Chapter 26 genetics
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Chapter 26: Genetics. Genes and chromosomes. Eye color. Hair color. Skin color. Nose size. Nose shape. Genes. Eye shape. hair texture. Ear size. widow’s peak. Ear lobes. Chromosome. Types of Chromosomes. Sex Cell. Body Cell. Chromosomes NOT paired.

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Chapter 26: Genetics

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Chapter 26: Genetics


Genes and chromosomes

Eye color

Hair color

Skin color

Nose size

Nose shape

Genes

Eye shape

hair texture

Ear size

widow’s peak

Ear lobes

Chromosome


Types of Chromosomes.

Sex Cell

Body Cell

Chromosomes NOT paired

Chromosomes are paired and therefore have two genes for every trait


A body cell has ___________ genes for every trait.

two

One

Sex cells only have ________ gene for every trait


egg

sperm

Fertilized egg


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


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


Terminology:

GENOTYPE – a person’s genesPHENOTYPE (physical appearance)

B B

Brown eyes

= HOMOZYGOUS Dominant

(pure dominant)

B b

= HETEROZYGOUS

(hybrid)

Brown eyes

b b

= HOMOZYGOUS recessive

(pure recessive)

Blue eyes


Possible Sperm

Possible Eggs

B

B

b

b

What are the possible

outcomes for the child?


Dad is B b

Mom is B b

Possible Sperm

Possible Eggs

B B = brown eyes

B

B

B b = brown eyes

b

B b = brown eyes

b

b b = blue eyes


Punnett Square

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

Mother’s Genes

B

b

B

B

B

B

b

Father’s

Genes

B

b

b

b

b


Sperm

Sperm

offspring

egg

offspring

egg

offspring

offspring


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


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


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


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:

GG

gg

G G

Gg

Gg

g

P1

All green

* yellow trait “disappeared”??

Gg

Gg

g

F1

G g

G

GG

Gg

3 green

1 yellow

Gg

gg

g

F2

yellow

green

green

green

*yellow trait “re-appeared”


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.


Proving Mendel’s 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


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