Chapter Six: Meiosis and Mendel

Section One: Chromosomes and Meiosis Cell Types Somatic Cells: cells that make up your body tissues and organs Gametes: sex cells; sperm and eggs

Section One: Chromosomes and Meiosis Homologous Chromosomes: two chromosomes-one from the mother and one from the father- that have the same length and general appearance Humans have 23 pairs of chromosomes Have the same set of genes as well Pairs 1-22 are autosomes: chromosomes that contain genes not directly related to the sex of an organism Pair 23: sex chromosomes: control the development of sexual characteristics XX=female XY=male

Section One: Chromosomes and Meiosis Haploid and Diploid Sexual Reproduction: involves the fusion of two gametes that result in offspring that area genetic mixture of the parents Fertilization: fusion of the sperm and egg Dipolid: the cell has 2 copies of each chromosome One copy from the mother and one copy from the father Somatic cells are diploid Haploid: the cell has only one copy of each chromsome Sex chromsomes are haploid X chromosome is always in the egg Sperm can contain the X or Y chromosme

Section One: Chromosomes and Meiosis Maintaining chromosome numbers is important for the body to function correctly Meiosis: the form of nuclear division that divides the diploid cell into haploid cells for formation of gametes Produces gametes Reduces chromosome number by half Creates 4 haploid cells

Section Two: Process of Meiosis Homologous Chromosomes and Sister Chromatids Sister chromatids: duplicated chromosomes that stay attached to each other Homologous Chromosomes: two chromosomes-one from the mother and one from the father- that have the same length and general appearance

Section Two: Process of Meiosis Two stages: Meiosis I and Meiosis II Meiosis I Prophase I, Metaphase I, Anaphase I, Telophase I MeiosisII Prophase II, Metaphase II, Anaphase II, Telophase II

Section Two: Process of Meiosis Meiosis I Prophase I Nuclear membrane breaks down Centrosomes and centrioles move Spindle fibers assemble Duplicated chromosomes condense Homologous chromosomes pair up

Section Two: Process of Meiosis Meiosis I Metaphase I Spindle fibers align the homologous chromosomes along cell equator

Section Two: Process of Meiosis Meiosis I Anaphase I Paired homologous chromosomes separate from each other and move toward opposite ends of the cell Sister chromatids stay attached

Section Two: Process of Meiosis Meiosis I Telophase I Spindle fibers disassemble and the cell undergoes cytokinesis

Section Two: Process of Meiosis Meiosis II Prophase II Nuclear membrane breaks down Centrosomes and centrioles move to opposite ends of the cell Spindle fibers form

Section Two: Process of Meiosis Meiosis II Metaphase II Spindle fibers align the chromosomes along the center of the cell

Section Two: Process of Meiosis Meiosis II Anaphase II The sister chromatids are pulled apart from each other and move to opposite ends of the cell

Section Two: Process of Meiosis Meiosis II Telophase II Nuclear membrane forms again Spindle fibers break apart Cell undergoes cytokinesis

Section Three: Mendel and Heredity Gregor Mendel and Genetics Traits: distinguishing characteristics that are inherited Genetics: the study of biological inheritance patterns and variations in organisms Purebred: genetically uniform The offspring of the purebred parents inherit all of the parents characteristics Cross: the mating of two organsims P= parental generation F1= first generation of offspring

Section Three: Mendel and Heredity Mendel’s Conclusions Law of Segregation Organism inherit two copies of each gene, one from each parent Organisms donate only one copy of each gene in their gametes, thus the two copies separate during gamete formation

Section Four: Traits, Genes, and Alleles Gene: a piece of DNA that provides a set of instructions to a cell to make a certain protein Consists of two alleles: an alternate form of a gene Homozygous: when the two alleles are the same Heterozygous: when the two alleles are different

Section Four: Traits, Genes, and Alleles Genes and Traits Genome: all of an organism’s genetic material Genotype: the genetic makeup of a specific set of genes Codes for phenotype Phenotype: physical traits

Section Four: Traits, Genes, and Alleles Genotype Determination Depends on dominant and recessive alleles Dominant allele: the allele that is expressed when two different alleles or two dominant alleles are present Recessive allele: the allele that is expressed only when two copies of it are present

Section Four: Traits, Genes, and Alleles Phenotype 2 genotypes can produce the dominant phenotype Ex: BB and Bb Only 1 genotype can produce the recessive phenotype Ex: bb

Section Five: Traits and Probability Punnett Squares A grid system for predicting possible genotypes resulting from a cross

Section Five: Traits and Probability Punnett Squares Monohybrid Cross: crosses that examine the inheritance of only one specific trait Homozygous crossed with homozygous Heterozygous crossed with heterozygous Homozygous crossed with heterozygous Test cross: a cross between an organism with an unknown genotype and an organism with the recessive phenotype

Section Five: Traits and Probability Punnett Squares Dihybrid Crosses: crosses that examine the inheritance of two different traits Law of Independent Assortment: the allele that pairs separate independently of each other during gamete formation

Section Five: Traits and Probability Heredity Patterns and Probability Probability: the likelihood that a particular event will happen

Section Six: Meiosis and Genetic Variation Unique Combinations Sexual reproduction creates a unique variety of traits Homologous chromosome pairing

Section Six: Meiosis and Genetic Diversity Crossing Over and Genetic Diversity Crossing Over: the exchange of chromosome segements between homologous chromosomes during prophase I of meiosis I.

Section Six: Meiosis and Genetic Variation Genetic Linkage Genes located close together tend to be inherited together