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Genetics Since Mendel Incomplete Dominance • Occurs when neither allele for a trait is dominant. • The phenotype produced is intermediate between the two homozygous parents • Ex. Coat color in purebred dogs Multiple Alleles • More than 2 alleles are multiple alleles • Traits controlled by multiple alleles produce more than 3 phenotypes. • In humans, blood type is controlled by 3 alleles (A,B,)- A & B are dominant. O is recessive Polygenic Inheritance • A group of gene pairs acts together to produce a trait, which creates more variety in phenotypes. • Many human traits are controlled by polygenic inheritance, such as hair and eye color, height, body build, shape of eyes, lips and ears. *Height is controlled by four genes working together. *Skin color is controlled by at least three genes, each one containing two different alleles. Various combinations of alleles produce the many skin colors in humans Mutations- genes that are altered or copied incorrectly • A mutation can be harmful, helpful, or have no effect • Chromosome disorders- caused by more or fewer chromosomes than normal • Down Syndrome- caused by 3 copies of chromosome 21 Significance of Mutations • Most are neutral • Eye color • Birth marks • Some are harmful • Sickle Cell Anemia • Down Syndrome • Some are beneficial • Sickle Cell Anemia immune to Malaria • Immunity to HIV What Causes Mutations? • There are two ways in which DNA can become mutated: – Mutations can be inherited. • Parent to child – Mutations can be acquired. • Environmental damage • Mistakes when DNA is copied Chromosome Mutations • Down Syndrome – Chromosome 21 does not separate correctly. – They have 47 chromosomes in stead of 46. – Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of inteligence. Chromosome Mutations • Cri-du-chat – Deletion of material on 5th chromosome – Characterized by the cat-like cry made by cri-du-chat babies – Varied levels of metal handicaps Recessive Genetic Disorders • Both parents have a recessive allele responsible for the disorder and pass it on to their child. • Because parents are heterozygous, they don’t show symptoms • Cystic Fibrosis is a homozygous recessive disorder Recessive Genetic Cont. • Genes that determine the sex of an organism are XX in females and XY in males. Males determine the sex of the offspring • Females produce eggs with x chromosomes only. Males produce sperm with either an x or a y chromosome. Sex Linked Disorders • 1. An allele inherited on an X or Y chromosome is a sex linked gene. • Colorblindness is a sex linked disorder caused by a recessive allele on the X chromosome. More common in malesfemales have to inherit it on both x’s. Example of sexlinked trait controlled by a recessive allele: red-green color blindness Affects more males than females What is a pedigree chart? • Pedigree charts show a record of the family of an individual • They can be used to study the transmission of a hereditary condition • They are particularly useful when there are large families and a good family record over several generations. © 2007 Paul Billiet ODWS Symbols used in pedigree charts • • • • • Normal male Affected male Normal female Affected female Marriage A marriage with five children, two daughters and three sons. The eldest son is affected by the condition. Eldest child Youngest child © 2007 Paul Billiet ODWS Organising the pedigree chart • A pedigree chart of a family showing 20 individuals © 2007 Paul Billiet ODWS Organising the pedigree chart – Generations are identified by Roman numerals I II III IV © 2007 Paul Billiet ODWS Organising the pedigree chart • Individuals in each generation are identified by Arabic numerals numbered from the left • Therefore the affected individuals are II3, IV2 and IV3 I II III IV © 2007 Paul Billiet ODWS Advances in Genetics • Genetic Engineering: Genes from one organism are transferred into the DNA of another organism • Used to produce medicine(insulin), improve crops, and cure genetic disorders Bright face of genetically modified corn plant: pestinfected non-GM (left) and pest-free GM plant (right) planted side-by-side in a field trial. (photo: Dr. Yu Jialin, China Agricultural University) French genetic researchers created Alba for artist Eduardo Kac. Thanks to genes borrowed from a jellyfish, the albino rabbit glows green when placed under special lighting. In regular light, Alba appears like any other furry white rabbit. But place her under a black light, and her eyes, whiskers and fur glow a otherworldly green. http://www.fluorescentpets.com/index.htm Gene Therapy • A normal allele is placed into a virus, which delivers the normal allele when it infects its target cell. • May be used to control cystic fibrosis and other genetic disorders Selective Breeding: Breeding organisms with desired traits so that their offspring will have those traits Hybridization: Breeding two genetically different individuals SELECTIVE BREEDING • The Liger is the result of breeding a female Tiger to a male Lion. • The liger has both stripes and spots. The stripes are inherited from its tiger parent and the spots from the lion parent. • On their hind legs, ligers stand approximately 12 feet tall. At most, ligers may weigh up to 1,000 pounds. The Cama is the result of breeding a Llama to a Camel. Parents in background of picture. The Zebroid is the result of breeding a female Horse and a male Zebra. The Zedonk / Zonkey is the result of breeding a female Donkey and male Zebra. The Mule is the result of breeding a female horse (mare) to a male donkey (jack). The mule is superior to the horse in strength, endurance, intelligence and disease resistance. The Human Genome Project: The main goal of the human genome project is to identify every gene in human DNA. How can this help improve modern medicine?