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Common Pedigree Symbols
Male
FemaleMarriage
Affected Female
Female Carrier of Sex-linked Recessive
Sex Unknown
Consanguineous Marriage
No Known Pregnancy
Unmarried
DeadDivorce and Remarried
Female Carrier (Heterozygous)
Common Pedigree Symbols
Pregnancy in Progress
3 Three Males
5Five Individuals (both sexes)
Dizygotic (nonidentical, fraternal) twins
Monozygotic (identical) twins
Spontaneous Abortion
Proband, propositus, or index case
Adopted Child
Mistakes in Meiosis
Examples:
– Down’s Syndrome (Trisomy-21)
– Klinefelter’s Syndrome
– Turner’s Syndrome
Chromosomes fail to separate properly during meiosis, i.e., nondisjunction
ANEUPLOIDY -- an abnormal number of chromosomes
Polygenic Inheritance
Most human characteristics are polygenic, meaning they are influenced by several genes, e.g. skin color influenced by 3-6 genes; also, eye color, height, hair color
Complex characters are those that are influenced strongly by both the environment and genes, e.g., diabetes, heart disease, stroke, skin color, height
More patterns of inheritance….. Multiple alleles - genes with three or more alleles, e.g.,
ABO blood groups Incomplete dominance – condition that results in a
display of a trait that is intermediate between the two parents
X-linked traits – determined by x-linked genes, e.g., color blindness
Sex-influenced traits – usually autosomal, e.g. baldness is influenced by testosterone
Single-allele traits – more than 200 human traits are governed by single dominant alleles, e.g., Huntington’s disease
Detecting Genetic Disease Genetic Screening – examination of a person’s genetic
makeup involving karyotypes, blood tests for certain proteins, or direct tests of DNA– 200 genetic disorders can be detected in the fetus– Amniocentesis – removal of amniotic fluid from the sac
that surrounds the fetus between the 14th and 16th week of pregnancy
– Chorionic villi sampling – sample of cells derived between the 8th and 10th week from the zygote - cells grow between the mother’s uterus and the placenta; cells chromosomes, and proteins analyzed
Detecting Genetic Disease
– Chorionic villi sampling – CVS can help identify chromosomal problems such as Down syndrome or other genetic diseases such as cystic fibrosis, Tay-Sachs disease and sickle cell anemia. CVS is considered to be 98% accurate in the diagnosis of chromosomal defects, such as Down syndrome.
Down’s Syndrome Smallest chromosomes with 1500 genes affected. Occurs in 1 out of every 800 babies.
– 40% congenital heart defects. Can result from maternal age or chromosome
defect.
Klinefelter’s Syndrome
Occurs in one out of every 1000 males. Results from extra X chromosome = XXY. Males tall, sterile, small testicles, and mentally
handicapped.
Turner’s Syndrome
Occurs in females. Results from XO condition. Female is short, sterile, and mentally impaired.
Single Gene Inheritance
Autosomal dominant traits– Huntington’s Disease on chromosome #4– Marfan Syndrome on chromosome #15– Breast Cancer on chromosomes #17
Pedigree Analysis
Autosomal recessive traits
– Tay-Sachs Disease on chromosome #15– Cystic Fibrosis on chromosome #7– Sickle Cell Anemia on chromosome #11
X-Linked Disease (Sex-Linked)
– Hemophilia --Duchenne’s muscular dystrophy– Color Blindness
Autosomal Dominant Traits
Present on any autosomal chromosome, i.e., 1-22.
One allele present = disease present, i.e., a person has it or he or she does not
Huntington’s Disease
Begins to show up by age 45-55, within 10-20 years, death is eminent.
Progressive degeneration of nervous system; irregular body movements and slurred speech.
If one parent has HD, offspring have 50% chance of inheriting disease.
Autosomal dominant on chromosome 4; 1 in 10,000 births
Marfan Syndrome
Symptoms: long limbs, loose joints, deformed vertebral column, crowded teeth, rupture of large arteries
1 in 20,000 Americans born with it Caused by lack of fibrillin-1, a major
component of connective tissue found in ligaments and blood-vessel sheaths
Autosomal Recessive Disease manifests itself if offspring inherits
one recessive gene from each parent. If parents are carriers, 25% of offspring
will have disease.
Tay-Sachs Disease 1 in 600 Jews of European descent born with it Lipids deposited in nervous system, causing brain to be damaged -- blindness,
loss of movement, mental deterioration. No break down of cellular wastes in lysosome due to absence of
hexosaminidase A – mutation causes nerve death
Symptoms appear around 6 months of age and victims die due to paralysis and/or convulsions before the age of five.
Tay-Sachs Disease
What are the genotypes of all individuals in this family?
Tt Tt
tt
TtTt
TT or Tttt Tt or TTTt or TT
TT or Tt
Cystic Fibrosis Found in Caucasians.
– Most common lethal genetic disorder among white Americans.
– Autosomal recessive on chromosome 7 Thick mucus produced in lungs, intestines,
and pancreas.
1/20 of Caucasian population are carriers.– One in 2,000 children born to white Americans
inherits the disorder.– CF kills ~500 children and young adults each year.
Sickle Cell Anemia Found in both African Americans and Hispanics of
Carribbean ancestry (1 in 500 African Americans) Hemoglobin (oxygen-carrying protein) differs by ONE amino
acid.
Sickling of cells occurs, clogging vessels -- stroke. In U.S., 60,000 people have it; 30 million carriers. Autosomal recessive on chromosome 11
X-Linked Disorders
Found on the 23rd pair of chromosomes, i.e., the sex chromosomes.
Usually shows up in males due to Y chromosome lacking genes, i.e., one recessive gene in males produces disorder.
Mother carriers pass gene to sons.
Hemophilia -- “Bleeder’s Disease”
Deficient blood coagulation due to absence of coagulation factor 8 that helps cause blood to clot.
50% of daughters will also be carriers.
XHXh XHY
1 in 7,000 born with it X-linked recessive on chromosome X
Duchenne’s Muscular Dystrophy
Progressive destruction of muscles.
Patients wheelchair bound by teens.
Female carriers can be detected by presence of creatine kinase.
Can be detected by the 20th week of gestation.
Multiple Alleles Blood type, using I gene. Human blood types include:
Phenotype Genotype–A IAIA or IAi–B IBIB or IBi–AB IAIB (Universal Recipient)–O ii (Universal Donor)
If a child has type O blood and its mother has type A, could a type B man be the father? Why couldn’t a blood test be used to prove he is the father?