Heredity

• Gregor Mendel (1822)• Grew up on a farm• Studied trees and flowers• At 21 joined the monastery• The monks taught him science• Conducted scientific experiments

• Went to Vienna to the University to receive training in teaching• Did well in classes• Could not pass the final tests

• Returned to the monastery

• Mendel’s Peas• Mendel noticed patterns in the appearance of

plants from generation to generation• Some traits appeared and disappeared each

generation• He noticed the same in other living things

also• Mendel decided to investigate

• Mendel decided to investigate• He chose pea plants• He was familiar with peas• They grew quickly• There were different varieties• They were able to self-pollinate

• They were able to self-pollinate• Self pollinating plants pollinate

themselves• Able to produce true breeding plants

• Could also be cross-pollinated•Cross pollinating plants need pollen from a second plant

• Mendel could then study the traits of different characteristic

• Mendel’s first experiment• Mendel crossed plants with seven different

characteristics• The first group of offspring are called first-

generation plants

• Mendel first crossed a purple flowered plant with a white flowered plant

• In the first generation all the plants had purple flowers????????

• Mendel discovered that one trait is always present in the first generation and the other trait disappeared.

• Mendel called the trait that appeared the dominant trait.

• Because the other trait seemed to fade into the background, Mendel called it the recessive trait.

• Mendel’s second experiment• Mendel allowed the first generation plants

to self-pollinate

• The recessive trait reappeared

• Mendel discovered that one trait is always present in the first generation and the other trait disappeared.

• Mendel called the trait that appeared the dominant trait

• Mendel determined that peas had some traits that were dominate while others were recessive

Characteristics Ratio

Flower Color 705 Purple 224 White 3.15 : 1

Seed Color 6,002 Yellow 2,001 Green

Seed Shape 5,474 Round 1,850 Wrinkled

Pod Color 428 Green 152 Yellow

Pod Shape 882 Smooth 299 Bumpy

Flower Position 651 Axial Stem 207 Terminal

Plant Height 787 Tall 277 Short

Dominant Trait Recessive Trait

3 : 1

2.8 : 1

3 : 1

3.1 : 1

2.8 : 1

3 : 1

3 : 1

3 : 1

3 : 1

Traits and Inheritance

• What did Mendel discover?• Dominant and recessive traits• Dominant traits over power the recessive

traits• Recessive traits stay hidden until the

second generation in which they reappear• In the second generation the ratio of

dominant to recessive traits is 3:1

• The organism’s appearance is known as its phenotype• The different genes of the appearances is

known as the genotype

• What did Mendel discover?• There are two sets of instructions for each

characteristic• Scientists now call these instructions genes• Each parent gives one set of genes to the

offspring• The offspring then has two forms of the

same gene for every characteristic• Each of the different form is known as an

allele

T = tallt = short

T

T

T

T

T

T

T T

T T

T T

Results

Tall = Short =

4 /4 or 100%0 /4 or 0%

T = tallt = short

t

T

t

T

T

T

T t

t T

t t

Results

Tall = Short =

3 /4 or 75%1 /4 or 25%

B = Brown Eyesb = Blue Eyes

B

B

B

B

B

B

B B

B B

B B

Results

Brown = Blue =

4 /4 or 100%0 /4 or 0%

B = Brown Eyesb = Blue Eyes

b

B

b

B

B

B

B b

b B

b b

Results

Brown = Blue =

3 /4 or 75%1 /4 or 25%

B = Brown Eyesb = Blue Eyes

b

b

b

B

B

b

B b

b b

b b

Results

Brown = Blue =

2 /4 or 50%2 /4 or 50%

Could you get 75% of the recessive and only 25% of the dominant?

No

F = Full Lipsf = Thin Lips

f

F

f

F

F

F

F f

f F

f f

Results

Full = Thin =

3 /4 or 75%1 /4 or 25%

QUIZ

R = Tongue rollingr = Non rolling

R

r

r

R

R

r

R r

R r

R r

Results

Full = Thin =

4 /4 or 100%0 /4 or 0%

QUIZ

D = Dwarfismd = Normal growth

D

d

d

D

D

d

D d

D d

D d

Results

Dwarf = Normal =

4 /4 or 100%0 /4 or 0%

QUIZ

U = Unattached earlobeu = Attached earlobe

U

u

u

U

U

u

U u

U u

U u

Results

Unattached = Attached =

4 /4 or 100%0 /4 or 0%

QUIZ

U = Unattached earlobeu = Attached earlobe

u

U

u

U

U

U

U u

u U

u u

Results

Unattached = Attached =

3 /4 or 75%1 /4 or 25%

QUIZ

S = Second longers = Big toe longer

s

S

s

s

s

S

s s

s S

s s

Results

2nd longer = Big toe =

2 /4 or 50%2 /4 or 50%

QUIZ

S = Second longers = Big toe longer

s

s

s

s

s

s

s s

s s

s s

Results

2nd longer = Big toe =

0 /4 or 0%4 /4 or 100%

QUIZ