Meiosis, karyotyping and mutations

1. 4. GENETICS

2. 4.1 Chromosomes,
genes, alleles, and
mutations

3. Inventory of your traits
Traits are observable characteristics, find out which traits
your share with the rest of the class.
First, fill out the inventory for yourself
Second, tally up the results of your group and then add
them to the entire class.
Third, draw a bar graph with the results
Homework: make a graph using excel just like we did in
class

4. Meiosis
Meiosis: A type of cell division that produces four cells, each with
half the number of chromosomes as the parent cell.
Homologous chromosomes: As a consequence of fertilization,
humans have pairs of chromosomes with one chromosome in a
pair from each parent. The two chromosomes of each matching
pair are called homologous.
Diploid: A nucleus with two chromosomes of each type. (2n)
Haploid: A nucleus with only one chromosome of each type. (n)

5. The process of meiosis
Meiosis I: Four stages. Previously, during
interphase, the chromosomes replicate, so
that each chromosome has an identical
chromatid (2n).
1) Prophase I: Homologous
chromosomes pair up and
stick together along their
length and exchange
genetic material in the
process called crossing
over.

6. 2) Metaphase I:
Homologous pairs
(tetrads) move to the
equator of the cell.
Orientation of maternal
and paternal on either
side is random and
independent.
3) Anaphase I:
Homologous pairs are
separated and migrate to
opposite poles of the
spindle.

7. The process of meiosis
4) Telophase I and
Cytokinesis: Each pole
now has a haploid
daughter nucleus
(eventhough each
chromosome consists of
two chromatids). No
replication occurs.
Cytokinesis splits the cell.
Nuclear membrane
appears and chromosomes
uncoil.

8. Meiosis II: Four stages as well.
1) Prophase II: Chromosomes condense, nuclear envelope
disintegrates, and a spindle forms.
2) Metaphase II: The chromosomes line up in the middle of the
cell.

9. The process of meiosis
3) Anaphase II: Centromeres separate and sister
chromatids are moved to opposite poles.
4) Telophase II and cytokinesis: The chromatids reach the
poles, nuclear envelope forms, cytokinesis splits the cell
again, producing four haploid daughter cells as a final
result.
www.biology.com: Online activity 10. 4

12. Non-disjunction
It occurs when homologous chromosomes fail to separate at anaphase.
The result will be a gamete (sex cell) that either has an extra
chromosome or is deficient in a chromosome.
An abnormal number of chromosomes will often lead to a person
possessing a syndrome, a collection of physical signs or symptoms
An example is Down syndrome, or trisomy 21, which is due to a non-
disjunction that leaves the individual with 3 chromatids of the
chromosome 21, instead of 2
Other examples of non-disjunction are Turner’s syndrome, Klinefelter’s
syndrome and Patau syndrome.

13. Karyotyping
Karyotype: It is the number and type of chromosomes that
the nucleus of a cell contains.
To build a karyotype, the chromosomes are stained, a
micrograph (microscopic photograph) is taken and then
the chromosomes are arranged according to their size and
structure, starting with the largest and ending with the
smallest.
As most cells are diploid, the
chromosomes in a karyotype usually occur in pairs.

14. Karyotyping
Two procedures for
obtaining the fetal
chromosomes to produce
the karyotype.
1)Amniocentesis: involves
passing a needle through
the mother’s abdominal
wall, to withdraw a sample
of amniotic fluid from the
amniotic sac of a
developing fetus.
2)Chorionic villus
sampling: This procedure
samples cells from the
placenta, specifically from
the villi of the
chorion, rather than the
amniotic fluid.

15. Complete Human Karyotype

16. Class activity
Make a Karyotype:
Part I: Cut and paste the chromosomes in order. Remember
to look for similar sizes, band patterns, and location of
centromeres.
Part II: Cut and paste the chromosomes in order. Analyze
the karyotype and write down whether the patient is male,
female and if they have a genetic disorder.

17. This graphic
should help
you locate
bands and
centromeres.

18. Mutations
2 kinds of mutations:
a) Gene mutations: Produce changes in a single gene
a1) Point mutations: Involve changes in one or a few
nucleotides, they occur at a single point in the DNA
sequence = substitutions.
a2) Frameshift mutations: They shift the reading frame
(every codon) of the genetic message, that changes every
amino acid that follows the point of mutation = insertion
or deletion.

20. Mutations
b) Chromosomal mutations: Involve changes in the
number or structure of chromosomes. They may change
the locations of genes on chromosomes and even the
number of copies of some genes =
deletions, duplications, inversions and translocations.

21. A. Deletion
B. Inversion
C. Translocation
D. Duplication