Chapter 6 Chromosomes Cell Reproduction 1 Prokaryotic bacterium

Chapter 6 Chromosomes & Cell Reproduction 1

Prokaryotic (bacterium) Cell Division Binary fission is form of asexual reproduction. Binary fission produces identical offspring Binary fission is the process by which bacteria reproduce 2

Eukaryotic cell reproduction Gametes – sex cells Male – Human sperm cell (23 chromosomes) Female – Human egg cell (23 chromosomes) Gametes – haploid cells (n number) Haploid number is ½ the organism’s body cell chromosome number. Human sperm and egg have 23 chromosomes. Humans the haploid number is 23 The symbol used to designate the haploid number is n 3

In humans gametes contain 22 autosomes and 1 sex chromosomes Males – sperm with either an x or y chromosome In human males determine the sex of child b/c males have one x and one y chromosome. The X and Y chromosome are called the sex chromosomes Female : XX : : male : XY 4

Chromosomes/Genes Chromosomes are made up of DNA, Genes and Protein. The DNA in Eukaryotic cells is packaged into structures called chromosomes. Chromatids – two exact copies of chromosome Genes on chromosomes are the units of inheritance A Gene is a segment of DNA that direct the production of a specific protein A gene is a segment of DNA that carries the instructions for producing a specific trait There are 1, 000’s of genes on a DNA molecule 5

The point at which two chromatids are attached to each other in a chromosome is called a centromere A picture of a cell’s chromosome is called a Karyotypes can be studied to lean about the number and structure of a chromosome in a somatic cell 6

Sets of chromosomes Homologous chromosomes – chromosomes that are similar to each other Somatic chromosomes are called body cell chromosomes Somatic cells – contain the diploid or 2 n number of chromosomes In humans the diploid number is 46 Gametes – sex chromosomes 7

Egg cell has 23 chromosomes and a sperm cell has 23 chromosomes. A Zygote has 46 chromosomes. A zygote is a fertilized egg cell. A diploid cell is one that – has two homologues of each chromosome – is designated by the symbol 2 n – Has chromosomes found in pairs 8

Change in chromosome number Each of an individual’s 46 chromosomes has thousands of genes. Sometimes an individual can have an extra copy or be missing one or more chromosomes. The failure of replicated chromosomes to separate is called nondisjunction A mutation in which a piece of a chromosome is lost during meiosis is called deletion 9

Abnormal syndromes Down’s syndrome – In humans, this is a specific condition caused by an extra chromosome 21 Down’s syndrome is also called trisomy 21 because it is a mutation that results in a cell having an extra chromosome People with Down’s syndrome have 47 chromosomes instead of 46 10

Human chromosomes – Exist in 23 pairs in all cells but gametes – Each contain thousands of genes – Form right before cells divide In order to fit within a cell , DNA becomes more compact by wrapping tightly around associated proteins. The shape of a bacterium’s chromosome is circular 11

1. How many chromosomes are in the body cell of an organism with the haploid number of 8? ____ 2. Diploid number is 46 then what is the number of chromosomes found is a human ovum ? ___ 3. Diploid : somatic : : haploid : ______ 12

1. 16 If the haploid or sex chromosome number was 8 then Diploid (2 n) would be 2(8)=16 2. 23 If the diploid number was 46 then the haploid number would be ½ which is 46/2 = 23 3. Gamete Diploid cell and somatic cell are the same. Therefore what word means the same as haploid? Gamete is the same as haploid 13

The Cell Cycle Section 2 CELL CYCLE – sequence of events that occurs in a cell from one mitotic division to the next. Normal cell growth and cell division are stimulated by PROTEINS The information needed by a cell to direct its activities and to determine its characteristics is contained in molecules of DNA After cell division, each new cell will contain the same genetic information as the original cell. Asexual reproduction can occur by mitosis 14

Cell Cycle Cell cycle (G 1 – S – G 2 – M – C) – Interphase G 1 – first growth phase S phase – Synthesis phase G 2 – 2 nd growth phase – Mitosis Prophase Metaphase Anaphase Telophase – Cytokinesis Cytoplasm divides 15

Interphase is the phase that the cell cycle occupies most of the cell’s life Cell spends 90% of its time in this phase The first three phases of the cell cycle are collectively known as Interphase 16

Section 3 Mitosis – is a process by which the nucleus is divides into two nuclei Mitosis – is a process by which a cell’s nucleus divides Spindles – structures that will move chromosomes during cell division A spindle fiber is a specialized from of microtubule Stages of Mitosis Prophase Metaphase Anaphase Telophase 17

Prophase – 1 st stage of mitosis - Chromosomes coil up into short, fat rods - Chromosomes coil up and become visible - The nuclear membrane dissolves 18

Metaphase/Anaphase/Telophase Metaphase - The arrangement of all chromosomes along the equator of the cell Anaphase – – The stage in which the centromeres divide. – Chromosomes move toward opposite poles Telophase– Spindle dissolves – Nuclear membrane forms around each set of new chromosomes – Chromosomes uncoil – Cell membrane begins to pinch inward – In plant cells = a cell wall begins to form 19

Cytokinesis – last stage of the cell cycle Mitosis ends and Cytokinesis begins Cytokinesis - Cytoplasm of the cell is divided into half, and the cell membrane grows to enclose each cell. After mitosis and cytokinesis, each new cell has a complete set of the parent’s chromosomes 20

Plant and Animal cells both undergo cell division Plant and animal cells have different strategies for cytokinesis Animal cell - cell division – No cell wall – Cell membranes form Plant cell – cell division – Cell membrane forms – Cell Wall Forms Cytokinesis in plant cells involves the formation of a cell plate 21

CANCER Cancer is a disease characterized by uncontrolled cell growth Normal cells become cancerous when – Regulation of cell growth and division is lost – Cell’s do not respond normally to control mechanisms – Cells continue to divide without passing through G 1 22

Pg 130 Be able to place sketches in correct order for mitosis Prophase Metaphase Anaphase Telophase 23