Download Genotypes

DO NOW
1.Take our your vocab HW.
2.Talk to your table – which
characteristics do people
inherit from their parents?
Chapter 3:
“Heredity”
Vocabulary
•Heredity – the passing of traits from
parent to offspring (children).
•Trait – a characteristic of an
organism
• Gregor Mendel (“Father of genetics”)
was the first scientist to study
genetics and how traits are passed
from parents to offspring.
Pea Plants
•
Mendel bred pea
plants and was able
to see that some
traits are passed
down to offspring
and some skip a
generation.
Pollination
• Pea plants are bred
through pollination, which
is the fertilization of
plants that contains both
male & female
reproductive structures.
• Fertilization occurs when
a sperm from the pollen
travels through the stigma
and enters the egg in an
ovule.
Pea Plants Create Offspring By…
1. Self-Pollination: pollen (male part) from
one flower can fertilize the ovule (female
part) of the SAME flower.
Pea Plants Create Offspring By…
2. Cross-Pollination: pollen (male parts) from
one plant can fertilizes the ovule (female
parts) of a flower on a DIFFERENT plant.
Why Mendel used pea plants:
1.
Grow & reproduce quickly.
2.
Easy self- pollination &
cross-pollination
3.
Many observable traits.
4.
Traits are easily observed
Examples: seed shape,
flower color & plant height
T
R
A
I
T
S
Breeding Pea Plants
•
Mendel bred one characteristic at a time.
•
He used true-breeding plants, in which all of
the offspring will have the same trait as the
parent.
–
Example: Purple flowers have purple offspring
and white flowers have white offspring.
Mendel’s First Experiment
•
He used cross-pollination for two true-bred
plants with different traits
•
He took a true-bred purple pea plant & crosspollinated it with a true-bred white pea plant.
RESULTS
All pea plants came
back purple!
Mendel’s Conclusions
•
He found that one trait always showed up and the
other trait disappeared.
•
He called them:
1.
Dominant– The trait that always appears (purple).
Shown as an upper case letter -“P”
2. Recessive - The trait that always disappears
(white). Shown as a lower case letter “p” )
Mendel’s Second Experiment
•
Mendel allowed each offspring plant from the
first experiment cross to self-pollinate.
•
Results – Some came back dominant (purple)
and some came back recessive (white).
Simple Dominance
Mendel’s experiment was an example of
simple dominance.
• Simple Dominance – When one trait is
completely dominant to the other.
– Example: Red and white flowers that are
crossed only produce either red or white
flowers.
• They will NEVER produce pink flowers.
Generations
• The true-breeding cross is called the
P or parental generation.
• The offspring of a cross-pollination
are called the F1 or first generation.
• The offspring from a F1 cross is
called the F2 or second generation.
Ratios
•
Mendel created a ratio of dominant to recessive
traits to determine the reason for the results.
•
Each parent donates genes to their children, so each
offspring has two forms of genes called alleles.
(Ex. “AA”, “Aa”, “aa”)
Genes Can Be:
Heterozygous (Hybrid)- One dominant & one recessive
trait (Aa, Bb, Cc, Dd, etc.)
Homozygous – Both dominant or both recessive traits
•
•
Homozygous Dominant = AA
Homozygous Recessive = aa
“P (Parental) Cross”
True-Bred Short
X
True-Bred Long
Resulted in 100% long offspring (F1)
“F1 (First Generation) Cross”
Cross pollinated 2 of the long offspring
produced in the “P” generation
F1 long X F1 long
Results:
75% long and 25% short
EXAMPLES
• R= dominant gene for red
• r= recessive gene that appears white
• RR=homozygous dominant, red
• rr=homozygous recessive, white
• Rr=heterozygous, red
•
Genotype - the actual letters (alleles)
that represent genes.
•
•
Example: GG, Gg, or gg
Phenotype - The physical appearance of
those genes.
•
Ex: Green or Yellow Peas
PUNNETT
SQUARES
Punnett Squares
• Punnett Squares –a model used to
represent crosses between organisms.
Example: What are the possible
offspring of a cross between a
homozygous dominant green plant and a
homozygous recessive green plant?
Steps in doing a Punnett Square:
Step #1: Identify the alleles
Example: What are the possible offspring of a
cross between a homozygous dominant green
plant and a homozygous recessive green plant?
Homozygous dominant = GG parent
Homozygous recessive = gg parent
Steps in doing a Punnett Square:
Step #2: Draw a square with 4 boxes
Example: What are the possible offspring of a
cross between a homozygous dominant green
plant and a homozygous recessive green plant?
Steps in doing a Punnett Square:
Step # 3: Put the alleles from one parent on
the top of the box & the alleles from the
other parent on the side of the box
gg parent
G
g
g
GG parent
G
Steps in doing a Punnett Square:
Step # 4: Cross multiply to find the
genotypes of the children
G
g
g
Gg
G
Steps in doing a Punnett Square:
Step # 4: Cross multiply to find the
genotypes of the children
G
G
Gg
Gg
Gg
Gg
g
g
Steps in doing a Punnett Square:
Step # 5: Write the phenotypes of each
child in the boxes
g
g
G
G
Gg
Gg
Green
Green
Gg
Gg
Green
Green
Steps in doing a Punnett Square:
Step # 6: Calculate genotypic and
phenotypic ratios of the offspring
g
g
G
G
Gg
Gg
Green
Green
Gg
Gg
Green
Green
List all Genotypes:
GG
Gg
gg
List all Phenotypes:
green
yellow
Steps in doing a Punnett Square:
Step # 6: Calculate genotypic and
phenotypic ratios of the offspring
g
g
G
G
Gg
Gg
Green
Green
Gg
Gg
Green
Green
Count how many
Genotypes:
GG = 0/4
Gg = 4/4
gg = 0/4
of each:
= 0%
= 100%
= 0%
Phenotypes:
green = 4/4 = 100%
yellow = 0/4 = 0%
Now try this one…
What are the possible offspring of a cross
between a pea plant which is heterozygous
for green peas and a pea plant which is
homozygous recessive for green peas?
g
g
G
g
Gg
gg
Green
yellow
Gg
gg
Green
yellow
Count how many
Genotypes:
GG = 0/4
Gg = 2/4
gg = 2/4
of each:
= 0%
= 50%
= 50%
Phenotypes:
green = 2/4 = 50%
yellow = 2/4 = 50%
Another example…
What are the possible offspring of a
cross between 2 pea plants which are
both heterozygous for green peas?
G
G
g
GG
Green
g
Gg
Green
Gg
gg
Green
yellow
Count how many
Genotypes:
GG = 1/4
Gg = 2/4
gg = 1/4
of each:
= 25%
= 50%
= 25%
Phenotypes:
green = 3/4 = 75%
yellow = 1/4 = 25%
INCOMPLETE
DOMINANCE
Incomplete Dominance
• Sometimes there are two dominant alleles and
no recessive alleles.
• This means that one trait is not completely
dominant over the other. Both are dominant!
– Ex: flower color
In some flowers, red & white are both dominant.
A red flower has the
RED
phenotype ______
and the genotype RR .
A white flower has
the phenotype
WHITE and the
______
genotype WW .
What if you cross a RED (RR) flower
with a WHITE (WW) flower?
W
R
R
RW
RW
RW
RW
What color are the offspring?
R
R
W
RW
RW
W
RW
RW
WHITE
+
RED
PINK
What is the
phenotype of
this flower?
PINK
What is the
genotype of this
flower?
RW
What Are The Genotypes & Phenotypes?
R
W
W
R
Genotypes
RW
RW
Pink
Pink
0%
•RR
=
•WW =
0%
•RW = 100%
RW
RW
Phenotypes
Pink
Pink
•Red
=
0%
•White = 0%
•Pink = 100%
So, when a trait is inherited by
incomplete dominance, there are
3
____
possible phenotypes
Red
White
Pink
3 possible genotypes.
and ____
RR
WW
RW
Practice
• Red and White flowers are incompletely
dominant. Cross a pink flower and a
white flower
Genotypes
W
W
R
W
RW
pink
WW
white
RW
WW
pink
white
•RR
= 0%
•WW = 50%
•RW = 50%
Phenotypes
•Red
= 0%
•White = 50%
•Pink
= 50%
Practice
• Red and White flowers are incompletely
dominant. Cross a pink flower and a pink
flower
Genotypes
Phenotypes
More Practice
Genotypes
Phenotypes
Multiple Alleles
Sometimes, there are more than 2 possibilities.
There are any set of 3 or more alleles.
Examples:
–
hair color, eye color, skin color
Co dominance
• Co dominance - When 2 alleles are equally
dominant.
– Example: Blood Type
Genotype
• 2 Dominant alleles – A & B AA
AO
• 1 recessive allele – O
BB
BO
AB
OO
Phenotype
A
A
B
B
AB
O
HOMOGYGOUS VS. HETEROZYGOUS
HOMOZYGOUS
DOMINANT
HOMOZYGOUS
RECESSIVE
HETEROZYGOUS
CO
DOMINANT
AA
OO
AO
AB
BB
BO
What if you cross a AO parent with
a BO parent?
B
O
A
O
AB
BO
AO
OO
Genotypes
•AB = 25%
•BO = 25%
•AO = 25%
•OO = 25%
Phenotypes
•AB = 25%
•A
= 25%
•B
= 25%
•O = 25%
You get all possible blood types in the offspring!
Practice
What if you cross a AB
parent with a O parent?
Exit Slip
• In your own words
explain what incomplete
dominance is…