CHAPTER 5 Principle of Genetics Review

Transcription

1 CHAPTER 5 Principle of Genetics Review I. Mendel s Investigations Gregor Johann Mendel Hybridized peas Formulated Principles of Heredity published in 1866 II. Chromosomal Basis of Inheritance A. MEIOSIS - Every cell has 2 chromosomes bearing genes for each trait w/ same shape & size Homologous Pairs - Each copy may not be identical (differ forms) Alleles - 2 Divisions result in a halving of the chromosomal # Diploid (2N) Haploid 2 nuclear divisions 1 chromosomal division

2 - Phases similar to Mitosis (except 1 st division) 1 st DIVISION PROPHASE I * homologous sets align (synapse) form bivalents w/ 4 DNA stands (tetrad) METAPHASE I * align homologous sets (each=dyad) ANAPHASE I * Dyads separate (not centromeres) TELOPHASE I * end w/ ea. daughter cell w/ one homolog (2 chromatids) so 2N 2 nd DIVISION PROPHASE II METAPHASE II ANAPHASE II identicle to Mitosis TELOPHASE II

3 B. SEX DETERMINATION Autosomes Vs Sex Chromosomes Varying Systems: XX-XY (F-M) Humans, animals XX-XO (F-M) Hemiptera ZW-ZZ (F-M) Birds, Moth, Butterfly, Fish Sex determined by environmental or behavioral conditions: - invertebrates & lower vertebrates Lack of Sex Chromosomes: - reptiles, many fish Temperature determination: Low temp = Female High temp = Male Behavioral determination: Hermaphroditic (fish) posses both gonads (social environ. determines)

4 III. Mendelian Laws of Inheritance A. MENDEL S FIRST LAW Law of Segregation Homologous Pairs segregate independently of one another in Meiosis MONOHYBRID CROSSES: Phenotype vs Genotype F 1 x F 1 F 2 x F 2 F 3 Dominant vs Recessive Homozygous Heterozygous 3 Steps to Solving Heredity: 1. Determine Parents Genotypes 2. Determine Parents Gametes 3. Punnett Square solves F 1 genotypes

5 Testcross: determine unknown genotype by crossing w/ known genotype Patterns of Inheritance: 1. Simple Dominance/Recessive 2. Intermediate Inheritance (Incomplete Dominance) snapdragons, chicken feathers, 3. Codominance human blood types 4. Multiple Alleles pigmentation, height, weight

6 B. MENDEL S SECOND LAW Law of Independent Assortment Pairs align independently DIHYBRID CROSSES: Probability p= # of times an event happens total # trials or possibilities (Role 3 on dice = 1/6) Product Rule product of individual Probabilities (Roll 3 twice = 1/6 x 1/6 = 1/36) Other Gene Interactions: 1. Polygenic Inheritance 2. Pleiotropy 3. Epistasis (1 gene effects other gene expressions) 4. Sex-Linked (males carry 1 allele = Hemizygous)

7 5. Crossing Over - allow for separation of linked alleles - exchange of homologous DNA in prophase I 6. Chromosomal Aberrations: est. 5 in 1,000 humans have serious genetic defect A. Euploidy Aneuploidy by Nondisjunction (single chromosome) Polyploidy (1 or more chromosome sets) B. Structural Aberrations Inversion Translocation Deletion Duplication

8 IV. Gene Theory A. GENE CONCEPT Extrons Introns (extra DNA) B. ONE GENE-ONE ENZYME HYPOTHESIS Beadle & Tatum 1940's V. Storage & Transfer of Genetic Info A. NUCLEIC ACIDS nucleotides 1. DNA antiparallel double stranded helix 2. RNA differ by sugar & one base

9 3 types: rrna trna mrna 3. Replication Template of old DNA a. separation b. complementary base pairing c. joining (DNA polymerase) 4. Genetic Code 64 possible words for 20 a.a. Universal Codons

10 5. Transcription DNA mrna using RNA polymerase A U only one DNA strand used initiated by AUG methionine includes both intron + extron end product = capped & excised 5' cap of methylated guanine 3' end tail of adenine nucleotide 6. Translation mrna Protein occur at Ribosome in cytoplasm a. mrna attaches to Ribosome b. trna delivers amino acids & charges with trna synthetases c. Anticodon on trna read codon 5' to 3' d. Amino acids build peptide bonds & assembly continues to end codon

11 7. Regulation every cell genetically equivalent (differentiate during development) Control: a. Transcriptional Control b. Translational Control c. Gene Rearrangement d. DNA Modification

12 VI Molecular Genetics 1. Recombinant DNA Restriction Endonucleases cut at specific locations result in sticky ends DNA readily joins DNA Ligase seals ends together 2. Polymerase Chain Reaction (PCR) Primers (short chains of nucleotides) serve as sites of initiation DNA Polymerase + lots of free nucleotides stimulate process of replication at primer sites (may be specific genes) Uses: a. clone genes (new to very old) b. ID DNA samples (drop of blood)

13 3. Genomics Scientific field of Mapping, Sequencing, & analyzing genomes Human Genome Project: estimated 30,000 to 40,000 human genes coded in 3 to 6 billion pairs of bases potential to ID 4,000 human diseases already ID 300 genetic disorders expanded to other organisms transgenic organisms

14 VII. Sources of Phenotypic Variation A. Sexual Reproduction 1. Independent Assortment of Chromosome 2. Chromosomal Crossing Over 3. Random Fusion of Gametes B. Gene Mutations alter the base sequence of DNA Substitution, Deletion, Addition, etc Mutations may be Neutral Beneficial Deleterious Estimated Frequency: Drosophila 1 in 10,000 loci (0.01%) Human 1 in 10,00 to 100,000 (every third person carrying new mutation) each egg & sperm has 1 mutant allele

15 VIII. Molecular Genetics of Cancer Neoplastic Growth - unrestrained proliferation of cells due to altering of 2 genes: 1. Oncogenes normal proto-oncogenes that code for cell division mutate 2. Tumor-Suppressor genes normally constrain cell proliferation ie: p53 protein turns genes on/off triggers apoptosis (cell death) control progression G1 to S promote repair of damage DNA