Review 4: Heredity & Molecular Genetics

Review 4: Heredity & Molecular Genetics AP Biology

Heredity & Molecular Genetics • Meiosis produces haploid gametes. • Different versions of same gene are called alleles. • Mendelian inheritance • Non-Mendelian inheritance • Chi-square analysis • DNA & RNA • Central Dogma • Regulation of Genes • Mutations • Biotechnology

Meiosis Produces Haploid Gametes • Meiosis 1 separates homologous pairs: reduction division • Meiosis 2 separates sister chromatids: produces 4 sex cells

Different Versions of Same Gene are Called Alleles • Dominant vs. Recessive • Homozygous vs. Heterozygous • Phenotype vs. Genotype

Mendelian Inheritance • Monohybrid Crosses • -Aa x Az = 3:1 ratio • -Law of Segregation • Alternative alleles of a character segregate and remain distinct. • Dihybrid Crosses • -AaBb x AaBb = 9:3:3:1 ratio • -Law of Independent Assortment • Genes that are located on different chromosomes assort independently during meiosis. • Test Cross • -Determine genotype of individual showing dominant phenotype. • -Unknown (A_) x aa (homozygous recessive)

Non-Mendelian Inheritance • Incomplete Dominance (pink flower color) • Co-dominance (blood type) • Sex linked (mainly X-linked: color blindness, hemophilia) • Epistasis (coat color) • Pleiotrophy (dwarfism, giantism) • Polygenic (skin color)

Epistasis • The effects of one gene are modified by one or several other genes

Pleiotropy & Polygenic • A single gene influences multiple phenotypic traits • Examples: Dwarfism, Gigantism • Polygenic

Chi-square analysis • Determining if observed results are significantly different from expected results • Know how to use formula when given & how to interpret results • -degrees freedom (1 less than number of classes of results) • -less than p=.05, then difference can be due to random • chance alone & null hypothesis is accepted

DNA & RNA • DNA: ACTG nitrogen bases, double helix • - A:T, C:G • RNA: ACUG nitrogen bases, single helix

Central Dogma • DNA -> RNA -> protein -> trait • Transcription (DNA -> mRNA) • Translation (mRNA -> protein)

Transcription • Production of RNA copy of DNA sequence • In nucleus • RNA polymerase copies coding strand & produces mRNA

Translation • mRNA -> protein • In cytoplasm • Codons on mRNA read by ribosome • Matched to anticodons of tRNA • tRNA carries amino acids to mRNA & ribosome assembles polypeptide chain • Start codon (Met) & stop codons, redundancy in code • Universal code (single common ancestor)

Regulation of Genes • Operons • -Prokaryotes • -Cluster of genes for enzymes in a pathway • -Controlled by repressor protein • -Repressible operon (synthesis pathway = tryp operon) vs. inducible operon (digestive pathway = lac operon) • Transcription Factors • -Proteins which enable bonding of RNA polymerase to gene

Operons • Functioning unit of genomic material containing a cluster of genes under the control of a single regulatory signal or promoter

Mutations • Fuel for evolution = variation, genetic change • Gene duplication, point mutation, insertions, deletion

Biotechnology • Scientists can modify an organism’s genome by inserting foreign DNA. • Techniques

Modify Organism’s Genome • Bacterial Transformation (human insulin gene in E. coli) • Possible because of universal genetic code

Techniques • Restriction digest: Restriction enzymes, sticky ends • Transformation: Restriction enzymes, sticky ends, ligase, amp selection, lacZ screening • Gel electrophoresis: DNA moves in an electrical field (negative -> positive), small pieces move further • PCR: DNA amplification • RFLP: DNA fingerprinting • Sanger sequencing: Human Genome Project

Review 4: Heredity & Molecular Genetics