Mendel and Using Punnett Squares

GENETICS Robert Perry Malibu High School

1.

GENETICS 1 • • • •

A little history of Genetics.

Introductory vocabulary.

Solving problems with one trait.

Using a Punnett Square to solve problems.

The modern science of GENETICS and HEREDITY began with ???

__________________

The modern science of GENETICS and HEREDITY began with GREGOR MENDEL

Gregor Mendel (1822-1884)

Who was Gregor Mendel ?

Who was Gregor Mendel ?

Gregor Mendel was an Austrian monk whose experimental work became the basis of modern hereditary theory.

Who was Gregor Mendel ?

Gregor Mendel was an Austrian monk whose experimental work became the basis of modern hereditary theory.

As a substitute teacher at the technical school in Br端nn, Mendel became actively engaged in investigating variation, heredity, and evolution in plants at the monastery's experimental garden.

pea plants

pea plants

Between 1856 and 1863 he cultivated and tested at least 28,000 pea plants, carefully analyzing seven pairs of seed and plant characteristics. His tedious experiments resulted in the enunciation of two generalizations that later became known as the THEORIES of heredity.

pea plants

Between 1856 and 1863 he cultivated and tested at least 28,000 pea plants, carefully analyzing seven pairs of seed and plant characteristics. His tedious experiments resulted in the enunciation of two generalizations that later became known as the laws of heredity.

His observations also led him to coin two terms still used in present-day genetics: dominant, for a trait that shows up in an offspring; and recessive, for a trait masked by a dominant gene.

= Pure Green pea

= Pure Yellow pea

(P1) Parent generation

F1 generation

100% Yellow F2 generation

3 : 1 RATIO

(Pure Green pea)

yy y HAPLOID SPERM

DIPLOID OFFSPRING

y HAPLOID OVUM

Every normal body cell is diploid, which means it has TWO genes for every trait.

Exception: gametes, which are haploid, only ONE gene for every trait.

yy

YY

yy

= Pure Green pea

YY

= Pure Yellow pea

(P1) Parent generation

F1 generation

100% Yellow F2 generation

3 : 1 RATIO Where did this greenie come from ?

yy

yy

Yy

= Pure Green pea

YY

YY

= Pure Yellow pea

(P1) Parent generation

Yy Yy Yy

F1 generation

100% Yellow (Yy) F2 generation

YY

Yy

Yy

yy

3 : 1 RATIO

Both YY and Yy are yellow.

But Yy “carries” the green gene.

yy

yy

Yy

= Pure Green pea

YY

YY

= Pure Yellow pea

(P1) Parent generation

Yy Yy Yy

F1 generation

100% Yellow (Yy) F2 generation

YY

Yy

Yy

yy 25 % of peas will be green

Yy = Yellow is dominant over green !

So yy is the only way to be green.

Using a Punnett Square to get results.

First Step: Choose symbols for each combination of alleles.

Using a Punnett Square to get results.

yy

= Green pea

YY = Yellow pea Yy

= Yellow pea

Symbols

Using a Punnett Square to get results.

yy

= Pure Green pea

YY =

Pure Yellow pea

Yy

= Heterozygous Yellow pea

Second, write the parent genotypes.

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

YY

= Pure Yellow pea

Parent #1 genotype

Parent #2 genotype

yy

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Next make gametes from each parent.

yy

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Next make gametes from each parent.

Y

Y

yy

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Next make gametes from each parent.

Y

Y

y yy y

Using a Punnett Square to get results.

yy

= Pure Green pea

YY Y

Parent #2 genotype

YY

= Pure Yellow pea

Parent #1 genotype

Y

Parent #1 gametes

y yy y Parent #2 gametes

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Match up the gametes to make offspring.

Y y

yy y

Y Possible Offspring Genotypes

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Y y

Y

y

Y

Y

yy

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Y

Y

y

Y

Y

y

Y

Y

yy

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Y

Y

y

Yy

Yy

y

Y

Y

yy

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Y

Y

y

Yy

Yy

y

Yy

Yy

yy

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Y

Y

y

Yy

Yy

y

Yy

Yy

yy

Using a Punnett Square to get results.

yy

= Pure Green pea

YY Y

y

Yy

Yy

y

Yy

Yy

yy Parent #2 gametes

= Pure Yellow pea

Parent #1 genotype

Y

Parent #2 genotype

YY

Parent #1 gametes

Possible Offspring Genotypes

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Y

Y

y

Yy

Yy

y

Yy

Yy

Final Step: Count Up Results and Analyze Data !

yy

Using a Punnett Square to get results.

yy

= Pure Green pea

YY

= Pure Yellow pea

YY Y

Y

y

Yy

Yy

y

Yy

Yy

yy

4/4 = 4 Yy out of 4 possibilities 100% Yy 100% Yellow

Using a Punnett Square to get results.

yy

= Pure Green pea

YY =

Pure Yellow pea

Yy

= Heterozygous Yellow pea

Now let’s cross 2 Yy (yellow) peas.

yy

= Pure Green pea

YY =

Pure Yellow pea

Yy

= Heterozygous Yellow pea

First Step: Choose symbols for each combination of alleles.

Now let’s cross 2 Yy (yellow) peas.

yy

= Pure Green pea

Yy

YY =

Pure Yellow pea

Yy

= Heterozygous Yellow pea

Second, write the parent genotypes.

Yy

Now let’s cross 2 Yy (yellow) peas.

Yy Next make gametes from each parent.

Y Yy y

Y

y

Yy Y

y

Y

YY

Yy

y

Yy

Yy yy

Next match-up the gametes to make the offspring.

Last, count up and analyze the results !

Yy Y Y

YY

y Yy

Yy

3/4 Yellow 1/4 Green

y

Yy

yy

1 YY 2 Yy 1 yy

3 : 1 RATIO of Phenotypes 1 : 2 : 1 RATIO of Genotypes

Not until the late 1920s and the early '30s was the full significance of his research realized, particularly in relation to evolutionary theory.

Mendel

As a result of years of research in population genetics, investigators were able to demonstrate that Darwinian evolution can be described in terms of the change in gene frequency of Mendelian pairs of characteristics in a population over successive generations.

Mendel came to an important conclusion:

Mendel came to an important conclusion: The principle of segregation:

Mendel came to an important conclusion: The principle of segregation: According to the principle of segregation, for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring.

Mendel came to an important conclusion: The principle of segregation: According to the principle of segregation, for any particular trait, the pair of alleles of each parent separate and only one allele passes from each parent on to an offspring. (The process of producing gametes with one set of genes was later identified as MEIOSIS).

Which allele in a parent's pair of alleles is inherited is a matter of chance. We now know that this segregation of alleles occurs during the process of sex cell formation.

REVIEW CHECKPOINT:

REVIEW CHECKPOINT: 1. Who is considered “the Father of Genetics?”

REVIEW CHECKPOINT: 1. Who is considered “the Father of Genetics?”

2. What type of organisms did this man use in his research?.

REVIEW CHECKPOINT: 1. Who is considered “the Father of Genetics?”

2. What type of organisms did this man use in his research?

3. If a trait is “carried” but not visible, it is called ______________.

REVIEW CHECKPOINT: 1. Who is considered “the Father of Genetics?”

2. What type of organisms did this man use in his research?

3. If a trait is “carried” but not visible, it is called ______________.

4. One member of a gene pair is known as a(n) ________________.

REVIEW CHECKPOINT: 1. Who is considered “the Father of Genetics?”

2. What type of organisms did this man use in his research?

3. If a trait is “carried” but not visible, it is called ______________.

4. One member of a gene pair is known as a(n) ________________.

5. Name two cells in the human body that only have ONE set of genetic info.

6. Show a cross between a pure yellow and a pure green pea. What % of all offspring will be green peas?

6. Show a cross between a pure yellow and a pure green pea. What % of all offspring will be green peas?

7. Show a cross between two heterozygous peas. What % of all offspring will be yellow peas ?

6. Show a cross between a pure yellow and a pure green pea. What % of all offspring will be green peas?

7. Show a cross between two heterozygous peas. What % of all offspring will be yellow peas ?

8. Show a cross between one heterozygous pea and one green pea. What % of all offspring will be green peas ?

6. Show a cross between a pure yellow and a pure green pea. What % of all offspring will be green peas?

7. Show a cross between two heterozygous peas. What % of all offspring will be yellow peas ?

8. Show a cross between one heterozygous pea and one green pea. What % of all offspring will be green peas ?

9. What is the Principle of Segregation ?