1. Chapter 8
Cell Reproduction
Introduction to Chromosomes

2. Important Words
 Chromosomes – tightly coiled  Strands of DNA wrap
packages of DNA; they are rod around proteins called
shaped and proteins hold them Histones.
together.

4. Important Words
 Chromatid – each half of
a chromosome; forms as
DNA copies itself before
cell division
 Centromere – holds the
chromatids together until
they separate

5. Important Words
 How many chromosomes
do humans have?
 Each species has a unique
number of chromosomes.  46 chromosomes or 23
pairs.

6. Types of Chromosomes
 2 Types of Chromosomes:
 1. Sex Chromosomes – are the chromosomes that
determine the sex of an organism.
 Female: XX
 Male: XY
 2. Autosomes – all other chromosomes
 Humans: 44 autosomal chromosomes

7. Karyotype: Picture of
Chromosomes. What do you
notice about the arrangement?

8. Chromosomes
 Karyotype – is a picture
of the chromosomes in
a somatic (body) cell.
 22 homologous pairs
of autosomes.
 2 sex chromosomes
 Is this person male
or female?
 Male: XY
 Normal or abnormal
 Normal: 23 pairs

9. Chromosomes
 Homologous chromosomes – two
copies of each autosome (maternal and
paternal)
 Homologous chromosomes are the
same size, shape, and carry genes for
the same trait.
 Final pair is not numbered: Sex
Chromosomes.

10. Compare the karyotypes.
Record your observations
Karyotype A Karyotype B

11. Comparisons
Karyotype A Karyotype B
 19 pairs: Not Human  23 pairs: Human
 Sex: Male (XY)  Sex: Female (XX)
 Sister chromatids are still  Single Copy of each
attached at their chromosome.
centromeres (these are  This picture was taken
double copies of each AFTER the cell divided!
chromosome).  Be prepared to analyze a
 This is a picture karyotype regardless of
BEFORE the cell divided! when the picture of the
chromosomes was taken.

12. Human Karyotype: Male

13. Human Karyotype: Female

14. Chromosomes
 Diploid – cells have two sets (maternal and
paternal) of chromosomes.
 Have all 46 chromosomes.
 Represented by 2n (means a full set of DNA)
 Somatic Cells (cells making up the body)
 Haploid – cells have one set of
chromosomes.
 Have 23 chromosomes.
 Represented by n (means a half set of DNA)
 Gametes (reproductive cells : egg and sperm)

15. Haploid Cells
 Reproductive Cells
 Gametes - sperm and
egg cells; they have 23
chromosomes
 Fertilization 23 in
sperm + 23 in egg =
46 in zygote
 Gametes are produced
through Meiosis (cell
division results in 4
genetically different
cells)

16. Diploid Cells
 Somatic Cells
 Cells that make
up the body of
organisms.
 Somatic Cells are
produced through
Mitosis (cell
division results in
2 genetically
identical cells).