Genetic Recombination Remember Crossing Over is the exchange of genes between homologous chromosomes during prophase I of meiosis. The new combination of genes produced by crossing over and independent assortment is called genetic recombination

Gene Linkage Gregor Mendel’s Law of Independent Assortment states that when two or more traits are inherited, individual traits are transmitted independently of one another, giving different traits an equal opportunity of occurring together. The linkage of genes on a chromosome results in an exception to Mendel’s law of independent assortment because linked genes usually do not segregate Independently.

Crossing Over Crossing Over occurs more frequently between genes that are Further apart than those that are Closer together. A drawing called a Chromosome Map shows the sequence of genes on a chromosome and can be created by using crossover data.

Polyploidy Polyploidy is the occurrence of having more than two paired (homologous) sets of chromosomes. Most eukaryotes are diploid, meaning they have two sets of chromosomes—one set inherited from each parent.

Polyploidy A triploid organism would be designated 3n, which means that is has three sets of chromosomes. Various commercial plants like strawberries and coffee are polyploids.

Recessive Genetic Disorders in Humans A recessive trait is expressed when the individual is homozygous recessive (rr) for the trait. Therefore, those with at least one dominant (R) allele will not express the recessive (r) trait. An individual who is heterozygous for a recessive disorder is called a carrier.

Cystic Fibrosis Cystic fibrosis is a progressive, genetic disease that causes persistent lung infections and limits the ability to breathe over time. It affects the mucus producing glands, digestive enzymes, and sweat glands. Chloride ions are not absorbed into the cells of a person with cystic fibrosis but are excreted in the sweat. Without sufficient chloride ions in the cells, a thick mucus is secreted.

Albinism Caused by altered genes, resulting in the absence of the skin pigment melanin in the hair and eyes. White hair Very pale skin Pink pupils

Tay-Sachs Disease Tay-Sachs is a rare inherited disorder that progressively destroys nerve cells (neurons) in the brain and spinal cord Caused by the absence of the enzymes responsible for breaking down fatty acids called gangliosides. Gangliosides accumulate in the brain, inflating brain nerve cells and causing mental deterioration.

Galactosemia Recessive genetic disorder characterized by the inability of the body to digest the sugar galactose. During digestion, an enzyme (GALT) breaks down lactose from milk into galactose and glucose. Persons with galactosemia lack or have defective GALT and should avoid milk products.

Dominant Genetic Disorders in Humans Huntington’s Disease is a fatal genetic disorder that causes the progressive breakdown of nerve cells in the brain. Achondroplasia (a form of dwarfism) is a genetic condition that causes small body size and limbs that are comparatively short.

Pedigrees A pedigree is a diagram that traces the inheritance of a particular trait through several generations.

Inferring Genotypes and Predicting Knowing physical traits can determine what genes an individual is most likely to have. Predicting Disorders Record keeping helps scientists use pedigree analysis to study inheritance patterns, determine phenotypes, and determine genotypes.

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