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Genes
 A gene is the entire
sequence of DNA bases
responsible for the
synthesis of a protein.
 A mutation occurs when
the sequence of bases in a
gene is altered.
 Mutations may interfere
with the ability to produce
vital protein and may lead
to a new variety within the
species, hence, evolution.
Genes
 Recently, geneticists have
learned that only some
parts of genes, called
exons, are actually
transcribed into mRNA
(most of the nucleotide
sequences in genes are
not expressed during
protein synthesis.
 Some noncoding
sequences, called introns,
are initially transcribed
into mRNA and then
clipped out.
Regulatory Genes
• Genes that code for the production of
proteins that can bind to DNA and modify the
action of genes.
• Many are active only during certain stages of
development.
Homeobox Genes (Hox genes)
• An evolutionarily ancient family of regulatory
genes (highly conserved) that directs the
development of the overall body plan and the
segmentation of body tissues.
Homeobox mutation
Cell Division
 Cell division results in production of new cells.
 During cell division:
 Cells are involved with normal cellular and metabolic
processes.
 The cell’s DNA becomes tightly coiled.
 DNA is visible under a microscope as chromosomes.
Chromosome Structure
• A chromosome is composed of a DNA
molecule and associated proteins.
• During normal cell functions, chromosomes
exist as single-stranded structures.
• During cell division, chromosomes consist of
two strands of DNA joined at the centromere.
• Since the DNA molecules have replicated, one
strand of a chromosome is an exact copy of
the other.
Chromosomes and Genetics
• Each species is characterized by a specific
number of chromosomes (see chart on pg.
59).
– Humans have 46 chromosomes.
Housefly 12
Corn 20
Humans 46
Chicken 78
Types of Chromosomes
 Autosomes - govern all physical characteristics
except sex determination.
 Sex chromosomes - X and Y chromosome.
 Mammal females have two X
chromosomes.
 Mammal males have one X and one Y
chromosome.
Mitosis
• Mitosis is cell division in somatic cells.
• Mitosis occurs during growth and
repair/replacement of tissues.
• The result of mitosis is two identical daughter
cells that are genetically identical to the
original cell.
• Here’s the steps…
Mitosis
• The cell is involved
in metabolic
activities.
• DNA replication
occurs, but
chromosomes are
not visible.
Mitosis
• The nuclear
membrane
disappears, and
double-stranded
chromosomes are
visible.
Mitosis
• The chromosomes
align themselves at
the center of the
cell.
Mitosis
• The chromosomes
split at the
centromere, and the
strands separate and
move to opposite
ends of the dividing
cell.
Mitosis
• The cell membrane
pinches in as the cell
continues to divide.
• The chromosomes
begin to uncoil
(below).
Mitosis
• After mitosis is
complete, there are
two identical
daughter cells.
• The nuclear
membrane is
present, and
chromosomes are
no longer visible.
Meiosis
• Cell division in specialized cells in ovaries and
testes.
• Meiosis involves two divisions and results in
four daughter cells, each containing only half
the original number of chromosomes.
• These cells can develop into gametes.
Problems with Meiosis
• In order for fetal development to occur
normally, the meiotic process needs to be
exact
• If chromosomes or chromosome strands do
not separate during either of the two
divisions, serious problems can develop
• Failure to separate is called nondisjunction
Recombination
• Sometimes called crossing over; the exchange
of genetic material between partner
chromosomes during meiosis.
Mitosis
Meiosis
Evolutionary
Significance of Meiosis
• Meiosis and sexual reproduction are highly
important evolutionary innovations.
• Meiosis increases genetic variation at a faster
rate than mutation.
• Offspring in sexually reproducing species
represent the combination of genetic
information from two parents.
Recombinant DNA Technology
• A process in which genes from the cell of one
species are transferred to somatic cells or
gametes of another species.
• Human genes inserted into bacterium produce
genetically-needed material like Insulin.
• Genetic manipulation…
Clones
 Organisms that are genetically identical to another
organism.
 The term may also be used in referring to genetically
identical DNA segments, molecules, and cells.