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3.03: Pedigrees. 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 .
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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 I1? nn • Person IV2? Nn or NN • Who in this pedigree must be heterozygous? III1 and III2
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? XHXh • What is the genotype of Fred? XhY
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: • Chromosome abnormalities: missing chromosomes, extra chromosomes, or if chromosomes are malformed • The sex of the person
Karyotypes Normal Karyotype Down’s Syndrome
Genetic Disorders Down’s Syndrome: • 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). • 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. • Symptoms: learning disabilities, developmental disabilities, and impaired physical growth. • Occurrence: about 1 of every 9,000 births.
Genetic Disorders Cystic Fibrosis: • 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. • Inheritance: autosomal recessive disease caused by a mutation in a gene. • Occurrence: 1 in 3,900 children are born with this disease, and there is no cure.
Genetic Disorders Huntington’s Disease: • 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. • Occurrence: Up to 7 people in 100,000 have this disorder. • Inheritance: This is an autosomaldominant trait, so an affected individual needs just one copy of the gene to show the disease.
Genetic Disorders Sickle Cell Anemia: • 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. • Inheritance: a recessive trait. • 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. • Occurrence: 1 out of every 10 African-Americans has this trait.
3.04: Genetic Engineering • Genetic engineeringmeans making changes to an organism’s DNA code. • In a genetic engineering experiment, scientists use the following techniques:
Genetic Engineering • Cutting DNA using restriction enzymes. Restriction enzymes are bacterial enzymes that bind to short sequences of DNA, then cut the DNA between specific nucleotides. • Ex: the enzyme EcoRI recognizes the nucleotide sequence GAATTC and cuts between the G and A ATTCACGAGAATTCTACCG ATTCACGAG AATCTACCG
Genetic Engineering 2. The DNA fragments are separated using gel eletrophoresis. This creates a pattern of bands made out of those DNA fragments. These fragments can be put on a piece of paper and made into a DNA fingerprint. • In gel electrophoresis, an electric current is run through a gel containing the DNA. Larger sections of DNA move more slowly, and smaller sections move more quickly. In this way, we get a banding pattern that is unique to each person, since every person’s DNA is different.
3.04: DNA Fingerprinting • A DNA fingerprint is the pattern of dark bands that is made when a person’s DNA restriction fragments are separated by gel electrophoresis. • Because restriction enzymes cut different DNA sequences in different places, each individual has a unique pattern of banding.
DNA Fingerprinting • Uses of DNA fingerprinting: • Can be compared to establish whether people are related, such as in a paternity case. • Useful in forensics because it can use DNA found in blood, semen, bone, or hair. • Useful in identifying the genes that cause genetic disorders, such as Huntington’s and Sickle Cell Anemia.
3.04: Cloning • Another type of genetic engineering that you may have heard of is cloning. Cloning means to create a population of genetically identical cells from a single cell. • In 1997, a Scottish scientist Ian Wilmut cloned a sheep by nuclear transfer. How did he do it?
Cloning • An egg cell was removed from a sheep and the nucleus of the egg cell was removed. • The cell, now with no nucleus, was inserted into a donor cell taken from a different adult sheep. • The fused cell began dividing and the embryo was placed into a foster mother sheep where it developed normally.
Cloning • From this foster mother, the cloned sheep named Dolly was born. She looked and acted like a normal sheep and even had a baby of her own, but she died at an early age. This suggests that clones may not have as long a life expectancy as the organisms they come from.
Cloning • Since then, scientists have cloned cows, pigs, mice, and other mammals. They have been cloning bacteria and other microorganisms for much longer. • The use of cloning technology in humans is scientifically possible, but raises serious moral and ethical issues.
3.04: Recombinant DNA • Genetic engineering very often involves using recombinant DNA—DNA made from two or more different organisms. • A great example of this is the making of human insulin for diabetics. Insulin is a protein hormone that controls sugar metabolism. Diabetics don’t make enough insulin and so must inject it. We used to take insulin from the pancreases of slaughtered cows and pigs, but now we genetically engineer it.
Recombinant DNA • The human gene for insulin is cut out of the DNA using restriction enzymes and transferred into bacterial DNA. • The bacteria, now made of recombinant DNA since they contain human DNA along with their normal bacterial DNA, then transcribe and translate the human insulin gene using the same code a human cell would use in order to make human insulin.
Recombinant DNA • This is very efficient: since bacteria reproduce much more quickly than animals do, they can produce much more insulin. • This is also how we make other drugs, like Factor VII to help hemophiliacs’ blood to clot, and vaccines for viruses like smallpox and polio.
Recombinant DNA • When scientists use recombinant DNA technology they create transgenicorganisms. This is a plant, animal, or bacteria that contains another organism’s DNA. The bacteria that takes on the human insulin gene becomes a transgenic organism.
3.04: Human Genome Project • The Human Genome Project was a research project that was completed in 2003. Scientists from 6 different countries identified all of the base pairs that compose the DNA of a human. They identified all 3.2 billion base pairs of DNA that make up the human genome. • The goal of this project was to better understand human DNA to find causes and cures for common diseases.
Human Genome • Here is what they found: • Only 1 to 1.5 percent of the human genome is genes—DNA that codes for proteins. Each human cell contains about 6 feet of DNA, but less that 1 inch is made of genes. These genes are scattered about the genome in clumps. • Human cells only contain about 30,000 to 40,000 genes. This is only double the amount that a fruit fly has.
