Chapter 26: Genetics

1
Chapter 26 Genetics
2
Genes and chromosomes
Eye color
Hair color
Skin color
Nose size
Nose shape
Genes
Eye shape
hair texture
Ear size
widows peak
Ear lobes
Chromosome
3
Types of Chromosomes.
Sex Cell
Body Cell
Chromosomes are paired and therefore have two
genes for every trait
Chromosomes NOT paired
4
A body cell has ___________ genes for every trait.
two
One
Sex cells only have ________ gene for every trait
5
egg
sperm
Fertilized egg
6
B
Brown eyed Dad
b
Blue eyed Mom
b
B
Child has a gene for BLUE eyes and a gene for
BROWN eyes ????
B b
7
What happens when you have a gene for Brown eyes
AND a gene for Blue eyes??
A gene that will SHOW the trait
Dominant
B B ___________________ B b
___________________
Brown eyes
Brown eyes
A gene that will NOT show the trait if a dominant
gene is present.
Recessive
b b
Blue eyes
8
Terminology
GENOTYPE a persons genes PHENOTYPE

(physical appearance)
B B
Brown eyes
HOMOZYGOUS Dominant (pure dominant)
B b
HETEROZYGOUS (hybrid)
Brown eyes
b b
HOMOZYGOUS recessive (pure recessive)
Blue eyes
9
Possible Eggs
Possible Sperm
B
B
b
b
What are the possible outcomes for the child?
10
Dad is B b
Mom is B b
Possible Eggs
Possible Sperm
B B brown eyes
B
B
B b brown eyes
b
B b brown eyes
b
b b blue eyes
11
Punnett Square
A method for predicting the possible outcomes
(offspring) of a genetic cross
Mothers Genes
B
b
B
B
B
B
b
Fathers Genes
B
b
b
b
b
12
Sperm
Sperm
offspring
egg
offspring
egg
offspring
offspring
13
B
B
b
B b
B b
b
B b
B b
B B
b b
X
B b
B b
B b
B b
14
B
b
b
B b
b b
b
B b
b b
B b
b b
X
B b
b b
b b
B b
15
B
b
B
B B
B b
b
B b
b b
B b
B b
X
B B
b b
B b
B b
16
Gregor Mendel 1865

• Austrian monk
• Father of genetics
• Botanist
• Worked with pea plants.
• Discovered recessive and dominant genes using
  mathematics
• Genetics study of how traits are passed from
  parent to offspring

17
Mendels experiments
G G
GG
gg
Gg
Gg
g
P1
All yellow green trait disappeared??
Gg
Gg
g
G g
F1
G
GG
Gg
3 yellow 1 green
Gg
gg
g
F2
yellow
Yellow
yellow
green
green trait re-appeared
18
Mendel repeated this for all the traits of a pea
plant. Since the results were the same, he
concluded
TT x TT all tall
TT x Tt all tall
TT x tt all tall
Tt x Tt ¾ tall, ¼ short
Tt x tt ½ tall, ½ short
tt x tt all short
Mendel used statistics and punnett squares to
accurately predict the outcomes of all his
possible genetic crosses.
19
Proving Mendels work
T
T
T
T
T
T
T
t
T
T T
T T
T T
T T
T t
T t
T
T T
T T
T t
T t
T t
t
t
T t
4 tall
4 tall
4 tall
T
T
t
t
t
t
T t
T t
t
t
T
T T
T t
t t
t t
t
t
T t
t t
t t
t t
t t
t t
t
3 tall, 1 short
All short
2 tall, 2 short