2. Inheriting Traits
• Eye color, nose
shape and many
other physical
features are some
of the traits that are
inherited from
parents.
• An organism is a
collection of traits,
all inherited from it
parents.

3. Vocabulary
Heredity – passing of traits from parent to offspring
Genetics – the study of traits passed from parents to offspring
Trait – genetically determined variant of a characteristic
Trait vs. Characteristic – if a characteristic is “eye color”, blue
eyes would be a possible trait
Alleles – different forms of a trait

4. • Every sex cell has
one allele for each
trait
• Genetics is the
study of how traits
are inherited
through the
interactions of
alleles

5. Father of Genetics
• Gregor Mendel began experimenting with garden peas
in 1856
• Carefully observed the pea plants, resulting in the first
recorded study of how traits pass from one generation to
the next

6. • Used the math of
probability to
explain heredity
• The first to trace
one trait through
several
generations

7. Genetics in a Garden
• Each time Mendel studied a trait, he
crossed two plants with different
expressions of the trait and found that the
new plants all looked like one of the two
parents.

8. Genetics in a Garden
• He called these new plants hybrids
because they received different genetic
information, or different alleles, for a trait
from each parent.

9. Genetics in a Garden
Purebred – an organism that always produces the
same traits generation after generation
Ex. Tall plants that always produce seeds that produce
tall plants are purebred for the trait of tall height

10. Self-pollination – when
pollen from a plant is
transferred to a flower on
the same plant
Cross pollination – when
pollen from a plant is
transferred to a flower on
a different plant
*In his experiments, Mendel
used pollen from the
flowers of purebred tall
plants to pollinate by
hand the flowers of
purebred short plants

11. • Mendel found that tall plants
crossed with short plants produced
all tall plants.
• DOMINANT vs. RECESSIVE

12. • DOMINANT – Mendel called the tall form
dominant because it dominated, or
covered up, the short form
• RECESSIVE – He called the form that
seemed to disappear the recessive factor

13. Probability – Make a prediction
• Mendel used probability (a branch of math
that helps you predict the chance that
something will happen.)
• His predictions were accurate because he
worked with a large number of plants
(almost 30,000 pea plants in 8 years),
thereby increasing his chances of seeing a
repeatable pattern.

14. Punnett Squares
• A tool used to predict
results in genetics is
the Punnett square.
It helps you predict
what offspring would
look like.
• In a Punnett square,
letters represent
dominant and
recessive alleles.

15. An uppercase letter stands for a dominant
allele
An lowercase letter stands for a recessive
allele

16. • Punnett squares show the genotype or
the genetic makeup of an organism
inherited from its parents
• It also shows the phenotype, which is the
appearance of an organism (ex. Tall or
short)

17. • Most cells in your
body have two alleles
for every trait. The
alleles are located on
chromosomes within
the nucleus.
Ex. Trait - Height
T allele would be for Tall
t allele would be for
short

18. • An organism with
two alleles that are
the same is called
homozygous. Ex.
TT
• An organism that
has two different
alleles for a trait is
called
heterozygous.
Example Tt

19. Making a Punnett Square
B B
b Bb Bb
b Bb Bb

20. Dominance
• An allele’s effect is Dominant or recessive.
• More common traits tend to be dominant and
less common are recessive.
Ex. T – Tall, t – short
TT would be Tall
Tt would still be Tall (because big T is dominant
tt would be short

22. Activity
A = normal
pigmentation
a = albinism
1. What fraction of this couple’s children would you expect to be AA?
2. What fraction of this couple’s children would you expect to be Aa?
3. What fraction of this couple’s children would you expect to be aa?
4. What fraction of this couple’s children would you expect to have normal
pigmentation?
5. What fraction of this couple’s children would you expect to have albinism?

23. Mendel’s Laws of Genetics
1. Law of Segregation
2. Law of Independent Assortment

24. 1. Law of Segregation
• For any particular trait, the pair of alleles of
each parent separate and only one allele
passes from each parent on to an
offspring.
• Which allele in a parent’s pair is inherited
is a matter of chance.

25. Ex. Each parent gives only one allele to an
egg or sperm. When fertilization
occurs, the offspring’s gene pair is
determined by which allele each sex cell
carried.

26. 2. Law of Independent Assortment
• Different pairs of alleles are passed to
offspring independently of each other.
• This means that the offspring can have
combinations of genes that neither parent
has. So, the offspring can look differently
than both parents.
Ex. Explains why the human inheritance of a
particular eye color does not increase or
decrease the likelihood of having 6 fingers on
each hand.

28. Types of Genetic Crosses
• Monohybrid cross – cross involving
single trait
Ex. Flower color
• Dihybrid cross – cross involving two traits
Ex. Flower color and plant height

29. More Words
• P Generation – parent generation in a
genetic cross
• F1 generation – first generation offspring
resulting from a cross between parents
• F2 generation – second generation
offspring resulting from a cross between
the F1 offspring

31. Sex Determination
XX – girls
XY – boys
Females produce eggs
with X chromosomes
only.
Males produce sperm with
X and Y chromosomes

32. Sex-Linked Disorders
• An allele inherited on a sex
chromosome is called a
sex-linked gene.
Ex. Color blindness is a sex-
linked disorder in which
people cannot distinguish
between certain
colors, particularly red and
green

33. • This trait is a recessive allele on the X
chromosome.
• Because males have only one X
chromosome, a male with this allele on his
X chromosome is color blind.
• A color blind female occurs only when both
of her X chromosomes have the allele for
this trait.
So, are you color blind or
not?

34. Pedigree
• A visual tool for
following a trait through
generations of a family.
• Males – squares,
Females – circles
• Completely filled circle
or square – trait is seen
in that person
• Half colored – indicate
carriers
• Empty – do not have
the trait and are not
carriers

38. Homework
1. You are newly married and want to find
out the probability of you having kids with
blue eyes. You have brown eyes, while
your spouse has blue eyes. Will you
have kids with blue eyes? And if so, how
many?
2. What other sex-linked genetic disorders
are there? Give examples and a brief
description.