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How are our traits related to genes? Ch 9: Genes and Inheritance Each chromosome contains one very long DNA molecule How traits are passed from generation to generation Genes carry our traits Genes are sections of DNA Babies Inherit Half of Chromosomes from Mom & Half from Dad What is heredity? Typically bears >1000 genes Heredity – passing traits from parent to offspring The genes for certain traits are passed down in families from parents to children. For example, parents with Widow’s peaks will have kids with Widow’s peaks parents with short fingers will have kids with short fingers From Mom 22 chromosomes X chromosome 44 Chromosomes XX = Girl XY = Boy From Dad 22 chromosomes X or Y chromosome Genetics 101: Where do your genes come from? (4:14) http://www.youtube.com/watch?v=lJzZ7p-47P8&NR=1 Chromosomes are distributed randomly to sperm (or egg) Why are we different? Your Dad’s Chromosomes Your Mom’s Chromosomes Kids get ½ from mom and ½ from dad Circled chromosomes into sperm You Your Sister Circled chromosomes into egg During meiosis, a random assortment of chromosomes is placed in the nucleus Chances of getting same combinations of chromosomes is 0.5^46 = 1 in 70 trillion (extremely unlikely) Sperm Cell Crossing over creates even more variation How do we inherit specific traits? sister chromatids Crossing-over Synapsis of homologues Chromatids after exchange Recombinant daughter chromosomes We have 2 copies of each chromosome Each chromosome contains genes Genes code for proteins The chromosome pairs exchange DNA This produces hybrid chromosomes and Increases genetic variability The 46 chromosomes of a male Body structures, enzymes, etc Our traits © CNRI/SPL/Photo Researchers Ways we inherit traits: simple dominant-recessive inheritance Some traits are controlled by a single gene Two versions of the gene What is her genotype? The gene for freckles has 2 versions (alleles) A dominant version = F A recessive version = f W = Widow’s peak w = straight hairline Chromosomes are found in pairs Possible genotypes: The widow’s peak version of gene is dominant WW → Widow’s peak Ww → Widow’s peak ww → straight hairline F F F f Because gene F is dominant Diseases controlled by a single gene Cystic fibrosis Interferes with breathing And digestion Most common lethal genetic disease in US Caused by a recessive gene Symptoms: excessive secretion of a very thick mucus Symptoms usually appear shortly after birth. Dominant Disorders Achondroplasia is a common form of dwarfism. Caused by a mutation in the FGFR3 gene on chromosome 4 → abnormal bone and cartilage formation Just need 1 copy of mutated gene Ways we inherit traits: Ways we inherit traits Incomplete Dominance Very few of our traits are inherited by simple dominant/recessive inheritance. Curly hair Wavy hair Straight hair hh Hh HH A single dose of the gene gives an intermediate result The genes are not fully dominant or fully recessive Ways we inherit traits: Co-dominance Pleiotropy Normal Blood Cells Sickle Cells When a single gene affects more than 1 trait Due to a mutation in hemoglobin gene Versions of Gene are “Co-dominant” (both are expressed) If your genes are … SS → Normal Hemoglobin Ss → Some Normal AND Some Sickle Hemoglobin ss → Sickle Cell Anemia Ways we inherit traits: Red-green colorblindness Sex-linked disorders Involves genes located on X or Y chromosome Most are on the X chromosome X chromosomes contains nearly 2000 genes Y chromosomes contains only 80 genes Whether you’re male or female affects the pattern of inheritance Why? X-linked disorder due to a recessive gene on the X chromosome Red-green color blindness The light-sensitive cells in the eyes don’t function properly. Mostly found in males Prevalence: 5-10% of males A test for red-green colorblindness Sex-Linked Disorders Male pattern baldness Largely sex-linked, but other genes are also involved Gene is on the X chromosome Chromosome abnormalities passed from mother to son Happen when errors occur during meiosis Because the gene is recessive, a female needs two X chromosomes with the defect to show typical male pattern baldness Accidents During Meiosis Gametes with extra or missing chromosomes In nondisjunction, The members of a chromosome pair fail to separate Produces gametes with an incorrect number of chromosomes. trisomy Chromosome abnormalities Down Syndrome: An Extra Chromosome 21 Large segments of chromosomes can be missing, duplicated or exchanged Down Syndrome is also called trisomy 21. Beyond simple inheritance Most traits involve multiple genes Skin color is determined by several genes Most traits involve multiple genes Most traits involve multiple genes At least 180 genes control how tall a person will grow Also influenced by environment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Courtesy University of Connecticut/Peter Morenus, photographer; “Environmental” factors also influence skin color Many traits are multifactorial Sun Exposure Muscular development is controlled by the interaction of many genes Influenced by the environment Changes in Blood Flow Diet Some general conclusions about our traits: Most traits are determined by a combination of genes & the environment Even sex can be altered by environment! (ex. exposure to certain hormones/chemicals) Alters Melanin Production Red when Vessels Dilated Carotene Factors that influence our traits: Genes/DNA instructions for proteins Environmental Factors Nutrition, Exercise, Sunlight, Chemicals, Injuries, etc. BPA is a chemical used in making some plastics. Mimics estrogen and might alter reproductive anatomy and function in early development. Not Inherited But does not change genetic sex! (XY/XX) Identical twins (identical DNA) can have different characteristics Another factor influences our traits: Genes/DNA Environment Epigenetics involves chemical signals that switch genes off and on at strategic times Epigenetics Traits can be influenced by: the DNA sequence (As, Cs, Ts and Gs) the physical form of chromosomes condensed or not chemical tags on the DNA http://learn.genetics.utah.edu/content/epigenetics/intro/ Supercoiling of DNA silences genes Epigenetics: activating and silencing genes DNA wraps around proteins called histones The DNA is packed into an elaborate, multilevel system of coiling Highly condensed DNA is inactive What shapes our traits? Genes Environment Epigenetics changes in the physical form of chromosomes DNA modified by chemical “tags” Types of genetic disorders Single gene mutations Chromosome abnormalities Dominant, recessive, X-linked Abnormal number of chromosomes Missing or duplicated segments of chromosomes Multifactorial disorders Changes in several genes, environmental factors