Human Heredity Chapter 14

Chromosomal Inheritance 2 Human Genetic Disorders Autosome - Any chromosome other than a sex chromosome Genetic disorders caused by genes on autosomes are called autosomal disorders  Some genetic disorders are autosomal dominant ­An individual with AA has the disorder ­An individual with Aa has the disorder ­An individual with aa does NOT have disorder  Other genetic disorders are autosomal recessive ­An individual with AA does NOT have disorder ­An individual with Aa does NOT have disorder, but is a carrier ­An individual with aa DOES have the disorder

Chromosomal Inheritance 3 Autosomal Recessive Pedigree Chart

Chromosomal Inheritance 4 Autosomal Dominant Pedigree Chart

Chromosomal Inheritance 5 Autosomal Recessive Disorders Tay-Sachs Disease  Progressive deterioration of psychomotor functions Cystic Fibrosis  Mucus in bronchial tubes and pancreatic ducts is particularly thick and viscous Phenylketonuria (PKU)  Lack enzyme for normal metabolism of phenylalanine

Chromosomal Inheritance 6 Cystic Fibrosis Therapy

Chromosomal Inheritance 7 Autosomal Dominant Disorders Neurofibromatosis  Tan or dark spots develop on skin and darken  Small, benign tumors may arise from fibrous nerve coverings Huntington Disease  Neurological disorder  Progressive degeneration of brain cells ­Severe muscle spasms ­Personality disorders

Chromosomal Inheritance 8 Autosomal Dominant Disorders Neurofibromatosis  Tan or dark spots develop on skin and darken  Small, benign tumors may arise from fibrous nerve coverings Huntington Disease  Neurological disorder  Progressive degeneration of brain cells ­Severe muscle spasms ­Personality disorders

Chromosomal Inheritance 9 A Victim of Huntington Disease

Chromosomal Inheritance 10 Huntington Disease: Normal and Diseased Brain

Chromosomal Inheritance 11 Multiple Allelic Traits and Codominance Some traits controlled by multiple alleles The gene exists in several allelic forms (but each individual only has two) ABO blood types The alleles:  I A = A antigen on red cells, anti-B antibody in plasma  I B = B antigen on red cells, anti-AB antibody in plasma  I = Neither A nor B antigens, both antibodies Phenotype (Blood Type) Genotype A (actually AA or AO) I A I A or I A i B (actually BB or BO) I B I B or I B i AB IAIBIAIBIAIBIAIB O (actually OO) ii

Chromosomal Inheritance 12 Inheritance of Blood Type

Chromosomal Inheritance 13 Human X-Linked Disorders: Red-Green Color Blindness Color vision In humans:  Depends three different classes of cone cells in the retina  Only one type of pigment is present in each class of cone cell ­The gene for blue-sensitive is autosomal ­The red-sensitive and green-sensitive genes are on the X chromosome ­Mutations in X-linked genes cause RG color blindness:  All males with mutation (X b Y) are colorblind  Only homozygous mutant females (X b X b ) are colorblind  Heterozygous females (X B X b ) are asymptomatic carriers

Chromosomal Inheritance 14 X-Linked Recessive Pedigree

Chromosomal Inheritance What is a karyotype?What is a karyotype? What patterns of inheritance do human traits follow?What patterns of inheritance do human traits follow?  Dominant and Recessive Alleles  Codominant and Multiple Alleles How can pedigrees be used to analyze human inheritance?How can pedigrees be used to analyze human inheritance? How do small changes in DNA molecules affect human traits?How do small changes in DNA molecules affect human traits? What are the effects of errors in meiosis?What are the effects of errors in meiosis?  nondisjunction 15

Chromosomal Inheritance cell.html 16

Chromosomal Inheritance What is Sickle Cell Anemia? A serious condition in which red blood cells can become sickle- shaped A serious condition in which red blood cells can become sickle- shaped Normal red blood cells are smooth and round. They move easily through blood vessels to carry oxygen to all parts of the body. Normal red blood cells are smooth and round. They move easily through blood vessels to carry oxygen to all parts of the body. Sickle-shaped cells don’t move easily through blood. They’re stiff and sticky and tend to form clumps and get stuck in blood vessels. Sickle-shaped cells don’t move easily through blood. They’re stiff and sticky and tend to form clumps and get stuck in blood vessels. The clumps of sickle cell block blood flow in the blood vessels that lead to the limbs and organs. Blocked blood vessel can cause pain, serious infection, and organ damage. The clumps of sickle cell block blood flow in the blood vessels that lead to the limbs and organs. Blocked blood vessel can cause pain, serious infection, and organ damage.

Chromosomal Inheritance Normal and Sickled Red Blood Cells in Blood Vessels Figure A shows normal red blood cells flowing freely in a blood vessel. The inset image shows a cross-section of a normal red blood cell with normal hemoglobin. Figure B shows abnormal, sickled red blood cells clumping and blocking the blood flow in a blood vessel. The inset image shows a cross-section of a sickled red blood cell with abnormal strands of hemoglobin. Source from

Chromosomal Inheritance 8 What is cystic fibrosis (CF)?

Chromosomal Inheritance Cystic Fibrosis Inherited monogenic disorder presenting as a multisystem disease. Typically presents in childhood  7% of CF patients diagnosed as adults Most common life limiting recessive trait among whites

Chromosomal Inheritance Cystic Fibrosis Prognosis improving  >38% of CF patients are older than 18  13% of CF patients are older than 30 Median survival  Males: 32 years  Females: 29 years

22 Nondisjunction

23 Trisomy 21

Chromosomal Inheritance 24 Chromosome Number: Abnormal Sex Chromosome Number Result of inheriting too many or too few X or Y chromosomes Caused by nondisjunction during oogenesis or spermatogenesis Turner Syndrome (XO)  Female with single X chromosome  Short, with broad chest and widely spaced nipples  Can be of normal intelligence and function with hormone therapy

Chromosomal Inheritance 25 Chromosome Number: Abnormal Sex Chromosome Number Klinefelter Syndrome (XXY)  Male with underdeveloped testes and prostate; some breast overdevelopment  Long arms and legs; large hands  Near normal intelligence unless XXXY, XXXXY, etc.  No matter how many X chromosomes, presence of Y renders individual male

26 Turner and Klinefelter Syndromes

Chromosomal Inheritance 27 Chromosome Number: Abnormal Sex Chromosome Number Ploy-X females  XXX simply taller & thinner than usual  Some learning difficulties  Many menstruate regularly and are fertile  More than 3 Xs renders severe mental retardation Jacob’s syndrome (XYY)  Tall, persistent acne, speech & reading problems

Chromosomal Inheritance 28 Abnormal Chromosome Structure Deletion  Missing segment of chromosome  Lost during breakage Translocation  A segment from one chromosome moves to a non-homologous chromosome  Follows breakage of two nonhomologous chromosomes and improper re-assembly