Download Mendelian Genetics

Chromosomes & Inheritance
Chromosomes – linear, double stranded
*Number is specific to each species
*Most eukaryotes have 2 copies of each
-diploid
*Gametes have only one set of
chromosomes
-haploid
*Diploid organisms have homologous
chromosomes – pairs that contain the
same genes
Chromosomes & Inheritance
*Each member of the pair is called a
homolog – 1 inherited from each parent
*Chromosomes that contain different
genes & do not pair in meiosis
*Sex chromosomes – represented
differently in the 2 sexes
- Females have a matched pair
(XX) of sex chromosomes
- Males do not have a matched pair
(XY) of sex chromosomes
Chromosomes & Inheritance
*Chromosomes other than the sex
chromosomes are called autosomes
*Chromosomes differ in size and
appearance (morphology) within and
between species
*The point at which a chromosome is
constricted (pinched) is called the
centromere
*The position of the centromere is used
to classify eukaryotic chromosomes
Chromosomes & Inheritance
- Metacentric chromosome –
centromere is in the center
- Submetacentric chromosome –
one arm is longer than the other
- Acrocentric chromosome –
one arm and a bulb
- Telocentric chromosome –
centromere is on the end
Chromosomes & Inheritance
*Chromosomes also vary in size
*Chromosomes length and centromere
position are consistant for each
chromosome
*A complete set of all the
chromosomes in a cell is a karyotype
(two chromatids per chromosome)
- chromosomes from metaphase
are used since they are the most
compact and easily seen
Chromosomes & Inheritance
*Karyotypes are species specific
*Chromosomes are arranged according
to size and position of the centromere
*Human karyotype shows 46
chromosomes: autosomal (1-22) and
sex (23)
*They are numbered largest to smallest
to help in identification
*They are also arranged together with
similar morphologies (A-G)
Chromosomes & Inheritance
Chromosomes & Inheritance
•Shows some detail of the chromosomes.
•Can help determine the sex of an unborn child.
•Doctors look for some significant features
oCheck if the 46 chromosomes are present
oCheck the presence of the two identical
chromosomes
oCheck the sex chromosomes
oCheck if there are any missing or rearranged
chromosomes
Chromosomes & Inheritance
Karyotypes do not show …
•The presence and location of small mutations.
oSo if diseases are caused by small mutations
they cannot be predicted
•Individual DNA strands or genes
•The number of genes in any given area of a
chromosome
Chromosomes & Inheritance
*Size and morphology are not enough
to complete a karyotype
*There are staining procedures used to
“band” regions of the chromosomes
*Certain regions consistantly accept
more staining than others, so
chromosomal banding is specific
*Chromosomal nomenclature, based
upon banding pattern, has been
established
Chromosomes & Inheritance
*The nomenclature is used to reference
genes based upon regions of
chromosomes
*Each chromosome has 2 arms
separated by the centromere
*The smaller arm is designated ‘p ‘ and
the larger arm is desinated ‘q’
*Numbered regions and subregions are
then assigned from the centromere
outward (1 is closest to the centromere)
Chromosomes & Inheritance
- Example: Breast cancer
susceptibility gene is located at
17q21
-What does this mean?
-It is located on chromosome 17,
on the long arm in region 21
-Subregions are then indicated
with decimals after the region
Chromosomes & Inheritance
- Example: Cystic fibrosis gene
is located at 7q31.2-q31.3
-It is located on chromosome 7,
on the long arm and spans
subregions 2 and 3 of 31
Chromosomes & Inheritance
MITOSIS
-cellular reproduction
-cyclical
Cell -growth, mitosis (nuclear division),
cycle cytokinesis (cell division)
-somatic cells: 2 main phases of cell
cycle (1) M & (2) Interphase
-Interphase
-Interphase: G1, S, G2
Chromosomes & Inheritance
INTERPHASE
- G1 – growth, preparation for
chromosome replication
- S – replication of chromosomes
- G2 – preparation for cell division
-sister chromatids – 2 exact copies of
each other, held together by a
replicated, but unseparated centromere
-chromatids – one of the two subunits
of a replicated chromosome
Chromosomes & Inheritance
INTERPHASE
- daughter chromosome – separted
sister chromatids
Chromosomes & Inheritance
INTERPHASE
- daughter chromosome – separated
sister chromatids
MITOSIS
-Prophase
-Early Prophase –
1. Centrioles move apart
2. Chromosomes shorten, thicken
& start to become visible
3. Nucleolus begins to disappear
Chromosomes & Inheritance
MITOSIS
-Prophase
-Mid Prophase –
1. Centrioles continue to move
2. Spindles begin forming
3. Replicated chromosomes
become visible
-Late Prophase –
1. Centrioles reach opposite sides
2. Spindle continues to form
3. Nuclear envelope begins to
disappear
Chromosomes & Inheritance
MITOSIS
-Metaphase
1. Nuclear envelope is gone
2. Replicated chromosomes, attached at
the centromere, align in the center
(“equator”)
-Anaphase
-Early Anaphase –
1. Centromeres split, daughter
chromosomes migrate toward
opposite sides
Chromosomes & Inheritance
MITOSIS
-Anaphase
-Late Anaphase –
1. The 2 sets of daughter
chromosomes approach the
poles
2. Cytokinesis begins
Chromosomes & Inheritance
MITOSIS
-Telophase
1. Nuclear envelope begins forming
2. Chromosomes begin to extend, less
visible
3. Nucleolus reforms
4. Cytokinesis continues
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