Download Chapter 11 2016

Genetics
Unit
Chapters:
11 and 14
Father of Genetics
• Studied the genetics of
Pea Plants
• He found 7 distinct traits
(characteristics) in pea
plants.
Mendel’s Work
• He Cross-Pollinated
two different pea
plants and produced
a “HYBRID.”
• Hybrids are a mix of
genes from 2 parents.
• What height do you
think the offspring
would be?
Principles of Dominance
Cross-pollination
of a Pure-tall with
a pure-short plant
Section 11-1
P Generation
F1 Generation
P = Parental generation
F1 = first generation
Mendel next crossed two
F1 offspring…what do
you think the F2 offspring
looked like?
Tall
Short
Tall
Tall
Principles of Dominance
Crossing Two F1 Offspring…
Section 11-1
F1 Generation
Tall
Tall
F2 Generation
Tall
Tall
Tall
Short
These crosses lead to his first principle of
genetics…
Mendel’s Conclusions
• Principle of Dominance – some genes are
dominant and others are recessive.
• Genes are the factors that determine traits.
• Genes have different forms called “alleles.”
Ex: T – tall t - short
• Principle of Segregation – alleles separate
during meiosis (gamete formation). Ex: If
parent has alleles Tt, only one allele makes it
into an egg or sperm.
How Can Genes Be Predicted?
• Probability: the likelihood that an event
will occur.
What is the probability for a coin to land on heads?
• Chance (segregation) of alleles is random,
just like a coin flip…
What is the probability for a child to be a boy?
Males have 2 sex chromosomes XY. Meiosis separates the pair so
only ONE of the chromosomes makes it into a gamete. So, each
gamete (sperm or egg) has only one allele for a trait.
x
Y
Section 11-2
How to diagram using
Punnett Squares
Alleles segregate during
meiosis into separate
gametes
There
a 25%
Sectionis11-2
chance or ¼ chance
of getting a short
plant from these
parents.
What is the chance
that a tall offspring
will be produced?
Crucial Genetic Vocabulary!!!
You must memorize to understand genetic problems
• Homozygous – identical alleles for a trait
or pure.
Ex: tt, TT
• Heterozygous – two different alleles or
hybrid.
Ex: Tt
• Genotype – Allele forms for a trait.
Ex: TT, Tt, or tt
• Phenotype – physical characteristics of
the allele combination.
(TT and Tt are TALL, tt is SHORT)
Let’s Practice…
Purple flowers are dominant over white.
1. What is the allele for purple?
2. What is the allele for white?
3. What is the genotype for a purple
flower?
4. What is the genotype for a white flower?
5. What is the phenotype for Pp? pp?
6. What is the genotype for a
heterozygous purple flower?
7. What is the genotype for a homozygous
white flower?
Smooth seed coat is dominant over rough
seed coat.
1. Genotype for a rough seed coat?
2. Phenotype for a SS genotype?
3. Genotype for a homozygous smooth?
4. Genotype for a heterozygous smooth?
Cross a heterozygous smooth with a rough
coat. What % of the offspring would be
smooth?
What if there is more than one
trait involved in the problem?
Oh no!!!
Dihybrid Crosses
Genotypes:
•For 2 traits, there will be 4 letters in the
genotype (2 alleles per trait!)
One trait (hair color) – BB “black”, Bb “brown”, bb “blonde”
Two traits (hair color and earlobes) – BBEE, BbEe, BBEe, BbEE,
etc.
Phenotypes:
•Look at each letter group separately.
Ex: BBEE genotype would have the phenotype of:
“Black hair and Attached earlobes”
Gametes with Two Traits
• Determine Genotype of parent
– Ex: BbEe (heterozygous for both traits)
• Determine the different combinations of
hair color and earlobe alleles
– Use the FOIL method!!! (First, Outer, Inner, Last)
– BbEe genotype has gamete combos of:
• BE, Be, bE, be
• These are the allele possibilities found in egg or
sperm.
Principle of Independent
Assortment
• Mendel’s last principle
• During meiosis, alleles will align independently from each
other to give the maximum possible gamete combinations.
Solving Problems
• STEP 1: Determine letters you will use to specify
traits.
• STEP 2: Determine parent’s genotypes.
• STEP 3: Determine gametes from each parent
• STEP 4: Complete Punnett square cross and
determine possible offspring.
• STEP 5: Determine phenotypic possibilities.
Let’s Practice!!!!
A pure tall, pure green pea plant is crossed
with a short, white pea plant.
(Tall is dominant over short, green is dominant over white)
1.
2.
3.
4.
T = tall, t = short, G = green, g = white
Parents: TTGG x ttgg
Gametes: TG, TG, TG, TG and tg, tg, tg, tg
Punnett Square: 4x4
TG
TG
TG
TG
tg
TtGg
TtGg
TtGg
TtGg
tg
TtGg
TtGg
TtGg
TtGg
tg
TtGg
TtGg
TtGg
TtGg
tg
TtGg
TtGg
TtGg
TtGg
1. All offspring will be TtGg genotype which
makes them all Tall and Green phenotype
A homozygous tall, heterozygous green pea plant is
crossed with a heterozygous tall, heterozygous green pea
plant.
2. Parents: TTGg x TtGg
3. Gametes: TG,Tg,TG,Tg and TG,Tg,tG,tg
4.
TG
Tg
TG
Tg
TG
TTGG
TTGg
TTGG
TTGg
Tg
TTGg
TTgg
TTGg
TTgg
tG
TtGG
TtGg
TtGG
TtGg
tg
TtGg
Ttgg
TtGg
Ttgg
5. Tall/green: 12/16 or ¾
Tall/white: 4/16 or ¼
Short/green: 0/16
Short/white: 0/16
Two heterozygous tall and heterozygous green
pea plants are crossed.
2. Parents: TtGg x TtGg
3. Gametes: TG,Tg,tG,tg and TG,Tg,tG,tg
4.
TG
Tg
tG
tg
TG
TTGG
TTGg
TtGG
TtGg
Tg
TTGg
TTgg
TtGg
Ttgg
tG
TtGG
TtGg
ttGG
ttGg
tg
TtGg
Ttgg
ttGg
ttgg
5. Tall/green: 9/16
Tall/white: 3/16
Short/green: 3/16
Short/white: 1/16
Other Inheritance
Patterns…dominant doesn’t
always rule!
Incomplete Dominance
• A blending of the
alleles forming a
new heterozygous
phenotype.
• Blending of
phenotypes
• Neither allele is
dominant.
Ex: wavy hair, 4
o’clock flowers etc.
Ex: Incomplete Dominance
In Jellyfish, there are yellow
(Y) and blue (B) colors.
Some end up green due to
incomplete dominance.
a. Cross a yellow and blue
jellyfish
P = YY x BB F1 =
a. Cross a yellow and green
jellyfish
P = YY x YB
Codominance
• More than one allele
is dominant, thus both
are expressed in the
heterozygous
phenotype.
Ex: speckled chickens,
roan cattle, blood type,
sickle-cell anemia
In chickens, white and
black feathers are
codominant. A
heterozygous
chicken is speckled
with black and
white feathers.
a. Cross a speckled
and black
chicken.
Multiple Alleles
• Genes that have more than two alleles.
• More possible phenotypic characteristics.
• More possible genotypic combinations.
Ex: rabbit fur color, human blood types.
A man who has blood type O marries a
woman with type AB blood.
What is the chance that their child will have
a blood type of O?
Polygenic Traits
• Traits that are
controlled by more
than one gene.
• Ex: human skin
color, eye color,
body shape, height,
intelligence etc.