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Section 10.1. pg. 253. Mendel’s Laws of Heredity. WHY MENDEL SUCCEEDED. Gregor Mendel (1822-1884) Austrian Monk known as the “father of modern genetics” Found that inheritance follows certain laws later known as Mendel’s Laws of Inheritance

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section 10 1

Section 10.1

pg. 253

Mendel’s Laws of Heredity

why mendel succeeded

WHY MENDEL SUCCEEDED

Gregor Mendel (1822-1884)

Austrian Monk known as the “father of modern genetics”

Found that inheritance follows certain laws later known as Mendel’s Laws of Inheritance

Heredity is the passing on of characteristics from parent to offspring

Inherited characteristics are called traits(factors)

The branch of biology that studies heredity is called genetics – which was founded upon the rediscovery of his work.

why mendel succeeded3

WHY MENDEL SUCCEEDED

Mendel’s pea plant collection contained around 28,000 plants

Pea plants reproduce sexually by producing male and female sex cells (gametes)

Male gamete forms in pollen

Female gamete formed in ovary

Fertilization occurs when the male gamete unites with the female gamete

Pollination is the transfer of pollen to ovary in a plant – normal reproduction.

Remove male parts

Snipping the stamen could prevent self-pollination

flower parts

Flower parts

A similar figure is in the book on pg. 642

why mendel succeeded5

WHY MENDEL SUCCEEDED

Figure 10.1

Cross-pollination is transferring pollen of one plant to the ovary of another plant

Mendel did this to get certain plants to breed with others to be sure of the parents

Mendel was very careful with all of his work

mendel s monohybrid crosses

Figure 10.2

P1

MENDEL’S MONOHYBRID CROSSES

Short pea plant

Tall pea plant

F1

Mendel was able to create tall plants and short plants (purebreds)

He referred to the offspring of a purebred tall and a purebred short as a hybrid

Crossing a 6’ tall plant with a 2’ tall (short) plant resulted in all 6’ tall plants

Crossing the hybrid offspring resulted in 75% tall and 25% short

P1 refers to the “Parental generation”

F1 (“Filial”) refers to the offspring

All tall pea plants

F2

3 tall: 1 short

mendel s monohybrid crosses7

MENDEL’S MONOHYBRID CROSSES

So what does MONOHYBRID refer to?

Referring to figure 10.3:

When Mendel crossed a purebred tall with a purebred short he got all tall plants

When he crossed a purebred purple flower with a purebred white flower he got all purple flowers

He referred to the trait that was observed in these cases as ___________.

The trait that seemed to “disappear” he called _____________.

Mendel concluded that these plants have “factors” that control each of the traits (color, shape, height)

We call these factors genes (parts of DNA)

Alternative forms of genes (tall vs. short or yellow vs. green) are known as alleles.

slide8

Plant

height

Figure 10.3

Seed

shape

Seed

color

Flower

color

Flower

position

Pod

color

Pod

shape

Dominant

trait

axial

(side)

round

yellow

purple

green

inflated

tall

Recessive

trait

terminal

(tips)

wrinkled

green

white

yellow

short

constricted

mendel s monohybrid crosses9

P1

MENDEL’S MONOHYBRID CROSSES

Tall plant

Short plant

These two alleles for each trait can be expressed as a single letter

For plant height we can use the letters “T” & “t”

Dominant allele is ___.

Recessive is ___.

Mendel’s purebred tall plants were “TT”

His purebred recessive plants were “tt”

Fill in the blanks in the figure to the right which t goes where?

F1

All tall plants

T

T

T

T

T

t

t

t

mendel s monohybrid crosses10

MENDEL’S MONOHYBRID CROSSES

Mendel concluded that the allele (gene form) of tall plants was dominant to the allele for short plants

Confirming that the plants had two alleles for each trait (TT = Tall, Tt = Tall, or tt = short)

Knowing that traits are inherited from parents, he also concluded that these alleles are inherited

However a plant can only get one allele from each parent

The gametes (sex cells) contained either one or the other form of the gene (T or t)

The Law of _________________ states that every individual has two alleles of each gene and when gametes are produced, each gamete receives one of these alleles.

T

T

phenotypes and genotypes

PHENOTYPES AND GENOTYPES

It’s vocab time…

Phenotype refers to the organism’s physical characteristic (what you can see) Ex: Tall

Genotype refers to the organism’s genetic makeup (what you can’t see) Ex: TT or Tt

Homozygous/purebred represents two alleles that are the same (TT or tt)

Heterozygous/hybrid organisms have different alleles (Tt)

How are we going to distinguish Homo and Hetero?

Law of Dominance states that hybrid organisms (Tt) will express the dominant allele (ex: tall).

punnett squares

Monohybrid Cross (one trait)

PUNNETT SQUARES

Heterozygous

tall parent

T

t

T

t

T

t

1905 - Reginald Punnett devised an easy way to find expected genotype proportions of offspring from known parent genotypes based off Mendel’s laws

T

T

T

t

TT

Tt

t

t

Tt

tt

T

t

G= 50% Tt : 25% TT : 25% tt

Heterozygous

tall parent

P= 3 Tall : 1 short

punnett squares13

PUNNETT SQUARES

Round

Yellow

Round

green

Monohybrid crosses are easy to separate alleles according to Mendel’s Law of Segregation

If we have heterozygous parents (Tt X Tt) we can just separate the T from the t

For Dihybrid crosses, the gamete separation is a little tricky

If we have two parents that are heterozygous for seed shape (Rr) and seed color (Yy) their genotype is RrYy

To separate alleles into gametes we use the FOIL method from algebra

RrYy makes four different gametes

Using the FOIL method we get…

wrinkled

Yellow

wrinkled

green

RY

Ry

rY

ry

mendel s dihybrid crosses

RRYY

MENDEL’S DIHYBRID CROSSES

rryy

Mendel also crossed plants with two different traits

Round=R, wrinkled=r & Yellow=Y, green=y

What is the genotype of a purebred (homozygous) plant with Round Yellow seeds?

What is the genotype of a purebred (homozygous) plant with wrinkled green seeds?

Purebred (homozygous) RoundYellow seeds X Purebred (homozygous) wrinkledgreen seeds

Result of F1…All plants had Round Yellow seeds

However crossing the Dihybrid F1 gives a ratio of 9:3:3:1

Which leads us to Mendel’s second law…

The Law of __________________ states that genes for different traits are inherited independently of each other.

slide15

Round Yellow (RRYY) X wrinkled green (rryy)

P1

wrinkled green

Round Yellow

F1

All Round Yellow

F2

1

9

3

3

wrinkled green

Round Yellow

Round green

wrinkled Yellow

R_Y_

rrY_

R_yy

rryy

slide16

Gametes from RrYy parent

Starting here what are the gametes?

ry

RY

Ry

rY

RY

RRYY

RRYy

RrYY

RrYy

Ry

Gametes from RrYy parent

RRYy

RRyy

RrYy

Rryy

rY

RrYY

RrYy

rrYY

rrYy

ry

RrYy

Rryy

rrYy

rryy

probability

50%

PROBABILITY

75%

r

R

RR

Rr

R

Knowing the parents genotype we can predict the probable offspring genotype and phenotype

What is the probability of having Rr offspring?

What is the probability of having Round offspring?

Rr

rr

r

probability18

PROBABILITY

Given the parents genotype and number of offspring, you should be able to predict the number of each genotype and phenotype.

PROBABILITY PROBLEM

R=Round seeds & r=wrinkled seeds

1. P1 genotype: RR X rr

2. All of the F1 offspring will be ______.

3. Assume 140 F2 offspring are created from F1.

4. ________ will have their parents (F1) genotype.

5. ________ will have Round seeds.

6. ________ will have wrinkled seeds.

7. ________ will have the same genotype as the P1.

probability problem 2

R

R

Rr

Rr

PROBABILITY PROBLEM (#2)

r

2. All of the F1 offspring will be ______.

P1=RR X rr (always put first parent on top of square)

Rr

Rr

r

Rr (Round)

2. All of the F1 offspring will be ___________.

probability problem 4

R

r

# of F2 Offspring = _____

Expected % of genotype (Rr) that is same as parents= ______

50% (2/4) of 140 = _____

140 X .5 = 70

140

RR

Rr

PROBABILITY PROBLEM (#4)

R

50%

70

Rr

rr

4. ________ will have their parents (F1) genotype.

F1= All Rr

r

70

4. ________ will have their parents (F1) genotype.

probability problem 5

R

r

# of F2 Offspring = _____

Expected % of Round phenotype = ______

75% (3/4) of 140 = _____

140 X .75 = 105

140

PROBABILITY PROBLEM (#5)

75%

RR

R

Rr

105

5. ________ will have Round seeds.

rr

r

Rr

105

5. ________ will have Round seeds.

probability problem 6

R

r

# of F2 Offspring = _____

Expected % of wrinkled phenotype = ______

25% (1/4) of 140 = _____

140 X .25 = 35

140

PROBABILITY PROBLEM (#6)

25%

RR

R

Rr

35

6. ________ will have wrinkled seeds.

rr

r

Rr

35

6. ________ will have wrinkled seeds.

probability problem 7

R

r

# of F2 Offspring = _____

Expected % of RR or rr genotype = ______

50% (2/4) of 140 = _____

140

PROBABILITY PROBLEM (#7)

50%

RR

R

Rr

70

7. ________ will have the same genotype as the P1 (RR or rr).

rr

r

Rr

70

7. ________ will have the same genotype as the P1.