first toss does not affect
the second
Each TIME you toss the
coin, you have a 1 in 2
chance of getting
heads.
Probability & Genetics
How is probability related to Genetics?
(Think about Mendel’s results)
Each time Mendel repeated his experiment,
he got similar results. WHY?
Mendel was the first to discover that you
could PREDICT the outcome of a cross.
Purebred Tall Plant X Purebred Short Plant
ALL TALL PLANTS
Punnett Squares
Tool used by scientists to determine the
outcome of a genetic cross
Shows all the possible combinations of
offspring
Purebred
Short
Parent
T
T
t
Tt
Tt
t
Tt
Tt
OUTCOME: TALL OFFSPRING
Purebred
Tall
Parent
Hybrid
Offspring
Monohybrid Crosses
Involves ONE PAIR of contrasting traits
Homozygous – purebred (has the same type of
alleles)
Heterozygous – hybrid (has two types of alleles)
Genetic cross
between a tall plant
and a short plant
T
Genetic cross
between 2
heterozygous tall
plants
T
T
t
T
t
t
t
TERMS TO KNOW
Phenotype – the physical characteristic displayed by
the organism (PHYSICAL = PHENOTYPE)
Genotype – the actual combination of alleles held by
the organism (GENOTYPE = GENES)
Genotype = Rr
Phenotype = Red
Ratio’s
Phenotypic Ratio – the ratio of phenotypes that
appear in the offspring
Genotypic Ratio – the ratio of genotypes that
appear in the offspring
Genotypic Ratio = 4:0
Phenotypic Ratio = 4:0
Monohybrid Punnett Square
Review
Heterozygous Tall x Heterozygous Tall
Give phenotypic and genotypic ratios
TT x Tt
Give phenotypic and genotypic ratios
Dihybrid Crosses
Involves TWO PAIRS of contrasting traits
Homozygous – purebred (has the same type of
alleles)
Heterozygous – hybrid (has two types of alleles)
Genetic cross between a Purebred tall plant, purple
flower and a Purebred short plant, white flower
TTPP
x
ttpp
What are the possible gametes?
(ALL THE POSSIBLE COMBINATION OF GAMETES)
Determining Gametes – all possible
combinations
PARENT 1
TtPp
TP
Tp
tP
tp
PARENT 2
TtPp
TP
Tp
tP
tp
What are the possible gametes for these parents?
Heterozygous Tall plant w/ purple flower (TtPp) x
Heterozygous Tall plant w/ purple flower (TtPp)
TP
TP
Tp
tP
tp
Tp
tP
tp
Other Types of Dominance
Incomplete Dominance
 Two or more alleles influence the phenotype
An intermediate phenotype results; a blending of
traits
Red Flower x White Flower
(RR)
(rr)
Pink Flower
(Rr)
Incomplete dominance Punnett Squares
Red Flower x White Flower
R
r
r
Rr
Rr
Pink Flower x Pink Flower
R
r
R
RR
Rr
r
Rr
rr
R
Rr
Rr
Outcome =
ALL PINK FLOWERS
Outcome =
Red, White & Pink Flowers
Other Types of Dominance
Codominance
 Two or more alleles are expressed in the phenotype
A combination phenotype results
Red Cow x White Cow
(RR)
(WW)
Roan Cow
(RW)
Codominance Punnett Squares
Red Cow x White Cow
Roan Cow x Roan Cow
R
R
W
R
RR
RW
W
RW
WW
W
W
RW
RW
Outcome =
ALL ROAN COWS
R
RW
RW
Outcome =
Red, White & Roan Cows