C12- Mendelian Inheritance Of Human Traits Chp 12- pp. 308- 335.
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Transcript of C12- Mendelian Inheritance Of Human Traits Chp 12- pp. 308- 335.
C12- Mendelian InheritanceOf 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
• Almond Eyes• Thick Lips• Digital Hair
• Cleft Chin• Widow’s Peak• Hanging Earlobes• Hitchhiker’s Thumb
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 Syndrome- Trisomy 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