GENETICS!
GREGORY MENDEL
Born 1822; Died 1884
 Monk and a teacher
 Work not recognized until
1900
 Studied heredity by
studying pea plants
 What is heredity?

MENDEL’S PEA PLANTS
Observed seven
characteristics of pea
plants with two
different traits
 Controlled how each
plant was pollinated

Self-pollination or
cross-pollination
 What’s the difference?

MENDEL’S EXPERIMENTS

Grew true-breeding plants

What does it mean to be true breeding?
Starting strain called parent generation or P
generation
 Cross-pollinated P generation to produce offspring
called the first filial generation or F1 generation
 F1 generation self-pollinated and produce the second
filial generation or F2 generation

P
generation
x
P
generation
F1
generation
x
All of the
F1 showed
one color
P
generation
x
F1
generation
F2
generation
F2 produced
plants about
¾ one trait
and ¼ the
other trait
RESULTS









Factor was controlling the traits since there were two
traits there were two factors
Alleles: represent the factors - dominant CAPITAL
LETTERS; recessive lower case letters; They are
alternate forms of genes.
Dominant trait: Able to repress the other trait
Recessive trait: repressed by the dominant
Homozygous: same alleles; RR or rr – also called
purebred or true breeding
Heterozygous: one of each allele forming a hybrid Rr
Genotype: allele pairs/actual DNA: RR, Rr, or rr
Phenotype: physical appearance; red, yellow, green, tall,
short, etc. *You only see the recessive phenotype when
there are two of the recessive alleles. Whenever you see
the dominant phenotype, you cannot tell the genotype.*
Lead to the modern study of molecular genetics, the
study of chromosomes and genes.
Y
y
LAWS OF GENETICS


Law of Segregation: a pair
of factors is segregated or
separated during the
formation of gametes (i.e. the
homologous chromosomes are
separated during anaphase I
of meiosis I into different
gametes.)
Law of Independent
Assortment: factors for
different characteristics are
distributed to gametes
independently – factor for
different traits do not follow
each other into the same
gamete
PROBABILITY
Probability that a specific event will occur; expressed as
a decimal, fraction, or percent
 Probability =
Number of times an event happened
Number of possible opportunities
 The predicted results are more likely to occur the more
trials that are performed

MONOHYBRID CROSSES
Monohybrid cross: between individuals with one
pair of contrasting traits ( mono = one)
 Punnett squares are used to help predict the
probability of a trait

HOMOZYGOUS X HOMOZYGOUS
Crossing two plants
homozygous for color
(P)
 One dominant one
recessive
 PP x pp
 Genotype



4 Pp
Phenotype

4 purple
HOMOZYGOUS X HETEROZYGOUS
Crossing a homozygous
dominant with a
heterozygous plant for
color (P)
 PP x Pp
 Genotype

2 PP
 2 Pp


Phenotype

4 purple
HOMOZYGOUS X HETEROZYGOUS
Crossing a heterozygou
plant with a homozygou
recessive for color (P)
 Pp x pp
 Genotype

2 Pp
 2 pp


Phenotype
2 purple
 2 white

HETEROZYGOUS X HETEROZYGOUS
Both heterozygous for
color (P)
 Pp x Pp
 Genotype

1 PP
 2 Pp
 1 pp


Phenotype
3 purple
 1 white

TESTCROSS


Used to determine the genotype of a individual with an
unknown genotype
Must use an organism of an known genotype hence use
a homozygous recessive