Mendel’s Genetics
Monohybrid Cross
Gregor Mendel
 As discussed last
class, he was an
Austrian monk
 He worked at St.
Thomas Monastery
 He studied both
mathematics and
botany
Why did he actually
Succeed?
 He chose the appropriate organism to
study
 He designed and performed his
experiments correctly
 Analysis of the data was done properly
The Patient
 The common ______ also
known as Pisum sativium
 It was chosen for 4
reasons
 It was _________
available
 Easy to _____and mature
 The sex organs are entirely
________ in the flower
 Different varieties had
different ________
Purebred
 What is a purebred organism?
 _____________________________
_____________________________
 Why was this important to Mendel and
his pea plants?
 This is because he used purebred plants
to conduct all of his experiments
How did he make sure?
 How did Mendel make sure that his
organisms (pea plant) were pure bred?
 He bred them as everyone else bred plants, and
he looked at _____ ______ at a time
 He selected from the ________, only the plants
that had the trait that he was looking for
 He then bred them together (________) and
then he continued this for several generations
until no more of the other trait showed up
What happened Next?
 He repeated this for all the other
traits until he had pure bred plants
with each trait.
The first of the Crosses
 So what did he end up doing next?
 He started to _______________
 He designated the parents as the ____
generations and crossed a truebreeding _____pea plant, with a truebreeding ______ pea plant
 The offspring were of course the F1
generation and he also denoted them as
__________
That F1 Generation
 What do you think he saw?
 What was the phenotype of the
plants?
 ____________________________
 What is this type of crossing called?
Creatively
 Creatively the name given to this type
of cross is _____________
 It is a _______ cross between two
purebred plants giving us a hybrid
species
What did his experiment look
like?
That’s the Phenotype
 We have now seen the phenotype
 All of the F1 generations plants were _____
 What do you think the genotype must be of
the offspring?
 First we have to learn some more terms
Terms
 ___________________ (TT) – Two alleles
for a trait that are the same as a result of
pure breeding
 ___________________ – Having two
alleles for a trait that are different
 ___________________ - Two alleles for a
trait that are the same as a result of pure
breeding
The First Cross
Tall
Short
PF1
Lets back track
 Yesterday we looked at the different
combinations of alleles that an
individual can have
 We also talked about dominance and
recessiveness
 What did we say the dominant allele was?
 What about the recessive allele
What were the parents?
 The parent that was tall
had a double _______ allele
 The parent that was short
had a double _______ allele
 Both of these parents
were homozygous
When he Crossed
 When the parents were crossed, the
F1 generation was completely
____________
 They all expressed the dominant trait,
but why?
 _____________________________
_____________________________
So the First cross is done,
what about the second?
Second Cross Genotype
Mendelian Ratio
 As Mendel completed the experiment,
he found that ____of the offspring of
the F1 cross were the ________ (tall)
and ____ were the _______ (short)
 The Ratio of _____ is known as the
_________________
Based on observations, Why
did this happen?
 Each parent in his F1 Generation starts
with two hereditary “factors.” One
factor is _______ and the other
________
 The factors separate out in the and
only one of the two factors contribute
to the phenotype of the offspring
Why did this happen?
 The offspring inherit ____ factor from
____ and ____ from ____. If the dominant
factor is present, it will be _______, even if
the recessive one is present
 The recessive factors will be expressed ___
if the recessive factors are present
The first Law of heredity
 His results gave rise to his first law
The law of Segregation
The law of segregation
 His law of segregation states: __________
_________________________________
 These factors segregate in the gametes
(after meiosis)
 Mendel did not know that his factors were
actually genes, we know this today
What do we call this?
Punnett Square
What do they do for us?
 Well, they are used by geneticists so that
they can _________ the expected ratio
(__________) and to suggest possible
combinations of _______ in the offspring
 They also tell us something about the
__________ (the appearance of a trait in
an organism)
So we saw TT x tt
 And for that cross we ended up having
a ratio of?
 All were Heterozygous (100% - 0%)
 What about when we cross the F1 x F1
generations?
F1 X F1
 What’s the ratio when we are talking
about phenotype?
 3:1 as well, three of the offspring will
present the dominant gene while the
fourth will present the recessive gene
 What about the genotype ratio?
 _____________________________
_____________________________
_____________________________
Example
Class Work
 Read Pages 202 -212
 Complete Questions 205 #1, 5, 6
 Page 207 #1, 3, 6, 9, 10, 11, 12