Mendelian Genetics and Punnett SquaresGENETIC CONTINUITY, GREGOR MENDEL AND MONOHYBRID CROSSES

Lesson Objectives•Weekly Learning Goals

•Minds ON

•Reports (Bacteria / Parasites) handed back

•Pre-March Break Recap

•Mendel, Punnett Squares and Monohybrid Crosses

•Group Assignment Sign Up

• Homework

Learning Goals for This Week•We are learning to use the Punnett square method to solve basic genetics problems involving monohybrid crosses, incomplete dominance, codominance, dihybrid crosses, and sex-linked genes (D2.3)

•We are learning to investigate monohybrid and dihybrid crosses, and use the Punnett square method and probability rules to analyse the qualitative and quantitative data to determine the parent genotype (D2.4)

•We are learning to explain the concepts of genotype, phenotype, dominance, incomplete dominance, co-dominance, recessiveness, and sex linkage according to Mendelian laws of inheritance (D3.3)

•We are learning to explain the concepts of genotype, phenotype, dominance, incomplete dominance, codominance, recessiveness, and sex linkage according to Mendelian laws of inheritance (D3.3)

Minds ON With the people around you, try to unscramble these genetic words. (Note: these are terms we have already discussed in class). You have 3-5 min.

A. Soiemis

B. Lellaes

C. Tsamgee

D. Tpgeyeno

E. Tpheyone

F. Soimtsi

G. Zhymoouogs

H. Treoheoguzy

Minds ONA. Meiosis

B. Alleles

C. Gametes

D. Genotype

E. Phenotype

F. Mitosis

G. Homozygous

H. Heterozygous

Reports Handed Back… Overall, well-done!!

Some things to note for next time:

1. Hypothesis needs a specific direction or scope: go out on a limb and take a guess (DON’T state the obvious). The prediction is supposed to back up that belief.

2. Report writing involves the use of headings.

3. List of sources: “References”, not “Bibliography” or “Works Cited” (MLA)

4. References need to be alphabetical.

5. Follow instructions carefully.

6. Introductions can stand alone as one paragraph that includes purpose, hypothesis and prediction.

7. When in doubt, use citations –if it’s not your idea, give credit to the owner!

8. Embedded or in-text citations: using citations within a text: e.g. (Smith, 2014)

9. Hypotheses are “supported” or “not supported” --- NOT “proven” or “disproven”: A future experiment could yield different results!

The Week Before March Break Recap…MITOSIS•Purpose: Growth and repair

• Divisions: 1

•Parent Cell: 2n diploid

•Daughter Cells: 2 cells; 2n; identical to parent cell

•Product: Somatic cells (body cells)

MEIOSIS•Purpose: Sexual reproduction

•Divisions: 2

•Parent Cell: 2n diploid

•Daughter Cells: 4 cells; 1n; not identical to parent cells

•Product: Gametes (sex cells, germ cells)

The Week Before March Break Recap…

Alleles:

Variations of a certain gene (i.e. eye colour: many possibilities)

Dominant Traits:

If present, will always be shown (BB)• Homozygous dominant: Individual has two dominant pairs of alleles (BB); dominant trait expressed• Heterozygous dominant: Individual has a dominant and recessive allele (Bb); dominant trait expressed

Recessive Traits:

If present, will only be expressed if both parents give a recessive pair (bb)• Heterozygous recessive: Individual has two recessive alleles (bb); recessive trait expressed

Genotype:

The DNA makeup demonstrated by letter combination; can’t be seen (BB, Bb, bb)

Phenotype:

The physical trait expressed (brown eyes, blue eyes)

Gregor Mendel: The “Father” of Genetics•19th century Moravian monk

•Born Johann Mendel, in Austria (1822)

•Studied science to become a high school teacher at the University of Vienna

•Demonstrated laws of heredity using pea plant Pisum sativum.

•Completed his experiments from 1856-1868 and was elected Abbot of the monastery

•Died of a kidney disorder (1884)

His Work•Mendel was able to demonstrate laws of heredity by crossing his pea plants thousands of times to support his hypothesis that certain traits could be predicted.

•Mendel used pure breeds of pea plant Pisum sativum.

Looking at this diagram, why do you think he would choose a pea plant rather than a mouse or a bee?

Why the Pea? Mendel chose to use peas for a variety of reasons:

1. The pea plant can self pollinate, so Mendel could control the parental crosses by cutting off the stamens (male reproductive organ in plants) of one plant and using the pollen of another plant to fertilize the first plant.

2. Pisum sativum grows, matures and reproduces quickly, yielding a high number of seeds. This allows for many generations to be observed over a relatively short period of time.

3. These pea plants produce several pairs of obvious and contrasting characteristics.

Figuring Out the Pea Parental (P1 Generation)

1. First, Mendel self-pollinated the pea plants over several years in order to establish pure bred plants.

2. Next, he took two pure bred individuals and crossed (bred) them for a certain trait (i.e. colour). Purple is dominant for colour (PP) for and white plants are recessive for colour (pp).

3. When they mate, their offspring become the first filial generation (F1 generation).

4. Using a Punnett Square the possible outcomes can be predicted (see figure).

5. If the resulting offspring mate, they will create a monohybrid cross.

Monohybrid Crosses F1 Generation (PP x pp)

•Two purebred (homozygous recessive (pp)/dominant (PP)) peas crossed and ALL the offspring would have a purple phenotype because they have heterozygous dominant genotypes (Pp)

•Genotype ratio:

0:4:0 (PP:Pp:pp)

•Phenotypic ratio:

4:0 (Purple:white)

F2 Generation (Pp x Pp)

•Two heterozygous dominant (Pp) peas are crossed and 3 of the offspring have a purple phenotype and 1 of the offspring has a white phenotype because both parents were heterozygous dominant.

•Genotypic ratio:

1:2:1 (PP:Pp:pp)

•Phenotypic ratio:

3:1 (Purple:white)

Mendel’s First Three Principles of Inheritance•Genetic characteristics are controlled by unit factors (alleles) that exist in pairs in individual organisms

-Three possible combinations because there are two types of alleles (i.e. HH, Hh, hh)

•When two unlike unit factors (alleles) responsible for a single character are present in a single individual, one unit factor is dominant over the other, which is said to be recessive

-i.e. “H” is dominant over “h”

-Dominant and recessive also refer to designated traits (i.e. Tall stems are dominant over dwarf stems)

•During the formation of gametes, the paired unit factors separate or segregate randomly so that each gamete receives one or the other with equal likelihood

- i.e. If your father is heterozygous for height (has a tall allele a short allele), you have a 50% chance of getting either one

Let’s Try a Punnett SquareThe presence of horns (H) is dominant to not having horns (h).

Use a Punnett Square to determine the possible outcomes of the offspring.

Let’s Try a Punnett Square Prediction of offspring:

•As a phenotypic ratio:

4:0 horned

•As a genotypic ratio:

4:0 Hh

•As a phenotypic percent: 100% horned

Figuring Out Unknown Parental Genotypes: F2 Generation

Test Cross: Occurs when an individual of an unknown genotype is crossed with an individual that is homozygous recessive for a certain trait.

•This allows for the determination of the unknown individual’s genotype.

Group Assignment Sign UpThis is the culminating activity for the genetics unit.

It is a group assignment.

1. In groups of 3, you will pick from the list of topics on your sheet.

2. Read page 226 “Ethics and Genetics”

3. Prepare a 5 minute power point including all the aspects on the rubric.

4. Once you have chosen a topic, split the different aspects you need to include up and create a group assignment contract so I can see who has done what and so that if a person in your group fails to pull their weight, you won’t be affected.

5. First come, first serve basis for signing up!

Homework:•Hybrid Cross Sheet•Genetics Terms Sheet

•A little video cliphttp://www.youtube.com/watch?v=Mehz7tCxjSE