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Transcript
The Human Genome Chromosomes & Phenotype Genetic Disorders Foothill High School Science Department Autosomal vs Sex Linked Traits • Autosomes – All the chromosomes that do NOT play a role in sex determination • In humans, chromosomes 1 – 22 – Two copies » One from Mom » One from Dad » Same genes » Same location on chromosome » BUT may be different alleles (recipes) Foothill High School Science Department Autosomal vs Sex Linked Traits • Sex Linked Genes – Genes on the X or Y chromosome – X Chromosome • Large • Contains many genes, some essential for survival – Y Chromosome • Small • Few genes except those necessary to change fetal development from female to male Foothill High School Science Department Autosomal Disorders caused by Recessive Alleles • Recessive Alleles cause disorder – Heterozygotes are Carriers • Can pass damaged allele to offspring BUT don’t have the disease/disorder – Homozygous Recessive individuals have the disease/disorder Foothill High School Science Department Autosomal Disorders caused by Recessive Alleles Cystic Fibrosis • Mutation of CFTR gene on chromosome 7 • Causes thick mucus in lungs & blockage of gastrointestinal tract • Damages the pancreas • Fatal • Both parents must be heterozygous to have a child with the disease Foothill High School Science Department Autosomal Disorders caused by Dominant Alleles Dominant allele disorders far less common Huntington’s Disease • Mutation of HTT gene on chromosome 4 • Appears during adulthood – usually 35-44 yrs. old – Allow time for person with disease to reproduce • Nervous system disintegrates slowly over years • Fatal Foothill High School Science Department Autosomal Disorders caused by Dominant Alleles Neurofibromatosis Autosomal Dominant Disorder Chromosome 22 Foothill High School Science Department Sex-Linked Genes Sex Linked Genes Are Genes Located On The X & Y Chromosome X – Contains > 100 Genes Y – Contains Only A Few Genes Foothill High School Science Department Sex-Linked Genes Foothill High School Science Department Colorblindness The X Chromosome Contains Three (3) Genes Associated With Color Vision The Y Chromosome Is Missing Them All Therefore, Males Are Particularly Vulnerable To Colorblindness Foothill High School Science Department Colorblindness The Images Below are NOT Diagnostic Foothill High School Science Department Colorblindness Red-Green Colorblindness Most Common Form 1:10 Males 1:100 In Females Why The Difference? Foothill High School Science Department Colorblindness Colorblind Males Only Pass The Recessive Allele On To Their Daughters It is not on the Y Chromosome They Pass To Their Sons. (only daughters will receive the fathers X Chromosome) Thus - The Gene Appears To Skip A Generation And Will Only Reappear In His Grandchildren Foothill High School Science Department Hemophilia Two Important Blood Clotting Genes Are On The X Chromosome Occurrence Rate = 1:10,000 Males Foothill High School Science Department Hemophilia Mild Post-Injection Bleeding In A Patient With Hemophilia Foothill High School Science Department Duchenne Muscular Dystrophy Sex-Linked Abnormal Muscle Protein Patients Rarely Live Beyond Early Adulthood Occurrence Rate = 1:3000 Males Foothill High School Science Department In Mammals Female X-Chromosome Inactivation Males NO Only Have (1) X Chromosome Females Have Two (2) X Chromosomes Do Female Express Both X Chromosomes? Foothill High School Science Department In Mammals Female X-Chromosome Inactivation One X Chromosome Is Randomly Switched Off – That Chromosome Forms A Dense Region In The Nucleus Known As A Barr Body Foothill High School Science Department In Mammals Female X-Chromosome Inactivation Arrows Indicate Barr Bodies Foothill High School Science Department In Mammals Female X-Chromosome Inactivation Foothill High School Science Department Chromosome Disorders • Most Common Is Nondisjunction During Meiosis, Homologous Chromosomes Fail To Separate One Gamete Will Have An Extra Chromosome (Trisomy) The Other Will Have One Less Foothill High School Science Department Down Syndrome • Nondisjunction of Chromosome 21 (trisomy) • Occurs 1:800 Births • Mental Retardation May Be Mild To Severe • Increased Susceptibility To Disease Foothill High School Science Department Down Syndrome Why Would 3 Copies Cause Problems When 2 Copies Don’t? Don’t Know Yet Working Hard To Find Out Foothill High School Science Department Sex Chromosome Disorders • Turner’s Syndrome – Females – Nondisjunction Results In A XO Female – Sterile – Sex Organs Do Not Develop During Puberty Foothill High School Science Department Sex Chromosome Disorders • Klinefelter’s Syndrome – Males – Nondisjunction Results In A XXY Male – The Extra X Interferes With Meiosis – Generally Sterile – Also Found XXXY & XXXXY – Exhibit Female Body Patterns In Hips, Partial Breast Development, Female Pubic Hair Pattern Foothill High School Science Department Sex Chromosome Disorders No Babies Are Born Without At Least One X Chromosome Indicates The X Chromosome Carries At Least One Gene Required For Life Foothill High School Science Department Y Chromosome • If Present, Individual Is Male – Even When Multiple X Chromosomes Are Present – Contains At Least One Gene Required For Male Sexual Development No “Y” Present – Embryo Develops As A Female Foothill High School Science Department