Outline 10A: Chromosomes 5/24/2019 Outline 10A: Chromosomes 5/24/2019

I. Cell Division A. Production of new cells B. Also called cell reproduction C. Used for: 1. Growth & development 2. Repairing wounds 3. Reproduction a. Asexual - makes copies of cells b. Sexual - makes gametes, the reproductive cells 5/24/2019

D. Bacterial Cell Division 1. Bacteria have a single DNA strand a. It is circular & attached to cell membrane 2. They divide by a type of cell division called binary fission a. DNA is copied b. Bacterium divides in two  Grows new membrane & cell wall in between two DNA molecules c. End up with 2 identical bacteria (form of asexual reproduction) 5/24/2019

II. Eukaryotic Chromosomes A. Gene 1. Segment of DNA that codes for a protein or RNA molecule B. When DNA is being used it is stretched out long and thin, called chromatin C. As a eukaryotic cell prepares to divide, however, the DNA & its associated proteins, called histones, coil up into a structure called a chromosome 5/24/2019

D. Structure of a Chromosome 1. Chromosomes have 2 identical copies of DNA attached together. These are called chromatids a. This is because the DNA copies itself before cell division 2. The chromatids are attached at a point called the centromere 3. The chromatids will become separated from each other during cell division 5/24/2019

Centromere Sister chromatids

E. Drawing of a Chromosome Chromatid Chromatid Centromere 5/24/2019

F. Chromosome Numbers 1. Each human body cell has 23 pairs of chromosomes, for a total number of 46. This type of cell is called a somatic cell. 2. The 23 chromosomes differ in size, shape, and types of genes they carry. 3. Each chromosome contains thousands of genes for many different functions 5/24/2019

4. Sets of Chromosomes a. Each pair of chromosomes consists of two homologous chromosomes  These are chromosomes that are similar in size, shape, and genetic content  Each homologue comes from one of the two parents: 23 chromosomes from mother 23 chromosomes from father 5/24/2019

5. Chromosome Terminology a. If a cell contains two complete sets of chromosomes it is said to be diploid  Most cells in the human body are diploid b. If a cell contains only one set of chromosomes it is said to be haploid  This is only found in gametes (eggs or sperm in humans) 5/24/2019

6. Chromosome Symbology a. The symbol N is used to represent the number of chromosomes in one set of chromosomes.  This means the haploid number In humans, N= 23 b. 2N is used to represent the number of chromosomes in two complete sets of chromosomes  This means the diploid number In humans, 2N = 46 5/24/2019

c. Fertilization  When 2 haploid gametes fuse (Sperm fertilizes the egg)  The resultant fertilized egg now has two sets of chromosomes and is diploid (2N)  This cell is now called a zygote 5/24/2019

7. Chromosome Diversity a. Each organism has a characteristic number of chromosomes b. Table of Chromosome Numbers Organism Diploid # Haploid # Housefly 12 ? Frog ? 13 Mosquito 6 ? Dog ? 39 Orangutan 48 ? 5/24/2019

G. Chromosomes & Sex 1. 22 of the 23 pairs of human chromosomes are called autosomes a. These are chromosomes that are NOT directly involved in determining gender (sex) 2. 1 of the pairs IS directly involved & will determine sex of individual a. These are called the sex chromosomes 5/24/2019

3. In humans, the chromosomes are referred to as X and Y a. Genes on the Y chromosome cause a zygote to become male  Males = XY Females = XX 4. Since a female can only give her offspring an X chromosome, the sex of offspring is determined by the male 5. Other species have different sex chromosomes situations 5/24/2019