1. Complex Inheritance Patterns

2. Patterns of Inheritance
Complete dominance
One allele is expressed over another in the heterozygote
Mendel’s pea traits

3. Complete dominance
Example: pure tall x pure short T = tall t = short TT x tt Genotype ratio 0TT:4Tt:0tt Phenotype ratio 4 tall: 0 short T t Tt

4. Patterns of Inheritance
Incomplete dominance
The heterozygous condition has an intermediate phenotype

5. Incomplete Dominance
Example: pure red x pure white R = red R’ = white RR x R’R’ Genotype ratio 0RR:4RR’:0R’R’ Phenotype ratio 0red:4pink:0white R R’
RR’

6. Patterns of Heredity Codominance
Both alleles are equally expressed in the heterozygote

7. Codominance
Example: pure black x pure white CB = black CW = white CBCB x CWCW Genotype ratio 0CBCB :4CBCW :0CWCW Phenotype ratio 0black:4checkered:0white CB CW
CBCW

8. Patterns of Heredity Multiple Alleles
When one trait has more than 2 alleles
Produces multiple phenotypes
Example: human blood type has 3 alleles
IA, IB, i

9. Multiple Alleles Genotype Phenotype IAIA or IAi A type blood
IBIB or IBi
B type blood
IAIB
AB type blood ii
O type blood

10. Multiple Alleles
The alleles indicate the type of marker proteins found on the red blood cells

12. Sex-linked Inheritance
Thomas Hunt Morgan accidentally discovered sex chromosomes when studying fruit flies

13. Sex-linked Inheritance
Humans have 23 pairs of chromosomes
22 pairs are autosomes and the 23rd pair is sex chromosomes

14. Sex-linked Inheritance
Human males have sex chromosomes XY
Human females have sex chromosomes XX

15. Sex-linked Inheritance
Human Sex-linked Disorders
(caused by recessive alleles)
Red-green colorblindness
Hemophilia A
Duchenne’s
muscular dystrophy

16. Important Things to Remember
males pass their X-linked allele to ALL their daughters (never to sons)
Heterozygous (carrier) females have a 50% chance of passing a recessive allele to all her children
males receiving the recessive X from Mom will ALWAYS express
the trait

17. Sex-linked Inheritance
Red-green colorblindness is a disorder caused by a sex-linked recessive gene. Normal vision is dominant.
XB = normal vision Xb = colorblindness
(Y chromosomes don’t carry the gene)

18. Example a.
Find the results of a cross between a colorblind man and a homozygous normal woman.
XBXB x XbY

19. Genotypes M: all XBY F: all XBXb (carriers) Phenotypes M: all normal F: all normal
Example a. XB Xb
XBXb Y
XBY

20. Example b.
Find the results of a cross between a normal woman, whose father was colorblind, and a normal man.
XBXb x XBY

21. Genotypes M: ½ XBY, ½ XbY F: ½ XBXB, ½ XBXb Phenotypes M: ½ normal, ½ colorblind F: all normal
Example b. XB Xb
XBXB
XBXb Y
XBY
XbY

22. The Flintstones
Fred (dad)
Pebbles (daughter)
Wilma (mom)

23. Patterns of Inheritance
Polygenic Inheritance
When one trait is controlled by multiple genes
Produces a bell curve of phenotypes
Ex. Skin color, hair color

24. Polygenic Inheritance
Each dominant allele contributes one unit of color to the phenotype