1. Genetics

2. Review Chromosomes are paired (homologous) in a 2N organism.
Each chromosome contains many genes
Homologous chromosomes carry the same genes.
Homologous pair
of chromosomes

3. Review
Genes can have different versions of the same trait. These versions are called alleles.
Homologous chromosomes separate into different gametes.
alleles

4. Alleles - Dominant and Recessive
Each parent will donate one allele.
Alleles can be physically apparent (dominant) or physically hidden (recessive).
Mendel worked with traits that had only two alleles of each trait, one dominant and one recessive.
Alleles
Mother
Father

5. Mendel’s Laws The Law of Segregation The Law of Dominance
each pair of alleles separates during meiosis (gamete formation)
The Law of Dominance
When two alleles differ,
one can control the trait - Dominant
the other can be hidden - Recessive
The Law of Independent Assortment
Pairs of genes segregate into gametes randomly and independently (due to random separation of homologous pairs.

6. How Can We Demonstrate these Laws?
Mendel recorded phenotypes ( form of the trait that he “saw”)
Based on outcomes from matings (called crosses) over several generations, he could determine the genotypes (the actual genetic makeup for that trait) of previous generations
Homozygous - both alleles for a trait are the same
Heterozygous - alleles are not identical.

7. Monohybrid Crosses
Studying the inheritance of a single trait while ignoring all other traits
Start with 2 “pure parents”
P Generation
GG (only green)
gg (only yellow)
F1 generation
All green heterozygous

8. Determining Genotype (1 Trait)
PARENT
green
yellow F1 4
All green
Cannot see the yellow
in this generation
Self- fertilized F2
Self fertilization of this generation
produces a different pattern for
homozygous vs. heterozygous
Yellow
returns

9. Using a Punnett Square instead
Grid for Organizing Genetic Information
Shows Probability that a combination will occur
g g
Parent 2 Gg G Gg
1) Determine Parent alleles
2) Place alleles on edge of square
3) Combine alleles inside the boxes
4) Determine genotypes and phenotypes Gg Gg
Possible offspring genotypes for F1
Parent 1

10. Heterozygous cross G g G g Phenotypes vs. Genotypes
The recessive trait will show ONLY in the absence of the dominant (G) trait.
G g
GENOTYPE G g
GG : Gg or gG : gg
1 : : GG Gg
PHENOTYPE
Green Yellow
3 : 1 gG gg

11. Test Crosses
Purpose -
To distinguish between a homozygous dominant and a heterozygous dominant
Cross the unknown with a known homozygous recessive.
Create two Punnett squares.
Cross a homozygous dominant with a homozygous recessive
Cross a heterozygous dominant with a homozygous recessive
How are the patterns different?

12. Heterozygous + Homozygous Recessive
Phenotypes vs. Genotypes
The recessive trait will show ONLY in the absence of the dominant (G) trait. What will happen?
g g
GENOTYPE
GENOTYPE G g
GG :Gg or gG : g
: :
PHENOTYPE
Green Yellow :

13. Predicting any single outcome
Given Mendel’s Laws, the probability of an outcome for any one combination can be estimated.
Can Use coins to estimate probability
See Exercise on Probability.

14. Probabilities and Proportions
Should approximately match.
Are only estimates of what SHOULD happen.
Can be easily changed If “randomness” is compromised.

15. Dihybrid crosses RY RY ry Allow the study of two traits at a time.
Make a P cross (RRYY x rryy)
Cross F1 plants among themselves (RrYy x RrYy)
List all gametes
on a 4 x 4
Punnet Square
RY RY ry

16. Intermediate Inheritance
Mendel’s study
Dominant and recessive
Many genes have intermediate inheritance
Heterozygous phenotype not like either homozygous phenotype

17. Types of Intermediate Inheritance
Incomplete Dominance
Heterozygote phenotype is “inbetween “ the two homozygous phenotypes
EXAMPLE: Red + White = Pink Flowers
BUT: Gametes will contain either Red or White!
No dominant phenotype so only capital letters with superscripts are used.
Red = FrFr White = FwFw Pink = FrFw

18. Types of Intermediate Inheritance
Codominance
Both alleles express themselves fully
EXAMPLE: Blood types
A, B, AB

19. Polygenic Traits Trait is controlled by two or more gene pairs
Eye color, skin, hair
Tone amount, and distribution of pigments are all factors. Each is controlled by a different gene pair, for each attribute (color, skin, hair)

20. Multiple alleles Three or more alleles in a trait Blood type
IA IB and i
Both IA and IB are dominant over I
IA and IA are codominant.
NOT THE SAME as polygenic
A single pair of genes with > 2 alleles.

21. Environmental Stress on Genetics
Seasonal Changes( external changes)
Turning on “beard growth (internal changes)
Genes can be turned on and off.