Mendelian Genetics Notes
 Gregor Mendel
 Mendel was a
in the
 He grew
to see how characteristics were inherited.
 He looked at 7 traits
 Flower color, pea shape, pod shape, pea color, pod color, plant height, and position
of the flowers
 Mendel’s First Set of Experiments
 Mendel started by
the plants.
 This means that he had them mate with themselves.
 He called these plants
because when he did this they always
resulting in identical offspring
 Next he mated a PURE purple with a PURE white
flower.
 When you mate 2 different plants it is called
____________________________
 The offspring of these crosses were HYBRIDS.
They were no longer pure because they were
mixtures of two different plants.
 Finally, Mendel self-fertilized the offspring and
looked at the grand-offspring.
 Mendel described how the plants’ appeared, or their physical traits, with the term
and their genetic appearance, or genotypic traits, with the term
 Mendel’s Hypotheses
 Based on his experiments we found:
 There are alternative forms of genes called he called
(today we call these alleles)
GENE
ALLELES
Height
Tall (T) or Short (t)
Purple (P) or White (p)
Seed Shape
 For each characteristic an organism has 2 factors –
 If these 2 factors are the same we call it
 If these 2 factors are different we call it
Height
ALLELE
from MOM
Tall (T)
ALLELE
From DAD
Tall (T)
Flower Color
White (p)
Purple (P)
Seed Shape
Round (R)
Round (R)
GENE
Genotype?
(TT) Homozygous
 When two factors are different, the one that is expressed is
the one that is hidden is
.
GENE
ALLELE
from MOM
ALLELE
From DAD
Height
Tall (T)
Short (t)
Flower Color
White (p)
Purple (P)
Seed Shape
Round (R)
Round (R)
 The sperm and egg are able to carry
factors segregate during gamete production. This is called the
, while
Phenotype?
for each gene because the
 Mendel’s Second Set of Experiments
 He crossed
traits instead of just 1 (like you did with your mice).
 He followed the same experimental protocol:
 Two different pure
parents were cross –
fertilized
 Offspring were self –
fertilized
 He discovered that traits are inherited
black fur and red or black eyes). He called this his
of one another (you can have
Is Mendel right?
It turns out that Mendel’s hypotheses, and his two laws, hold true for garden peas and many human traits.
However, that is not the end of the story. Today we know…
 That while all genes have alternative forms, some genes have more than two… For instance while peas can
only be tall (T) or short (t), many human traits have more variety – like with blood we can have A (IA) , B
(IB) or O (i) alleles.
 That while a mixture of tall (T) and short (t) alleles in pea plants results in a tall phenotype, in humans it
does not. Tt in humans results in a medium height. Outside of the world of peas – not all traits have a clear
cut dominant and recessive.
 That while segregation should always occur during the process of meiosis, in rare cases – like Down
Syndrome – it does not.
 That while independent assortment does occur for many traits - it is not always true. For instance, in
humans if two genes are right next to each other on a chromosome chances are they will NOT sort
independently. We say they are linked. In these instances independent assortment does not occur.
 We will explore this further in Non-Mendelian genetics (or Mendelian extensions)
Scavenger Hunt
You are on a scavenger hunt to find all the diversity our classmates have to offer. In each square have a
person sign that represents that trait. You may fill in only one square for yourself. The first person to
finish with all of the squares is the winner!
Person an Attached Ear
Lobe
Person With Blonde
Hair
Person With A Free Ear
Lobe
Person With
Hitchhikers Thumb
Person With Dimples
Person With Forehead
Freckles
Person With Brown
Eyes
Person Without Hair
On Fingers
Person Who Can Taste
PTC Paper
Person Who Can Not
Roll Their Tongue
Person Without
Widows Peak
Person With Black Hair
Person With Five
Fingers
Person With Cleft Chin
Person Who’s Left
Thumb Is On Top Of
Interlocking Fingers
Person With Widows
Peak
Person Without
Hitchhikers Thumb
Person With Brown
Hair
Person Without Cleft
Chin
Person Who Can Not
Taste PTC Paper
Scavenger Hunt
You are on a scavenger hunt to find all the diversity our classmates have to offer. In each square have a
person sign that represents that trait. You may fill in only one square for yourself. The first person to
finish with all of the squares is the winner!
Person an Attached Ear
Lobe
Person With Blonde
Hair
Person With A Free Ear
Lobe
Person With
Hitchhikers Thumb
Person With Dimples
Person With Forehead
Freckles
Person With Brown
Eyes
Person Without Hair
On Fingers
Person Who Can Taste
PTC Paper
Person Who Can Not
Roll Their Tongue
Person Without
Widows Peak
Person With Black Hair
Person With Five
Fingers
Person With Cleft Chin
Person Who’s Left
Thumb Is On Top Of
Interlocking Fingers
Person With Widows
Peak
Person Without
Hitchhikers Thumb
Person With Brown
Hair
Person Without Cleft
Chin
Person Who Can Not
Taste PTC Paper