Transcript Chapter 6 Advanced Genetics

Chapter 6
Advanced Genetics
Section 6A
Chromosome and Gene Changes
Two types of Gene Changes
Chromosomal changes – the # of chromosomes or the
arrangement of genes on a chromosome
Gene Mutations – a change in the sequence of bases in
a gene.
Changes affecting # of Chromosomes
A genome is a complete haploid set of its
chromosomes.
A diploid cell has two complete genomes.
Review haploid and diploid cells if this is confusing.
Diploid organisms, like us, have to go through meiosis
to produce haploid gametes (either sperm or eggs).
Parthenogenesis
There are examples of haploid organisms.
These come from the development of unfertilized eggs.
This is called Parthenogenesis
An example of this in the natural world is worker
honey bees.
Euploidy
A chromosome number that is a multiple of the
haploid number (N).
For Example, the human haploid number is 23, this is
N. Our diploid chromosome number is 46, which is
2N.
Organisms can be polyploid, which means they can
have three or more genomes.
Euploidy (cont.)
n – one genome
2n (diploid) – two sets of the same genome
3n (triploid) – three sets of same genome
4n (tetraploid) – four sets of same genome
Liver cells in humans are tetraploid.
Polyploids
Many of the crops that we plant today are good
examples of polyploids.
Corn, wheat, cotton, seedless watermelons.
Polyploids can be produced by using colchicine to stop
the formation of the spindle fibers during mitosis.
This will from diploid gametes.
2n + 2n = 4n (tetraploid)
Aneuploidy
Lacking or have extra chromosomes
2n + 1 or trisomy
2n – 1 or monosomy
A chromosome will fail to separate during meiosis.
This is called nondisjunction.
Examples are Downs, Klinefleters, Turners, Trisomy X
Mutations
A change in the DNA of an organism
Think of the Chromosomes as a bead of pearls, like a
necklace. This necklace can be broken and repaired.
The repair can be out of order and moved, thus
causing a rearrangement of the genes.
Translocation
Remember crossing over in Meiosis. This is one form
of Translocation.
One piece of a chromosome coming loose and
attaching to another chromosome.
But this can also happen with nonhomologous
chromosomes and cause real problems.
Deletion
A complete loss of a section of chromosome is called
Deletion.
The piece that comes loose leaves the nucleus of the
cell and disintegrates.
This is harmful, if the other homologous chromosome
has a “bad” recessive gene and the dominant “normal”
gene is the one that is lost.
Cri du Chat
Inversion
Inversion is a segment of the chromosome breaks off
and reattaches at the same spot, but it is in reverse
order.
Gene Mutations
When one nucleotide is changed is called a point
mutation.
Examples are:
Substitution
Addition
deletion
Biological Effects of Mutations
Spontaneous mutations happen naturally
Mutagens can also induce mutations. Mutagens are gases,
chemicals, or radiation.
Somatic mutations are mutations in somatic cells (non-sex
cells)
Germ Mutations is a mutation in a cell that forms gametes.
Gene Expression
Gene expression is the activation or turning on of a
gene that results in its transcription and the
production of a specific protein.
Morphogenesis is a change in the form that an
organism undergoes, this is controlled by the
expression of genes.
Controls of gene expressions
Sex-linked characteristics are the results of gene
expression.
The presence or absence of sex hormones turns on or
off the genes that code for sex-limited characteristics.
EX. Feathers of birds, body hair, breast development.
Controls of gene expressions
Environmental Factors, temperature, light, chemical,
nutrients.
Temperature on the fur of the Himalayan rabbit.
Ice pack on the ears turns fur black, while heat turns
fur white.
Cancer
Cells that are not responsive to the normal controls of
the cell cycle.
Two genes that regulate the cell cycle are:
Proto – oncogenes – code for proteins that stimulate
cell division.
Tumor suppressor genes – Prevent uncontrolled cell
growth.
There has to be a balance between these two.
Chapter 6
Population Genetics
A population is a group of individuals of the same
species that live in the same area.
Gene pool is a sum of all of the alleles that all
members of an organism could possess.
The genotypic differences between individuals form the
same gene pool are called variations.