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Mendel’s Work. Chapter 3 Section 1 Pg 80-85. Gregor Mendel — the father of genetics. Genetics —the scientific study of heredity Heredity —the passing of traits from parents to offspring. Mendel’s Peas. Mendel could learn a lot from peas because:

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mendel s work

Mendel’s Work

Chapter 3 Section 1

Pg 80-85

Gregor Mendel—

the father of genetics

slide2
Genetics—the scientific study of heredity
  • Heredity—the passing of traits from parents to offspring
mendel s peas
Mendel’s Peas

Mendel could learn a lot from peas because:

  • Pea plants have many traits that exist in only 2 forms such as tall vs short plants, but no medium plants.
mendel s peas1
Mendel’s Peas

Mendel could learn a lot from peas because:

  • Peas produce a large number of offspring (kids) in each generation
mendel s peas2
Mendel’s Peas
  • Normally pea plants self pollinate. This means that pollen from the stamen of a plant enters the pistil of the same plant.
mendel s peas3
Mendel’s Peas
  • Mendel cross pollinated plants. This means that he took pollen from a plant and rubbed it on the pistil of a different plant from which the stamens had been removed (so they couldn’t self pollinate).
mendel s experiments
Mendel’s Experiments
  • Purebred—always produces offspring with the same form of a trait as the parent.
  • Ex. Purebred dogs. Like Cocker spaniels, golden retrievers, Poodles.

The opposite is hybrid.

This would be a pound

puppy

mendel s experiments1
Mendel’s Experiments
  • In his first experiment Mendel crossed purebred tall plants

(they only have tall genes) with purebred short plants (that only have short genes).

  • Filial (F1) generation—name

given to the offspring of the first cross.

mendel s experiments2

?

Mendel’s Experiments

Mendel cross-pollinated purebred tall plants with purebred short plants and got….

F1 generation

Tall plant (breed) short plants

P generation (think “parents”)

mendel s experiments3

P generation (think “parents”)

F1 generation

Mendel’s Experiments

All TALL pea plants in the F1 generation….

so we could look at it like this too

P generation

(cross pollinated)

F1 generation

(self-pollinated)

So we could look at it like this too…
mendel s experiments4
Mendel’s Experiments

Results of F2

  • Mendel allowed the F1 plants to self-pollinate.
  • He found that the F2 plants were a mix of tall and short plants in a ration of ¾ tall to ¼ short.
slide17

P generation

(cross pollinated)

F1 generation

(self-pollinated)

All tall

F2 generation

¾ tall and ¼ short

traits mendel studied in pea plants
Traits Mendel studied in Pea Plants
  • Mendel also studied _7_ traits of pea plants: They were : Seed shape, seed color, seed coat color, pod shape, flower position, flower color, and stem height.
dominant and recessive alleles
Dominant and Recessive Alleles
  • Pairs—the factors that control each trait exist in pairs.
    • Female parent—contributes one factor
    • Male parent—contributes one factor
    • Together these make a pair
dominant and recessive alleles1
Dominant and Recessive Alleles
  • Genes—are the factors that control traits.
  • Genes consist of pairs of alleles. One that comes from the mother parent and one that comes from the father parent.
dominant and recessive alleles2
Dominant and Recessive Alleles
  • Alleles—the different forms of a gene (such as tall or short, wrinkled or smooth).
  • Dominant allele—one whose trait always shows up when the allele is present.
  • Recessive allele—is masked (or covered up) when the dominant allele is present. Recessive alleles only show up if a dominant allele is not present.
examples

dominant

dominant

recessive

dominant

recessive

recessive

EXAMPLES

recessive

dominant

Recessive is the green box and dominant is the black box. Each of your parents has a pair of alleles that they can share. If they only give one… answer the following questions.

?

?

?

examples1
EXAMPLES

recessive

dominant

Recessive is the green box and dominant is the black box. Each of your parents has a pair of alleles that they can share. If they only give one… answer the following questions.

dominant

dominant

dominant

?

?

recessive

dominant

?

recessive

recessive

examples2
EXAMPLES

recessive

dominant

Recessive is the green box and dominant is the black box. Each of your parents has a pair of alleles that they can share. If they only give one… answer the following questions.

dominant

dominant

dominant

?

?

recessive

dominant

dominant

?

recessive

recessive

examples3
EXAMPLES

recessive

dominant

Recessive is the green box and dominant is the black box. Each of your parents has a pair of alleles that they can share. If they only give one… answer the following questions.

dominant

dominant

dominant

?

?

recessive

dominant

dominant

?

recessive

recessive

recessive

notice
Notice
  • The only time the green box (or recessive allele) could show up is when a black box (or dominant allele) was not present.
  • This will lead us into punnett squares.

recessive

recessive

recessive

punnett squares
Punnett Squares
  • So Mendel started out with 2 purebred plants. One was tall and one was short.
  • Capital T means “tall allele”, lowercase t means “short allel”
  • But, each of those two plants (tall one and short one) has 2 alleles. They received one from their mother and one from their father.
slide28
Options are T(tall) or t(short)
  • Tall plant was TT –purebred (top of ps)
  • Short plant was tt—purebred (left of ps)
  • What would Tt be? A tall/medium/or short plant?
  • You take this information and put it in a Punnett Square.
slide32
In a cross between two purebred plants (TT x tt), the probability of the offspring having the dominant characteristics is 100% (or 4 out of 4 which is the same as 4/4)
but what does it all mean
But what does it all mean?

Represents 4 possible offspring; the probability of children’s

height.

probability is
Probability is

The likelihood that a particular event will occur.

Tossing a coin—landing head us is ?

The larger the sample size (more tosses of a coin), the closer the actual results predicted by probability.

you said 50
You said 50%?
  • Lets go to the virtual coin toss…
  • http://pbskids.org/cyberchase/games/probability/cointoss.html
  • What about children. What is the likelihood that a woman would have a boy instead of a girl?
  • Mendel used probability in genetics.
mendel and probability
Mendel and Probability
  • Mendel was the first person to realize that probability can be used to predict the results of genetic crosses.
  • In other words he could use probability to “know” that all the offspring of the first generation would be tall… without even seeing them.
punnett squares1
Punnett Squares
  • Can be used to calculate the probability that offspring will have a certain combination of alleles.
  • Can also be used to predict the probability of an offspring possessing a certain trait.
  • Get used to this… we will do it a lot.
slide39
In a cross between 2 hybrid tall plants (? x ?), the probability of offspring having the dominant characteristic is 75% (or 3 out of 4 or ¾) while the probability of the offspring having the recessive characteristic is 25% (or 1 out of 4 or ¼)
punnett square for 2 hybrid plants to determine height of offspring
Punnett Square for 2 Hybrid plants to determine height of offspring.

What letters should go on the top and to the side? You have to know what hybrid/ heterozygous means.

punnett square for 2 hybrid plants to determine height of offspring1
Punnett Square for 2 Hybrid plants to determine height of offspring.

Right! But…

What do we do now?

punnett square for 2 hybrid plants to determine height of offspring2
Punnett Square for 2 Hybrid plants to determine height of offspring.

We put each allele in a spot on the top and left. It doesn’t matter if the t is above or below the T as long as they are both there.

punnett square for 2 hybrid plants to determine height of offspring3
Punnett Square for 2 Hybrid plants to determine height of offspring.

Right! Now you move the alleles over…

punnett square for 2 hybrid plants to determine height of offspring4
Punnett Square for 2 Hybrid plants to determine height of offspring.

Right! Now you move the alleles over…and DOWN!!!

day 2
Day 2
  • REMINDER: Science fair projects are DUE today and tomorrow!
but what does this square mean
But what does this square mean?

First we have to learn about phenotype and genotypes.

phenotype and genotype
Phenotype and Genotype
  • Phenotype—The physical appearance of the offspring. (ex. Tall or short)
  • Genotype—The genetic makeup or allele combination of the offspring.
    • Homozygous (purebred)—2 of the same alleles
      • TT or tt
    • Heterozygous (hybrid)—2 different alleles
      • Tt or tT which are the same thing.
remember
Remember
  • If there is one dominant (capital letter) trait, then that is the physical characteristic that shows up.
  • Recessive traits only show up if there are no dominant traits present.
codominance
Codominance
  • Alleles are neither dominant nor recessive. Neither allele is covered up. Both show up.
  • Write them as capital letters with superscripts. (F or F = black / white feathers).
  • This means that F F heterozygous chickens have both black and white feathers.

B

W

B

W

codominance1
Codominance
  • Red hair and White hair are codominant in cattle. Heterozygous ( H H ) cattle have red hairs and white hairs. They are called roan.

R

W

f feathers w white b black1

W

F=feathers; W-white B-black

F

F

F F

W

W

B

F F

F F

B

W

B

W

F F

F F

W

W

W

W

W

what color are they
What color are they?

F

F

F F

W

W

B

F F

F F

B

W

B

W

F F

F F

W

W

W

W

W

activities for them
Activities for them
  • Pea Soup
  • Animated Cross
future activities
Future activities
  • Princess and Wrinkled Pea, Biologica
  • Dragon Genetics, Biologica
  • Mendel’s Peas, Biologica
  • Cloning, Brain Pop
  • DNA, Brain Pop (digestion, avian flu too)
resources for me
Resources for me
  • Serendipity Labs
  • Holy moly animations
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