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

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 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

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. Centrioles 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 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

The Formation of Gametes

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 Telophase II

4 daughter nuclei Each cell has a haploid chromosome number

and all are in the unduplicated state Gametes (sperm, egg)

Meiosis Video Clips

pull up video on flash drivecopy & paste address:

http://highered.mheducation.com/sites/0072507470/student_view0/chapter28/animation__how_meiosis_works.html