gregor mendel & punnett squares
TRANSCRIPT
11.1-11.2 Gregor Mendel&Punnett Squares
Pages 262 - 266
PD -old
Goal 1
Describe how Mendel Studied inheritance in peas
Austrian Monk 1800’s
Taught High School
Managed monastery gardens
Pea plant observations
1. True-breeding plantsa) Self pollination =
offspring identical to parents
2. Cross pollination used to study inheritancea) Tall plant x short plant
b) Green seeds x yellow seeds
Goal 2
Summarize Mendel’s conclusions about inheritance
• 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
• 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
Goal 3
Explain the principle of dominance
• 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
Creative commons Image credit: Madprime
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
Goal 4
Describe what happens to alleles during segregation in
meiosis
• 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
Example on the board…
Goal 5
Use Punnett Squares to:
determine genotypic and phenotypic ratios
of a crossto
Predict outcomes
• 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)
• 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
• 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
B
b
b
B
Parent 1: homozygous dominantParent 2: homozygous recessive
BbBb
Bb Bb
B
b
B
b
Parent 1: heterozygousParent 2: heterozygous
bbBb
BB Bb
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
?
?
?
?
Parent 1: heterozygous (Bb)Parent 2: homozygous recessive (??)
????
?? ??
B
b
b
b
Parent 1: heterozygous (Bb)Parent 2: homozygous recessive (bb)
bbBb
Bb bb
B
b
b
b
bbBb
Bb bb
Genotypic ratio of offspring ?? : ??
Phenotypic ratio of offspring ?? : ??
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)
Thanks to the following people who have generously shared images on Flickr
creative commons:
Unertlkm… pea plant
Z e n… butterfly and pea bloom