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My second quarter portfolio for 2008-2009

### Transcript of Second Quarter Portfolio

• Christopher Long

Biology I

Mr. Snyder

October 20th, 2008

Activity OneMendel and the Laws of Chance;

Calculation of Genetic Ratios:

A great scientist once wrote all science is measurement. In genetics, much of

that which is measured concerns the ratios of different phenotypes (outward

appearances) and genotypes (genetic makeup). These genetic relationships arise

from probability relationshipsthe chancesegregation and assortment of genes

in games, and their chance combination to form a zygote (a diploid cell resulting

from the union of two gametes).

In this activity, you explore how the determination of genetic ratios is derived

from two basic laws of chance.

In applying mathematics to the study of genetics, Mendel was stating that the

laws of chance apply to biology as well as they do to the physical sciencesa

radical concept for the times!

Laws of Chance:

Materials needed per group:

! Two double-sided plastic coinsmarked heads and tails

! Student Study and Analysis Sheet (one per student)

Toss the twosided coin. The chance that it will turn up heads is !. If two coins

are tossed, the chance that both will turn up heads is again !. The chance that

the second will also turn up heads is !. The chance that both will turn up

heads is ! x ! or ".

Summary:

The probability of two independent events occurring together is simply the

probability of one occurring alone multiplied by the probability of the other

occurring alone.

We can diagram this probability relationship in a checkerboarda Punnet Square

(as below), which indicates that the combination in each square has an equal,

independent chance of occurring.

• !Note: The Punnet square was named after an english geneticist who first used this sort of diagram for the analysis of genetically determined traits.

1. What would the the probability (chance) be, if there were three plastic

coins?

! !

2. Place two plastic coins in a shaker cup. Shake and toss the pieces onto

the table top 100 times. Keep track of the results: record totals in the

spaces below. Do the results come close to those predicted by the Punnet

Square.

! Tails/Tails: 25

3. Suppose you toss both plastic coins 1,000 times instead of 100. What

would this larger sample allow?

! The odds would even outthe ratio of your own findings would draw

nearer to the expected ratio.

• Calculation of Genetic Ratios:

On the basis of Mendelian principles, a diploid (double set of chromosomes) adult

of genetic constitution Aa may give rise to two games, A, and a. If the genetic

constitution of the parents is not given, two possible explanations (hypotheses)

exist which can account for the presence of phenotypes. A or a in the offspring.

The answer, in terms of probability is to assume that the parents Aa produce two

types of gametes, A and a, equally well and the aa parent produces only one type

of gamete, a. Any combination of gametes depends upon the frequency or

probability of each type of gamete furnished by the parents. Thus the formation

of a zygote is the result of two independent events (two gametes), each with

their own probabilities, which now occur together.

Summary:

The probability that a particular zygote will be formed is equal to the

product of the probabilities of the gametes that compose it.

4. Complete the two checker boards below to calculate the values:

!

• 5. Complete the following statement for the Aa x Aa cross:

! How many possible kinds of zygotes can be formed?

4

! The probability that the A phenotype will occur?

#

! The probability that a zygote can be heterozygous (i.e. Aa or aA)

!

! The probability that a zygote can be either AA, Aa, or aA?

#

! The probability that a zygote can be either AA, Aa, or aA?

#

! The probability that a zygote can be either AA, Aa, or aA?

1

! What are the genotype and phenotype ratios?

Genotypic Ratio: 1AA:1Aa:1aA:1aa

Phenotypic Ratio: 3A:1a

6. Complete the following statement for the Aa x aa cross:

! Do both genotypes occur with equal frequency?

Yes

! The probability that the A phenotype will occur?

#

! What are the genotype and phenotype ratios?

Genotypic Ratio: 1Aa:1aa

Phenotypic Ratio: 1A:1a

• Christopher Long

Biology I

Mr. Snyder

October 20th, 2008

Activity TwoA Monohybrid Cross

This activity investigates crosses between pea plants that are different in but a

single characteristic (gene difference)a monohybrid cross.

Materials needed per group:

! Cup shaker

! Four discs representing gamete cells.

! Two Red Allele Discs each having W for the purple flow on each side.

! Two Red Allele Discs each having w for the white flow on each side.

! Student Study and Analysis Sheet

! One wax pen

Note: A pea plant homozygous for purple flower color is represented by WW in genetic shorthand. The gene for purple flow coloring is designate W because of a convention by which geneticists, in

indicating a pair of alleles, use the first letter of the less common form (white). The capital indicated the dominant,, the lowercase the recessive. Use the wax pen provided to write the allele

type (W or w) on Each side of the disc.

Read and become familiar with the information presented in the Student Study

Sheet.

1. Place two W allele disc in the cup, representing the union (fertilization) of

male and female gametes. Shake and toss them onto the table. Repeat nine

more times. Record your results (genotypes, phenotype) below:

! Genotype: 1WW

! Phenotype: 1w

2. Repeat Step 1 (above), but this place two w allele discs in the cup. Shake

and toss. Repeat nine additional times. Record the genotype and phenotype

below:

! Genotype: 1WW

! Phenotype: 1w

• 3. Cross two purple (W) plants created from zygote unions in Step 7 by

allowing them to selfpollinate as Mendel did. Draw a Punnet square and

record the genotypes and phenotypes.

!

4. Write a statement that explains why these plants would continue to breed

true

! The plant continue to breed true because each has only one distinct

factor for each characteristic.

5. If white plants (w) were substituted for purple (W), would there be any

change in the expected outcome?

! If white plants were substituted for purple plants, there would be no

change in the expected outcome, besides a different phenotype.

• Christopher Long

Biology I

Mr. Snyder

October 20th, 2008

Activity ThreePrinciple of Segregation

In this activity you will study single gene differences in various monohybrid

crosses that led Mendel to the discovery of the Principle of Segregationthe

ability to predict the segregation between two different alleles in a single gene

pair and their behavior in each generation.

Materials needed per group:

! Two yellowcolored plastic discsrepresenting purebred (homozygous)

yellow pod color trait

! One greencolored plastic discrepresenting purebred (homozygous)

green pod color trait

! One redcolored plastic discrepresenting purebred (homozygous) purple

flower trait

! One blue colored plastic disc

! Clear sticky tape (not provided)

! Student Study and Analysis Sheet

Mendel conducted experiments on seven traits (see table 1) whose characteristics

(itself and its alternate) were clearly defined. This activity will simulate crosses

among two of these: flower and pod color.

1. Simulate a cross between a plant homozygous (GG) for the green pod color

trait (greencolored plastic disk) by crossing it with another homozygous

(gg) for yellow pods (yellowcolored plastic disc).

2. Conduct another simulated cross, this time using redcolored discs to

represent a plant hozygous (WW) purplecolored flowers with yellow

colored discs to represent a plant homozygous (ww) whitecolored flowers.

Secure plastic discs with sticky tape.

3. What generation do both these disc crosses represent?

! They represent the F1 generation

• 4. Hold each disc (representing a cross result) set up to the light and record

the dominant observed color below.

! Cross GG x gg: Green

! Cross WW x ww: Red

5. What phenotypic trait is hidden in each cross?

! Cross GG x gg: Yellow pod color

! Cross WW x ww: White flower color

6. Describe the relationship of dominant and hidden traits

! Dominant traits are dominant, and conceal hidden traits, which are

recessive

7. Complete the Punnet Squares below, writing in both genotype and

phenotype for each of the above crosses.

!

8. Write a statement that describes each cross.

! The offspring resulting from each cross will be be heterozygous

• 9. Use the information from Step 6 to allow each plant variety (pod and

flower color) to self pollinate. Can you (like Mendel) predict the results?

Complete another Punnet square for each crossrecord phenotype and

genotype.

!

10.In what ratio do the dominant and recessive traits appear?

! 3:1

Is there a similar relationship concerning all of the seven traits studied by

Mendel?