Mendel’s Legacy
Section 9.1
 Genetics- the field of biology devoted to
understanding how characteristics are
transmitted from parents to offspring
 Genetics was founded with the work of
Gregor Johann Mendel
Gregor Johann Mendel
 Austrian monk who experimented with garden
peas
 1842- age 21; entered a monastery in Brunn
 1851- entered the University of Vienna
 Heredity- the transmission of characteristics
from parents to offspring
Mendel’s garden peas
 Mendel observed 7 characteristics of pea
plants, each occurring in 2 contrasting traits.
 Traits- plant height (long or short stems),
flower position along stem (axial or terminal),
pod color (green or yellow) pod appearance
(inflated or constricted), seed texture (smooth or
wrinkled), & flower color (purple or white)
 Mendel collected seeds from his pea
plants
 He observed that both purple-flower and
white-flower plants grew from the seeds
of purple-flower plants
 He also observed that both tall and short
plants grew from seeds obtained from
tall plants
 Mendel wanted to find an explanation for
the variations
Mendel’s methods
 Mendel documented the traits of each
generation’s parents by controlling how much
the plants were pollinated
 Pollination- occurs when pollen grains
produced in the male reproductive parts of the
flower (anthers) are transferred to the female
reproductive part of the flower (stigma)
 Self-pollination- occurs when pollen is
transferred from the anthers of a flower to
either the stigma of the same flower or a
flower on the same plant
 Cross-pollination- involves flowers of 2
separate plants
 Self-pollination can be interrupted (and crosspollination performed) by removing the anthers
from a flower and manually transferring the
anther to the stigma of another plant
 By doing this, Mendel was able to protect his
flowers from receiving pollen that might be
transferred by wind or insects, giving him more
control over the pollination of his pea plants
Mendel’s experiments
 Plants that are pure for a trait always
produce offspring with that trait
 strain- denotes plants that are pure for a
trait
 P1 generation- each parental generation
 F1 generation- the first filial generation
 F2 generation- the second filial
generation
Mendel’s Crosses & Results
P cross
F1 generation
Axial X Terminal = Axial
Tall X Short =
Inflated X
tall
inflated
Constricted =
Green X yellow =
(pods)
Smooth X
Wrinkled =
Yellow X Green =
(seeds)
Purple X White =
green
smooth
yellow
purple
F2 generation
651 axial
207 terminal
Actual ratio
3.14:1
Probability ratio
3:1
787 tall
277 short
2.84:1
3:1
882 inflated
299 cons.
428 green
152 yellow
5,474 sm.
1,850 wrink.
6,022 yellow
2,001 green
705 purple
224 white
2.95:1
3:1
2.82:1
3:1
2.96:1
3:1
3.01:1
3:1
3.15:1
3:1
Recessive & Dominant
traits
 Dominant factor- dominates the other
factor of a specific characteristic
 Recessive factor- the trait that did not
appear in the F1 generation but
reappeared in the F2 generation
Law of segregation
 States that a pair of factors is
segregated, or separated, during the
formation of gametes.
Law of independent
assortment
 States that factors for different
characteristics are distributed to gametes
independently.
Chromosomes & Genes
 Molecular genetics- the study of the
structure and function of chromosomes
and genes
 Allele- each of several alternatives of a
gene (Mendel's factors are now called
alleles.)