Mcat 2015 Genetics

8.1 Introduction to Genetics

DNA as the Genetic Information of the Cell

* DNA as basis of genetic hereditary modeled with conferring virulence to mice (Griffith, Avery-MacLeod-McCarty Experiment) and radiolabeled isotopes (Hersey-Chase Experiment)

* During quiescent (resting cells), DNA is not broken down

Genes and Alleles

* Gene def.: length of DNA that encodes for specific gene product (can be coding/non-coding)

* Locus def.: specific location of gene in genome

* Homologous chromosomes (Xm) def.: non-identical copies of a Xm (ex. diff. allele at same locus)

* Allele def.: diff. versions of a gene, carry out gene’s function differently

Genotype vs. Phenotype

* Genotype def.: DNA sequence of an allele

* Phenotype def.: physical expression of a genotype

* Homozygote (CC or cc) vs. heterozygote (Cc)

* If an allele can mask the other allele, said allele is dominant (vs. recessive for masked allele)

8.2 Meiosis

* Occurs in specialized cells (spermatogonia in males and oogonia in females)

Meiosis I | 2n, 4x |

Prophase I | - Xm condense, nuclear envelope breaks down - homologous Xm pair (synapsis) in bivalent or tetrad formation, crossing over or recombination may occur (lengthiest stage in meiosis) -Synaptonemal Complex: SYCP2/3 attach to homologous chromatin structures (laterally), align and connect via a central region (SYCP1) “zipper orientation” -SC formation and recombination are independent but disturbed together |

Metaphase I | -tetrads align at metaphase plate (vs. chromatid alignment in mitosis) |

Anaphase I | -homologous chromosomes separate |

Telophase I | -divide into 2 cells |

Meiosis II | 1n, 2x |

PMAT II | -identical to mitosis except cells are already haploid |

Nondisjunction

* Def.: failure of homologous chromosomes or sister chromatids to separate

* Zygote with 3 copies of a chromosome (trisomy) or one copy (monosomy)

8.3 Mendelian Genetics

* Law of segregation: two alleles of...