Mendelian Genetics and
Punnett Squares
GENETIC 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 ON
A. 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
MEIOSIS
•Purpose: Growth and repair
•Purpose: Sexual reproduction
• Divisions: 1
•Divisions: 2
•Parent Cell: 2n diploid
•Parent Cell: 2n diploid
•Daughter Cells: 2 cells; 2n; identical to parent
cell
•Daughter Cells: 4 cells; 1n; not identical to
parent cells
•Product: Somatic cells (body 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 18561868 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)
F2 Generation (Pp x Pp)
•Two heterozygous dominant (Pp) peas are
•Two purebred (homozygous recessive
(pp)/dominant (PP)) peas crossed and ALL the crossed and 3 of the offspring have a purple
phenotype and 1 of the offspring has a white
offspring would have a purple phenotype
phenotype because both parents were
because they have heterozygous dominant
heterozygous dominant.
genotypes (Pp)
•Genotype ratio:
•Genotypic ratio:
0:4:0 (PP:Pp:pp)
1:2:1 (PP:Pp:pp)
•Phenotypic ratio:
•Phenotypic ratio:
4:0 (Purple:white)
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 Square
The 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 Up
This 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 clip
http://www.youtube.com/watch?v=Mehz7tCxjSE