Mendel's Hypotheses
Methods of research
choose Garden Peas
. . - had available several varieties
. . - could control breeding
started with "pure bred" [homozygous] or
true-breeding plants,
. . - P-1 = parental generation
produced "hybrid" [heterozygous] offspring to
compare traits to parents,
. . - F-1 = first filial generation
crossed hybrid to hybrid offspring to follow trait
further,
. . - F-2 = second filial generation
[inbred]
. . - F-n = nth filial generation [inbred]
Mendel's hypotheses
Each organism receives one allele for each trait
from each parent
[therefore] all organisms must have two alleles
for each trait
Alleles segregate independently during gamete formation
Alleles are paired by fertilization,
a random pairing of gametes
(Some) traits exhibit "dominance"
. . - heterozygote resembles one of homozygotes
Independent segregation in di-hybrid, tri-hybrid, etc.
Gamete formation in monohybrid
parental
genotype |
gametes |
| AA |
A |
A |
| Aa |
A |
a |
| aa |
a |
a |
Gamete formation in dihybrid
parental
genotype |
gametes |
| AA BB |
A B |
A B |
A B |
A B |
| AA Bb |
A B |
A b |
A B |
A b |
| AA bb |
A b |
A b |
A b |
A b |
| Aa BB |
A B |
A B |
a B |
a B |
| Aa Bb |
A B |
A b |
a B |
a b |
| Aa bb |
A b |
A b |
a b |
a b |
| aa BB |
a B |
a B |
a B |
a B |
| aa Bb |
a B |
a b |
a B |
a b |
| aa bb |
a b |
a b |
a b |
a b |
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© 2004 Prof. LaFrance, Ancilla College