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11.1-11.2 Gregor Mendel &Punnett Squares Pages 262 - 266 PD - old

Gregor Mendel & Punnett Squares

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Page 1: Gregor Mendel & Punnett Squares

11.1-11.2 Gregor Mendel&Punnett Squares

Pages 262 - 266

PD -old

Page 2: Gregor Mendel & Punnett Squares

Goal 1

Describe how Mendel Studied inheritance in peas

Page 3: Gregor Mendel & Punnett Squares

Austrian Monk 1800’s

Taught High School

Managed monastery gardens

Page 4: Gregor Mendel & Punnett Squares

Pea plant observations

1. True-breeding plantsa) Self pollination =

offspring identical to parents

Page 5: Gregor Mendel & Punnett Squares

2. Cross pollination used to study inheritancea) Tall plant x short plant

b) Green seeds x yellow seeds

Page 6: Gregor Mendel & Punnett Squares

Goal 2

Summarize Mendel’s conclusions about inheritance

Page 7: Gregor Mendel & Punnett Squares

• Results of Mendel’s experiment– Cross pollination of true breeding parents (P)– Offspring (F1) only show one trait– No “blending” of traits

Tall plant x short plant = all tall plants

P P F1

Page 8: Gregor Mendel & Punnett Squares

• Mendel’s 1st conclusions about inheritance

1. Inheritance determined by factors passed from one generation to the next

2. Each trait determined by one gene that occurs in two different forms (alleles)

3. Trait of height located on one gene as either short or tall alleles

Page 9: Gregor Mendel & Punnett Squares

Goal 3

Explain the principle of dominance

Page 10: Gregor Mendel & Punnett Squares

• He tried again with F1 generation– Cross pollination of F1 offspring– ¾ F2 offspring show one trait ¼ F2 show

“hidden” trait

F1 x F1 = F2

Tall plant x Tall plant = 3/4 tall plants

¼ short plants

Page 11: Gregor Mendel & Punnett Squares

Creative commons Image credit: Madprime

Page 12: Gregor Mendel & Punnett Squares

Principle of dominance states:

some alleles are dominant and others are recessive

– If dominant allele present, it will be expressed

– Recessive alleles only expressed if NO dominant allele present

Page 13: Gregor Mendel & Punnett Squares

Goal 4

Describe what happens to alleles during segregation in

meiosis

Page 14: Gregor Mendel & Punnett Squares

• Alleles separate during meiosis

• Alleles segregate into one allele per gamete

• Two types of gametes can be produced

• Alleles pair up randomly when gametes unite during fertilization

Page 15: Gregor Mendel & Punnett Squares

Example on the board…

Page 16: Gregor Mendel & Punnett Squares

Goal 5

Use Punnett Squares to:

determine genotypic and phenotypic ratios

of a crossto

Predict outcomes

Page 17: Gregor Mendel & Punnett Squares

• Phenotype = the expressed physical trait– What can be seen (brown hair)– Dependent on genotype

• Genotype = the alleles of a genetic code– Genetic code (one maternal, one paternal)

• Homozygous = alleles are the same (BB or bb)• Heterozygous = alleles are different (Bb)

Page 18: Gregor Mendel & Punnett Squares

• Recessive phenotype– Genotype MUST be homozygous recessive– Genotype bb expresses phenotype blond hair

• Dominant phenotype– Genotype may be homozygous dominant

• BB expresses brown hair

– Genotype may be heterozygous• Bb also expresses brown hair

Page 19: Gregor Mendel & Punnett Squares

• Genotypes are used to create Punnett Squares and compare possible combinations of gametes

Parent 1 gamete possibilities

Parent 2 gamete possibilities

Possible

Combination

Possible

Combination

Possible

Combination

Possible

Combination

Page 20: Gregor Mendel & Punnett Squares

B

b

b

B

Parent 1: homozygous dominantParent 2: homozygous recessive

BbBb

Bb Bb

Page 21: Gregor Mendel & Punnett Squares

B

b

B

b

Parent 1: heterozygousParent 2: heterozygous

bbBb

BB Bb

Page 22: Gregor Mendel & Punnett Squares

B

b

B

b

Genotypic ratio of offspring 1BB : 2Bb : 1bb

Phenotypic ratio of offspring 3 brown hair : 1 blond hair

(75% chance) (25% chance)

bbBlond hair

BbBrown hair

BBBrown hair

BbBrown hair

Page 23: Gregor Mendel & Punnett Squares

?

?

?

?

Parent 1: heterozygous (Bb)Parent 2: homozygous recessive (??)

????

?? ??

Page 24: Gregor Mendel & Punnett Squares

B

b

b

b

Parent 1: heterozygous (Bb)Parent 2: homozygous recessive (bb)

bbBb

Bb bb

Page 25: Gregor Mendel & Punnett Squares

B

b

b

b

bbBb

Bb bb

Genotypic ratio of offspring ?? : ??

Phenotypic ratio of offspring ?? : ??

Page 26: Gregor Mendel & Punnett Squares

B

b

b

b

bbBb

Bb bb

Genotypic ratio of offspring 2Bb : 2bb

Phenotypic ratio of offspring 2 brown hair : 2 blond hair

(50% chance) (50% chance)

Page 27: Gregor Mendel & Punnett Squares

Thanks to the following people who have generously shared images on Flickr

creative commons:

Unertlkm… pea plant

Z e n… butterfly and pea bloom