LEQ: What did Mendel
discover about the passing on
of traits?
9.1 to 9.3
Early Misconceptions
 Lemark – proposed a theory
of evolution based on the
idea that acquired traits are
inherited
 Lamark thought that
organisms adapted to
changes in their
environment through
altered behaviors. The
behaviors lead to selective
use or disuse of given
structures causing them to
increase or decrease in size.
 Lamark went on to claim
that this acquired change
was then passed on to the
offspring.
Early Misconceptions
 Blended Inheritance – the
traits of parents blend in
the offspring
Gregor Mendel
 Father of Genetics –
deduced the fundamental
principles of inheritance
 Published in 1866 – not
recognized as important
until long after his death

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Pea Plant Experiments
 Mendel used pea plants for
his heredity experiments
because…
 Controlled breeding
 Cheap
 Easy to grow and maintain
 Grow many in a small
space
 Quick generation time
 7 contrasting traits
Fertilization in Pea Plants
 Self-fertilization
 Pollen of one plant
fertilizes the egg of the
same plant
 Cross-fertilization
 Pollen of one plant
fertilizes the egg of a
second plant
True-breeding vs. Hybrid
 True-breeding
 Organisms that when selfpollinated (or crossed with
one of the same) produce
an organism identical to
self
 Hybrid
 Offspring produced from
crossing 2 dissimilar
organisms
Generations
 P – Parent Generation; the
original cross
 F1 – First Filial Generation;
Offspring of the parent
cross
 F2 – Second Filial
Generation; Offspring of
the F1 generation
Seven Characteristics
Monohybrid Crosses
 Genetic cross of individuals
differing in one trait
 Trait – a characteristic that
is inherited from parent to
offspring; controlled by a
gene
 Examples: flower color,
plant height, etc…
 Punnett Square – diagram
used to predict the possible
outcome of a given cross
Vocab…
 Allele –
 different forms of a gene
 Example: flower color could be white or purple; plant height
could be tall or short
 Homozygous
 alleles are the same
Heterozygous
alleles are different
 Dominant
 Allele that is expressed when it is present; represented using
capitol letters
 Recessive
 Allele that is only expressed in the absence of the dominant
allele; represented using lower case of dominant letter
 Phenotype
 Physical appearance
Genotype
Genetic Make-up (the letters)
Mendel’s Experiment
Mendel’s Law of
Segregation
 A sperm or egg carries only 1 allele for each
inherited trait because allele pairs separate from
each other during the production of gametes
 When does segregation occur?
 Anaphase I of meiosis when homologous
chromosomes are separated.
LEQ: How are Punnett Squares used
to predict the outcomes of a cross?

4 boxes

Define parents


Define alleles



A = normal pigment
a = albino
Possible alleles from one parent across the top


Aa X Aa
A or a
Possible alleles from 2nd parent along the side

A or a

Fill in boxes bring letters down and across

Give genotype and phenotype ratios


1 AA: 2Aa: 1aa
3 normal: 1 albino