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Human Pedigree and Genetic Disease. Gregor Mendel. Thomas Bayes. Common Pedigree Symbols. Male. Marriage. Female. Sex Unknown. Consanguineous Marriage. Affected Female. No Known Pregnancy. Female Carrier of Sex-linked Recessive. Unmarried. Female Carrier (Heterozygous).

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Human pedigree and genetic disease

Human Pedigree and Genetic Disease

Gregor Mendel

Thomas Bayes

Common pedigree symbols
Common Pedigree Symbols




Sex Unknown

Consanguineous Marriage

Affected Female

No Known Pregnancy

Female Carrier of Sex-linked Recessive


Female Carrier (Heterozygous)

Divorce and Remarried


Common pedigree symbols1
Common Pedigree Symbols

Pregnancy in Progress

Dizygotic (nonidentical, fraternal) twins

Three Males


Five Individuals (both sexes)

Monozygotic (identical) twins


Spontaneous Abortion

Adopted Child

Proband, propositus, or index case

Human pedigree and genetic disease

Happy new wife!

Famous Kid

Bad Divorce


Mistakes in meiosis
Mistakes in Meiosis

  • Chromosomes fail to separate properly during meiosis, i.e., nondisjunction

  • ANEUPLOIDY -- an abnormal number of chromosomes

  • Examples:

  • Down’s Syndrome (Trisomy-21)

  • Klinefelter’s Syndrome

  • Turner’s Syndrome

Polygenic inheritance
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
More patterns of inheritance…..

  • Multiple alleles - genes with three or more alleles, e.g., ABO blood groups

  • Incompletedominance – condition that results in a display of a trait that is intermediate between the two parents

  • X-linkedtraits – determined by x-linked genes, e.g., color blindness

  • Sex-influencedtraits – 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
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 disease1
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
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
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
Turner’s Syndrome

  • Occurs in females.

  • Results from XO condition.

  • Female is short, sterile, and mentally impaired.

Single gene inheritance
Single Gene Inheritance

Pedigree Analysis

  • Autosomal dominant traits

    • Huntington’s Disease on chromosome #4

    • Marfan Syndrome on chromosome #15

    • Breast Cancer on chromosomes #17

  • 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
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
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

Huntington s disease1
Huntington’s Disease



What are the genotypes of the parents?

Marfan syndrome
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
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
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 disease1
Tay-Sachs Disease




TT or Tt

Tt or TT

Tt or TT

What are the genotypes of all individuals in this family?

TT or Tt




Cystic fibrosis
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
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
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
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.

  • 1 in 7,000 born with it

  • X-linked recessive on chromosome X



Duchenne s muscular dystrophy
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
Multiple Alleles

  • Blood type, using I gene.

  • Human blood types include:

    Phenotype Genotype

    • AIAIA or IAi

    • BIBIB or IBi

    • ABIAIB (Universal Recipient)

    • Oii (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?