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Inheritance Patterns & Human Genetics Chapter 12 Bellwork: Complete with your partner on the white board The synthesis of polypeptides from the genetic information encoded in mRNA is A. Transcription B.Translation C. Transposon D. DNA Methylation At the end of DNA replication, each of the daughter molecules has one old strand and one new strand. This explains why DNA replication is described as _____________. Chromosomes & Inheritance A. Thomas Hunt Morgan- early 1900’s -experiments with fruit flies -observed 4 pairs of chromosomes -noticed that 3 pairs were the same in males & females but that 1 pair was different. - called these “sex chromosomes”. Autosomes & Sex Chromosomes Sex chromosomes- contain genes that determine the gender of an individual. Autosomes- the remaining pairs of chromosomes that do not directly determine sex. In mammals - 2 X chromosomes= FEMALE (XX) - 1 X + 1 Y is a MALE (XY) In mammals, males determine the sex of the offspring -each sperm has an equal chance of having an X or a Y -however- the only option for eggs is to receive an X chromosome. 1:1 male to female ratio Karyotypes Karyotype with an extra chromosome Linked & Sex-Linked Genes A. Linked genes Genes which are close together on same chromosome. Inherited together Linked genes do not exhibit Mendel’s law of independent assortment Chromosome Mapping The farther apart two genes are located on a chromosome, the more likely a cross-over will occur. Researchers use recombinant percentages to construct chromosome maps showing relative gene positions. Sex-Linked traits are traits that are coded for by alleles on a sex chromosome. Genes found on the X chromosome are Xlinked genes Since the X chromosome is larger- there are more X-linked than Y- linked traits. NOTE: Since males have only 1 X- a male who carries the recessive allele will show the Xlinked trait. Sex Linked Traits Mutations Mutation -a change in the nucleotide-base sequence of a gene or DNA - Germ cell- occurs in gametes - can affect offspring - Somatic Cell-occur in organism’s body cells - may affect the organism (ex-cancer) - does NOT affect offspring Mutations - Lethal Mutations-cause death, often before birth - Beneficial Mutations- result in phenotypes that are beneficial . Types of Chromosome Mutations 1. Deletion- loss of a piece of chromosome due to breakage. 2. Inversion – a chromosome piece breaks off, flips around backwards & reattaches 3. Translocation – a piece of chromosome breaks off & attaches to a non-homologous chromosome 4. Non-Disjunction – a chromosomes fails to separate from its homologue during meiosis. On your white board, with your partner, explain why your assigned answer is either correct or incorrect. Your assigned answer is the letter on your whiteboard! Types of Chromosome Mutations Types of Chromosome Mutations An example of a human disorder with a deletion error: Cri du chat syndrome missing part of chromosome 5 cry of infants is similar to that of a meowing kitten, due to problems with the larynx and nervous system. About 1/3 of children lose the cry by age 2. Types of nondisjunction: Trisomy- an extra chromosome leads to an individual with an extra chromosome in every cell of his/her body. Monosomy- is a deficiency in number of chromosomes and is defined as only one copy of a chromosome that is normally present in two copies. When fertilized, the outcome is 45 chromosomes in total. Monosomies are less likely to survive when compared to trisomies. What causes non-disjunction? cause of non-disjunction is unknown. non-disjunction occurs more frequently in the eggs of women as they get older. Non- Disjunction Disorders with an extra chromosome (these folks have 47 instead of the normal 46 chromosomes in people): Down syndrome- extra 21 Edward’s Syndrome- extra 18 Patau syndrome – extra 13 Examples Non disjunction: Extra #21= Down’s Syndrome Extra #18= (most don’t live beyond 1st 7 months) This girl is now 6.) http://starbulletin.com/96/03/25/news/story2.html Sex-chromosome abnormalities may also be caused by nondisjunction. Klinefelters Syndrome- XXY ( extra X) Turners Syndrome – only 1 X- missing a second X (XO) Super males XYY Any combination (up to XXXXY) produces maleness. Males with more than one X are usually underdeveloped and sterile. XXX and XO women are usually sterile Gene Mutations changes in one or more of the nucleotides in a gene. Types of Gene Mutation 1. Point Mutation- the substitution, addition or removal of a single nucleotide, occurs within a single gene or segment of DNA 2. Substitiution- one nucleotide replaces another 3. Frameshift Mutation- if some nucleotides are deleted- whole segment moves 4. Insertion Mutation – one or more nucleotides added- also causes a frameshift Gene Mutations Which type of gene mutation do you think would cause the most serious errors? Point mutation Substitution Frameshift Example: substitution error Just 1 Amino Acid is a Substitution ERROR in Sickle Cell Hemoglobin Causes Hb to be sickle shaped instead of roundcan’t fit into red blood cells & changes their shape too. On your white board, with your partner, explain why your assigned answer is either correct or incorrect. Objective Check3210.4.3 Apply data to complete and interpret a genetic pedigree. SPI 3210.4.5 Apply pedigree data to interpret various modes of genetic inheritance. Inheritance of Traits Pedigree - a diagram that shows how a trait is inherited over several generations Creating the foldable Reading a pedigree males are represented by squares females by circles. SHE HE An individual who exhibits the trait , (for example, someone who suffers from Marfan syndrome), is represented by a filled symbol. A horizontal line between two symbols is a mating DAD MOM Reading a Pedigree The offspring: are connected to each other by a horizontal line above the symbols and to the parents by vertical lines. Example pedigree: Is the mom or dad in generation I affected by a trait? How many offspring are shown in generation II? How many daughters & sons in generation II? How many have the trait? How many offspring does daughter #1 have? How many have the trait? Dominant traits are passed on to a son or daughter EVEN if only one parent has it. Every affected individual has at least one affected parent Affected individuals who mate with unaffected individuals have a 50% chance of transmitting trait to each child Two affected parents may have unaffected children. Recessive Pedigree Where did the trait seen in generation III come from? Traits can be passed on to children if both parents, even if they may seem "normal”, are carriers of the recessive trait. Recessive pedigree: If individuals 2 + 3 in generation 3 have more childrenwill they be affected? Can Individual #8 in gen. 3 have any unaffected children? Can individual #9 in gen 3 have affected children? Example pedigree of cystic fibrosis www.cfscreening.com.au/.../CF/CFInherited.shtml Objective 3210.4.4 Compare different modes of inheritance: sex linkage, co-dominance, incomplete dominance, multiple alleles and polygenic traits 3210.1.6 Describe the connection between mutations and human genetic disorders 3210.4.7 Assess the scientific and ethical ramifications of emerging genetic technologies Polygenic Inheritance - traits influenced by several genes (most human characteristics) example- skin color is additive effect of 6 genes Complex Characters traits influenced by both genes & environment Example- height 3. Multiple Alleles genes with 3 or more alleles. Example- human blood type. IA, IB, i 3 alleles- both IA & IB are dominate over i, Codes for sugars that are on blood cell surface. four different blood typesA, B, AB, O What are the 2 genotypes for “type B? Which blood type can donate to all the others? (universal donor?) Which blood type makes antibodies (will clot against) both A & B blood types? Incomplete Dominance there is an intermediate phenotype Human example- wavy hair is the intermediate between straight & curly hair (remember chapter 9 plant example: - pink 4 o’clock flowers, In between red & white flowers) X-linked Traits Traits that are on the X chromosome. Since males only have one X chromosome- they are affected more than females Females have 2 chances to get a good copy of the gene but males only get 1 chance. Examples of human Xlinked traits Hemophilia- blood clotting disorderboys may bleed to death Duchene muscular dystrophy -affects cardiac and skeletal muscle, as well as some mental functions. Fragile-X syndrome- part of X chromosome has errors- most common cause of mental retardation in males Red-green color blindness- males cannot see these 2 colors. Sex- Influenced Traits males & females show different phenotypes with same genotype example- male pattern baldness 7. Single Allele Traits trait controlled by 1 allele- Dominant or Recessive Dominant Examples: Achondroplastic dwarfism- dwarf size Polydactly is the presence of a sixth digit. Huntington's disease (also called Woody Guthrie's disease)-progressive destruction of brain cells after age 30 Marfans Syndrome- progressive connective tissue disorder. (some cases are new mutations with no family history) Single allele recessive traits: Albinism lack of pigmentation in skin, hair, and eyes, -Homozygous recessive (aa) people make no pigments PKU (Phenylketonuria) - lack enzyme to use the amino acid phenylalanine, buildups breakdown products leads to mental retardation. 1 in 15,000 infants has- treat with DIET! (no phenylalanine) Tay-Sachs Disease- degeneration of the nervous system. Children rarely survive past five years of age. Maple Syrup Urine Disease (MSUD) –like PKU amino acids leucine, isoleucine, and valine More single allele recessive examples: Sickel Cell Anemia- single amino acid substitution in hemoglobin causes lack of oxygen to body Cystic fibrosis- body creates sticky thick mucus – chloride ions- detected in SWEAT TEST. - was once considered a fatal childhood disease- modern treatments can increase lifespan to 30 years plus. Detecting Genetic Disease 1. Testing Amniocetesis- Dr removes some amniotic fluid, 14th-18th week of pregnancy, analyze fluid for proteins & look at chromosomes- some risk of pregnancy loss Chorionic Villi Sampling- clip cells from placental area- 8-14th week pregnancy 2. Treatments- vary with disease