Gregor Mendel. Pea Plants and Inheritance Patterns. Who is Gregor Mendel?. Mendel was born in 1822 in Austria His father was a peasant farmer, tenanted to a local aristocrat who was very interested in scientific crop improvement The family was very poor
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Pea Plants and Inheritance Patterns
Mendel’s Model Organism –
The Garden Pea
Crossed Pure TallxPure Short
All offspring (F1)tall
Ratio of 787 tall to 277 short (3:1)
Similar to chance events from flipping 2 pairs of coins
A cross between individuals differing in single character is a monohybrid cross.
The analysis of monohybrid crosses allowed Mendel to deduce the Law of Segregation…
Genes come in pairs that separate in the formation of sex cells (and these sex cells unite randomly at fertilization).
Staying the Course –Crosses to the F2
F1 Tall x Dwarf
The reappearance of the recessive trait in ¼ of the F2, suggests genes come in pairs that separate in the formation of sex cells.
Therefore, the Law of Segregation indeed is a general principle of genetics.
Principle of Independent Assortment: The assortment of one pair of genes into gametes is independent of the assortment of another pair of genes.
The alignment of one pair of homologs is independent of any other.
Height is a polygenic trait
The AB phenotype (genotype IA IB) is an example of codominance
male / sperm
female / eggs
2 normal parents,
but mother is carrier
Mendel performed dihybrid crosses to find out.
Note that we’re simultaneously applying the Principles of Segregations and Independent Assortment.