1. COMPLEX PATTERNS OF INHERITANCE

2. Simple Dominant Traits
Simple dominant traits need only 1 allele in order to express phenotype – RR or Rr
Examples: Huntington’s disease
Cleft chin, widow’s peak

3. Simple Dominant Traits
1 homozygous dominant
2 heterozygous
1 homozygous recessive
R r RR Rr rr R r

4. Huntington’s Disease
Huntington's disease is an inherited disease that causes the progressive breakdown of nerve cells in the brain. Huntington's disease has a broad impact on a person's functional abilities and usually results in movement, thinking (cognitive) and psychiatric disorders.

5. Simple Recessive Disorders
Recessive Disorders affect offspring with 2 recessive alleles
(homozygous recessive)
Most genetic disorders are caused by recessive alleles

6. Recessive Disorders Cystic Fibrosis
1 in 28 white Americans carry recessive allele
Defective PROTEIN in plasma membrane
Accumulate mucus in lungs and digestive tract

7. Recessive Disorders Tay-Sachs
Absence of ENZYME that breaks down LIPIDS
Lipids accumulate in cells

8. Recessive Disorders Phenylketonuria (PKU)
Absence of ENZYME to convert phenylalanine to tyrosine
Phenylalanine cannot be broken down
Accumulates in cells
Damages CNS
Mental retardation

9. COMPLEX PATTERNS OF INHERITANCE

10. INCOMPLETE DOMINANCE

11. INCOMPLETE DOMINANCE
Incomplete dominance occurs when one allele is not completely dominant over another allele
Results in heterozygote being phenotypically expressed as a mix
A third phenotype appears

12. Snapdragon plant
RED
PINK
WHITE
R R
R R´
R’ R´

13. INCOMPLETE DOMINANCE
Flowers contain enzymes that control pigment production
The R allele makes red pigment
W defective enzyme that makes no pigment

14. INCOMPLETE DOMINANCE RR plenty red pigment = red
RW has one R allele and can produce half the amount of red pigment = pink
WW can produce no pigment =
white

15. A red carnation is crossed with a white carnation
INCOMPLETE DOMINANCE
A red carnation is crossed with a white carnation
1. Write the genotypes of the two parent carnations.
2. Use a Punnett square to determine the percentage of the offspring expected to be pink.

16. INCOMPLETE DOMINANCE Parents = RR x WW 100% are expected to be pink!RW RW W RW RW
100% are expected to be pink!

17. CODOMINANCE

18. CODOMINANCE Heterozygote has both alleles Use BOTH uppercase letters
Both alleles show equally
What would happen if you bred…
Black rooster
White hen x

19. CODOMINANCE
Black rooster
White hen WW BB
Black & White Chicken BW

20. Black rooster WW BB BW

21. Sickle Cell Anemia
Sickle Cell Anemia is a genetic disorder found in African Americans
Hemoglobin is the protein in red blood cells that carries oxygen. The normal allele for the gene differs by only one DNA base (what mutation?)
Results in abnormal hemoglobin that is less soluble in blood, and decreases oxygen levels
Decreased oxygen levels lead to sickle shaped cells that stick together

22. SICKLE-CELL ANEMIA (CODOMINANCE)
Hemoglobin, the oxygen-carrying protein, differs by one amino acid, which changes shape of red blood cell
Abnormal shape slows blood flow and blocks small vessels

25. SICKLE-CELL ANEMIA Sickled cells have shorter life span  anemia
(low # of red blood cells)
Sickled cells get stuck in blood vessels, preventing blood flow that causes pain, fever, swelling, and tissue damage that can lead to death

26. SICKLE-CELL ANEMIA NN NS SS
Individual who are heterozygous for the allele produce both normal and sickled red blood cells (codominance)
Able to produce enough hemoglobin to have no serious health problems
“have the sickle-cell trait”
NN NS SS

27. SICKLE-CELL ANEMIA
A boy is born with sickle-cell anemia. Neither parent has the disease.
Write the boy’s genotype for this disease.
2. Use a Punnett square to determine the genotypes of both parents.

28. SICKLE-CELL ANEMIA Boy’s genotype = SS Parents’ genotypes = N? x N?NN
N__ ?
N__ SS
Parents’ genotypes = NS x NS

29. SICKLE-CELL ANEMIA
Why is the sickle cell anemia mutation so common among African Americans?
Most carriers can trace their ancestry to west Africa, an area afflicted with malaria.

30. Why does the sickle cell allele persist? (must be some advantage)
Carriers (with one sickle gene and one normal hemoglobin gene) have some protective advantage against malaria
The frequencies of sickle cell carriers are high where malaria is prevalent (as great as 40%!)

31. People who have sickle cell anemia are less likely to die from malaria.
The parasite is carried by the Anopheles mosquito.
Cells that sickle make a poor home for this parasite. The body can eliminate it before the parasite spreads too widely, before the person gets seriously ill.

34. Sickle Cell Anemia
In this case, scientists believe that sickle cell carriers have been NATURALLY SELECTED because their trait has some resistance to malaria.
Evolutionary trade off because if both parents are carriers of sickle cell anemia, then they have a 50% chance of their offspring being carriers, 25% of having sickle cell, and 25% of having no trait for sickle cell, and therefore no advantage against malaria.

35. Sickle Cell Anemia
Scientists now know that sickle cell is an example of CODOMINANCE, because three phenotypes are possible:
1 – normal hemoglobin
2 – sickle cell anemia
3 – carrier of sickle cell disease; advantage against malaria; when infected with parasite, their red blood cells sickle and are filtered out, along with the parasite, by the spleen

36. POLYGENIC INHERITANCE

37. POLYGENIC TRAITS Trait is controlled by more than one gene
EX: skin color controlled by more than four different genes
Different combinations of alleles for these genes produce a range of phenotypes.
All heterozygotes are intermediate phenotype

38. POLYGENIC INHERITANCE
Eye color
height, weight
intelligence in people

39. Quick Check
1. In what type of inheritance does the heterozygote show BOTH alleles? 2. What type of inheritance is sickle cell anemia? 3. What is the advantage of having the sickle trait? 4. What type of inheritance can produce a pink flower from a cross between red and white flower? 5. What controls flower pigment? 6. What type of molecule is hemoglobin? 7. Polygenic inheritance produces a __ of phenotypes.