gregor mendel genetics
TRANSCRIPT
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Gregor MendelWhen two heterozygous
plants are crossedthe expected andobserved phenotypicratio will always be3:1
This was the same for all 7 of his tests
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Gregor MendelMendel concluded that the two alleles for
each characteristic separate during gamete production.
This segregation of alleles corresponds to the distribution of homologous chromosomes to different gametes in meiosis
Known as the law of segregation
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Gregor MendelGenotype of alleles:
R = red flowerr = orange flower
All genes occur in pairs, so 2 alleles affect a characteristic
Possible combinations are:
Genotypes RR Rr rr
Phenotypes RED RED ORANGE
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PracticeFor each genotype: heterozygous (He) or
homozygous (Ho)
Which of the genotypes would be purebred?
__________________________________________________
Which of the genotypes would be hybrid?
__________________________________________________
TT_____ Bb______ DD______ Ff ______ tt _____
Dd_____ ff ______ Tt ______ BB______ dd_____
HoHo
HoHo
HoHoHe
HeHe
He
TT, ff, DD, BB, tt, dd
Dd, Bb, Tt, Ff
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PracticeDetermine the phenotype for each genotype
Yellow body color is dominant to blue
YY_______________ Yy _______________yy _______________
Square shape is dominant to round
SS________________Ss_______________ ss________________
Yellow Yellow Blue
Square Square Round
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PracticeFor each phenotype, give the possible genotypes
A tall head (T) is dominant to short (t)
Tall_______________ Short_______________
Pink body color (P) is dominant to yellow (p)
Pink_______________ Yellow______________
TT, Tt tt
PP, Pp pp
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Genetic CrossesMonohybrid cross: cross involving a single
traitFlower color, plant height
Dihybrid cross: cross involving two traitsFlower color & plant height
Punnett squares help determine the possible combinations of genotypes that can occur in the offspring.
It also shows the probability of each genotype occurring
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Genetic Crosses
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Genetic CrossesSolving Punnett squares only takes a few steps:1. Determine the genotypes of the parent
organisms2. Write down your ‘cross’3. Draw your Punnett square4. ‘Split’ the letters of the genotype for each
parent & put them ‘outside’ the Punnett square
5. Determine the possible genotypes of the offspring by filling in the Punnett square
6. Summarize the results (both genotype and phenotype of the offspring)
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Genetic Crosses1. Sometimes the question already tells you,
other times you need to understand the vocabulary. Read carefully!
2. Write down the genotypes of the parentsEx: Tt x tt
3. Draw the Punnett square
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Genetic Crosses4. Split the letters of our cross Tt x tt
This ‘split’ represents the process of meiosisThe vertical represents the male gameteThe horizontal represents the female gamete
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Genetic Crosses5. Each box represents a possible genotype of
the offspring
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Genetic Crosses6. Summarize the results of the offspring; both
genotype and phenotype
Genotype:50% TT 50% tt
Phenotype:50% tall 50% short
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SpongeBob is heterozygous for his square shape, but SpongeSusie is round. Create a Punnett square to show the possibilities if they had children. (look at old questions!)
Cross: ___________ x ___________Punnett Square
Genotypes: Genotypic ratio:Phenotypes: Phenotypic ratio:
Practice
____ ____
____
____
ssSs
S
s
s s
Ss
Ss
Ss
ss
Square, Round
Ss, ss 3:1
3:1
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Patrick met Patti at a dance. They are both heterozygous for their pink body color, create a Punnett square to show the possibilities if they had children. (look at old questions!)
Cross: ___________ x ___________Punnett Square
Genotypes: Genotypic ratio:Phenotypes: Phenotypic ratio:
Practice
____ ____
____
____
PpPp
P
p
P p
PP
Pp
Pp
pp
Pink, yellow
PP, Pp, pp 1:2:1
3:1
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Gregor MendelIn one dihybrid cross, Mendel studied the
inheritance of seed color and seed shape
The allele for yellow seeds (Y) is dominant to the allele for green seeds (y).
The allele for round seeds (R) is dominant to the allele for wrinkled seeds (r).
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Gregor MendelHe crossed true-breeding plants that has
yellow, round seeds (YYRR) with true-breeding plant that had green, wrinkled seeds (yyrr)
One possibility is that the two characteristics are transmitted from parents to offspring as a packageThe Y and R alleles and the y and r alleles
stay together
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Gregor MendelThe Y and R alleles and
the y and r alleles staytogether
This was not consistentwith Mendel’s results
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Gregor MendelAn alternative hypothesis is that the two
alleles segregate independently of each otherKnown as the law of independent
assortment
The presence of one specific allele for one trait has no impact in the presence of a specific allele for the second trait.
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Gregor MendelIn our example, the F1 offspring would still
produce yellow, round seeds. (YyRr)
However, when the F1’s produced gametes, genes would be packaged into gametes with all possible allelic combinations.
Four classes of gametes (YR, Yr, yR, and yr) would be produced in equal amounts.
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Gregor Mendel