NOTES 24 – Genetic NOTES 24 – Genetic Disorders and Hereditary Disorders and Hereditary

DiseasesDiseases

What is a genetic disorder?What is a genetic disorder?

A A genetic disordergenetic disorder is a condition is a condition caused by any abnormality in a caused by any abnormality in a person’s genes or chromosomesperson’s genes or chromosomes

Genetic disorders have 2 main Genetic disorders have 2 main causescauses

Cause #1Cause #1 An error during meiosis causes a sperm An error during meiosis causes a sperm

cell or an egg cell to have some defect.cell or an egg cell to have some defect. If one of these gametes is involved in If one of these gametes is involved in

fertilization, it usually results in fertilization, it usually results in miscarriage, but in a few cases, a baby miscarriage, but in a few cases, a baby will develop and be carried to term with will develop and be carried to term with a genetic disordera genetic disorder

EX. Down Syndrome is caused by an EX. Down Syndrome is caused by an extra 21extra 21stst chromosome in the sperm or chromosome in the sperm or egg cellegg cell

Cause #2Cause #2

A defective gene present in one or A defective gene present in one or both of the parents is inherited both of the parents is inherited directly by the child causing a directly by the child causing a disorderdisorder

These kinds of disorders are calle These kinds of disorders are calle hereditary diseaseshereditary diseases and follow the and follow the same rules of inheritance as other same rules of inheritance as other human traitshuman traits

Hereditary Diseases Caused by Hereditary Diseases Caused by Dominant GenesDominant Genes

Only one copy of the gene (from Only one copy of the gene (from either parent) is needed for a person either parent) is needed for a person to have the diseaseto have the disease

A person with a dominant hereditary A person with a dominant hereditary disease usually has at least one disease usually has at least one affected parentaffected parent

Parents have a 50% chance of Parents have a 50% chance of passing these types of diseases to passing these types of diseases to childrenchildren

Ex. Huntington’s DiseaseEx. Huntington’s Disease Caused by the inheritance of a dominant Caused by the inheritance of a dominant

genegene Affects the nervous systemAffects the nervous system Produces incorrect protein that eventually Produces incorrect protein that eventually

leads to destruction of brain cellsleads to destruction of brain cells Symptom’s include abnormal body Symptom’s include abnormal body

movements, lack of coordination, impaired movements, lack of coordination, impaired mental abilities and altered personalitymental abilities and altered personality

Patients generally live 15 to 20 years after Patients generally live 15 to 20 years after the appearance of the first symptomsthe appearance of the first symptoms

Currently no cureCurrently no cure

Hereditary Diseases Caused by Hereditary Diseases Caused by Recessive GenesRecessive Genes

Two copies of the defective gene must Two copies of the defective gene must be inherited (one from each parent)be inherited (one from each parent)

Affected persons usually have two non-Affected persons usually have two non-affected parents who are carriersaffected parents who are carriers

Two carrier parents have a 25% chance Two carrier parents have a 25% chance of having a child with the diseaseof having a child with the disease

Ex. Sickle-Cell AnemiaEx. Sickle-Cell Anemia

Caused by the inheritance of two recessive Caused by the inheritance of two recessive genesgenes

Causes red blood cells to be abnormally Causes red blood cells to be abnormally shapedshaped

Cells may stick to each other or become Cells may stick to each other or become stuck in blood vessels preventing oxygen stuck in blood vessels preventing oxygen flow which may lead to organ damage or flow which may lead to organ damage or strokestroke

Individuals are often well, but experience Individuals are often well, but experience painful, possibly fatal attacks from time to painful, possibly fatal attacks from time to timetime

Sickle Cell AnemiaSickle Cell Anemia

Hereditary Disease Caused by Hereditary Disease Caused by Sex-Linked Recessive GenesSex-Linked Recessive Genes

Caused by defective genes carried on Caused by defective genes carried on the X chromosomethe X chromosome

Males affected more than womenMales affected more than women Males inherit one defective gene on X Males inherit one defective gene on X

from mother to have disorderfrom mother to have disorder Females only affected if they inherit 2 Females only affected if they inherit 2

defective genes (one from each defective genes (one from each parent)parent)

Ex. HemophiliaEx. Hemophilia

Caused by the inheritance Caused by the inheritance of one recessive gene on of one recessive gene on the X (males) or two the X (males) or two recessive genes on both recessive genes on both X’s (females)X’s (females)

Affects blood – blood does Affects blood – blood does not clotnot clot

Leads to severely Leads to severely increased risk of bleeding increased risk of bleeding from common injuriesfrom common injuries

Potentially fatalPotentially fatal

HemophiliaHemophilia