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Topic: Genetics
Aim: How do we use pedigree charts to
follow a trait through generations of a
family?
Do Now: next slide
HW: Genetic Engineering Reading notes
due tomorrow!
T = tall t = short
Cross two heterozygous plants.
Tt x Tt
T
t
T T T Tt
t Tt
tt
T
t
T T T Tt
t Tt
tt
Phenotype %:
75% tall
25% short
Genotype %:
25% homozygous
dominant
50% heterozygous
25% homozygous
recessive
Humans have 46
chromosomes in EVERY
somatic cell in the body.
Out the 46 chromosomes,
2 of them are
sex chromosomes that
determine gender.
The other 44
chromosomes are called
autosomes.
1. Identify the
sex
chromosomes
found in males.
• XY
2. Identify the
sex
chromosomes
found in
females.
• XX
•
X
chromosome
is
3. Study
larger than the Y
Figure 8 on
p.138. How do
chromosome
the X and Y
chromosome
differ in shape.
How is the sex of an individual
determined?
• Eggs = X
• Sperm = X or Y
Female chromosomes
Male chromosomes
The X chromosome
carries a couple of
thousand genes but few, if
any, of these have
anything to do directly
with sex determination.
The X chromosome likely
contains genes that
provide instructions for
making proteins. These
proteins perform a variety
of different roles in the
body.
The Y chromosome likely
contains genes that provide
instructions for making
proteins. The genes on this
chromosome tend to be
involved in male sex
determination and
development. Sex is
determined by the SRY gene,
which is responsible for the
development of a fetus into a
male. Other genes on the Y
chromosome are important for
male fertility.
• To follow a trait
4. Explain
through generations
what a
pedigree chart of a family
is used for.
5. Identify how each of the following is
represented in a pedigree chart.
a. Male Square
b. Female Circle
c. A male with the trait Completely filled square
d. A female with the trait Completely filled circle
e. A carrier Half colored circle or square
f. A normal male (does not have the trait)
Empty square
a. A normal female (does not have the trait)
Empty cirlce
9. What does the
horizontal line between
the male and female
represent?
They have children with
each other
10. What do the vertical
lines represent?
Offspring
11. How many offspring did
the first generation have?
4
12. How many offspring from
the first generation were born
with the trait?
None
13. One of the females in
the 2nd generation had
children with a male with
the trait.
a. How many children
were born with the
trait?
2
b. What is the genotype
of the children with the
trait?
homozygous recessive
14. What is the mom’s genotype?
heterozygous
6. How many offspring did
the 1st generation have?
3
7. How many offspring
from the 1st generation
were born with the trait?
1
8. Individual 3 had
children with individual 4.
a. How many children did 3
and 4 have?
2
b. Which child was born
with the trait? male
c. What were the
genotypes of individuals 3
and 4? heterozygous
9. What is the genotype of
individual 2?
Tt
10. If individual 2 had
children with a normal
female (without the trait),
can they have children
with the trait?
No
Let’s Review:
1. What are “regular” chromosomes called?
2. Explain the difference between sex
chromosomes in a male and sex
chromosomes in a female.
3. Put the following terms in order from smallest
to largest:
chromosomes, nucleus, DNA, genes
4. Put the following terms in order from largest
number to smallest number:
chromosomes, nucleus, DNA, genes
http://www.brainpop.com/science/cellularlifeandgenetics/heredity/
1
3
5
4
14
2
15
6
16
17
7
18
19
8
9
10
22
20
21
1. Identify the genotypes of 1 and 2.
2. How many offspring did 1 and 2 have?
3. Identify the genotype of 3.
11
12
13
25
23
24
1. Identify the genotype of
the father. RR
2. Identify the genotype of
the mother. rr
G = green
g = yellow
Cross a pure green plant with a
hybrid plant.
GG X Gg
G
G
G GG GG
g Gg Gg
G
G
G GG GG
g Gg Gg
Phenotype
percentages:
100% green
Genotype percentages:
50% heterozygous
50% homozygous
dominant