Chapter 12
When Heredity Rules are Different
Complex Patterns of Heredity
• Most traits are not simply dominant or
recessive
• Incomplete dominance: when the phenotype
of the heterozygous individual is in between
those of the two homozygotes (a mixture)
• Red flower color (RR)
• White flower color (rr)
• Pink colored flowers (Rr)
• Codominace: when the alleles of both
homozygotes (BB or WW) are expressed
equally in the heterozygous individual
– black chicken (BB)
– white chicken (WW)
– offspring will be checkered
• Sex-linked traits: traits controlled by genes
located on sex chromosomes
– Sex chromosomes: 23rd pair in humans that
determine a person’s sex (X or Y)
Females are XX, males are XY
• X-linked disorders:
generally passed on
from mother to son
– is found on the X
chromosome
• Example: Down’s
Syndrome (trisomy 21)
• colorblindness
• Y-linked disorders:
only passed on from
father to son
• Examples: excessive
hair growth of the ears
& male infertility
Colorblindness Tests
Normal color:
Colorblind sees:
yellow square &
yellow square
faint brown circle
Colorblind sees:
the number 17
Normal Color sees:
the number 15
Test Name: Ishihara Test
• Polygenic inheritance: when one trait is
controlled by many genes.
• Examples: height, eye color, skin color, &
blood type
Changes in Chromosomal Numbers
• Humans have 23 pairs of chromosomes
• (46 total); more or less = disorder
• Autosomes: a non-sex chromosome
– Known as chromosomes 1-22
8 Environmental Factors That Can Also
Influence Gene Expression
• 1. temperature
• 5. infectious agents
• 2. light
• 6. hormones
• 3. nutrition
• 7. structural differences
• 4. chemicals
• 8. age
*** know examples***
Chapter 12:
Patterns of Heredity & Human
Genetics
Mendelian Inheritance of Human
Traits
Making a Pedigree
• When genetic inheritance is represented by a
picture, this is called a pedigree.
– It is a diagram made of symbols that identify three
things:
• 1. Male or female
• 2. Individuals affected by the trait being studied
• 3. Family relationships
Symbols of a pedigree:
***need to know***
Carrier –
heterozygous individual
Constructing and Reading a pedigree
I.
1
2
II.
1
2
3
4
5
III.
1
2
3
4
5
***Roman Numerals (I, II, III) refers to the generations.***
*Arabic numbers refers to individuals. (1, 2, 3, 4, 5, …)
6
Reading the pedigree…
I.
1
2
II.
1
2
3
4
5
6
7
III.
1
2
3
4
How many generations are there?
How many children did II-1 have? II-7?
How are III-5 and III-2 related?
Who is III-2 in reference to I-2?
5
Simple Recessive Heredity
• Most genetic disorders are caused by
recessive alleles. This means the disorder is
inherited when both parents have a recessive
allele.
• Ex: Cystic Fibrosis (CF), Tay-Sachs Disease
Pedigree for Cystic Fibrosis
Pedigree for Tay-Sachs
Simple Dominant Heredity
• Dominant disorders: Only one dominant allele
has to be inherited from either parent.
• Simple Dominant Traits
– 1. cleft chin
– 2. unattached earlobes
– 3. almond shaped eyes
– EX: Huntington’s Disease
Is it Dominant or Recessive…
I.
1
2
3
4
II.
1
2
4
3
5
6
III.
1
2
3
Dominant, only one parent has the disorder.
Is it Dominant or Recessive…
I.
1
2
3
4
II.
1
2
4
3
5
6
III.
1
2
3
Recessive, neither parent has the disorder. Both are
heterozygous.