Genetics. 11.1 – Gregor Mendel Heredity Inheritance of traits - study of heredity.
Genetics the study of heredity
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Transcript of Genetics the study of heredity
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Geneticsthe study of heredity
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Gregor Mendel“Father of Genetics”
• Heredity -the transfer of characteristics from parents to offspring through their genes
• Gregor Mendel -used garden peas to study heredity
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Mendel’s Experiments• cross fertilization: Mendel crossed
two parent plants with opposite traits (purple x white). This was the Parental generation (P). The First generation (F1) were identical (purple).
• self fertilization: Mendel allowed the purple flowers from the First generation (F1) to self-pollinate. Self pollination produced the Second generation (F2).
Muskopf, ShannanMuskopf, Shannan
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Mendel’s Conclusions• The F1 generation all showed the purple trait (called the dominant
trait)• In the F2 generation the (white) trait reappears in ¼ of the flowers
(called the recessive trait)• Each flower has two alleles that determine the appearance • The alleles are represented by letters (uppercase letter represents the
dominant allele; lowercase letter represents the recessive allele)• P is dominant and represents purple• p is recessive and represents white• The Dominant Is Expressed No Matter What• Need 2 Copies Of The Recessive Allele In Order To Be Expressed• PP = purple flower Pp = purple flower pp = white flower
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Alleles
– homozygous: organisms that have 2 identical alleles for a trait (could be two capital or two lowercase letters)• PP • pp
– heterozygous: organisms that have 2 different alleles for a trait• ex: Pp (the dominant allele P is expressed so
this flower would be purple)
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• Genotype: letters used for the alleles– ex: PP, Pp, pp
• Phenotype: what an organisms looks like– ex: purple, white
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Punnett square
• A Punnett square is used to show the possible allele combinations in the offspring of 2 parents.
• Monohybrid cross = cross involving only 1 trait
The four boxes represent the four possible offspring
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A plant heterozygous with green peas (Gg) is crossed with a plant that has yellow peas (g).
• Step 1: Choose a letter for the alleles (green is dominant; yellow is recessive)
• G : green pea g: yellow pea
• Step 2: Write the genotypes of the parents
• heterozygous plant with green peas : Gg• plant with yellow peas: gg• parents: Gg x gg
Example of a Monohybrid Cross
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G g g
g
gg ggggggGg
G g G g G g g
g
g
g
g
g
GgGg
gggg Gg
Step 3: Set up the punnett square with one parent on each side
Step 4: Fill out the punnett square middle
G g g
g
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• Step 5: Look at the four boxes from Step 5 and determine the
genotypes of the four offspring – Genotypic ratio: 2 Gg: 2 gg
• Step 6: Look at the genotypes in Step 6 and determine the phenotypes;
– Green (G) is dominant over yellow (g), plants that have G in their offspring have green peas
– Phenotypic ratio: 2 green: 2 yellow
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Practice-Monohybrid Crosses Cross an individual with blue eyes with an individual with
homozygous brown eyes. Brown eyes (B) is dominant to blue eyes (b).
Phenotypes:
Genotypes:
B B
b
b
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Cross an individual with blue eyes with an individual with homozygous brown eyes. Brown eyes (B) is dominant to blue eyes (b).
Phenotypes: All Brown Eyes
Genotypes: All Bb
B B
b Bb Bb
b Bb Bb
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Practice-Monohybrid Crosses A child is diagnosed with a recessive genetic disease. Neither
parent has the disease. What are the genotypes of the parents?
Phenotypes:
Genotypes:
N ?
? nn
N
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A child is diagnosed with a recessive genetic disease. Neither parent has the disease. What are the genotypes of the parents?
Genotypes of the parents are Nn
N n
n Nn nn
N NN nn
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Incomplete Dominance = BlendingIn snapdragons, there is not a dominant allele. The flower color can be red, pink, or white. A heterozygous flower (Rr) will a blending of red and white (pink).
•Muskopf, Shannan. Online Images. The Biology Corner. 20 April 2007. http://www.biologycorner.com/bio1/celldivision-chromosomes.html
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Codominance: the recessive & dominant traits appear together (both are dominant, no recessive allele)
– Ex: Cross a red cow with a white cow. What will the offspring be?
R R
W
W
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– phenotype: all red and white speckled– genotype: all RW
W RW RW
W RW RW
R R
Muskopf, Shannan. Online Images. The Biology Corner. 20 April 2007. http://www.biologycorner.com/bio1/celldivision-chromosomes.html
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Polygenic Traits: “many genes” act together resulting in a range of phenotypes
– Ex: skin, hair, eye color
Skin color is a polygenic trait because it shows a range of colors. There is not a dominant and recessive color.
Farabee, M.J. “Skin Pigmentation.” 2001. Online Image. Online Biology Book. 5 May 2007. http://www.emc.maricopa.edu/faculty/farabee/biobk/BioBookgeninteract.html
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Multiple Alleles: genes that have more than two alleles– There are four blood types (phenotypes): A, B, AB, and O– Blood type is controlled by three alleles: A, B, and O– Each individual only inherits two alleles (one from each
parent).– A and B are codominant– O is recessive, two O alleles result in type O Blood
Blood Types Possible Genotypes
Dominant A AA or AO
Dominant B BB or BO
Codominant AB AB
Recessive O OO
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Practice: Cross a Type AB with a Type O.
AB x OO
A B
O AO BO
O AO BO
1. Set up punnett square with one parent on each side
2. Fill out the punnett square middle
What are the possible blood types of the four offspring?
Genotype Blood Type
2 AO 2 Type A
2 BO 2 Type B
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A woman heterozygous for Type A blood marries and a man with Type AB blood. Show the cross and the possible offspring.
1. Write the genotypes of the parents:• woman heterozygous for Type A: AO
• man with Type AB: AB
2. Set up punnett square with one parent on each side and fill in the middle.
Practice
A O
A AA AO
B AB BO
Blood types of possible offspring:
AA: Type A blood
AO: Type A blood
AB: Type AB blood
BO: Type B blood
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If a Type O individual marries a Type B individual can they have
offspring with Type O blood? What type of blood can the offspring have?
Practice
B ?
O
O
Blood types of possible offspring:
AA: Type A blood
AO: Type A blood
AB: Type AB blood
BO: Type B blood
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If a Type O individual marries a Type B individual can they have
offspring with Type O blood? What type of blood can the offspring have?
B O
O BO OO
O BO OO
Yes, they can have a child with type O or type B blood.
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If 2 individuals with Type AB blood marry, what percentage of their offspring will have Type AB blood?
A B
A
B
Practice
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50% of their offspring could be Type AB
A B
A AA AB
B AB BB
If 2 individuals with Type AB blood marry, what percentage of their offspring will have Type AB blood?
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Review of Terms
• Allele A form of a gene• Homozygous Both Alleles are the
Same• Heterozygous Alleles are Different• Homozygous Dominant AA• Homozygous Recessive aa• Heterozygous Aa• Genotypic Ratio 2 PP : 2 pp• Phenotypic Ratio 2 Purple : 2 White