Honors Genetics
Chapter 2: Mitosis and Meiosis
INTRODUCTION:
Every living thing, except some viruses, contains DNA as the genetic material that
houses the information to control the structure and function of the organism.
A molecule of DNA is organized into units called genes, the products direct the
metabolic activities of cells.
DNA is organized into chromosomes which serve as the vehicles for transmitting
genetics information. Chromosomes are only visible during mitosis and meiosis.
During Interphase, when the cell’s nucleus is not dividing, DNA is organized as
chromatin (spaghetti on a plate).
Mitosis: leads to the production of two new cells, each with the same number of cells
as the original parent cell. Occurs in somatic (body) cells.
Meiosis: reduces the genetic content and the number of chromosomes precisely in
half. This reduction is essential if sexual reproduction is to occur without doubling the
amount of genetic information in each generation. Occurs in gamete (sex) cells.
2.1: Cell Structure is Closely Tied to Genetic Function
Prokaryotic Cell
Example: bacteria
Eukaryotic Cell
Example: animal and plant cells
Lacks nucleus
Contains nucleus
Lacks membranous organelles
Contains membrane-bound organelles
DNA present as long, circular PLASMID
compacted in nucleoid area
DNA contained within nucleus as
chromatin
DNA does not coil into chromosome prior
to cell division
DNA does coil into chromosome prior to
mitosis and meiosis
STRUCTURE
Plasma (cell) membrane
GENERAL FUNCTION
GENETIC FUNCTION
Glycocalyx
Nucleus
Chromatin
Chromosomes
Nucleolus
Cytoplasm
Endoplasmic reticulum
Mitochondria
Chloroplasts
Centrioles
Spindle fibers
2.2: Chromosomes Exist in Homologous Pairs in Diploid Organisms
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Each chromosome contains a constricted region called the centromere; this
provides a general appearance of each chromosome.
o p arm = shorter arm above the centromere. (p = petite)
o q arm = longer arm below the centromere
Chromosome classification based on centromere location
o Metacentric
o Submetacentric
o Acrocentric
o Telocentric
Diploid number: (2n)
o Homologous chromosomes: each pair of diploid chromosomes with
identical size, shape, and centromere location. Contains identical
genes.
 Locus: identical gene sites on homologous pairs.
 In humans, all chromosomes EXCEPT sex chromosomes, the
23rd pair are homologous.
 Alleles: alternative forms of a gene; provides variation in traits.
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o Karyotype: human mitotic chromosomes are photographed, printed,
and cut out to match with their homologous pairs.
o Sister chromatids: identical side of chromosome held together by a
centromere; allowed to separate into two daughter cells during cell
division.
Haploid number: (n)
o Equal to one half the diploid number.
o Contains the genome of the species.
Essential point: In diploid organisms, chromosomes exist in homologous pairs; one coming
from the maternal parent and one from the paternal parent.
2.3: Cell Cycle Clock
INTERPHASE
G0:
G1:
G2:
MITOSIS