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Genetics Learning Objectives Know what is meant by base pairing within DNA and what can happen if there is a deletion or substitution. Know the difference in genotype and phenotype. What is an allele and how does it affect different traits? Know what a Punnett Square is, when it is used in inheritance disorders and how to interpret it. (A Punnett Square shows all possible combinations of alleles in offspring) Know the following classifications of genetic disorders and examples of each: o Single gene autosomal dominant: Marfan’s, neurofibromatosis o Single gene autosomal recessive: PKU, Tay-Sachs disease o Single gene X-Linked: Fragile X o Multifactorial inheritance disorder: cleft lip/palate o Chromosomal disorders with deletion or translocation such as Down’s syndrome (trisomy 21) o Sex chromosome disorders: Turner’s / Klinefelter’s Know that the incidence of Down’s syndrome is higher with advanced maternal age. Name common disorders caused by environmental factors (fetal alcohol / radiation/folic acid deficiency/Accutane) and state what problems they can cause. Know what systems will be affected in the developing fetus if a pregnant woman is exposed to radiation during the first trimester of pregnancy? NOTES Genes within cell tell cell how to function, when to die, what to do (control center) Genes are info in the cell o Control inheritance and cell function Determine types of proteins and enzymes within a cell Chromosomes o Where DNA is distributed o Humans have 23 pairs (autosomes: 1 from mother and 1 from father) 1 pair contains sex chromosomes
DNA: contain genetic information and used for cell structure and function o Double stranded helix 1953: by Watson and Crick Pairing: A:T & G:C o Nucleotides: phosphoric acid, 5 carbon sugar (deoxyribose), 1 of 4 nitrogenous bases o Nitrogen bases Pyrimidine: bases with 1 nitrogenous ring Thymine, cytosine Purines: base with 2 nitrogenous rings Adenine, guanine o Packing of DNA is tight Chromatin: coiled structure with DNA, RNA or protein RNA: nucleotide (synthesis of proteins) Proteins play role in functional diversity of cells o Proteome: complete set of proteins encoded by a genome o Proteomics: study of proteome Genetic code o Bases: G C T A (IN RNA, uracil is used instead of T) o Codon: 3 base sequence, triplet code used in transmission of genetic information in protein synthesis (tells body what protein to create) Example: UGG codes for tryptophan o Stop codon: signals end of a protein molecule 3 codons are stop codons o 64 combinations 61 codons code for amino acids Only 20 amino acids are used for protein synthesis DNA replication o Cell has cell cycle o Chromosome untightens and unzips and create duplicate model DNA repair o Mutations or errors: occur with the following Duplication (2 X’s) Substitution (one base pair is in place for another) Deletion or loss (adding or losing one or more base pairs Rearrangement
Humans: have 46 chromosomes (22 pairs of autosomes, 23rd^ or extra pair is sex chromosome or what type of sex we have) o XY = female o XX = male Mitosis: somatic cells o Each daughter receives 23 pairs of chromosomes o Most of cells cycle occurs in interphase here o G1 phase, S phase, G2 phase, mitosis (prophase, metaphase anaphase, telophase) Meiosis: sex cells: result in single set of 23 chromosomes o Meiosis 1: There is Prophase 1, metaphase 1, anaphase 1, telophase 1 o Meiosis 2: Then prophase 2, metaphase 2, anaphase 2, telophase 2 o Go from 1 cell to 2, then to 4 Chromosome structure: karyotype (photo of our chromosomes) Patterns of inheritance (likelihood of occurrence of a specific trait) o Genotype: info in the genetic code o Phenotype: recognizable or physical traits o Expressivity: expression of a gene in the phenotype o Penetrance: ability of a gene to express its function o Gene locus: area on DNA molecule which controls inheritance o Allele: alternate forms of genes at a gene locus (example: AA: blond hair, then Aa: brown hair) GENOTYPE (alleles) PHENOTYPE (physical appearance) AA Yellow (dominant) Aa Yellow (dominant) Aa Green (recessive) Genetic imprinting o Epigenetics: influence of the environment upon cells & DNA Example: set of twins are born, parents decide to give the babies up for adoption, 1 baby goes to London & the other stays in US……possible being that they have same DNA, 1
can ger breast cancer and the other may not (due to environmental factors such as radiation or exposure to chemicals) Genogram: parent of origin has a particular mutated gene May include a carrier within family Mutated gene may be passed down to offspring but all don’t get it Gregor Mendell o Law of segregation: during gamete (sex cell) formation, the alleles for each gene separate from one another so that each gamete carries only 1 allele (table below) LAW OF SEGREGATION EXAMPLE First Generation (dominant red) Second Generation Rr Rr Rr Rr Law of Independent Assortment: genes for different traits can separate independently during formation of gametes/sex cells Law of dominance: some alleles are dominant while other traits are recessive Punnett squares: used to predict single gene disorders o Dominant: traits expressed in either homozygous (same) or heterozygous (different) 1 member of gene pair codes for trait o Recessive: traits only expressed in homozygous pairing Both gene pair members code for trait o Carrier: heterozygous for recessive trait but does not obtain trait Example: Both parents are unaffected carriers and have 4 children (1 is unaffected, 2 are unaffected carriers, and 1 is affected) Rr Rr Rr rr
Body systems affected Skeletal: joint hypermobility (bending joints backward), scoliosis, longer arms Vision: myopia (cant see things far ) Cardiovascular: dissecting aorta aneurysms (tearing of the aorta) o Neurofibromatosis: neurogenic/brain tumors Develop in schwann cells Type 1: NF-1, von Recklinghausen disease Evaluated if patient have numerous amounts of Café-au-lait spots (6 or more) Type 2 bilateral acoustic NF 2 Autosomal Recessive disorders o PKU (phenylketonuria) Deficiency of phenylalanine hydroxylase Found in products such as diet soda Can cause irreversible brain damage o Tay-Sachs Disease: difciency of hexosaminidase A (failure to break down GM2 gangliosides of cell membrane) Result in physical & mental delays/deterioration (begins in birth) o X-Linked Recessive Disorders Most associated with X chromosome Males with X are affected Can result in glucose-6-phosphate dehydrogenase deficiency, result from patients with Hemophilia A, X-linked agammaglobulinemia Fragile X Syndrome: elongated look, results in intellectual disability (1 in 1250 males, 1:1500 fem) o Multifactorial inheritance Can be caused by multiple genes &environmental factors Examples: cleft lip or cleft palate o Chromosomal abnormality Loss of information (deletion) Translocation: info moved around
Inversion: info is switched or inverted Ring formation: chromosomes connect with themselves or wrong place Aneuploidy: having abnormal # of chromosomes Nondisjunction: failure of autosomes or sex chromosomes to separate Monosomy: presence of only 1 member of chromosome pair Polysomy: presence of 2 or more chromosomes per set Trisomy 18 (Edwards syndrome) Trisomy 13 (patau syndrome) Trisomy 21 (downs syndrome) Numeric Sex Chromosome Disorders Turner syndrome: missing some or all of 1 (X) chromosome Klinefelter syndrome: males testicular dysgenesis ( or more X chromosomes in addition to normal XY o Mitochondrial gene disorder Mitochondria contain their own DNA Inherited on the maternal line Affect tissues that are dependent on oxidative phosphorylation to meet their metabolic needs o Disorder due to environmental influences Embryos are subject to non genetic influences (alcohol, smoking, pollution) Period of vulnerability: organogenesis Folic acid deficiency is important for organ development Teratogenic (harmful) Agents: to embryo or fetus Ionizing radiation Chemicals or drugs (fetal alcohol syndrome: birth defects) Medications (Accutane: Vit A and can be toxic to liver & create defects to baby) Anticonvulsant medications (side effects of seizure meds) Infectious agents o Toxoplasmosis, varicella, rubella (baby death or miscarriage), herpes
