Download The Toolbox of Science

Genetics: The science of
Heredity.
Where to begin?
Gregor Mendel
Gregor Mendel
 The "father of modern genetics”
 Born on July 22, 1822 in Heizendorf,
Austria.
 Mendel raised and tested over 28,000 pea
plants between the years 1856 and 1863,
carefully analyzing seven pairs of seed and
plant characteristics.
Gregor Mendel
 He specifically studied plant height, pod
shape, pod color, flower position, seed
color, seed shape and flower color.
 He made two very important generalizations
from his pea experiments, know today as
the Laws of Heredity.
Gregor Mendel
 Law of Segregation
• Mendel's First Law
 Law of Independent Assortment
• Mendel's Second Law
A few terms…...
 Traits

Physical characteristics
 Heredity

The passing of traits from parents to offspring.
 Genetics

The study of heredity
 Purebred

Always produces offspring with the same traits
as the parents.
Back to Mendel
 His first experiment……using pea plants he
crossed purebred tall plants with purebred
short plants plants.
 What do you think he got?
• CD
Back to Mendel
 Turns out, the first generation of plants were
all tall! No short ones!
More of Mendel
 He then took two of the offspring plants and
crossed them…….What do you think he
got?
• CD
More of Mendel
 Holy Smokes…He got 75% Tall plants and
25% short plants!..How could this be?
• CD
Mendel Explained…..
 From this experiment and others, Mendel
concluded that factors must control the
inheritance of traits.
 These factors must exist as pairs..one from
the male parent and one from the female
parent.
Mendel Explained…..
 Today, we call these genes

factors that control traits.
 The different forms of a gene are called
alleles.
Mendel Explained…..
 Individual alleles control the inheritance of
a trait.
 Some alleles are dominant while others are
recessive.
 A Dominant allele trait always shows if the
organism has the allele
 A recessive allele is masked if a dominant
allele is present.
How can we look at this...
 Scientist use a simple grid to help sort out
genetics and inheritance called a Punnett
Square.
Punnett Squares
 Chart that shows all possible combinations
of alleles that can result from a genetic
cross.
Punnett Squares
Parent Generation P
Punnett Squares
Parent Generation P
Offspring Generation F1
Punnett Squares
Offspring Generation F1
Punnett Squares
Offspring Generation F1
Offspring Generation F2
Punnett Squares
If an offspring has two
different alleles for a trait, it
is called a hybrid.
Hybrid: Two different alleles
for a trait.
Punnett Squares
Let’s predict another...
Offspring Generation F2
Couple more terms….
 Now that we have a basic concept of how
gene pairs mix to express traits, we should
give this mixing and expressing some niffy
science terms….
 Phenotype: An organisms physical traits.

Height, color, shape, ear attachment etc.
 Genotype: An organisms genetic makeup or
allele combination.
Still More…...
 A touch more detail…….
 If an organisms genotype has two identical
alleles it is called homozygous
 Homozygous: Two identical alleles.
Which ones are Homozygous?
Still More…...
 If an organisms genotype has two different
alleles it is called heterozygous
 Heterozygous: Two different alleles.


The same thing Mendel called a hybrid.
Hybrid is still commonly used.
Which ones are Heterozygous?
What about us?
 Does this all work the same for humans?
 Sure it does!
 Let’s start with the simplest to sort…Male
and Female
Human Genetics
Female sex cell…Egg
Male sex cell…sperm
How about sex-linked genes
 Color blindness is carried only on the X
chromosome. Usually expressed as XC or
Xc. What if you have a color blindness
carrier(not color blind) for a mom and a
normal father?
Sex-linked genes