Download Mendel*s Work With Garden Peas Introduced Hereditary Genetics

Bellringer
•Please answer the following questions on your
bellringer sheet:
•Based off of what you remember from the
Human Heredity Activity we did in class on
block day, what does it mean when a trait is
dominant? Recessive?
Learning Targets
• Please write down at the top of your notes:
• Explain Mendel’s experiments and data, including the
Law of Segregation.
• Explain how there can be many forms of a one gene
and how genes influence the development of traits.
• Describe the purpose of monohybrid crosses, and use
them as tools to calculate inheritance probabilities.
MENDELIAN GENETICS
18 Things You Should Know About Genetics
genetics video

Gregor Mendel: Hereditary Genetics
• Garden peas are:
• Self-pollinating
• Easy to experimentally cross-pollinate
• Clear traits—pure purple, pure white, etc.
• Trait: any single feature of an organism

What Mendel Discovered!
• P Generation (“Parent”)
• F1 Generation (“First Filial”) (Kids)
Whoa!
• F2 Generation (“Second Filial”)
(Grandkids)
Did You Catch That?
• Where did that short plant
(trait) come from?
• Was it hiding?

Recessive Traits “Hide” Behind Dominant
Traits
• Sexual Organisms
have two of each
trait (homologous
pairs)
• One of each pair is
passed on to
offspring by each
parent.

Recessive Traits “Hide” Behind Dominant
Traits
• Different forms of
the same trait are
called alleles
PLANT HEIGHT
• What TRAIT is
being studied in
this experiment?
“Tall”
… and …
“Short”
• What are the TWO
ALLELES (forms)
of the trait being
studied?
Other Traits That Mendel Studied
(Which word below is a synonym for “allele”?)
ALLELES
ALLELES
Try one
• What trait is being studied?
• What’s the dominant allele of the trait?
• What’s the recessive allele of the trait?
Note the Percentages
50:50
100:0
~75:25
50
50 Short
• In P Gen: ____%
Tall, ____%
100
0
• In F1 Gen: ____%
Tall, ____%
Short
~75
~25 Short
• In F2 Gen: ____%
Tall, ____%

Mendel proposed that
“Factors” segregate
(separate) from pairs to
be passed on to
offspring, one from
each parent!
(Sounds familiar?)
Think – Pair -Share
•Why does this sound familiar?
During what process does this occur?
Turn to your shoulder partner and discuss what
you think the process is.
3 groups will be asked to share.
(Sounds familiar?)
(Sounds familiar?)
Homologous chromosomes split up in
anaphase I so that only one allele of each trait
gets passed on in your gametes!

The pair of alleles you have (for any trait) is called
your GENOTYPE
Example Trait: Nose Shape
(Let us pretend that round nose is dominant to pointy nose)
(usually, letters are used to represent alleles, upper case for dominant)
n
N
• Alleles: ___ (dominant), ___ (recessive)
NN Nn nn
• Genotypes: ____, ____, ____
“Homozygous
Dominant”
“Heterozygous”
“Homozygous
Recessive”
The pair of alleles you have (for any trait) is called
your GENOTYPE
Again!
NN Nn nn
• Genotypes: ____, ____, ____
This genotype is
described as
“Homozygous
_______________
Dominant”
___________
(Purebred)
This genotype is
This genotype is
described as
described as
“Heterozygous”
“Homozygous
_____________ _______________
(hybrid or carrier)
Recessive”
___________
(Purebred)
NN
One from Mom
One from Dad

Each set of alleles is a homologous pair, one
from Mom and one from Dad!
What is this person’s
genotype?
• This is called your
 PHENOTYPE (an
expressed feature
you can see!)
NN
________________
Homozygous Dominant
What kind of nose do they have?
Round? Or Pointy?
Nn
• Remember:
Dominant
overshadows
recessive!
________________
Heterozygous
What is this person’s PHENOTYPE?
Round? Or Pointy?
nn
• Recessive alleles
show only if no
dominant is
present!
________________
Homozygous Recessive
What is this person’s phenotype?
Round? Or Pointy?
Gregor Mendel Research and Principles
• Mendel Video
Mendel’s Principles
• Principles of Segregation
• States that every individual possesses a pair of alleles for any particular
trait and that each parent passes a randomly selected copy (allele) of only
one of these to its offspring. The offspring then receives its own pair of
alleles for that trait. (Factors for a particular trait occur in pairs.)
• Principle of Independent Assortment
• States that genes for different traits can segregate independently during
the formation of gametes. (Factors segregate randomly during anaphase I
of meiosis.)
• Principles of Dominance
• States that some alleles are dominant and others are recessive. (Dominant
factors mask recessive ones.)
Another Example:
• What’s the TRAIT?
• What are the ALLELES?
• Which is dominant?
PP
pp
Pp
Remember: Only one of each allele is passed on
from each parent!
• What is Mom’s genotype?
 Pp
Rr
Heterozygous
• What is Dad’s genotype?
Ova
(either)
Heterozygous

GERM
CELL
Pp
Sperm
(either)
GERM
CELL
Let’s Look At
the
Offspring
Probabilities
Ova
(either)
• What if this
egg meets this
sperm?
Sperm
(either)
What if this egg
meets this sperm?
What if this egg
meets this sperm?
What if this egg
meets this sperm?
What if this egg
meets this sperm?

This Is Called
A Punnett
Square
• Punnett squares
allow us to
predict
probabilities
about offspring
What percentages does this Punnett square predict?
• How many
75% (3/4)
Purple? ______
• How many
White? ______
25% (1/4)
• How many
homozygous
dominant? 25%
___(1/4)
• How many
heterozygous?
______
50%
(2/4)
• How many
homozygous
recessive? ___
25% (1/4)
25%
25%
25%
25%
What is the probability that this couple
will have a baby with the “a” disease?
• Healthy allelle = A
• Disease allele = a
25%
(1/4)
What is the probability that this couple will have a
baby who is a CARRIER for the “a” disease?
• Healthy allelle = A
• Disease allele = a

50%
(2/4)
A CARRIER is a heterozygote
(he or she can “pass on” the
trait)

Your Turn! (For disease “a”):
What if a homozygous dominant man marries a
carrier woman?
AA
Aa
____ X ____
Dad
Mom
A
a
A
AA
Aa
A
AA
Aa
Offspring
Genotype:
- HD (AA) = ___%
50
- Het (Aa)= ___%
50
- HR (aa)= ___%
0
Offspring
Phenotype:
- Healthy* = ___%
100
- Disease = ___%
0
- *(Healthy) Carrier =
50
_____%

One More Time! (For disease “a”):
What if a carrier man marries a
woman with the disease?
Aa
____ X aa
____
Dad
Mom
a
a
A
Aa
Aa
a
aa
aa
Offspring
Genotype:
0
- HD (AA) = ___%
50
- Het (Aa)= ___%
50
- HR (aa)= ___%
Offspring
Phenotype:
- Healthy* = 50
___%
50
- Disease = ___%
- *(Healthy) Carrier =
50
_____%
Note the Percentages
50:50
100:0
~75:25
50 Short
50
• In P Gen: ____%
Tall, ____%
0
100 Tall, ____%
• In F1 Gen: ____%
Short
~25 Short
~75 Tall, ____%
• In F2 Gen: ____%