Chromosomes & Phenotype Genetic Disorders The Human Genome Chromosomes & Phenotype Genetic Disorders

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)

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

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

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

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

Autosomal Disorders caused by Dominant Alleles Neurofibromatosis Autosomal Dominant Disorder Chromosome 22

Sex-Linked Genes Sex Linked Genes Are Genes Located On The X & Y Chromosome X – Contains > 100 Genes Y – Contains Only A Few Genes

Sex-Linked Genes

The X Chromosome Contains Three (3) Genes Associated With Color Vision 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

Colorblindness The Images Below are NOT Diagnostic

Red-Green Colorblindness Most Common Form 1:10 Males 1:100 In Females Why The Difference?

(only daughters will receive the fathers X Chromosome) 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

Hemophilia Two Important Blood Clotting Genes Are On The X Chromosome Occurrence Rate = 1:10,000 Males

Mild Post-Injection Bleeding In A Patient With Hemophilia

Duchenne Muscular Dystrophy Sex-Linked Abnormal Muscle Protein Patients Rarely Live Beyond Early Adulthood Occurrence Rate = 1:3000 Males

In Mammals Female X-Chromosome Inactivation NO Males Only Have (1) X Chromosome Females Have Two (2) X Chromosomes Do Female Express Both X Chromosomes?

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

In Mammals Female X-Chromosome Inactivation Arrows Indicate Barr Bodies

In Mammals Female X-Chromosome Inactivation

During Meiosis, Homologous Chromosomes Fail To Separate 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

Down Syndrome Nondisjunction of Chromosome 21 (trisomy) Occurs 1:800 Births Mental Retardation May Be Mild To Severe Increased Susceptibility To Disease

Down Syndrome Why Would 3 Copies Cause Problems When 2 Copies Don’t? Don’t Know Yet Working Hard To Find Out

Sex Chromosome Disorders Turner’s Syndrome Females Nondisjunction Results In A XO Female Sterile Sex Organs Do Not Develop During Puberty

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

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

No “Y” Present – Embryo Develops As A Female 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