Pedigrees 4/13/2010

Pedigrees The risks of passing on a genetic disorder to offspring can be assessed by genetic counseling, prenatal testing, and by analyzing a pedigree. A pedigree is a family history diagram that shows how a trait is inherited over several generations. A pedigree can be mapped out to determine if individuals are carriers or if their children might inherit the disorder. Carriers are individuals who are heterozygous for an inherited disorder but do not show symptoms. Carriers can then pass the allele for the disorder on to their children.

Pedigrees In a pedigree, females are indicated by circles, males are indicated by squares. Shaded figures represent individuals with the trait, a carrier could be 1/2 shaded (but not always!). Generations are numbered with roman numerals ( I, II, III, IV ) from top to bottom. People within generations are numbered (1, 2, 3) from left to right. People that are married (or just having children together) are connected by a horizontal (left to right) line. Offspring of individuals are connected to their parents by a vertical (up and down) line.

Pedigrees By analyzing a pedigree you can tell if a trait is dominant or recessive and if it is autosomal or sex-linked. One parent has the disease, and none of the three children inherited it. We can tell that this is a recessive trait because not many people in the family have it. If it were a dominant trait, many more would have inherited it. Both males and females show the trait, so we know this is not sex-linked but is an autosomal trait.

Pedigrees We can also analyze a pedigree to figure out people’s genotypes. If we know this is an autosomal recessive trait, then anyone shaded in must have the genotype (nn). Anyone not shaded must have either (NN or Nn). What is the genotype of person I 1? nn Person IV 2? Nn or NN Who in this pedigree must be heterozygous? II1, II2, II3, III 1 and III 2

Only women are carriers, and only men show the trait. Therefore, this must be a sex-linked trait. We can also tell this is a recessive trait, because not many people have it. In order for a trait to have carriers, it must be recessive. If a trait is dominant, people either have it or they don’t. Since this is a sex-linked recessive trait, what is the genotype of Alice? XHXhXHXh What is the genotype of Fred? XhYXhY Pedigrees

Karyotyping and genetic disorders 4/14/2010

Karyotypes Genetic disorders may be detected by using prenatal testing and pedigrees. They can also be detected using karyotypes. A karyotype is a photograph of an individual’s chromosomes in a dividing cell during mitosis. The chromosomes are arranged by size and numbered.

Karyotypes A karyotype can show you two things: 1.Chromosome abnormalities: missing chromosomes, extra chromosomes, or if chromosomes are malformed 2.The sex of the person

karyotypes Normal KaryotypeDown’s Syndrome

Genetic disorders Down’s Syndrome: o A chromosomal disorder caused by an extra chromosome 21. For this reason it is also known as Trisomy 21 (which means 3 chromosome 21’s). o Caused by nondisjunction, which means that during meiosis a gamete is produced with an extra copy of chromosome 21. This is not an inherited trait, it happens in the egg or the sperm before fertilization. o Symptoms: learning disabilities, developmental disabilities, and impaired physical growth. o Occurrence: about 1 of every 9,000 births.

Genetic disorders

Cystic Fibrosis: o Symptoms: causes thick mucus to coat the lungs leading to severe breathing problems. It also causes the pancreas to not secrete enzymes as efficiently as it should, causing poor growth, diarrhea, and vitamin deficiency. o Inheritance: autosomal recessive disease caused by a mutation in a gene. o Occurrence: 1 in 3,900 children are born with this disease, and there is no cure.

Genetic disorders

Huntington’s Disease: o Symptoms: a genetic neurological disorder characterized after onset by uncoordinated, jerky body movements and a decline in some mental abilities. People with Huntington’s Disease have too many CAG’s in a gene on their DNA and so form a mutant protein from too many glutamines. o Occurrence: Up to 7 people in 100,000 have this disorder. o Inheritance: This is an autosomal dominant trait, so an affected individual needs just one copy of the gene to show the disease.

Genetic disorders

Sickle Cell Anemia: o A blood disorder in which the red blood cells are not flexible and round but are rigid and sickle-shaped (like a crescent moon). This restricts the blood cells’ movement throughout the blood stream and decreases the amount of oxygen the cells can carry through the body. o Inheritance: a recessive trait. o Symptoms: misshapen blood cells cause the blood to not carry enough oxygen throughout the body. Individuals most often feel fine, but their lives are interrupted by periodic painful attacks. The only treatment is pain medication during these attacks. o Occurrence: 1 out of every 10 African-Americans has this trait.

Genetic disorders