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Genetics According to Mendel. The Father of Genetics, AKA the Pea’s Worst Nightmare, AKA Monk of the Millennia, AKA GENEous , AKA Your Favorite Scientist. Oh, hello there. My name is Gregor Mendel. You’ve probably heard of me…. I mean, I am the father of modern genetics….

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Genetics according to mendel

Genetics According to Mendel

The Father of Genetics, AKA the Pea’s Worst Nightmare, AKA Monk of the Millennia, AKA GENEous, AKA Your Favorite Scientist


Oh, hello there. My name is Gregor Mendel. You’ve probably heard of me…

I mean, I am the father of modern genetics…

…huh? You haven’t?!?

Well, lets start at the beginning.

In 1842, when I had completed all of the formal education my family could afford, I entered the monastery. I was 21, and I needed a way to continue my education.

The monastery paid for me to attend the University of Vienna, where I studied physics, chemistry, zoology, and botany. I also studied a new field called ‘statistics’.

After finishing school, I returned to the monastery and began teaching science at the local high school.

Go Vienna!

But it was not meant to be… due to a dispute with the examiners the during my oral exam to become a teacher. They would not hear my ideas about heredity, which explains how traits are passed down from one generation to another.

Whoooo… celibacy!

Well, forget them, cause myideas form the basis of modern genetics.


So how did i rock the world of genetics
So, how did I rock the world of genetics?

  • I had several stocks of “true breeding” pea plants.

  • This means that the pea plants reproduce sexually by self-pollination. We’re very familiar with this at the monastery.

  • Because the plants self-pollinate, they only produce offspring that are identical to themselves.

I played with my peas!


Crossing pollinating peas
Crossing Pollinating Peas

  • I took two true breeding pea plants with different traits and cross pollinated them with each other.

  • This was tricky, because pollination takes place before the pea flowers open up.

  • I had to open a flower, before pollination, and cut off the male parts, which make the pollen. Somehow this reminds me of the monastery every time I do it…

  • Then I used a paint brush to dust the remaining female parts of the flower with pollen from a different plant.

Can you explain to your partner why I had to mutilate all those flowers?


The results
The Results…

  • The first plants I crossed were a true breeding tall plant with a true breeding short plant. I called these plants the parent or P generation.

  • Once I grew the resulting seeds, all of the offspring plants were tall! I called the results of this monohybrid cross the first filial, or F1 generation.

Get it?!? Pea generation? Smart, famous, and funny. Too bad for the ladies I’m a monk.


Principle of dominance
Principle of Dominance

  • Somehow, the short gene had been masked by the tall gene. Did the short gene disappear?

  • To find out, I allowed one of the F1 plants to self-pollinate.

  • The resulting offspring were called the second filial, or F2 generation.

  • This confirmed my (brilliant) idea that the short trait was simply hidden in the tall plants.


Principle of dominance1
Principle of Dominance

Answer the following:

Which traits are dominant and which traits are recessive?

Explain the reasoning you used to determine the dominance or recessiveness of the traits.

Yes, I can make up words like recessiveness… I’m Gregor Mendel! I do what I want!

The chart above shows the results for many crosses for many traits.


Punnett squares
Punnett Squares

Male Gametes

Punnett squares represent the possible outcomes of a cross.

Female Gametes

Possible combinations of those gametes… AKA offspring!


Punnett squares1
Punnett Squares

True breeding tall plant

Hybrid Tall Plant

T

T

t

T

t

Tt

T

TT

Tt

Tt

True breeding short plant

Hybrid Tall Plant

Tt

Tt

Tt

tt

t

t

F1 Generation

F2 Generation

Now, make a Punnett square showing the F1 and F2 generation for each of the traits in the table.


Principle of dominance summary
Principle of Dominance Summary

  • An individual’s characteristics are determined by factors that are passed from one parental generation to the next.

  • When cross breeding two different traits, the recessive trait is masked by the dominant trait in the F1 generation. The recessive trait will reappear in the F2 generation.

  • Gregor Mendel is the best scientist ever. OK, that has nothing to do with this. But it is still true.


For my next trick
For my next trick…

One thing started to bother me. Well, besides being forever alone as a monk.

I wondered if these traits were inherited together as a unit, or if each trait was inherited individually from each other.

To figure this out, I would need to cross two plants which were true breeding for two traits, and keep track of both traits in F1 and F2 generations. This is called a dihybrid cross.

One possibility was that the traits were inherited as a unit.

The other possibility is that the traits are inherited independently.

This seems like a lot… but us monks have lots of time on our hands. I crossed a RRYY plant with a rryy plant.

R: round seed, r: wrinkled seed

Y: yellow seed, y: green seed


Results of the dihybrid cross
Results of the Dihybrid Cross

Don’t get too tangled up in how to draw a dihybrid Punnett square… at least not yet.

  • All of the offspring had round yellow seeds. Their genotype was all RrYy. When I crossed these F1 plants, the F2 generation had all kinds of phenotypes, with many possible genotypes.

  • This called the Rule of Independent Assortment. It states that during gamete formation, the alleles of each gene segregate from each other, so that each gamete carries only one allele for each gene.


In a certain breed of rabbits, black fur (B) is dominant to white fur (b). If a homozygous black male is crossed with a heterozygous female, what are the possible phenotypes and genotypes of their offspring?

BB

Black

Black fur (B) is dominant, so it will ‘mask’ the white fur (b) trait.

Bb

Black

bb

White

Heterozygous = two different genes (Bb)

Black fur

Black fur

Homozygous black = two black fur (B) genes

Phenotype = physical appearance

Bb

BB

Genotype = genes

b

B

B

B

B

B

BB

B

BB

100 % Black fur

b

Bb

Bb

50% BB, 50% Bb


So, I hoped you enjoyed learning about white fur (bme, after all, it’s my favorite subject.

Now, complete the next problem on the worksheet that Ms. Leffel gave you.

Remember to respect teachers; after all, even I couldn’t handle the job!


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