Genetic Mutations & Pedigrees

Genetic Mutations & Pedigrees Alleles that code for defective proteins can cause mutations & even deadly disorders, which are passed on to us as inherited traits.

Mutations can Cause Disorders Sickle Cell Anemia: Is caused by a mutated allele that produces a defective form of a blood protein called hemoglobin. Hemoglobin is found inside our red blood cells & is important because it carries oxygen throughout the body.

Sickle Cell Anemia This disease causes red blood cells to bend into a sickle shape. Sickle-shaped cells burst easily & do not function in carrying oxygen very well.

Sickle Cell Anemia For most sickle cell anemia is considered harmful, but for some it is beneficial. The recessive allele responsible for bending cells into a sickle shape helps protect some individuals in Africa and other countries from contracting another disease called malaria, a disease caused by parasitic protists that invade red blood cells & is carried by mosquitoes.

Sickle Cell Anemia People who are heterozygous for sickle cell anemia have a mix of normal red blood cells and sickle-shaped cells.

Sickle Cell Anemia Sickle-shaped cells can’t be invaded by parasites & normal red blood cells provide enough oxygen for all body tissues, so a person with sickle cell anemia has the benefit of normal blood cells to give oxygen & sickle cells, which parasitic protists can’t invade.

Sickle Cell Anemia People who are homozygous recessive do not have this protection from malaria and all of their red blood cells are sickle-shaped due to the defective protein hemoglobin.

Hemophilia Hemophilia is a condition that impairs the blood’s ability to clot. Two of the genes that code for proteins that cause this condition are found on only on the X chromosome. Because of this, males have an increased risk of inheriting this disorder because it is a sex-linked trait.

Chromosomes & Mutations Each of our 46 chromosomes contain thousands of genes that play an important role in determining how our bodies grow and function. All genes must be present in order for our bodies to function properly. Think about it… would a car drive without an engine, transmission or wheels?

Chromosomes & Mutations In most cases, humans that are missing even one chromosome do not survive embryonic development and are never born. When a chromosome is missing, this condition is called a monosomy. When there is a chromosome has an extra copy this condition is called a trisomy.

Chromosomes & Mutations Monosomies, trisomies and other genetic abnormalities can be detected by looking at a karyotype of a person’s chromosomes.

Chromosomes & Mutations A karyotype is a picture of each pair of chromosomes in a cell.

Chromosomes & Mutations Down’s syndrome (also known as Trisomy 21) is a genetic deviation that results in short size, a round face & varying degrees of mental retardation. Why do you think this occurs?

Chromosomes & Mutations What events cause an extra copy of a chromosome to occur? When a cell divides normally each chromosome & its homologue separate in a process called disjunction.

Chromosomes & Mutations When normal disjunction (separation of chromosomes) does not occur nondisjunction results so that one of the new cells ends up getting both chromosomes of the pair and the other cell gets none.

Chromosomes & Mutations Prenatal testing can be performed on a pregnant woman to detect genetic abnormalities: 1. Chorionic villi sampling 2. Amniocentesis

Prenatal Testing Chorionic villi sampling- performed at 8-10 weeks. A sample is taken from the villi that extend down into the mother’s uterus. The villi contain the same genetic information as the fetus so the cells can be used to construct a karyotype to detect genetic abnormalities in the fetus.

Prenatal Testing

Prenatal Testing Amniocentesis- performed at 14-16 weeks A sample of amniotic fluid is taken from the sac surrounding the fetus which contains fetal cells, which are used to make a karyotype.

Genetic Mutations While rare, changes in an organism’s chromosome structure can occur. Some changes can cause mutations in the genes like these: 1. Deletions 2. Duplications 3. Inversion 4. Translocation

DELETIONS This mutation that occurs when a fragment of a cell breaks off as the cell divides.

DUPLICATION A mutation that occurs when a chromosome contains an extra segment of DNA.

INVERSION A mutation that occurs when a chromosome fragment re-joins its original chromosome, but its nucleotides are reversed.

TRANSLOCATION A mutation that occurs when a fragment of DNA joins a nonhomologous chromosome.

Chromosome Abnormalities Many chromosomal abnormalities can occur on the sex chromosomes. For example: XXY- Kleinfelter’s Syndrome is caused by an extra chromosome. XO- Turner’s Syndrome is caused by a missing chromosome.

Kleinfelter’s Syndrome Karyotype of a male with an extra X chromosome

Kleinfelter’s Syndrome Male with Kleinfelter’s syndrome

Turner’s Syndrome Karyotype of a female missing an X chromosome

Turner’s Syndrome The most common characteristics of Turner syndrome include: short stature lack of ovarian development webbed neck arms that turn out slightly at the elbow low hairline in the back of the head also prone to cardiovascular problems, kidney and thyroid problems, skeletal disorders such scoliosis (curvature of the spine) or dislocated hips, and hearing and ear disturbances.

Tracking Family Traits using Pedigrees How might you learn if you have genetic abnormalities or mutations in your family? In order to study heredity, scientists use pedigrees to analyze a family history. These help identify which relatives exhibit certain traits.

Tracking Family Traits using Pedigrees Pedigrees can determine if a trait is sex-linked & whether a particular trait is dominant or recessive.

Tracking Family Traits using Pedigrees If a female carries the gene for a trait, but does not actually have that trait she is called a carrier. In sex-linked traits mothers are usually carriers that pass a trait on to their sons on the X chromosome. * Add to your notes!

Tracking Family Traits using Pedigrees Look at the last page of your notes to try and track the trait of albinism (a lack of pigmentation) in a family by using a pedigree. Is the trait sex-linked? Is the trait dominant or recessive? Is it caused by one gene or by several?

ALBINISM