heredity mendel’s laws s-b-8-1_heredity powerpoint
TRANSCRIPT
Heredity
Mendel’s Laws
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Heredity
Source: http://en.wikipedia.org/wiki/Habsburg
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How are traits inherited?
• Selective Breeding– Domestication of plants
• Higher yielding crops• Mature faster, set fruit earlier• Attractive fruit
– Domestication of animals• Desired behaviors• Desired qualities
Gray Wolf
http://animal.discovery.com/mammals/wolf/ http://www.akc.org/breeds/
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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
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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
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Pisum sativum-The Pea
http://www.tutorvista.com/content/biology/biology-iii/heredity-and-variation/mendels-experiments.php
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Artificial Pollination
Removing Stamen from flower
Exposing Stigma and dusting with pollen
Covering the flower with bag and labeling
stem
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Monohybrid Cross
• Crossed Tall plants with Short plants, the parents or P
• Called the hybrid offspring, the First Filial, F1, generation
What would you expect the F1 Generation to look like?
X
F1
P
All offspring are tall.
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Rule of Dominance• recessive traits
– The trait that is not expressed, or hidden, in the F1 generation
• DOMINANT traits – The trait expressed in
hybrid offspring, the F1 generation
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The F2 Generation
Mendel allowed the F1 plants to self pollinate.
What would you expect the offspring to look like?
F1
P
F2
X
787 tall plants and 277 dwarf plants
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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:– Homozygous individuals have
identical factors .• TT or tt
– Heterozygous individuals have 2 different factors.
• Tt
F1
P
F2
X
TT
Tt
tt
TT ttTt Tt
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Genetics
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.
Dwarf allele
Tall allele
Genes at the same location
HOMOLOGOUS CHROMOSOMES
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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.
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THINK-PAIR-SHARE
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?
Xhttp://www.countryfarm-lifestyles.com/raising-rabbits.html
http://athomepets.blogspot.com/2008/03/bunnies-born-for-easter-crowd.html
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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.
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Law of SegregationMendel’s Explanation
• Alleles separate when forming gametes.
• Parents pass only one allele for each trait.
Modern Genetics• What process ensures
that alleles separate during gamete formation?
http://www-bcf.usc.edu/~forsburg/meiosis.html
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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
http://image.wistatutor.com/content/feed/u2044/Punnet%20square.gif
XP
F1
F2
32101108315
Y-Yellow
y-green
R-Round
r-wrinkled
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Law of Independent Assortment
Mendel’s Explanation• Traits are inherited
independently from one another.
Modern Genetics• What process ensures
that genes are randomly assorted among the gametes?
http://www.palaeos.com/Fungi/Lists/Glossary/GlossaryM.html
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Punnett Squares
• 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
Punnett Square of Dihybrid CrossParent Genotype RrYy
Gametes’ Genotype
Ga
me
tes
’ G
en
oty
pe
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Using Punnett Squares
Both parents are hybrids or heterozygous for
black fur.
♂Bb and ♀Bb
Step 1
Write the genotypes of the parents.
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?
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Using Punnett Squares
STEP 2
List the different gametes that each parent can
make.
To find the number of different gametes is 2n,
where n is the number of heterozygous gene pairs
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 ♀ gametes B and b B and b
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Using Punnett Squares
STEP 3
Make a grid of horizontal and vertical lines.
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?
Since the male and female can make 2 different gametes the
grid will be 2 x 2.
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Using Punnett SquaresBlack 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 4
Put the gametes from one parent on the top and the other parent’s gametes on the side.
B b
B
b
♂ gametes
♀ g
ame
tes
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Using Punnett SquaresBlack 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
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Using Punnett SquaresBlack 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.
B b
B
b
BB BbBB Bb
Bb bb
1-BB
2-Bb
1-bb
3-Black colored fur
1-Tan colored fur
}
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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
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Problems with Two TraitsBlack 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
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Problems with Two Traits
STEP 2
List the different gametes that each parent can
make.
BH,
Step 1
Write the genotypes of the parents.
♂BbHh and ♀BbHh
♂ gametes
Bh bH bhBH, Bh, bH, bh
♂ gametesBH, Bh, bH, bh ♀ gametes
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Problems with Two TraitsSTEP 3
Make a grid of horizontal and vertical lines.
STEP 4Put the gametes from one parent on the top and the other parent’s gametes on the side.
BH
Bh
bH
bh
♀ g
amet
es
♂ gametes
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Problems with Two Traits
BH
Bh
bH
bh
♂ gametes
BH Bh bH bh
♀ g
amet
es
STEP 5Fill in the boxes by
copying the row and column headings.
BBHH BBHh BbHH BbHh
BBHh BBhh BbHh Bbhh
BbHH BbHh bbHH bbHh
BbHh Bbhh bbHh bbhh
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Problems with Two Traits
STEP 6Determine the phenotypes of
the possible offspring.
BBHH BBHh BBHhBbHH BbHH BbHhBbHh 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
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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?
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Step 1:Hybrid parent Purebred Parent
HhTt hhtt
Step 2: Hybrid gametes Purebred gametesHT, Ht, hT, ht ht
Step 3:Step 4: ht
HT Ht hT ht
Step 5:HhTt Hhtt hhTt hhtt
Step 6: HhTt
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
There is a 1 in 4 chance that the offspring will have long hair and a short tail
There is a 1 in 4 chance that the offspring will have long hair and tail
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• 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?
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Complete Dominance
Every example so far has been complete dominance, when one allele completely masks another.
Sometimes it’s more complicated than that.
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Codominance
• Codominance is when two alleles are expressed simultaneously. They are dominant together.
• Ex. People with AB blood type, Roan Horses
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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.
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Sex Linked Traits
• Genes located on the X or Y chromosome (usually X)
• Males are more susceptible than Females. Why?
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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.
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• 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.
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• 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?
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X Y
X
Xh
Which sex is most likely to have hemophilia?
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XX XY
XXh XhY