Download C12- Mendelian Inheritance

C12- Mendelian Inheritance
Of Human Traits
Chp 12- pp. 308- 335
Contents
• 12-1 Mendelian Inheritance
• 12-2 Complex Inheritance
• 12-3 Complex Inheritance of Human
Traits
C12-Mendelian Inheritance of Human Traits
• Making a Pedigree
• Symbols identify sex,
genotype and
relationship between
parents, siblings &
spouses.
• Half-shaded Carrier
• Horizontal row
generation
• Practice on p. 310.
Analyzing a Pedigree
• Determine likelihood
of being a carrier.
• Probability for
offspring being
affected.
Simple Recessive Heredity
• Most genetic
diseases are caused
by recessive alleles:
• Cystic fibrosis
• Tay Sachs
• Phenylketonuria
Simple Dominant Heredity
•
•
•
•
Cleft Chin
Widow’s Peak
Hanging Earlobes
Hitchhiker’s Thumb
• Almond Eyes
• Thick Lips
• Digital Hair
Simple Dominant Heredity
• Huntington’s Disease
• Lethal genetic disorder
• Onset between 30 to 50
12-2 When Heredity Follows Different Rules
• Complex Inheritance
– Incomplete
Dominance
– Codominance
– Multiple Alleles
– Sex Determination
– Sex-linked
– Polygenic Inheritance
Complex Inheritance
• Incomplete dominance
• Appearance of a third phenotype blending the
first two
Complex Inheritance
• Codominance
• Both alleles
expressed equally in
heterozygotes
• Use uppercase for
both
• Ex. Checkered
chickens
Complex Inheritance
• Multiple Alleles
• Traits controlled by
more than 2 alleles
• Ex. Feather color in
pigeons
Complex Inheritance
• Sex Determination
• 23rd pair of
chromosomes
• Female 2 X s
• Male X Y
Complex Inheritance
• Sex-Linked Traits
controlled by genes
on sex chromosomes
• Thomas Hunt
Morgan (1910)
discovered rules
governing SLT by
studying fruit flies
eye color.
• Females red eye
males ½ red ½ white
Complex Inheritance
• Polygenic
Inheritance
• Skin color & height
controlled by many
genes
• Heterozygotes
intermediate
phenotype
Environmental Influences
• Can determine how
or whether gene is
expressed:
• Internal Environment
– Hormones, structural
differences, age
• External
– Temperature,
nutrition, light,
chemicals, infectious
agents.
12-3 Complex Inheritance of Human Traits
• Codominance
– Sickle-cell anemia
– Differs from normal
hemoglobin by one
amino acid
– Moon-shaped cells
block blood flow
causing tissue
damage and pain.
Multiple Alleles
• Blood Type- A, B, AB or O types determined by
presence or absence of molecules
• Gene has 3 alleles IA, IB, I
• Incompatible blood causes clumping
Sex-linked Traits in Humans
• Red-green
colorblindness
• Hemophilia-blood
clotting disorder
Sex-linked Traits in Humans
• ♀ Carrier X ♂ C
• 50% offspring CB in
this example
• Responsible gene on
X
Polygenic Inheritance
• Eye Color
• Skin Color
• 3 or more genes
involved
Changes in Chromosome Number
• Abnormal number
autosomes
• Trisomy usually
results from
nondisjunction.
• Metaphase
chromosomes are
photographed &
charted into a
Karyotype.
Changes in Chromosome Number
• Down’s SyndromeTrisomy 21
• Only autosomal
trisomy that survives
to adulthood.
• Occurs 1 in 700 live
births
• Some degree of
mental retardation
Changes in Chromosome Number
•
•
•
•
•
•
•
Abnormal number of Sex chromosomes
XO female Turner Syndrome
XXX female
XXY male Klinefelter Syndrome
XYY male
Infertility
Some mental retardation possible