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S-B-8-1_Heredity PowerPoint
Heredity
Mendel’s Laws
S-B-8-1_Heredity PowerPoint
Heredity
Source: http://en.wikipedia.org/wiki/Habsburg
S-B-8-1_Heredity PowerPoint
How are traits inherited?
• Selective Breeding
– Domestication of plants
• Higher yielding crops
• Mature faster, set fruit earlier
• Attractive fruit
Gray Wolf
– Domestication of animals
• Desired behaviors
• Desired qualities
http://animal.discovery.com/mammals/wolf/
http://www.akc.org/breeds/
S-B-8-1_Heredity PowerPoint
Gregor Mendel
• Born in 1822, Brno, Moravia (now
the Czech Republic), the only son
of a farming family
• Showed promise in school and
entered the monastery to continue
his education
• Went to the University of Vienna,
studying physics and math
• Came back to the Abbey in Brno
to teach and experiment in the
garden
S-B-8-1_Heredity PowerPoint
Mendel’s Experiment
• Mendel investigates
inheritance in pea plants
for eight years.
• He chose peas because:
– They are easy to cultivate.
– They reproduced sexually.
– They have easy to
distinguish traits.
http://www.scientificamerican.com/article.cfm?id
=gene-behind-mendels-green&ref=rss
S-B-8-1_Heredity PowerPoint
Pisum sativum-The Pea
http://www.tutorvista.com/content/biology/biology-iii/heredity-and-variation/mendels-experiments.php
S-B-8-1_Heredity PowerPoint
Artificial Pollination
Removing Stamen
from flower
Exposing Stigma and
dusting with pollen
Covering the flower
with bag and labeling
stem
S-B-8-1_Heredity PowerPoint
Monohybrid Cross
• Crossed Tall plants with
Short plants, the parents
or P
• Called the hybrid
offspring, the First Filial,
F1, generation
P
What would you expect
the F1 Generation to
look like?
All offspring are tall.
F1
X
S-B-8-1_Heredity PowerPoint
Rule of Dominance
• DOMINANT traits
– The trait expressed in
hybrid offspring, the F1
generation
• recessive traits
– The trait that is not
expressed, or hidden,
in the F1 generation
S-B-8-1_Heredity PowerPoint
The F2 Generation
Mendel allowed the F1
plants to self pollinate.
X
P
What would you expect
the offspring to look
like?
F1
787 tall plants and 277 dwarf plants
F2
S-B-8-1_Heredity PowerPoint
Rule of Unit Factors
Mendel’s Explanation
• Individuals have two “heritable”
factors for a trait .
• The two factors may or may not
contain the same information:
X
P
TT
– Homozygous individuals have
identical factors .
tt
F1
• TT or tt
Tt
– Heterozygous individuals have 2
different factors.
• Tt
F2
TT
Tt
Tt
tt
S-B-8-1_Heredity PowerPoint
Genetics
Tall allele
Genes at the same location
Dwarf allele
HOMOLOGOUS
CHROMOSOMES
Modern Genetics
• Individuals have two copies of a
gene (one on each homologous
chromosome).
• The various forms of a gene are
called alleles:
– Dominant alleles are expressed
when they are present.
– Recessive alleles are expressed
only when the individual is
homozygous for the gene form.
S-B-8-1_Heredity PowerPoint
Phenotypes vs. Genotypes
• Phenotypes refer to
what is expressed or
the organism’s
outward appearance.
– TT and Tt pea plant
will be over 6 feet tall.
– tt pea plant will be
under 2 feet tall.
• Genotypes refers to
the specific alleles
that make up the
organism.
– A TT pea plant is
homozygous Tall while
a tt pea plant is
homozygous dwarf.
– A Tt pea plant is
heterozygous Tall.
S-B-8-1_Heredity PowerPoint
THINK-PAIR-SHARE
http://www.countryfarmlifestyles.com/raising-rabbits.html
X
http://athomepets.blogspot.com/2008/
03/bunnies-born-for-easter-crowd.html
1. If the black rabbit and the
white rabbit were bred
and all the offspring were
black, what conclusion
can you make?
2. If the hybrid offspring
were allowed to mate,
would you expect some of
the litter to be white?
Why?
S-B-8-1_Heredity PowerPoint
THINK-PAIR-SHARE
1. Are the genotypes homozygous dominant,
homozygous recessive, or heterozygous?
•
•
•
•
DdFF
RrYy
LLww
ggSs
2. The letters used in genotypes usually
represent the dominant trait, e.g., Y-yellow
seed and y-green seed. Decide on traits to
represent the genotypes above, and describe
the phenotypes.
S-B-8-1_Heredity PowerPoint
Law of Segregation
Mendel’s Explanation
• Alleles separate when
forming gametes.
• Parents pass only one
allele for each trait.
http://www-bcf.usc.edu/~forsburg/meiosis.html
Modern Genetics
• What process ensures
that alleles separate
during gamete formation?
S-B-8-1_Heredity PowerPoint
Dihybrid Cross
• Mendel repeated his
experiment with plants
that are bred true for
two traits.
• He again allowed the
F1 generation to self
pollinate.
• Phenotypic ratio:
9:3:3:1
P
X
F1
F2
315
108
101
32
Y-Yellow
R-Round
y-green
r-wrinkled
http://image.wistatutor.com/content/feed/u2044/Punnet%20square.gif
S-B-8-1_Heredity PowerPoint
Law of Independent Assortment
Mendel’s Explanation
• Traits are inherited
independently from one
another.
http://www.palaeos.com/Fungi/Lists/Glossary/GlossaryM.html
Modern Genetics
• What process ensures
that genes are
randomly assorted
among the gametes?
S-B-8-1_Heredity PowerPoint
Punnett Squares
Punnett Square of Dihybrid Cross
Parent Genotype RrYy
Gametes’ Genotype
Gametes’ Genotype
• British biologist
Reginald Punnett
used a matrix to show
the Laws of
Segregation and
Independent
Assortment.
• The Punnett Square
shows the probability
of an offspring having
a particular genotype.
http://image.wistatutor.com/content/feed/u2044/Punnet%20square.gif
S-B-8-1_Heredity PowerPoint
Using Punnett Squares
Black colored fur (B) is dominant to tan colored fur (b) in
dogs. Suppose you cross two hybrid dogs with black fur.
What are the possible phenotypes and genotypes of the
puppies? What are the expected ratios for each genotype
and phenotype?
Step 1
Write the genotypes of
the parents.
Both parents are
hybrids or heterozygous
for black fur.
♂Bb and ♀Bb
S-B-8-1_Heredity PowerPoint
Using Punnett Squares
Black colored fur (B) is dominant to tan colored fur (b) in
dogs. Suppose you cross two hybrid dogs with black fur.
What are the possible phenotypes and genotypes of the
puppies? What are the expected ratios for each genotype
and phenotype?
To find the number of
different gametes is 2n,
STEP 2
where n is the number of
heterozygous gene pairs
List the different gametes
that each parent can
make.
♂ gametes
♀ gametes
B and b
B and b
S-B-8-1_Heredity PowerPoint
Using Punnett Squares
Black colored fur (B) is dominant to tan colored fur (b) in
dogs. Suppose you cross two hybrid dogs with black fur.
What are the possible phenotypes and genotypes of the
puppies? What are the expected ratios for each genotype
and phenotype?
STEP 3
Make a grid of horizontal
and vertical lines.
Since the male and female can
make 2 different gametes the grid
will be 2 x 2.
S-B-8-1_Heredity PowerPoint
Using Punnett Squares
Black colored fur (B) is dominant to tan colored fur (b) in
dogs. Suppose you cross two hybrid dogs with black fur.
What are the possible phenotypes and genotypes of the
puppies? What are the expected ratios for each genotype
and phenotype?
♂ gametes
STEP 4
♀ gametes
Put the gametes from
one parent on the top
and the other parent’s
gametes on the side.
B
B
b
b
S-B-8-1_Heredity PowerPoint
Using Punnett Squares
Black colored fur (B) is dominant to tan colored fur (b) in
dogs. Suppose you cross two hybrid dogs with black fur.
What are the possible phenotypes and genotypes of the
puppies? What are the expected ratios for each genotype
and phenotype?
STEP 5
Fill in the boxes by
copying the row and
column headings.
B
b
B
b
BB
Bb
Bb
bb
S-B-8-1_Heredity PowerPoint
Using Punnett Squares
Black colored fur (B) is dominant to tan colored fur (b) in
dogs. Suppose you cross two hybrid dogs with black fur.
What are the possible phenotypes and genotypes of the
puppies? What are the expected ratios for each genotype
and phenotype?
STEP 6
Determine the phenotypes of
the possible offspring.
1-BB
2-Bb
1-bb
}
3-Black colored fur
1-Tan colored fur
B
b
B
BB
Bb
b
Bb
bb
S-B-8-1_Heredity PowerPoint
THINK-PAIR-SHARE
1. What would a Punnett
square look like for a
monohybrid cross of a
purple flowered pea plant
allowed to self pollinate?
2. What are the genotypic
ratios of the monohybrid
cross?
http://en.wikipedia.org/wiki/File:Punnett_square_mendel_flowers.svg
S-B-8-1_Heredity PowerPoint
Problems with Two Traits
Black colored fur (B) is dominant to tan colored fur (b) in
dogs while smooth hair (h) is recessive to wire hair texture
(H). Suppose you cross two hybrid dogs with black wiry
coats. What are the possible phenotypes and genotypes
of the puppies? What are the expected ratios for each
genotype and phenotype?
Step 1
Write the genotypes of
the parents.
Both parents are
hybrids or
heterozygous for black
and wiry coats.
♂BbHh and ♀BbHh
S-B-8-1_Heredity PowerPoint
Problems with Two Traits
Step 1
Write the genotypes of
the parents.
STEP 2
List the different gametes
that each parent can
make.
♂BbHh and ♀BbHh
BH, Bh, bH, bh
BH, Bh bH bh
♂ gametes
♂
gametes
BH,
Bh, bH, bh
♀ gametes
S-B-8-1_Heredity PowerPoint
Problems with Two Traits
STEP 3
Make a grid of horizontal and vertical lines.
STEP 4
Put the gametes from
one parent on the top
and the other parent’s
gametes on the side.
♀ gametes
♂ gametes
BH
Bh
bH
bh
S-B-8-1_Heredity PowerPoint
Problems with Two Traits
STEP 5
Fill in the boxes by
copying the row and
column headings.
♂ gametes
♀ gametes
BH
Bh
bH
bh
BH
BBHH BBHh BbHH BbHh
Bh
BBHh BBhh BbHh
bH
BbHH BbHh bbHH bbHh
bh
BbHh Bbhh bbHh
Bbhh
bbhh
S-B-8-1_Heredity PowerPoint
Problems with Two Traits
STEP 6
Determine the phenotypes of
the possible offspring.
BBHH BBHh BBHh
BbHH BbHH BbHh
BbHh BbHh BbHh
Bbhh Bbhh BBhh
bbHh bbHh bbHH
bbhh
There is a 9 out of 16 chance that the offspring
will have a black wiry coat.
There is a 3 out of 16 chance that the offspring will
have a black smooth coat.
There is a 3 out of 16 chance that the offspring will
have a wiry tan coat.
There is a 1 out of 16 chance that the offspring will
have a smooth tan coat
S-B-8-1_Heredity PowerPoint
THINK-PAIR-SHARE
In guinea pigs, short hair (H) is dominant
to long hair (h) and a short tail (T) is
dominant to long tails (t). If a hybrid
short hair and tail guinea pig is crossed
with a long hair and tail guinea pig,
what are the expected genotypic and
phenotypic ratios?
S-B-8-1_Heredity PowerPoint
Hybrid parent
Step 1:
HhTt
hhtt
Hybrid gametes
HT, Ht, hT, ht
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Purebred Parent
ht
HhTt
Hhtt
HT
HhTt
Purebred gametes
ht
Ht
hT
ht
Hhtt
hhTt
hhtt
There is a 1 in 4 chance that the offspring will have short hair
and tail
There is a 1 in 4 chance that the offspring will have short hair
and a long tail
hhTt
There is a 1 in 4 chance that the offspring will have long hair
and a short tail
hhtt
There is a 1 in 4 chance that the offspring will have
long hair and tail
• In pea plants Tall (T) is dominant to Short
(t) and Purple flowers (P) are dominant to
white (p). Cross two individuals who are
heterozygous for both traits.
• What is the genotype ratio? Phenotype
ratio?
S-B-8-1_Heredity PowerPoint
Complete Dominance
Every example so far has been complete
dominance, when one allele completely
masks another.
Sometimes it’s more complicated than that.
S-B-8-1_Heredity PowerPoint
Codominance
• Codominance is when two alleles are
expressed simultaneously. They are
dominant together.
• Ex. People with AB blood type, Roan
Horses
S-B-8-1_Heredity PowerPoint
S-B-8-1_Heredity PowerPoint
Incomplete Dominance
• Similar to codominance but neither allele
is completely expressed.
• Example: a red flower and a white flower
give rise to a pink flower. (red and white
are being expressed incompletely.
S-B-8-1_Heredity PowerPoint
S-B-8-1_Heredity PowerPoint
Sex Linked Traits
• Genes located on the X or Y chromosome
(usually X)
• Males are more susceptible than Females.
Why?
S-B-8-1_Heredity PowerPoint
Example:
• In guinea pigs Black hair (B) is dominant
to white (b) and Short hair (H) is dominant
to long hair (h). Cross a male that is
homozygous recessive for fur color and
heterozygous for hair length with a female
that is heterozygous for both color and
length. List the genotype and phenotype
ratios.
S-B-8-1_Heredity PowerPoint
• In human blood typing, A and B are both
dominant and O is recessive. If blood
typing displays codominance, what would
result from a cross between a male with
AB and a female with AO.
S-B-8-1_Heredity PowerPoint
• Hemophilia is a sex-linked genetic
disorder on the X chromosome. If a normal
male was crossed with a carrier female,
what are the possible genotypes of the
offspring?
S-B-8-1_Heredity PowerPoint
X
Y
X
Xh
S-B-8-1_Heredity PowerPoint
Which sex is most likely to have
hemophilia?
XX
XXh
XY
XhY
S-B-8-1_Heredity PowerPoint