4 Types of Genetic Disorders Single gene –Change in the DNA sequence –More than 6000 known disorders –Autosomal or sex linked –1 in 200 births –cystic fibrosis, sickle cell anemia, Marfan syndrome, Huntington’s disease
Types of Genetic Disorders Multifactoral –combination of environmental factors and mutations in multiple genes –more complicated –heart disease, high blood pressure, Alzheimer’s disease, arthritis, diabetes, cancer, and obesity
Types of Genetic Disorders Chromosomal –abnormalities in chromosome structure as missing or extra copies or gross breaks and rejoining –Down Syndrome
Types of Genetic Disorders Mitochondrial –rare type of genetic disorder –caused by mutations in the non-chromosomal DNA of mitochondria
Genetic Disorders On our chromosomes are a total of about 100,000 genes. Among these 100,000 genes, each person has on average 5-8 bad genes. However, these seldom have any effect at all. But sometimes there are serious errors in our genetic code and these can give us the blueprint for genetic disorder. When we have a serious genetic error, there are three primary ways that the error can be inherited (passed from generation to generation). These three patterns of inheritance are: Dominant genetic disorders Recessive genetic disorders Sex-linked genetic disorders On our chromosomes are a total of about 100,000 genes. Among these 100,000 genes, each person has on average 5-8 bad genes. However, these seldom have any effect at all. But sometimes there are serious errors in our genetic code and these can give us the blueprint for genetic disorder. When we have a serious genetic error, there are three primary ways that the error can be inherited (passed from generation to generation). These three patterns of inheritance are: Dominant genetic disorders Recessive genetic disorders Sex-linked genetic disorders
Dominant Genetic Disorders: In the dominant genetic disorder pattern of inheritance, one bad gene from either parent will cause the genetic disorder. Since only one bad gene causes the disorder, if either parent has the disorder the chance of the child inheriting the bad gene and developing the disorder is 50% with each conception.
Recessive Genetic Disorders: To develop a recessive genetic disorder both parents must contribute the same defective gene. The parents usually don't have the disorder, but are carriers for the disorder. They carry one defective gene, which is recessive, and one normal dominant gene.
Sex-linked Genetic Disorders: These disorders occur due to errors in the 23rd pair of chromosomes (the chromosomes responsible for gender). These genetic disorders occur only in males. Since males have an XY sex chromosome combination, they are vulnerable to defects on their X chromosome that lacks a partner gene on the Y. These disorders do not appear in females (which are XX) because if one of the X chromosomes has an affected gene, the partner X chromosome carries a normal gene. In females, the other X will compensate any defect on one X. Since males get a Y, there is no compensation. Although the female can carry a defective gene, females do not develop the disorder – they are carriers for the disorder.
14 Sex-linked Traits Traits (genes) located on the sex chromosomesTraits (genes) located on the sex chromosomes Sex chromosomes are X and YSex chromosomes are X and Y XX genotype for femalesXX genotype for females XY genotype for malesXY genotype for males Many sex-linked traits carried on X chromosomeMany sex-linked traits carried on X chromosome copyright cmassengale
15 Sex-linked Traits Sex Chromosomes XX chromosome - femaleXy chromosome - male fruit fly eye color Example: Eye color in fruit flies copyright cmassengale
16 Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X R Y x X r X r Remember: the Y chromosome in males does not carry traits. RR = red eyed Rr = red eyed rr = white eyed XY = male XX = female XRXR XrXr XrXr Y copyright cmassengale
17 Sex-linked Trait Solution: X R X r X r Y X R X r X r Y 50% red eyed female 50% white eyed male XRXR XrXr XrXr Y copyright cmassengale
Other Genetic Disorders: Other genetic disorders do not fall neatly into one of these three patterns. These involve having too many or too few chromosomes.
Turners Syndrome 1 in 5,000 births 45 chromosomes X only #23 Monosomy Nondisjunction
Turners Syndrome 96-98% do not survive to birth No menstruation No breast development No hips Broad shoulders and neck
Cri-Du-Chat Syndrome 1 in 216,000 births 46 chromosomes XY or XX #5 Deletion of lower arm
Cri-Du-Chat Syndrome Moon-shaped face Heart disease Mentally retarded Malformed larynx Normal lifespan
Aniridia-Wilms Tumor Syndrome 1 in 50,000,000 births 46 chromosomes XY or XX #11 Deletion of upper arm
Aniridia-Wilms Tumor Syndrome Mentally retarded Growth retarded Blindness Tumors on kidneys Short lifespan
Thirteen Q Deletion Syndrome 1 in 500,000 births 46 chromosomes XY or XX #13 Deletion of lower arm
Thirteen Q Deletion Syndrome Mentally retarded Deformed face No thumbs Heart disease Short lifespan
Prader-Willi Syndrome 1 in 5,000,000 births 46 chromosomes XY=97% XX=3% #15 Deletion of lower arm
Prader-Willi Syndrome Small bird-like head Mentally retarded Respiratory problems Obesity Short lifespan
Eighteen Q Deletion Syndrome 1 in 10,000,000 births 46 chromosomes XY or XX #18 Deletion of lower arm
Eighteen Q Deletion Syndrome Mentally retarded Heart disease Abnormal hands and feet Large eyes Large ears Normal lifespan
Cat-Eye Syndrome 1 in 1,000,000 births 46 chromosomes XY or XX #22 Deletion of bottom arm
Cat-Eye Syndrome Fused fingers and toes Mentally retarded Small jaw Heart problems Normal lifespan
Four-Ring Syndrome 1 in 10,000,000 births 46 chromosomes XY or XX #4 Inversion
Four-Ring Syndrome Cleft palate Club feet Testes don’t descend Short lifespan
Down Syndrome 1 in 31,000 births 46 chromosomes XY=97% XX=3% #14/21 Translocation 1 in 1,250 births 47 chromosomes XY or XX #21 Trisomy Nondisjunction Down Syndrome Trisomy
Down Syndrome Short, broad hands Stubby fingers Rough skin Impotency in males Mentally retarded Small round face Protruding tongue Short lifespan
Patau’s Trisomy Syndrome 1 in 14,000 births 47 chromosomes XY or XX #13 Trisomy Nondisjunction
Patau’s Trisomy Syndrome Small head Small or missing eyes Heart defects Extra fingers Abnormal genitalia Mentally retarded Cleft palate Most die a few weeks after birth
Edward’s Trisomy Syndrome Small head Mentally retarded Internal organ abnormalities 90% die before 5 months of age
Jacob’s Syndrome 1 in 1,800 births 47 chromosomes XYY only #23 Trisomy Nondisjunction
Jacob’s Syndrome Normal physically Normal mentally Increase in testosterone More aggressive Normal lifespan ?
Klinefelter Syndrome 1 in 1,100 births 47 chromosomes XXY only #23 Trisomy Nondisjunction
Klinefelter Syndrome Scarce beard Longer fingers and arms Sterile Delicate skin Low mental ability Normal lifespan
Triple X Syndrome 1 in 2,500 births 47 chromosomes XXX only #23 Trisomy Nondisjunction
Triple X Syndrome Normally physically Normal mentally Learning disabilities Taller than average Behavior Problems
Huntington’s Chromosome 4 mutation *involuntary twitching or movement *onset 40 yrs. *deterioration of the CNS that affects muscle control
Sickle-cell Anemia Moon shaped RBC that has low hemoglobin Shows up more often in African Americans; or whose ancestors once inhabited parts where malaria is a high risk. Sickle-shaped cells clog capillaries so that cells cannot get oxygen and nutrition Blood transfusions, pain killers, and drugs Pain, strokes, jaundice.
Cystic Fibrosis Chromosome 7 mutation Affects mucus, salivary and sweat glands. Many respiratory problems Thick, sticky mucus in lungs and digestive tracts.
Tay-Sachs No Hex A enzyme Recessive genetic disorder most often found in Jewish or eastern Europe origin. Appears in children starting at 6 mo. Child cannot metabolize a certain lipid which incases the CNS and prevents the brain from expanding. Fat builds up in the brain causing blindness & paralysis Death occurs in early childhood
Hemophilia Blood has less than 1% of the normal clotting factor Bleeds longer because blood won’t clot.
Color-blindness Cones in the eye do not perceive certain colors Most common form is reds/greens but some are brown/blue Seen as gray