Beyond Mendel… I.Mutations,Mutations II.Gene Linkage,Gene Linkage III.Gene-Mapping,Gene-Mapping IV.X-linked Traits,X-linked Traits V.Polygenic Traits,Polygenic Traits VI.Non-disjunction disorders,Non-disjunction VII.Prenatal DiagnosisPrenatal Diagnosis VIII.PedigreesPedigrees

Mutations A.DefinitionDefinition B.Mutations in GenesMutations in Genes 1.Point Mutations 2.Frame-shift Mutations C.Mutations in ChromosomesMutations in Chromosomes 1.Deletion 2.Duplication 3.Inversion 4.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 b.Example of Deletion: Back to Mutations CGCATGGAATACC T THEFATCATATETHERAT H TEFATCATATETHERAT

A A A A B B B B AB AB AB C C C C C C D D DD EE ED BC E EE F F F F F FGH GH GH GH GH GH 1. Deletion: A segment of the chromosome is removed (not just one nucleotide); e.g. Duchenne Muscular Dystrophy CDEFGH AB CDEFGH MNO MNOPQRPQR 3. Inversion: A segment within a chromosome is reversed 2. Duplication: A segment of the chromosome is repeated; e.g. Huntington’s Disease 4. Translocation: A segment from one chromosome moves to another, non-homologous one Back to Mutations

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 F 1 grey flies always have normal wings and will black flies always have small wings?

Actual Results 8.5% 41.5% 41.5% 41.5% 41.5% Will the F1 grey flies always have normal wings and will black flies always have small wing sizes? No! However, most of the F1 flies will have either a grey body and normal wings OR a black body with small wings, like their parents WHY?

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, unless crossing over segregates the linked genes. G W G W g w g w Independent Assortment Back to “Beyond Mendel”

Gene Mapping Back to “Beyond Mendel” Black Body Small wings Grey Body Normal 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

Sex-Linkage or (X-linked) XX XY When a gene is found on the X chromosome. This is considered X-linked. What would be the phenotype of this female fly? Rr These are the X and Y chromosomes of a male fly. How is the Y chromosome different from the X? Does the gene for eye color exist on the “Y” chromosome? Why or why not? What would be the phenotype of this male fly? r In fruit flies, (R) is the dominant gene for red eyes, and (r) is the recessive gene for white eyes.

Sex-Linkage or (X-linked) 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 X R. How would you write the allele for white eye? X r Watch this video to clarify your knowledge of sex-linked traits

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 red- eye male. Predict the F 1 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 Back to “Beyond Mendel” Skin Color Height Let’s look at our height histograph to see if it formed the same pattern!

Non-disjunction Disorders Back to “Beyond Mendel” Meiosis I Meiosis II Abnormal Gametes Definition: When members of homologous chromosomes fail to separate during Meiosis I – or – when sister chromatids fail to separate during Meiosis II. Examples: Down Syndrome, Turner’s syndrome, Klinefelter’s syndrome Normal Gametes

Prenatal Diagnosis: Amniocentesis Fetus (14 – 16 weeks) Placenta Uterus Cervix 1. Amniotic fluid withdrawn 2. Centrifuge Fluid Fetal Cells Cell culture 3. Karyotype Several weeks later

Prenatal Diagnosis: Chorionic villus sampling (CVS) Fetus (8 – 10 weeks) Placenta Chorionic villi 1. Suction tube inserted through cervix Fetal cells 2. Karyotype Several hours

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 male female Mating couple Children/Siblings Shaded = trait being followed aa A = tongue roller a = can not roll tongue ? ? ? ?? aa Aa AA Can you figure out the rest of the genotypes on your own?

Other Pedigree Symbols Fraternal twins Identical twins Examples of connected symbols:

Affected X-linked Autosomal carrier Deceased Other Pedigree Symbols

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. b.If it is a 50/50 ratio between men and women the disorder is. X-linked 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. dominant a.If the disorder is dominant, one of the parents must have the disorder. recessive 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.