history of genetics
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History of Genetics. Biology. Genetics. How characteristics are transmitted from parents to offspring. Gregor Mendel. Gregor Mendel (1822-1884). worked with Pisum satium (pea plant). Mendel studied 7 characteristics. Flower color - PowerPoint PPT PresentationTRANSCRIPT
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History of
Genetics
Biology
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Genetics
• How characteristics are transmitted from parents to offspring
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Gregor Mendel
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• worked with Pisum satium (pea plant)
Gregor Mendel (1822-1884)
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• Flower color • Flower position along stem
• Seed color• Seed shape• Pod shape• Pod color• Stem length
Mendel studied 7
characteristics
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Mendel’s Experiments
Mendel’s First Cross
• Crossed “purebred” purple with “purebred” white + P (parent) generation
- F1 – purple
• Crossed F1 hybrids + produced F2 generation
- 3 purple : 1 white
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• Alternative versions of genes (alleles) account for variations in inherited characters. + each gene resides at a particular location of a chromosome and can exist in variable forms (two different forms for flower color)
Mendel’s Ideas of Inheritance
P
p
Pp
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Mendel’s Ideas of Inheritance• For each characteristic, an organism inherits two alleles, one from each parent. + an organism is either homozygous (two of the same alleles) or heterozygous (two different alleles)
Homozygous Heterozygous
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• If the two alleles differ, the dominant allele is fully expressed and the recessive allele has no noticeable affect on appearance. + heterozygotes express the dominant trait
Mendel’s Ideas of Inheritance
RR rr
Rr
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• The two alleles for each character segregate duringgamete production.
+ ovum/sperm get only one of the two alleles (haploid)
Mendel’s Law of Segregation
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P generation Phenotype: Purple/White Genotype: PP/pp
F1 generation Phenotype: Purple Genotype: Pp
F2 generation? Genotype/Phenotype can be predicted using a Punnet Square
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Mendel’s Law of Independent Assortment
Each pair of alleles segregates into gametes independently.
WH wHwh Wh
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Mendel’s Law of Independent Assortment
Parental Genotypes GGWW ggww
Parental Gametes? GW gw
GgWw
GW Gw gW gw
F1 Genotypes?
F1 Gametes?
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Beyond Mendel...
Different Types of Inheritance:
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Complete Dominance Incomplete Dominance Mendel’s Traits Snapdragon Color
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Incomplete DominanceOne allele does not dominant the other in the heterozygous condition. Both alleles are expressed but a new phenotype appears that is intermediate.
RR rrRr
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Codominance
Both alleles in the Heterozygous condition are dominant.
CC Cc cc
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Codominance & Multiple Alleles
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