| A | B |
|---|
| DNA replication happens | in the S phase of the cell cycle, and must be completed before meiosis or mitosis begin |
| DNA structure | The whole molecule is a double helix. Each backbone of the helix is a backbone of 5C sugars and phosphates. Attached to the backbones are base pairs (nucleotides) which include purines (A, G) and pyrimidines (C, T) |
| How do A & T combine and how do G & C combine | A & T bind to each other with 2 H bonds; G & C bind to each other with 3 H bonds |
| The two backbones of the double helix run antiparallel to each other, which means | their subunits run in opposite directions |
| 3' and 5' refer to | the orientation of the Cs within the sugars of the DNA backbone. The 3' end of the strand has a carbon #3 (and its hydroxyl group) sticking out. The 5' end of the strand has a carbon #5 (and its phosphate group) sticking out |
| DNA is always synthesized from | the 5' end to the 3' end so new nucleotides are added to the 3' end of a molecule |
| How are new nucleotides bonded? | Covalently (phosphodiester bonds). This bonding is coupled with a hydrolysis reaction (which is exergonic, providing energy for the endergonic formation of the bond) |
| What does it mean that DNA replication is semiconservative? | One of the two original strands of DNA (the parent strand) serves as a template in the production of a new DNA strand |
| DNA ligase | For leading strand, binds 3' end to the rest of strand. For lagging strand, joins Okazaki fragments |
| DNA polymerase | synthesizes and elongates DNA strands (or Okazaki fragments) |
| helicase | unwinds the template (original, parental) strand of DNA at the replication fork |
| nuclease | cuts DNA to repair mistakes during replication (or to repair damage after replication) |
| single-strand binding protein | keeps single strands of DNA apart so they can act as templates and be replicated |
| topoisomerase | relieves pressure on DNA from twisting/untwisting; always found ahead of the replication fork |
| Mechanisms to ensure good copying: | 1. Specificity of base pair matching prevents some mutations 2. mismatch repair - mismatches in nucleotide pairing can be fixed by any of 100 enzymes 3. nucleotide extension repair - entire segments of DNA cut our by nuclease enzymes and repaired |
| What is in an organism's genome? | All of its DNA. DNA is arranged in the form of one or more chromosomes (prokaryotes have circular, eukaryotes have linear) |
| Expressed regions (exons) and unexpressed regions (introns) | Expressed regions show up in the phenotype. Unexpressed regions do not. More complex organisms tend to have more introns than less complex organisms |
| The intergenetic DNA region is made up of: | 1. Regulatory sequences 2. pseudogenes (vestigial genes) 3. repetitive DNA 4. Transposable elements (DNA that has moved to another location in the genome) |
| multigene families | Formed when there are 2+ copies of a gene. Can be identical or nearly identical |
| regions of the genome evolve (change over time) due to | duplication, rearrangement, mutation, or transposable elements |
| Mendel's Law of Segregation | Two heritable elements (genes but Mendel didn't know) separate into different gametes. Mendel was actually describing independent assortment in anaphase I of meiosis (which actually begins with random alignment durring metaphase I) |
| Mendel's law of independent assortment | Each heritable element sorts separately from each other. Mendel is describing independent assortment in anaphase I of meiosis |
| Linkage | is an exception to mendel's law of independent assortment. It happens when genes that are adjacent or beside each other on a chromosome don't assort independently |
| Complete dominance | If a dominant allele is present, it is expressed in the phenotype. Recessive alleles are masked and don't show up in the phenotype unless in homozygous recessive form. Ex. Red flower x White = Red |
| Incomplete dominance | The heterozygote expressed intermediate traits, halfway between dominant and recessive alleles. Ex. red x white = pink flowers |
| Codominance | Both dominant and recessive alleles are expressed in the heterozygote. Ex. Red x white = splotchy red and white flowers |
| Plieotropy | A single gene, when expressed, is the cause of multiple phenotypic traits. In multiple allelic inheritance (blood groups) >2 allelic versions of a single gene produce different phenotypes |
| Polygenic interitence | Means a single phenotype is caused by multiple genes being expressed. These phenotypes are called quantitative traits as they display a broad range. Ex. human height, skin, eye, hair color |
| Epistasis | Means that one gene affects the expression of another. |
| Genomics vs. proteomics | Genomics studies multiple genes, including the ways that they change, their effects, and their interactions. Proteomics is one type of genomics, connecting proteins to the genes that code for them and the proteins' phenotypic effects |
| Where does meiosis happen? | in the germ cell lines. In animals it happens in the gonads - in mammals, testes for males and ovaries for females |
| What does meiosis produce? Mitosis? | it produces haploid gamete cells (1 copy of each of the 22 autosomal chromosomes and 1 copy of the sex chromosome). Mitosis makes diploid somatic cells |
| Meiosis: Interphase | Similar to what occurs before mitosis. Chromosomes and cell contents duplicated. Checkpoint occurs after this |
| Meiosis: Prophase I | Longest phase of meiosis. Chromatin condenses to chromosomes. Synapsis occurs (the pairing and physical connection of duplicated homologous chromosomes, which are connected by the synaptonemal complex), tetrads (paired, duplicated homologous chromosomes) formed, crossing over occurs. As in mitosis, spindle apparatus forms. nuclear envelope breaks down, nucleoli disappear, spindle apparatus' microtubules attach to kinetochores |
| Meiosis: Metapahse I | Tetrads arranged randomly along metaphase plate (to allow for independent assortment in ana I). Both chromatids of the homologue attach to a single centrosome (so that sister chromatids get transported together) |
| Meiosis: Anaphase I | Checkpoint occurs after this. Homologous replicated chromosomes move towards opposite poles, each pole gets EITHER maternal or paternal chromosomes, this is independent assortment |
| Meiosis: Telophase I and Cytokinesis | Unlike in mitosis, these stages occur together. Nuclear envelopes and nucleoli might or might not reform, and cell splits into two gamete precursor cells |
| Meiosis II: Prophase II | Unlike Prophase I, this is not preceded by interphase. The spindle apparatus forms, sister chromatids attach to this |
| Meiosis II: Metaphase II | Sister chromatids align on the metaphase plate |
| Meiosis II: Anaphase II | The third and final checkpoint occurs here. Centromeres fule degenerate, sister chromatids separate and move towards poles |
| Meiosis II: Telophase and cytokinesis | Nuclei and nucleoli re-form. Cytokinesis forms 4 haploid gametes, each with one copy of each chromosome |
| Sources of genetic variation in meiosis and syngamy (fusion of gametes) include: | 1. mutations (at any time) 2. crossing over (in prophase I) 3. independent assortment (anaphase I) 4. the syngamy partner during fertilization of gametes |
| Parts of the chromosome include | DNA, histone proteins, and telomeres (at ends of chromosomal arms). |
| What do telomeres do? | They protect the ends of chromosomes from degeneration during/after mitotic divisions |
| Barr bodies | In female eutherian mammals, each cell deactivates one of its X chromosomes via methylation, thus creating a mosaic pattern. Males don't make barr bodies because they only have one X chromosome |
| Mosaicism occurs when | an individual has multiple genomes in their body. Can be due to somatic mutation, hematopoietic cell transfers, viruses (which have undergone the lysogenic cycle, horizontal gene transfer), or chimerism |
| chromosomes can be homologs | inherited from a common ancestorq |
| chromosomes can be orthologs | shared after a speciation event |
| chromosomes can be paralogs | shared after a chromosomal duplication event |
| chromosomes can be xenologs | horizontally transfered, from a different species |
| what is aneuploidy? | organisms with differences in chromosome number. Can be monosomic or trisomic, and can be seen in karyotypes |
| penetrance | when dominant traits aren't always expressed in the phenotype. it is affected by genetic factors like modifier genes, environmental factors, and age. An example of this is in Huntingtons disease, which can have onset between 30 and 60 |
| genomic imprinting | genes on only one of the two homologs are expressed . |
| cytonuclear interactions | when the genomes of the organelles (mitochondria/chloroplasts) interact with the genome of the nucleus they can impact the phenotype. This can be seen in verigated plants |
| How are we all mosaics? | Viruses that have undergone the lysogenic cycle insert their DNA, and somatic mutations create genetic differences (that are then replicated due to mitosis) |
| What are the causes of aneuploidy? | 1. DNA doubling: occurs in the S phase of meiosis and mitosis 2.Non-dysjunction: Occurs in anaphase of mitosis and anaphase I/II of meiosis when sister chromatids or homologous chromosomes stay together instead of splitting to opposite poles |
| Sexual reproduction is avoided by | Eubacteria and archaebacteria; many plants, protists, and fungi; some anamalia like most invertebrates, some fish and reptiles |
| syngamy v karyogamy | Syngamy is gametic fusion while karyogamy is the combining of gametic nuclei. The two occur in sexual reproduction |
| isogamy v anisogamy | Isogamy is the fusion of two gametes of similar form. Anisogamy is the fusion of two distinct classes of gametes (ie. egg and sperm) that are produced by two distinct classes of individuals (ie. male and female) |
| What are the 5 costs of sex? | 1. it takes time 2. it can destroy high fitness genotypes due to haphazard recombination 3. individuals must attract a mate 4. parasite/pathogen transmission 5. anisogamy (female puts in most of the work but genes are diluted by 50%) |
| heteroblasty | progressive change in the form or size of successive organs. it can change the way genes are expressed in the phenotype |
