The Cellular Basis of Inheritance Chapter 9 The Cellular Basis of Inheritance

Reproduction Asexual – process in which a single cell or set of cells produces offspring that inherit all their genetic material from one parent Ex. Binary fission – bacteria Sexual – process in which genetic material from two parents combines and produces offspring that differ genetically from either parent Fertilization – egg fuses with sperm (zygote) Cellular division – division of the genetic material of a cell in which two new cells are created

Chromosome Structure Nucleus – control center of cell Contains DNA Chromatin – thin fibers of protein and DNA found in a non-dividing cell Chromosomes – Condensed, coiled, chromatin, that forms in dividing cells Chromatid (sister) – each half of a duplicated chromosome Centromere – Site of attachment for chromatids

Chromosome Structure

Chromosome Numbers Each species has a characteristic number of chromosomes Humans – 46, 23 pairs Fruit Flies – 8 Chimps – 48 Carrot - 18

Chromosome Numbers Male XY Female XX Humans Sex Chromosomes (2) Determine the sex Male XY Female XX Autosomal Chromosomes (44)

Chromosome Numbers Homologous Chromosomes – One of a pair of morphologically similar chromosomes (mother, father) Carry genes for the same traits Karyotype – a technique for examining the chromosome makeup of an individual

Chromosome Numbers Somatic cells – body cells Diploid (2N) Cells that contains 2 of each type of chromosome Somatic cells – body cells Haploid (1N) Cells that contain only 1 set of chromosomes Germ cells – those that give rise to gametes

Cell Cycle Cell Cycle Sequence of events from the production of a eukaryotic cell to the time the cell itself reproduces Three Stages in the cell cycle Interphase Mitosis Cytokinesis

Cell Cycle Interphase Period of cell growth and development before cell division (90% cells life) 3 Phases of Interphase G1 – Time of cell growth S – Cells DNA is copied (replicated) G2 – Cell prepares for division

Cell Cycle Mitosis Cell (nuclear) division in which the number of chromosomes is kept the same from parent cells to daughter cells 2N parent cell creates 2 diploid daughter cells 4 stages of Mitosis Prophase Metaphase Anaphase Telophase

Cell Cycle Mitosis Spindle – football shaped framework of microtubules Prophase 1. Each duplicated chromosome (consisting of two sister chromatids) condenses from thread-like form to rod-like form 2. Nuclear envelope and nucleolus disappear 3. Centrosomes form and move to opposite ends of the cell and give rise to spindle fibers Spindle – football shaped framework of microtubules

Cell Cycle Mitosis Metaphase (midway between) Spindle fibers (microtubules) attach to the centromeres of the chromosomes and align them in the center of the cell (spindle equator)

Cell Cycle Mitosis Anaphase Sister chromatids of each chromosome separate and move to opposite poles Each chromatid is now its own “daughter” chromosome

Cell Cycle 1. Chromosomes return to threadlike form Mitosis Telophase 1. Chromosomes return to threadlike form 2. Nuclear envelopes begin to reform and separate the 2 new sets of chromosomes 3. Spindle fibers disassemble 4. Nucleolus forms in each of the newly forming cells

Cell Cycle Cytokinesis Division of the cytoplasm Splitting of a parent cell into daughter cells Plants Cell plate – vesicles containing cell wall building substances fuse together and separate the two new cells Animals Cleavage furrow – area of cell membrane that pinches inward until 2 new cells are formed

Mitosis Video Clip

Meiosis Meiosis Cell (nuclear) division in which the chromosome number is cut in half 2N cell divides to form 4 (1N) cells Two cell divisions – 2 stages Meiosis I Prophase I, Metaphase I, Anaphase I, Telophase I Meiosis II Prophase II, Metaphase II, Anaphase II, Telophase II

Meiosis Prophase I 1. Chromosomes condense to rod-like form 2. Nucleolus and nuclear membrane disappear 3. Centrosomes form and move to poles, give rise to spindle fibers 4. Homologous chromosomes pair up creating a tetrad (4 chromatids) Crossing over – part of chromatid may break off and attach to adjacent chromatid on the homologous chromosome Genetic recombination – regrouping of genes due to an exchange of maternal and paternal genetic material

Meiosis Metaphase I Spindle fibers attach to the centromeres, and homologous pairs line up side by side (tetrad) on the spindle equator

Meiosis Anaphase I Homologous chromosomes are separated and moved to opposite poles

Meiosis Telophase I Cytokinesis occurs and produces 2 haploid (1N) cells Each new cell contains one chromosome from each homologous pair

Meiosis Prophase II Spindle fibers form and attach themselves to the centromeres of the chromosomes

Meiosis Metaphase II Chromosomes are moved to the equator of the cell

Meiosis Anaphase II Chromatids separate and move toward opposite poles of the cell

Meiosis Gametes (sperm, egg) Telophase II 4 daughter nuclei Each cell has a haploid chromosome number and all are in the unduplicated state Gametes (sperm, egg)

Meiosis Video Clip