Transcript Ch.6: Chromosomes and Cell Reproduction

Ch.6: Chromosomes and Cell
Reproduction
Biology
Cell Division/Cell Reproduction
2 Main Types of Cell Reproduction
1) Asexual-requires only one parent
Ex: Bacterial Cells reproduce by
Binary fission- a) single circular DNA is
copied, b) cell divides into 2 cells
Each cell is identical to the other.
2) Sexual-requires two parents
involving the union of 2 gametes (sex
cells)
• Eukaryotic cells form chromosomes before cell
divisions.
Gene-segment of DNA that codes for a protein or
RNA molecule. Before the cell divides, DNA is
copied and then begins to coil up into
chromosomes.
Chromosome-structure made up of DNA and
proteins
A chromosome is made up of 2 chromatids
joined together by a centromere.
Somatic Cells
• Somatic Cells-are all the cells in the body other
than the gametes. They contain 23 pairs of
different chromosomes or a total number of 46.
Body cells have 2 sets of chromosomes, one set
from each parent. They are diploid (2n). These
chromosomes differ in size, shape, and the
genes they carry.
• Each of the 23 pairs of chromosomes are made
up of homologous chromosomes (which means
they are similar in size, shape, and the genes
they carry).
Gametes
• Gametes-egg and sperm. They are
haploid which means they have 1 set of
chromosomes (n).
• When egg(n) and sperm(n) unite, they
form 1 cell called a zygote (2n). A zygote
is a fertilized egg cell. A zygote repeatedly
divides by mitosis to form a complete
organism.
• Human somatic cells have 23 pairs of
chromosomes. 22 of the 23 pairs are
called autosomes. Autosomes are
chromosomes that are NOT involved in
determining the sex of an individual.
Sex Determination
• The 23rd pair (sex chromosomes)
determine the sex of an individual.
The 2 sex determining chromosomes: X
chromosome and Y chromosome.
Egg and sperm carry 1 copy of each
autosome and 1 copy of sex chromosome.
• The egg always carries an X chromosome.
• The sperm may carry an X or Y.
Females: XX
Males: XY
**It is the presence or absence of the Y
chromosome that determines the sex of
the individual.**
Karyotype-a picture of the chromosomes
found in an individual’s cells.
Cell Cycle – repeating sequences of cellular
growth and division during the life of an
organism; cell spends 90% of its time in the
first 3 phases of the cell cycle which is
collectively known as interphase.
1) Interphase - a) “First growth” (G1)-cell grows
& carries out normal functions; cell spends
most time here; cells not dividing stay here; b)
“Synthesis” (S)-DNA is copied; c) “Second
Growth” (G2)-cell prepares for division by
assembling more membranes & microtubules.
2) Mitosis – division of nucleus and
chromosomes (Prophase, Metaphase,
Anaphase, & Telophase)
3) Cytokinesis – the process during which the
cytoplasm divides and results in 2 cells.