Download Chromosomes and Cell Reproduction

Chromosomes and Cell
Reproduction
Chromosome structure and role in
development and reproduction
What allows a few cells to grow into a
human being?
During cell division, what allows each
cell to receive the proper genes?
Objectives
• Identify examples of cell division in prokaryotes
and eukaryotes
• Distinguish between a gene, a DNA molecule, a
chromosome, and a chromatid
• Differentiate between homologous
chromosomes, autosomes, and sex
chromosomes
• Compare haploid and diploid cells
• Predict how changes in chromosomes can affect
development
Why cell division?
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Growth
Tissue repair
Replace worn out cells
Asexual reproduction
Why are we interested in
chromosomes?
• Vitally important that each
new cell receives the proper set
of chromosomes to function
properly
• Each organism has a
characteristic number of
chromosomes
• We need to understand the
structure of chromosomes and
the role of chromosomes in the
cell
Different types of cell division – all
involve passing on DNA
• Bacterial cell division – Binary Fission
• Division of body cells in eukaryotes - Mitosis
• Formation of gametes (reproductive cells) in
eukaryotes - Meiosis
Prokaryotic Cell Division
• Called Binary Fission
• Form of asexual reproduction
• Single parent passes on exact
copies of all DNA to offspring
• First stage = single circular
DNA molecule is copied
• Second stage = Cell divides
Eukaryotic Cell Division
• Much more complicated
process due to larger amount
of genetic information (genes)
• Genes = segment of DNA that
codes for a protein or RNA
molecule
• When genes being used, DNA
(chromatin – DNA and its
associated proteins) is
stretched out
• Before cell division, DNA must
divide and then coil up into
chromosomes
Chromatids and Centromere
• Chromatids will become
separated during cell division
• 1 Chromatid will be placed into
each new cell
• This ensures that each new cell
will have the same genetic
material as the original cell
Chromosome Number and Structure
• Each human body cell
(excluding sperm and egg
cells) has 2 copies of 23
different chromosomes
• Total chromosomes = 46
• Each chromosome contains
thousands of genes
• Genes play important role in
how person’s body develops
and function
Homologous Chromosomes
• Each pair of chromosomes =
homologous chromosomes
• Chromosomes similar in size,
shape and genetic content
• Each homologue comes from
one of the two parents
• One set = Ma
• One set = Pa
Somatic Vs Sex Cells =
Diploid Vs Haploid
• Body cells (non-sex cells) = somatic cells
• A cell that contains 2 sets of chromosomes (i.e. a somatic cell) =
diploid or 2n
• A cell that contains only one set of chromosomes (i.e. a sex cell or
gamete) = haploid or n
• For humans n = 23. That is how many chromosomes our gametes
have. 2n = 46. That is how many chromosomes our somatic cells
have
Zygote
• Fusion of two haploid
gametes = fertilization
• Diploid zygote formed by
fertilization = first cell of
a new individual
Different Types of Chromosomes
Autosomes
Sex Chromosomes
• Chromosomes that are not
directly involved in
determining the sex (gender)
of an individual
• One of the 23 pairs of
chromosomes in humans
• Determine the sex of the
individual
• Humans and many other
animals - X and Y
chromosomes
• Anyone with a Y chromosome
is male.
• Female = XX; Male = XY
• Female can only give an X, so
sex of offspring determined by
father
Change in chromosome number
• Genes help determine how body
develops and functions
• All 46 chromosomes must be
present for normal
development/function
• Too many or too few
chromosomes leads to problems
• Abnormalities in chromosome
number detected by a karyotype
- a photo of chromosomes in
dividing cell - shows
chromosomes arranged by size
Down Syndrome – Trisomy 21
• Extra copy of chromosome 21
• Short stature, round face,
mental retardation
• Occurs more frequently in
older mothers
• Mothers younger than 30 – 1
in 1500 births
• Mothers over 45 – 1 in 46
births
How does someone end up with an
extra chromosome?
• When sperm and egg cells
form (during meiosis) each
homologous pair separates
(disjunction)
• If chromosomes fail to
separate (non-disjunction) one
gamete ends up with both
chromosomes and the other
gamete gets none
• Trisomy – gamete with both
chromosomes fuses with
normal gamete
Changes in chromosome structure
• Mutations = changes in
chromosome structure
• Chromosome breakage  4
types of mutations
• Duplication = chromosome
fragment attaches to
homologous chromosome
(which then carries 2 copies of
set of genes)
• Inversion = chromosome
fragment reattaches to original
chromosome but in reverse
order
• Translocation =
chromosome fragment
reattaches to non-homologous
chromosome
• Deletion = a piece of a
chromosome breaks off
Types of mutations
Inversion
Translocation
Types of Mutations
Deletion
Duplication