Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Genetics Chapter 13 Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Outline Structure of DNA DNA Functions Transcription Translation Mutation Cytogenetics Mendelian Genetics Quantitative Traits Linkage

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Structure of DNA DNA molecule organized into chain of nucleotides composed of three parts:  Nitrogenous Base  5-Carbon Sugar (Deoxyribose)  Phosphate Group Nucleotides bonded to each other forming a helix.  Hydrogen bonds hold each base on one side of the helix to another base on the other side.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Structure of DNA Four types of DNA nucleotides:  Purines - Adenine (A) and Guanine (G)  Pyrimidines - Cytosine (C) and Thymine (T)

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies

DNA Functions Storage of Genetic Information  Gene - Segment of DNA that directs protein synthesis. - Protein may act as an enzyme influencing cell activities.  Genome - Sum total of DNA in an organism’s chromosomes. - Codon - Groups of three nucleotides.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies DNA Functions Replication of Information  Occurs during S phase of cell cycle. - Strands of double helix unzip allowing DNA polymerase to pair individual nucleotides with the template strands.  Semi-Conservative Replication  Occurs simultaneously in both directions, and begins at several points simultaneously.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies DNA Replication

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies DNA Functions Expression of Information  Different subset of the genetic information is read in each cell type.  Expression requires two processes. - Transcription - Copy of gene message using RNA. - Translation  Messenger RNA (mRNA) translated to produce proteins.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Transcription Three different types of RNA produced:  Messenger RNA (mRNA)  Transfer RNA (tRNA)  Ribosomal RNA (rRNA) RNA Synthesis  Nucleotides added to single stranded DNA molecule by RNA polymerase. - Only portions of the genome replicated.  Remainder is noncoding DNA.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Transcription Promoter Region signals transcription enzymes to attach to the DNA.  Single-stranded RNA transcript produced. Chromosomes contain genes for building tRNA.  Each form of tRNA has a specific anticodon loop. - Base pairs with codon. Genes for rRNA also transcribed in the nucleus - Used to construct ribosomes.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Translation mRNA transcripts are decoded into proteins.  Genetic code based on codons possible combinations  Code for 20 amino acids. tRNA acts as a translator.  Anticodon binds to mRNA codon. Start of translation signaled by a ribosome in the cytoplasm binding to the mRNA.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Central Dogma of Molecular Dogma

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Mutation Mutations - Changes in DNA sequence.  Mutagens - Agents that alter DNA. - Ultraviolet light - Ionizing radiation  Somatic Mutation - Occurs in body cell.  Germ-Line Mutation - Occurs in tissues that will produce sex cells. - Passed on to future generations. All genetic variability due to mutations.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Cytogenetics Cytogenetics is the study of chromosome behavior and structure, from a genetic point of view. Changes in Chromosome Structure  Inversion - Chromosomal piece is broken and reinserted in the opposite orientation.  Translocation - Chromosomal piece breaks off and attaches to another chromosome. - Important in speciation.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Cytogenetics Changes in Chromosome Number  Mistakes during chromosome pairing and separation can result in gametes carrying extra or missing chromosomes. - Aneuploid - Carries, or is missing, an extra chromosome(s). - Polyploid - Has at least one complete extra set of chromosomes.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Mendelian Genetics Mendel crossed self-pollinated pea plants and recorded his observations.  Crossed a tall plant with a short plant.  Parental Generation (P) - All offspring were tall. - First Filial Generation (F 1 )  Cross offspring yielded a ratio of three tall individuals to one short individual.  Second Filial Generation (F 2 )

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Mendelian Genetics Law of Unit Characters  Factors (Alleles), which always occur in pairs, control the inheritance of various characteristics. - Genes are always at the same position (locus) on homologous chromosomes. Law of Dominance  For any given pair of alleles, one (dominant) may mask the expression of the other (recessive).

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Mendelian Genetics Phenotype refers to an organism’s physical appearance. Genotype refers to the genetic information responsible for contributing to the phenotype.  Homozygous - Both alleles identical.  Heterozygous - Alleles are contrasting.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Monohybrid Cross A cross is made between two true-breeding parents differing for a single trait, producing an F 1 generation.  These plants are intercrossed to produce an F 2 generation.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Dihybrid Cross Cross made for parents differing in two traits.  Mendel’s Law of Independent Assortment - Factors (genes) controlling two or more traits segregate independently of each other.  Linked genes do not segregate independently. - Punnett Square used to determine genotypes of the zygotes.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Mendelian Genetics Backcross  A cross between a hybrid and one of its parents. - Can be used to test inheritance theory. Incomplete Dominance  Some genes exhibit traits in which a heterozygote is intermediate in phenotype to the two homozygotes.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Quantitative Traits Quantitative traits exhibit a range of phenotypes rather than discrete phenotypes studied by Mendel.  Molecular geneticists are able to identify chromosomal fragments, quantitative trait loci, associated with quantitative traits.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Extranuclear DNA Entranuclear DNA is found in both mitochondria and chloroplasts.  Endosymbiont Hypothesis theorized mitochondria and chloroplasts were free- living, and at some point became incorporated into cells of organisms that evolved into plants and established a symbiotic relationship.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Linkage and Mapping Genes that are together on a chromosome are said to be linked.  Each gene has a specific location (locus) on a chromosome. - Crossing-over should be more likely between two genes located far apart on a chromosome that between two genes located closer together.  Crossing over frequency can be used to construct a genetic map.  1 map unit = 1% crossing over.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Hardy-Weinberg Law Hardy-Weinberg states the proportions of dominant alleles to recessive alleles in a normally interbreeding population will remain the same from generation to generation in the absence of external forces.

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Review Structure of DNA DNA Functions Transcription Translation Mutation Cytogenetics Mendelian Genetics Quantitative Traits Linkage

Stern - Introductory Plant Biology: 9th Ed. - All Rights Reserved - McGraw Hill Companies Copyright © McGraw-Hill Companies Permission Required for Reproduction or Display