Chapter 26: Genetics

Genes and chromosomes

Chromosome

Genes

Eye color

Hair color

Skin color

Nose size

Nose shape

Eye shape

hair texture

Ear size

widow’s peak

Ear lobes

Types of Chromosomes.

Sex Cell Body Cell

Chromosomes are paired and therefore have two genes for every trait

Chromosomes NOT paired

A body cell has ___________ genes for every trait.

Sex cells only have ________ gene for every trait

two

One

sperm

egg

Fertilized egg

B = b =

Child has a gene for BLUE eyes and a gene for BROWN eyes…

????

B b

B b

Brown eyed Dad Blue eyed Mom

What happens when you have a gene for Brown eyes AND a gene for Blue eyes??

A gene that will SHOW the trait

A gene that will NOT show the trait if a dominant gene is present.

B B = ___________________

B b = ___________________

b b =

Brown eyes

Brown eyes

Blue eyes

Terminology:

= HOMOZYGOUS Dominant

(pure dominant)

= HETEROZYGOUS

(hybrid)

= HOMOZYGOUS recessive

(pure recessive)

GENOTYPE – a person’s genes PHENOTYPE (physical appearance)

Brown eyes

Brown eyes

Blue eyes

B

b

B

b

Possible EggsPossible Sperm

B

b

B

b

Possible EggsPossible Sperm

Punnett SquareA method for predicting the possible outcomes (offspring) of a genetic cross

Mother’s Genes

Father’s

Genes

B b

B

b

B B

B b

B b

b b

egg offspring

Sperm

egg

Sperm

offspringoffspring

offspring

X

B B b b

B B

b

b

B b B b

B b B b

B b B bB bB b

X

B b b b

B b

b

b

B b b b

B b b b

B b b bb bB b

X

B b B b

B b

B

b

B B B b

B b b b

B B b bB bB b

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

Mendel’s experiments:G G

g

g

GG gg

G g

G

g

Gg Gg

Gg Gg

GG Gg

Gg gg

yellow Yellow yellow green

P1

F1

F2

All yellow

* green trait “disappeared”??

3 yellow

1 green

*green trait “re-appeared”

Mendel repeated this for all the traits of a pea plant. Since the results were the same, he concluded:

Mendel used statistics and punnett squares to accurately predict the outcomes of all his possible genetic crosses.

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 tall

tt x tt = all short

Proving Mendel’s workT T

T

T T

TT TT

TT

t

t

t

t

tt

t

tt

t

t

t

T

T T

T T

T T

T T

T T

T TT T

T t T t T tT t

T tT t

T tT 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

3 tall, 1 short 2 tall, 2 short All short