1. Dominant Traits Recessive Traits Freckles No freckles Widow’s peak
Figure 9.8A
Dominant Traits
Recessive Traits
Freckles
No freckles
Figure 9.8A Examples of single-gene inherited traits in humans
Widow’s peak
Straight hairline
Free earlobe
Attached earlobe 1

2. Table 9.9
Table 9.9 Some Autosomal Disorders in Humans 2

3. Variations of Mendelian Genetics
5.5 and 5.6

9. Dihybrid Cross
Looks at two pairs of contrasting traits at the same time

10. Dihybrid Cross Example
Round or wrinkled and green or yellow
Law of segregation still applies
4 different alleles, 9 possible genotypes, 4 possible phenotypes

11. Independent Assortment
The inheritance of an allele for one characteristic does not affect the inheritance of an allele for a different characteristic.
Related to independent orientation during meiosis- homologous chromosomes randomly line up on the left and right side.
Independent assortment still applies even if the alleles for the different characteristics are on the same chromosome because of crossing over which occurs during prophase I of meiosis

13. Law of Segregation vs. Law of Independent Assortment
Law of segregation is talking about how haploid gametes are produced through the process of meiosis
Law of independent assortment is talking about how the inheritance of one characteristic does not effect the inheritance of other characteristics

14. Complete Dominance Pea Plant
Genotype
Phenotype
Homozygous dominant (PP)
Purple
Heterozygous (Pp)
Homozygous recessive (pp)
White
2 different alleles, 3 possible genotypes, 2 possible phenotypes

16. Incomplete Dominance Neither allele is purely dominant or recessive
The phenotype of the heterozygote is a result of both alleles being expressed
Results in an intermediate phenotype

17. Incomplete Dominance Example
Many common garden flowers like the snapdragon have genes for flower color that display incomplete dominance.

18. Incomplete Dominance Snapdragon
Genotype
Phenotype
Homozygous for red (RR)
Red
Heterozygous (RW)
Pink
Homozygous for white (WW)
White
2 different alleles, 3 possible genotypes, 3 possible phenotypes

19. Incomplete Dominance Hypercholesterolemia
One example of incomplete dominance in humans is hypercholesterolemia, in which
dangerously high levels of cholesterol occur in the blood and
heterozygotes have intermediately high cholesterol levels.

20. Genotypes Hh Heterozygous
Figure 9.11B
Genotypes Hh Heterozygous
HH Homozygous for ability to make LDL receptors
hh Homozygous for inability to make LDL receptors
Phenotypes
LDL
LDL receptor
Figure 9.11B Incomplete dominance in human hypercholesterolemia
Cell
Normal
Mild disease
Severe disease 20

21. Co-dominance Neither allele is purely dominant or recessive
The phenotype of the heterozygote is a result of both alleles being expressed
Does not result in a blend or intermediate characteristics
Both alleles are expressed separately and equally

22. Co-dominance Example
Many mammals have genes for hair color that display co-dominance

23. Co-dominance Horse Hair
Genotype
Phenotype
Homozygous for red (RR)
Red
Heterozygous (RW)
Roan
Homozygous for white (WW)
White
2 different alleles, 3 possible genotypes, 3 possible phenotypes

24. Multiple Alleles
In each example we’ve looked at so far, the trait is a result of the interaction of 2 different alleles.
With many traits, however, there are more than 2 possible alleles that you could inherit.

25. Multiple Alleles Example
There are 3 possible alleles for blood type and they display a combination of complete dominance and co-dominance.
Allele for blood type A and B are both dominant over the allele for blood type O
Allele for blood type A and B are co-dominant

26. Multiple Alleles ABO Blood Type
There are three possible alleles: IA, IB, and i.
The combination of two of those alleles determines an individuals blood type.
Blood Types (Phenotypes)
Possible Genotypes
Type A
IAIA or IAi
Type B
IBIB or IBi
Type AB
IAIB
Type O ii

27. Multiple Alleles ABO Blood Type
3 different alleles, 6 possible genotypes, 4 possible phenotypes

28. Polygenic Inheritance (Multiple Genes)
Multiple genes at different loci and/or on different chromosomes effect a single characteristic
Most human traits have some degree of polygenic inheritance
Skin color, hair color, eye color, height, body build, intelligence…

29. Polygenic Inheritance (Multiple Genes) Example
There is at least 3 genes that control skin color
Combinations result in a blend from very light to very dark
Behavior and the environment play an important role as well

30. Polygenic Inheritance (Multiple Genes) Skin Color
6 different alleles, 27 possible genotypes, 7 possible phenotypes

31. Sex Determination Humans have 46 chromosomes (23 pairs)
22 pairs of autosomes and one pair of sex chromosomes
Sex chromosomes determine the sex and we represent them with an X and a Y.
Female = XX
Males = XY
It is the man’s gene that determines the sex of the child

32. Sex-Linked Traits X chromosome is much larger than the Y chromosome
Genes on the X chromosome are important for both males and females
Genes on the Y chromosome are what make a male a male
In females characteristics are determined by the interaction of the alleles on each X chromosome
In males, since they only have one X chromosome and the Y chromosome is much smaller, some characteristics are determined by a single allele on the X chromosome.

33. Sex-Linked Traits Example
Red-green colorblindness
Reduced amount of a chemical in the retina of their eyes
Red-green colorblindness is a recessive characteristic that is found on the X chromosome

34. Sex-Linked Trait Red-Green Colorblindness
Male
Genotype
Phenotype
XNY
Normal
XnY
Colorblind

35. Sex-Linked Trait Red-Green Colorblindness
Female
Genotype
Phenotype
XN XN
Normal
XN Xn
Xn Xn
Colorblind
Carrier- a carrier for an X-linked trait is a female individual who does not exhibit the characteristic but does carry the gene for the trait

36. Sex-Linked Trait Colorblind father x Heterozygous mother
Father with normal vision x Heterozygous mother
Colorblind father x Homozygous mother with normal vision
Father with normal vision x Colorblind mother

37. Pedigree
Chart that geneticists use to trace the presence or absence of a trait in a number of generations
Square = male
Circle = female
Shaded = has trait
Not shaded = does not have trait

38. Hemophilia X-linked recessive trait “Bleeder’s disease”
Hemophilia- genetic disorder that causes individuals to lack an enzyme in the blood that is essential for normal blood clotting
Normally minor cuts, bruises, and scrapes can become very serious
In the past, individuals with this disorder typically died very young
Modern medication can replace the enzyme

39. Pedigree