1. More Genetics

2. Complete Dominance The pattern we’ve seen so far
Homozygous dominant and heterozygous are indistinguishable
YY and Yy will both make yellow seed

3. Complete Dominance Autosomal recessive pattern::
AA, Aa are “normal”
aa has the condition
Autosomal dominant pattern:
AA, Aa have the condition
aa is “normal”

4. Some patterns of inheritance don’t follow the rules.
Incomplete dominance
Heterozygotes have a blended appearance between both alleles
Ex. Blended colors in flowers
Codominance
Heterozygotes have the phenotype of both alleles expressed at the same time
Ex. Roan horses (next slide)

6. What would you expect in each situation?
INCOMPLETE DOMINANCE
Red flower x white flower =
pink
CODOMINANCE
Red flower x white flower =
red and white flower mix

7. Multiple Alleles
Instead of just two alleles (A vs. a), more than two alleles control a trait
Human blood types work this way
Alleles = IA, IB, i
IA & IB = Codominant

8. Blood Typing Phenotype (Blood Group) Genotype(s) Type A IAIA or IAi
IBIB or IBi
Type AB
IAIB
Type O ii

9. Blood Typing Problem:
A man who is heterozygous for Type A blood marries a woman who is homozygous for Type B blood. What possible blood types might their children have?

10. Blood Typing Problem 2:
A woman is IAIB. She has a child that is Type AB. Which genotypes might the father have had?

11. Polygenic Inheritance: the effect of 2 or more genes acting upon a single phenotypic character (eg. skin color, height)

12. These girls are fraternal twins!
remee-hodgson-turn-seven/

13. Pleiotropy: one gene influences multiple, seemingly unrelated phenotypic traits

14. Note the differences! Pleiotropy Multiple alleles
One gene influences many phenotypes
The “Frizzle Gene” mutation makes chickens have curled feathers. This ALSO causes issues with body temperature, metabolism, blood flow, digestion.
Multiple alleles
More than two alleles code for a trait
IA, IB, i
Polygenic inheritance
More than two genes influence a trait
Gene 1, gene 2, gene 3, gene 4 all influence skin color

15. Lethal Alleles First, cross Ll x Ll
Some genotypes are lethal and cause death (generally, before an organism is born)
LEAVE OUT LETHALS when figuring genotype, phenotype, and probability. DEAD IS DEAD! You have no phenotype if you are dead.
The ratios that would result if ll was lethal:

16. Practice
For a certain disease, HH is a lethal allele that causes death before an organism is born. If two parents, Hh x Hh, have kids, what is the chance that they will have a child that is homozygous recessive?

17. Some traits are non-nuclear
Genes on chloroplasts and mitochondrial DNA do not follow Mendelian rules
During meiosis, chloroplasts and mitochondria are randomly assorted to gametes.
Also, since mitochondria are passed via the egg only, certain traits come only from your mother

18. Nature and nurture
Both genetic and environmental factors influence phenotype
Example: hydrangeas change color/intensity based on the pH and aluminum content of the soil

19. Pedigrees- diagrams to show the relationship between parents/offspring across 2+ generations.

20. Identify each pedigree as autosomal dominant inheritance, autosomal recessive, or neither.

21. Identify each pedigree as autosomal dominant inheritance, autosomal recessive, or neither.

22. Identify each pedigree as autosomal dominant inheritance, autosomal recessive, or neither.

23. Identify each pedigree as autosomal dominant inheritance, autosomal recessive, or neither.

24. Genetic Testing
Most children with recessive disorders are born to parents with normal phenotypes, so determining if parents are heterozygous is useful.
Many tests are around that can screen for carriers of disorders like Tay-Sachs, sickle-cell, CF, and others.
Consider health insurance. What sorts of ethical issues might knowing your phenotype (especially if a disease will manifest later) bring up?
What about employers—if they don’t understand what “carrier” means and they get a hold of your data, what might that lead to?
Tests are out there for Huntington’s. Would you want to know?

25. Genetic Testing
You will read more about genetic testing and ethical issues in your book

26. Autosomal Recessive Disorder: Cystic Fibrosis
Most common lethal genetic disease in the U.S.
Normal allele: codes for membrane protein that transport chloride ions
Mutant allele: codes for defective (or no) membrane protein
Pleiotropic effects: poor absorption of nutrients from intestines, chronic bronchitis, recurrent bacterial infections

27. Autosomal Recessive Disorder: Sickle Cell Disease
Most common inherited disorder among those of African descent
Point mutation in hemoglobin gene
When oxygen is low, the sickle cell hemoglobin molecules change shape, which may clump and clog blood vessels

28. Autosomal Recessive Disorder: Sickle Cell Disease
Phenotype varies due to genotype.
ss = sickle cell disease = full sickle cell disease
Ss = sickle cell trait = usually healthy, but may have some sickle-cell symptoms during prolonged periods of reduced blood oxygen
SS = normal = no sickle cell at all
IMPORTANT! Sickle cells cannot be infected by malaria.
So…there is an advantage to being Ss…if you have sickle cell trait, you can’t get malaria and you are also mostly normal.

30. Autosomal Dominant Disorder: Huntington’s Disease
Is a lethal dominant…but the “lethal” part kicks in after reproductive age
Degenerates nervous system
No phenotypic effects until age ; irreversible and fatal

31. Autosomal Dominant Disorder: Achondroplasia
Homozygous dominant is lethal
Heterozygous individuals will have the dwarf phenotype
Homozygous recessive individuals (99.99% of the population!) are not dwarfs
How can a family with dwarf parents have a non-dwarf child?