1. Theoretical Genetics
Mrs. Ragsdale
Bio SL

2. A Lil Vocab Genotype – the actual genes (alleles)
Each gene has two alleles
Example: Aa, AA, aa
Phenotype – the physical characteristic expressed
Blue eyes vs green eyes
Dominant – the allele that is always expressed if its present
Recessive – an allele that is only expressed when a dominant allele isn’t around

3. Some More Vocab… Homozygous – when both alleles are the same
AA or aa
Both dominant or both recessive
Heterozygous – when one allele is dominant, the other recessive Aa
Locus – the location of a gene on a chromosome

4. GREGOR MENDEL “FATHER OF MODERN GENETICS” STUDIED PEA PLANTS
GENETICS – THE STUDY OF HUMAN HEREDITY
STUDIES HOW TRAITS ARE PASSED FROM PARENT TO OFFSPRING

5. Law of Segregation GAMETES – SEXUAL REPRODUCTIVE CELLS
EGG AND SPERM
LAW OF SEGREGATION – EACH PARENT PASSES ON ONE OF THEIR ALLELES FOR A GENE TO THEIR OFFSPRING

6. LAW OF INDEPENDENT ASSORTMENT
GENES FOR DIFFERENT TRAITS CAN SEPARATE DURING GAMETE FORMATION
They separate and assort themselves independently of each other
ALL OF YOUR MOM’S DNA DOES NOT END UP IN ONE GAMETE AND ALL OF YOUR DAD’S IN A DIFFERENT GAMETE
EACH OF YOUR GAMETES WILL BE A MIXTURE OF YOUR MOM AND DAD’S GAMETES

7. GENETIC PROBABILITY PUNNETT SQUARES DOMINANT ALLELES – CAPITAL LETTERS
RECESSIVE ALLELES – LOWER CASE

8. Punnett Example
Two heterozygous blue flowering pea plants are crossed.
Blue is dominant over white
What is the probability of a white flowering pea plant being produced?

9. B b Bb bb Punnett Example 2
A heterozygous blue flower is crossed with a homozygous white flower. What are the possibilities of the offspring and to what predicted probability? B b Bb bb

10. Dihybrid Crosses T=tall, t=short, R=red, r=white
Tall white x short red
Ttrr x ttRr
Phenotypes: Tall red, Tall white, short red, short white tR tr Tr
TtRr
Ttrr
ttRr
ttrr

11. INCOMPLETE DOMINANCE
SOMETIMES ONE ALLELE IS NOT COMPLETELY DOMINATE OVER ANOTHER
INCOMPLETE DOMINANCE IS A BLEND OR A MIXTURE OF TWO ALLELES
ONLY CAPITAL LETTERS ARE USED

12. Test Cross
Let’s say you have a flower that is dominant when red and recessive when white
If you have a red flower, how can you know if it is homozygous dominant or heterozygous?
Test cross – in order to test if something is AA or Aa, cross the unknown with a homozygous recessive aa.
If the subject was AA the offspring will all be Aa
If the subject was AA the offspring will be 50/50 Aa and aa

13. INCOMPLETE DOMINANCE
THE OFFSPRING OF A CROSS BETWEEN DOMINATE RED AND DOMINATE WHITE IS A BLENDED PINK

14. CODOMINANCE
BOTH ALLELES ARE SHOWN IN A PHENOTYPE

15. MULTIPLE ALLELES
WHEN A GENE HAS MORE THAN 2 DIFFERENT ALLELES THAT CONTROL IT’S PHENOTYPE Ex: Rabbit color
C = full color
cch = gray
ch = white with some brown
c = albino

16. Blood Groups: ABO
Human blood inheritance is a perfect example of both a multiple allele and codominance situation
Three alleles all based on the letter I
IA and IB are codominant to each other. Both these alleles are dominant to i
The Allele hierarchy is IA = IB and both are > i

17. Punnett Squares Revisited
IA IB
IA i i
IAi
IBi
IAIA
IAi ii IA i

18. POLYGENIC TRAITS CHARACTERISTICS CONTROLLED BY MORE THAN ONE GENE
EXAMPLES: HUMAN SKIN AND EYE COLOR

19. Polygenic Inheritance
-skin color
ABC 
 ABc 
 AbC
Abc 
aBC 
 aBc 
 abC
 abc
ABC 6 5 4 3
ABc 2
AbC
Abc 1
aBC
aBc
abC

20. Polygenic Inheritance
Height
Eye color
Continuous variation
Continuous variation
Different amounts of melanin
Polygenic Inheritance

21. Two Main Types of Chromosomes:
Sex Chromosomes
Chromosomes that determine the sex of the individual
In humans – X and Y
Females have XX
Eggs always donates X
Males have XY
Sperm donates either X or Y
Autosomes
Every other chromosome is an autosome

22. Human Sex Determination
Females XX
Males XY
Always a 50/50 chance of male or female at birth

23. Karyotyping
Photographic display of human chromosomes arranged in homologous pairs
Paired based on size, centromere location and banding

25. Sex Linkage
Sometimes, certain diseases and disorders only affect you based on your sex
These alleles are typically found on the sex chromosomes X or Y
For recessive alleles, women become carriers while men display the phenotype (the actual disease).
Examples:
Hemophilia
Color Blindness

26. Hemophilia: Recessive Sex-Linked Disease
Carried by women, expressed by males
The hemophiliac allele (Xh)is recessive to the normal allele (XH)
Females can be either homozygous or heterozygous for sex linked diseases
**Heterozygous females are called carriers because they have the allele but don’t express it

27. Pedigree Charts Modified family tree
Shows relationships within a family

28. Example Pedigree

29. Royal Pedigree