Name _____________________________
Notes – Ms. Banas
Chapter 6 Section 1 Chromosomes Pages 118-124
Formation of New Cells by Cell Division
•Cell division, also called cell reproduction, occurs in humans and other
organisms at different times in their life.
•The formation of gametes involves yet a special type of cell division. Gametes
are an organism’s reproductive cells, such as sperm or egg cells.
•When a cell divides, the DNA is first copied and then distributed
Prokaryotic Cell Reproduction
•Prokaryotes reproduce by a type of cell division called binary fission.
•Binary fission is a form of asexual reproduction that produces identical offspring.
•In asexual reproduction, a single parent passes exact copies of all of its DNA to
its offspring.
•Binary fission occurs in two stages: first, the DNA is copied (so that each new
cell will have a copy of the genetic information), and then the cell divides.
•Eventually the dividing prokaryote is pinched into two independent cells.
1
Name _____________________________
Notes – Ms. Banas
Eukaryotic Cell Reproduction
•A gene is a segment of DNA that codes for a protein or RNA
molecule.
•When genes are being used, the DNA is stretched out so that the
information it contains can be used to direct the synthesis of proteins.
•As a eukaryotic cell prepares to divide, the DNA and the proteins
associated with the DNA coil into a structure called a chromosome.
•The two exact copies of DNA that make up each chromosome are
called chromatids.
•
•The two chromatids of a chromosome are attached at a point called
a centromere.
•
•The chromatids, which become separated during cell division and
placed into each new cell, ensure that each new cell will have the
same genetic information as the original cell.
2
Name _____________________________
Notes – Ms. Banas
How Chromosome Number and Structure Affect Development
Sets of Chromosomes
•Homologous chromosomes are chromosomes that
are similar in size, shape, and genetic content.
•
•Each homologue in a pair of homologous
chromosomes comes from one of the two parents.
•
•The 46 chromosomes in human somatic cells are
•When a cell, such as a somatic cell, contains two sets of chromosomes, it is said
to be diploid.
•
•When a cell, such as a gamete, contains one set of chromosomes, it is said to
be haploid.
•
•The fusion of two haploid gametes—a process called fertilization—forms a
diploid zygote. A zygote is a fertilized egg cell.
Chromosome
Number of
Various
Organisms
Sex Chromosomes
•Autosomes are chromosomes that are not directly involved in determining
the sex (gender) of an individual.
•
•The sex chromosomes, one of the 23 pairs of chromosomes in humans,
contain genes that will determine the sex of the individual.
•
•In humans and many other organisms, the two sex chromosomes are referred
to as the X and Y chromosomes.
3
Name _____________________________
Notes – Ms. Banas
Change in Chromosome Number
•Humans who are missing even one of the 46 chromosomes do not
survive.
•
•Humans with more than two copies of a chromosome, a condition
called trisomy, will not develop properly.
•
•Abnormalities in chromosome number can be detected by analyzing
a karyotype, a photo of the chromosomes in a dividing cell that
shows the chromosomes arranged by size.
Change in Chromosome Structure
•Changes in an organism’s chromosome structure are called
mutations.
•
•Breakage of a chromosome can lead to four types of mutations:
1. deletion mutation
2. duplication mutation
3. inversion mutation
4. translocation mutation
Karyotype
4
Name _____________________________
Notes – Ms. Banas
5