Download RY, Ry, rY, and ry

Genetics
EQ: How are traits passed down through generations?
Gregor Mendel =
Father of Genetics
1857
Worked with garden pea plant
Mendel’s Experiments
• Peas are a “model system.”
•
• Small, easy to grow.
• Makes them convenient to
study.
• Help explain how organisms
inherit traits
• Started with “true breeding”
plants
• Trait: specific characteristic
(e.g., seed color, plant height) of
an individual
• Hybrid: created from cross of
true-breeding individuals
Pollination and Fertilization in Plants
Plants have the ability to self-pollinate (self-fertilize)
because they have both reproductive parts.
Male part
Female part
Cross-Pollination
Taking pollen from one plant and using it to
fertilize the eggs of another plant
Pollen
Pea Characteristics of Mendel’s peas
Mendel studied these characteristics to observe
patterns in traits across generations.
Mendel’s Crosses
When Mendel crossed plants with contrasting traits, the hybrid
offspring showed traits of only one parent.
Dominant and Recessive Traits
When a yellow pea plant is crossed with a
green pea plant, the resulting offspring are
yellow.
Yellow seed color is
to green seed color.
Green seed color is
to yellow seed color.
dominant
recessive
Principle of Dominance
• Some alleles are dominant, some recessive.
• An organism with at least one dominant allele will exhibit that
trait.
• An organism with a recessive allele will exhibit the trait only in
the absence of a dominant allele.
dominant
recessive
dominant
Genes and Alleles
Traits (seed shape, seed color) are determined by genes.
•Genes: passed from one generation to the next; genetic code that
determines an individual’s characteristics
Forms of traits (yellow/green, round/wrinkled) are called alleles.
•Alleles: the different forms of a gene.
Characteristics such as pod color
are determined by genes
.
Yellow and green pod colors are
determined by alleles
.
The allele for green pods is recessive
to the allele for yellow.
The P1 and F1 Generation
P1 generation
True-breeding
F1 generation
Hybrids
Let’s figure out how we can predict the F1 gen from the P1 gen.
Monohybrid Cross
= One Trait
“Height”
Tall Pea x Short Pea
T = Dominant
t = Recessive
TT x tt
“Homozygous
Dominant”
“True Breeding” = Homozygous
X
“Homozygous
Recessive”
Heterozygous and Homozygous
Homozygous: has two identical
alleles for a gene
Heterozygous: has two different
alleles for a gene
Which are:
homozygous?
1, 4
heterozygous?
2, 3
1
2
3
4
1st LAW OF HEREDITY
“Law of Segregation” =
– The 2 alleles for each trait must separate when
gametes (sperm/egg) are formed.
-A parent passes on, at random, only one allele
for each trait to each offspring
A
aa

Segregation
Random
Fertilization
The Formation of Gametes
Eggs and
sperm
Fertilization
Making a Punnett Square
A cross of birds:
Beak size (B, b)
Combine gamete genotypes
Possible gametes
Gametes for a parent
along one side
Generations
P1 = Parent Plants
-True breed Tall x True breed Short
TT
x
tt
F1 = First Generation (children)
What’s the probability that the offspring will
be tall? ________ Short? _______
Genotype of offspring? ______________
Genotype=genetic makeup of organism
Phenotype of offspring? _____________
Phenotype=physical characteristics
Law of Probability
“Rules of Chance”
“Odds”
Numerator = winner
Denominator = # horses
1/12
20:1 5%
1:12 “odd”
10:1 10%
8% “chance”
2:1 50%
Probability?
“Chance” of getting a tail?
“Chance” of getting snake eyes on two dice?
“Chance” of getting a boy?
Male: Female
XY XX
½
1:2 odd Boy
1:2 odd Girl
50% chance
Survey Large Number
1:1
Alleles: Tall = Dominant (T)
Short = Recessive (t)
Dominant = Trait Observed
Recessive = Trait that disappeared
Genotype Phenotype
TT = Tall
Tt = Tall
tt = Short
Can’t always know
an organisms
genotype by
looking at its
phenotype?
Homozygous
Dominant
Homozygous
Recessive
tt
TT
T
t
Tt
Heterozygous
Change of colors to follow the parental alleles:
F1
Tt x Tt
Combination of Letters/Alleles?
F2
3 Tall and 1 Short
TT
Tt
Tt
tt
The F2 Generation – created from a cross
of two F1 generation offspring.
What proportion of F2
offspring were short?
1/4
What proportion of F2
offspring were tall?
3/4
Dihybrid Crosses:
Crossing for 2 characteristics/ traits
EXAMPLE
•2 TRAITS: Seed Shape and Seed Color
•Shape =Round (R) was dominant to Wrinkled (r)
•Color = Yellow (Y) was dominant to Green (y)
Making a Punnett Square: Two Factors
A cross of pea plants:
size (T, t) and pod color (G, g)
All possible gametes
All gametes for a parent
along one side
Combine gamete genotypes
Round Yellow Seeds
x
Wrinkled Green Seeds
Homozygous dominant for both traits
_RRYY_(Genotype)
Use FOIL to help you figure
out the combinations
(RR)(YY)
F(irst)
RY
O(uter)
RY
I(nner)
RY
L(ast)
RY
Homozygous recessive for both traits
1. We need to first
find all the possible
gamete
combinations of
each parent
ry
ry
ry
ry
Use FOIL to help you figure
out the combinations
(rr)(yy)
F(irst)
ry
O(uter)
ry
I(nner)
ry
L(ast)
ry
gametes
2. Place your gametes in a
Punnett square.
RY
(Genotype)
___rryy____
RY
RY
RY
gametes
3. Fill in the Punnett square.
ry
RY
RrYy
RY
RrYy
RY
RrYy
RY
RrYy
ry
RrYy
RrYy
RrYy
RrYy
ry
RrYy
RrYy
RrYy
RrYy
ry
RrYy
RrYy
RrYy
RrYy
So the P1 cross of true breeding plants:
Round Yellow Seeds
P1
Wrinkled Green Seeds
rryy
RRYY
produced
F1
RrYy
All plants Round Yellow Seeds
Now let’s cross two F1 generation plants.
1. We need to
first find all the
possible gamete
combinations of
each parent
Use FOIL!
RrYy
RY
Ry
rY
ry
RrYy
RY
Ry
rY
ry
The presence of one specific
allele for one trait has no impact
on the presence of a specific
allele for the second trait.
The two pairs of alleles
segregate independently
of each other.
Four classes of gametes
(RY, Ry, rY, and ry) would be
produced in equal amounts.
RY
Ry
RrYy
rY
ry
2. Place your gametes in a
Punnett square.
RY
RY
Ry
rY
ry
Ry
rY
RY
Ry
rY
ry
ry
RY
Ry
rY
ry
RrYy
Round Yellow
Round Green
RrYy
Wrinkled Yellow
Wrinkled Green
ND
2
LAW OF HEREDITY
• Law of Independent Assortment =
genes for different traits are
inherited “independently” of each
other.
•RrYy = the R and r will separate as well
as the Y and y.
•Alleles can recombine in 4 different ways.