C12- Mendelian Inheritance Of Human Traits Chp 12- pp

Contents 12-1 Mendelian Inheritance 12-2 Complex InheritanceComplex Inheritance 12-3 Complex Inheritance of Human TraitsComplex 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 23 rd 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 I A, I B, 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 femaleTurner Syndrome XXX female XXY maleKlinefelter Syndrome XYY male Infertility Some mental retardation possible