Gregor Mendel w “The Father of Genetics” w Studied peas: easy and quick to breed, can control...
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Transcript of Gregor Mendel w “The Father of Genetics” w Studied peas: easy and quick to breed, can control...
Gregor Mendel
“The Father of Genetics” Studied peas: easy and
quick to breed, can control mating
Mendel’s Pea PlantsPlant Height
Tall Short
Pod color
Seed ShapePod Shape
Seed Color
Green Yellow Green Yellow
RoundWrinkledSmooth Pinched
Mendel’s ExperimentsMendel mated “purebred” plants. (Homozygous)
Offspring always looked like parents.
X
Purebred Short Parents
Purebred Tall Parents
X
Short Offspring
Tall Offspring
Mendel’s First ExperimentMendel crossed purebred plants with opposite forms of a trait (like tall x short).
Called parental generation , or P generation.
Parent TallP generation
Parent ShortP generation
X
Offspring TallF1 generation
All of the offspring grew to be tall plants. None resembled the short parent. He called this generation of offspring the first filial , or F1 generation, (The word filial means “son” in Latin.)
Mendel’s Second ExperimentMendel then crossed two of the offspring from the F1 generation in his first experiment.
TallF1 generation
X
3⁄4 Tall & 1⁄4 ShortF2 generation
Mendel called this second generation of plants the second filial, F2, generation. It had both tall and short plants in a 3:1 ratio
Parent Plants Offspring
TT Tt
Tt
tt
T t
T
t
Genotype:
Tt x Tt 1 TT, 2 Tt, 1 tt
Mendel’s Law of Segregation
•Traits exist in different forms and one individual contains 2 factors (alleles) for each trait.
•When egg or sperm are formed, the two alleles separate (segregate) so only one factor is passed down -- at random.
Dominant and Recessive GenesMendel concluded that one factor masked the other factor.
Alleles that mask or hide other alleles, such as the “tall” allele, are said to be dominant.
A recessive allele, such as the short allele, is masked, or covered up, whenever the dominant allele is present.
What happens if you cross plants heterozygous for 2 traits?
Green Allele Yellow Allele
Round seed Allele Wrinkled seed allele
Yellow seeds are dominant over green and round seeds are dominant over wrinkled seeds.
X
X
Law of Independent AssortmentEach pair of alleles separate independently of each other in the production of eggs and sperm.
The process is random for each—
So if there are 4 possible outcomes in a monohybrid cross (cross of heterozygotes for 1 trait)
There are 4 x 4 = 16 possible outcomes in a dihybrid cross (cross of heterozygotes for 2 traits)
Most traits are not so simple
Incomplete dominance
A heterozygous individual has an intermediate phenotype
Codominance
Characteristics of both traits show up in the phenotype
Multiple Alleles
Each allele at multiple sites contributes to a phenotype
THE END