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Beyond Mendel… I. II. III. IV. V. VI. Mutations, Gene Linkage, Gene-Mapping, X-linked Traits, Polygenic Traits, Non-disjunction disorders, VII.Prenatal Diagnosis VIII.Pedigrees Mutations A. Definition B. Mutations in Genes 1. Point Mutations 2. Frame-shift Mutations C. Mutations in Chromosomes 1. 2. 3. 4. Deletion Duplication Inversion Translocation Back to “Beyond Mendel” Mutations • Definition: A change in the genetic material (DNA or RNA) of a cell – Somatic: If it occurs in body cells; can’t be passed on to next generation – Germ-line: If it occurs in gametes; can be passed on to next generation Back to Mutations Mutations in Genes 1. Point Mutation: Affects one nucleotide (One nucleotide is replaced by another) a. Three Types of point mutations i. Missense mutations: Codes for a different amino acid ii. Silent mutations: Codes for same amino acid iii. Nonsense mutations: Code for a stop codon b. Example: Sickle-cell Anemia Mutations in Genes 2. Frameshift Mutation: An insertion or deletion that shifts the triplet code reading frame a. Example of Insertion: TA CGCATGGAATACC b. Example of Deletion: H THE TEF ATC FAT CAT ATA TET ATE THE HER RAT AT Back to Mutations 1. Deletion: A segment of the chromosome is removed (not just one nucleotide); e.g. Duchenne Muscular Dystrophy A B C D E A segment F G H of the chromosome A B C Eis repeated; F G H 2. Duplication: e.g. Huntington’s Disease A B C D E F G H A B C B C D E A B C D E F G H A D C B E F G H 3. Inversion: A segment within a chromosome is reversed F G H 4. Translocation: A segment from one chromosome moves to another, non-homologous one Back to Mutations A B C D E F G H M N O P Q R M N O C D E A B P Q R F G H Linked Genes In flies, grey bodies (G) and normal-wing size (W) are dominant to black bodies (g) and small wing size (w). In this cross will the F1 grey flies always have normal wings and will black flies always have small wings? Actual Results 8.5% 8.5% 41.5% 41.5% WHY? No! However, mostflies of the F1 flies willnormal have either Will the F1 grey always have wings aand grey body and flies normal wingshave OR small a black body with will black always wing sizes? small wings, like their parents Linked Genes The genes for body color and wing size are linked, meaning they are found on the same chromosome. The linked genes are most likely inherited together and will not undergo Mendel’s Law of Independent Assortment , unless crossing over segregates the linked genes. G G g g W W w w Back to “Beyond Mendel” Gene Mapping Grey Body Black Body Normal wings Small wings • Genes that are closer together on the same chromosome are less likely to cross over, therefore segregate. • Genes that are farther apart on the same chromosome are more likely to cross over and segregate • Genes that are on different chromosomes will always segregate independently Back to “Beyond Mendel” Sex-Linkage or (X-linked) When a gene is found on the X chromosome. This is considered X-linked. In fruit flies, (R) is the dominant gene for red eyes, and (r) is the recessive gene for white eyes. Does the gene These are the for eye Y color X and exist on the “Y” chromosomes chromosome? of a male fly. Why Howor is why the Ynot? chromosome R r different from the X? XX r XY What Whatwould wouldbebethe the phenotype phenotypeofofthis thisfemale male fly? fly? Sex-Linkage or (X-linked) Watch this video to clarify your knowledge of sex-linked traits • When genes are sex-linked, we include the X and Y as part of their genotype. For example, the allele for red eye is not “R” but is written as XR. How would you write the allele for white eye? Xr White board practice What is/are the possible genotype(s) for this red-eye fly if it is a female? What is/are the possible genotype(s) for this red-eye fly if it is male? Answer the above questions again for this fly. White board practice You work in a fruit fly lab and you cross a heterozygote red-eye female with a redeye male. Predict the F1 offspring using a Punnett square. What is the phenotypic ratio? Back to “Beyond Mendel” Polygenic Traits • Definition: Traits controlled by two or more genes • Examples: Skin color, height Polygenic Traits Skin Color Height Let’s look at our height histograph to see if it formed the same pattern! Back to “Beyond Mendel” Non-disjunction Disorders Meiosis I Definition: When members of homologous chromosomes fail to separate during Meiosis I – or – when sister chromatids fail to separate during Meiosis II. Meiosis II Examples: Down Syndrome, Turner’s syndrome, Klinefelter’s syndrome Abnormal Gametes Normalto Back Gametes “Beyond Mendel” Prenatal Diagnosis: Amniocentesis 1. Amniotic fluid withdrawn 2. Centrifuge Fetus (14 – 16 weeks) Fluid Fetal Cells Several weeks later Placenta 3. Karyotype Uterus Cervix Cell culture Prenatal Diagnosis: Chorionic villus sampling (CVS) Fetus (8 – 10 weeks) 1. Suction tube inserted through cervix Fetal cells Placenta Chorionic villi Several hours 2. Karyotype Interpret these karyotypes Klinefelter’s syndrome Interpret these karyotypes Sex: Male Interpret these karyotypes Down Syndrome Back to “Beyond Mendel” A Pedigree is… Generally: A genetic family tree Specifically: It is a chart of the genetic history of family over several generations. Pedigree Aa ? A = tongue roller a = can not roll tongue aa ? ? ? ? AA aa Aa aa Can you figure out the rest of the genotypes on your own? male Mating couple female Children/Siblings Shaded = trait being followed Other Pedigree Symbols Examples of connected symbols: • Fraternal twins • Identical twins Other Pedigree Symbols • • • • Affected X-linked Autosomal carrier Deceased Interpreting a Pedigree Chart 1. Determine if the pedigree chart shows an autosomal or X-linked disease. a. If most of the males in the pedigree are affected the disorder is X-linked . b. If it is a 50/50 ratio between men and women the disorder is autosomal . Example of Pedigree Charts • Is it Autosomal or X-linked? Answer • Autosomal Interpreting a Pedigree Chart 2. Determine whether the disorder is dominant or recessive. a. If the disorder is dominant, one of the parents must have the disorder. b. If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous. Example of Pedigree Charts • Dominant or Recessive? Answer • Dominant Example of Pedigree Charts • Dominant or Recessive? Answer • Recessive Summary • Pedigrees are family trees that explain your genetic history. • Pedigrees are used to find out the probability of a child having a disorder in a particular family. • To begin to interpret a pedigree, determine if the disease or condition is autosomal or X-linked and dominant or recessive.