Gregor Mendel Genetics Experiments With Pea Plants

Gregor Mendel

Genetics Experiments

With Pea Plants

Mendel Noticed

Pea Plants varied by:

height, color of flowers, position of

flowers, seed color, seed shape,

pod color, pod shape

Mendel Hypothesized

Mendel Hypothesized

Variations in pea plant appearance was due to something (some information) passed along during reproduction by the parent plants.

Mendel’s Experimental Design

Mendel’s Experimental Design

Mendel raised pea plants to “breed true,” I.e. tall only produced tall, short only produced short

Mendel’s Experimental Design

Mendel raised pea plants to “breed true,” I.e. tall only produced tall, short only produced short

Mendel crossed one true-breeding variety with the alternate true-breeding variety, e.g. tall x short

P1 Tall X Short

P1 Tall X Short

F1 All Tall

P1 Tall X Short

F1 All Tall

F2 3/4 Tall 1/4 Short

Mendel Hypothesized

That something was passed from parents to offspring to determine height; he called this an allele

P1 Tall X Short

T t

F1 All Tall

T

F2 3/4 Tall 1/4 Short

T t

Mendel Hypothesized

That something was passed from parents to offspring to determine height; he called this an allele

Further, since the t allele was “hidden” in the F1, but reappeared in the F2, plants must have a pair of alleles for each trait.

P1 Tall X Short

TT tt

F1 All Tall

Tt

F2 3/4 Tall 1/4 Short

T? tt

When an organism had a pair of alleles the same, e.g. TT or tt, he called this homozygous

When an organism had an unlike pair of alleles, e.g. Tt, he called this heterozygous

These terms refer to an organism’s genotype

The appearance of the organism he called it’s phenotype

Practice VocabEx. Plant Height

Genotype

Phenotype

Pure or Hybrid

Homozygous/

Heterozygous

More practice

Genotype

Phenotype

Pure or Hybrid

Homozygous/

Heterozygous

Ex. Flower color

Mendel proposed several principles regarding his

findings If an organism is heterozygous and

only one phenotype appears, this is the dominant phenotype, the alternate is the recessive phenotype

When an organism reproduces, allele pairs must segregate and only one member of each allele pair is passed along to the next generation.

Solving Genetic Problems

T T t t

T T t t

T X t = T t F1

Punnett Square

TT X tt

T

T

t t

Tt Tt

Tt Tt

Genotype

4/4- Tt

Phenotype

4/4- Tall

Practice Space

Test Cross

What is the genotype of a short pea plant?______

What is the genotype of a tall pea plant?_____ or _____

Mendel developed a way of testing whether the tall plant is homozygous or heterozygous. It was the test cross

Test Cross problem

T_ X tt

Independent Assortment

The inheritance of any characteristic is independent of the inheritance of any other characteristic.

Ex. The inheritance of height is independent from pea color.

Mendel provided evidence for this through dihybrid crosses.

Dihybrid Cross

TtPp X TtPp

To solve this problem you can use a 16 block punnett square or the Forkline method.

16 Block Punnett Square

Fork Line Method

Ex. TtPp X TtPp

Practice with Fork Line Method

Practicing Punnett Squares

Inheritance patterns that Mendel did not know

about Incomplete dominance Codominance Multiple alleles Polygenic Inheritence Sex Linkage

Incomplete Dominance

Incomplete dominance does not involve an allele that masks recessive allele. Instead there is a blending of the two alleles.

Ex. Red flower X White flower =Pink

Cross Two Pink flowering plants

Example

Cross a two pink flowering plants

RW X RW

Codominance

Codominance does not involve an allele that masks recessive allele. Instead both alleles show in the phenotype

Ex. Brown horse X White horse =Spotted

Cross a brown horse with a spotted horse

Codominance Exmple

Cross a brown horse with a spotted horse.

BB X BW

Multiple Alleles

Some phenotypes can be determined by more than two alleles.

Ex. ABO Blood typeGenotypes Phenotypes

AA - A Blood Type

AO - A Blood Type

BB - B Blood Type

BO - B Blood Type

OO - O Blood Type

AB - AB Blood Type

Blood Type Problems

Cross a heterozygous A blood type with a heterozygous B blood type

iAiO X iBiO

Polygenic Inheritance

The inheritance of some characteristics are determined by more than two alleles.

Ex. Skin color, eye color, height, and noses. Phenotypes of polygenic inheritance are a result of the blending of many genes.

Sex Linkage

Who determines the sex of the baby?

How would a gene found on the X chromosome be inherited and expressed differently in males vs. females?

Sex Inheritance

X Y

X

X

XX XY

XX XY

Sex Linked ProblemsX-Linked

Color Blindness is carried on the X Chromosomes. It is recessive.

What are all of the different possible combinations of genotypes an individual could have?

Sex Linkage Problem

Cross a Colorblind male with a woman who is a carrier for colorblindness.

XcXC X XcY

Are you color blind?Lets find out together

http://colorvisiontesting.com/online%20test.htm

Practice Sex Linkage Problems