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GENETICSCHAPTER 1: INTRODUCTION TO GENETICS
Codeine is a painkiller and is also a cough suppressor (cough drinks). Codeine has
side effects: drowsiness (slaperigheid), nausea (misselijkheid), constipation
(verstopping), respiratory inhibition (ademhalingsremming) when using too high
doses in children.
Codeine is by itself not active but is activated by a CYP2D6 enzyme. When this
codeine is active it will be metabolized in morphine. The morphine is the actor as a
painkiller. You can be a slow metabolizer, but also a rapid metabolizer. When you’re
a rapid metabolizer, it means that you have a high CYP2D6 activity and metabolize
codeine rapid in morphine, so high concentrations of morphine are then concentrated
in the blood.
Genomics = studies the structure, function and evolution of genes and genomes
Proteomics = identifies a set of proteins present in cells under a given set of
conditions. Studies their functions and interactions
Bioinformatics = uses hardware and software for processing nucleotide and protein
data
- Human genome: 3.2 x 109 base pair
- 1 gene = 3,000 base pair
- <2% of genome codes for protein
- Rest is “junk DNA” (noncoding DNA)
- 20,000-25,000 genes & 250,000 proteins
- Differences between people: 0,1%
CHAPTER 2: MITOSIS AND MEIOSIS
Each chromosome contains a centromere, whose location establishes the general
appearance of each chromosome. Centromere placements can be at different
distances along the length of the chromosome. Extending from either side of the
centromere are the arms of the chromosome.
Chromosomes are classified in centromere location:
- metacentric (middle)
- submetacentric (between middle and end)
- acrocentric (close to end)
- telocentric (at end)
Short arm = p arm
Long arm = q arm
,Somatic cells are the cells in the body other than sex cells. In humans,
somatic cells are diploid (2n), meaning they contain two sets of
chromosomes, one inherited from each parent.
Haploid (n) = cell with a single chromosome exemplar. This is the case
of sex cells. You have 23 chromosomes.
Diploid (2n) = of each chromosome you have 2 exemplars. 1 from the
mother and 1 from the father. So you have pairs of chromosomes. 46
chromosomes, so 23 chromosome pairs.
The members of a chromosome pair are called homologous
chromosomes. So each pair has two corresponding chromosomes (same
length, centromere placement and locus). A locus is the position in a
chromosome of a particular gene or allele. So, there are 22 homologous
chromosome pairs (excepting the sex chromosomes). These chromosome
pairs are also called autosomes. There are exceptions to this rule. Many
bacteria and viruses have only one chromosome. Plants, on the other hand,
may actually contain more chromosomes per set. Tetraploid (4n), for example;
4 chromosomes per set.
Biparental inheritance = inheritance from two parents
Mitosis/karyokinesis is the chromosome segregation & cytokinesis is the cytoplasmic
segregation. Mother cell --> 2 daughter cells.
Zygote: Single-celled fertilized eggs of multi cellular organisms
Different checkpoints in the cell-cycle:
G1/S checkpoint - monitors cell size & evaluates condition of DNA
G2/M checkpoint - monitors if DNA replication is completed & monitors
damaged DNA
M checkpoint - Monitors successful formation of spindle fiber system and
attachment kinetochores
- Interphase (chromosomes are uncoiled and become visible)
- Prophase (the replicated chromosomes, each consisting of two closely
associated sister chromatids, condense. Outside the nucleus, the mitotic
spindle assembles between the two centrosomes, which have replicated and
moved apart)
- Prometaphase (starts with the breakdown of the nuclear envelope.
Chromosomes can now attach to spindle microtubules via their
kinetochores and undergo active movement)
,- Metaphase (the chromosomes are aligned at the equator of the spindle,
midway between the spindle poles. The kinetochore microtubules attach
sister chromatids to opposite poles of the spindle)
- Anaphase (the sister chromatids synchronously separate to form two
daughter chromosomes, and each is pulled slowly toward the spindle pole it
faces. The kinetochore microtubules get shorter, and the spindle poles also
move apart; both processes contribute to chromosome segregation)
- Telophase (the two sets of daughter chromosomes arrive at the poles of
the spindle and decondense. A new nuclear envelope reassembles around
each set, completing the formation of two nuclei and marking the end of
mitosis. The division of the cytoplasm begins with contraction of the
contractile ring)
- Cytokinesis (the cytoplasm is divided in two by a contractile ring of actin
and myosin filaments, which pinches the cell in two to create two
daughters, each with one nucleus)
Mitosis is replication & meiosis is the forming of sex cells. Meiosis
reduces the amount of genetic material by half (from 2n to n). It produces
haploid gametes or spores each containing one chromosome.
Meiosis 1: Reductional division (chromosome segregation)
Meiosis 2: Equational division (chromatid segregation)
Before mitosis begins, DNA
replication takes place (46
chromosomes --> 92
chromosomes), so that after cell
division, both daughter cells still
have 46 chromosomes
(diploid/2n).
In meiosis, you have this DNA
replication only before meiosis I.
In meiosis I you see 2 chromosome pairs, so 4 chromosomes in
total. These are separated into 2 cells, so you are left with 2 single
chromosomes per cell. In meiosis II, you see 2 single
chromosomes separated into chromatids. So you are left with 2
chromatids per cell after separation. So now you have developed
haploid cells.
2n --> n + n + n + n
, 3 processes unique for meiosis (according to mitosis):
- Prophase 1: synapsis (the chromosomes pair up at the end of
their arms) and crossing over
- Metaphase 1: forming a tetrad instead of individual replicated
chromosomes
- Anaphase 1: separation of homologous chromosomes instead of sister chromatids
Crossing-over can take place during meiosis. This is genetic
exchange between members of homologous pairs of
chromosomes. So exchange between the father
chromosome and the mother chromosome of the
chromosome pair. Chiasma is an area where chromatids are
intertwined. Each pair of chromosomes—called a tetrad, or a bivalent—consists
of four chromatids.
The pseudoautosomal regions, PAR1 & PAR2, are homologous sequences of
nucleotides on the X and Y chromosomes. So the X and Y chromosomes can
pair because of these PARs. Crossing over can then also take place, but this
rarely occurs. PAR1 is located at the terminal region of the short arms and PAR2
at the tips of the long arms of these chromosomes. Without PAR1 you get male
sterility, the X and Y chromosomes can't find each other anymore.
The development of gametes varies between spermatogenesis and oogenesis in the
ovary.
Male gametes: Produced by spermatogenesis in the testes. This process is
continuously. At the age of puberty boys start to produce sperm and they will do this
for the rest of their lives.
Female gametes: produced by oogenesis in the ovary. This
process is not in all animal species continuous. In humans, the
first division of all oocytes begins in the embryonic ovary, but
arrests in prophase I. Many years later, meiosis resumes in
each oocyte just prior to its ovulation.
CHAPTER 3: MENDELIAN GENETICS
Genotype = a description of the genes an organism contains
(gene for blue eyes)
Phenotype = the characteristics that can be observed in an organism. The phenotype
is determined by the interaction between genotype and environment (gene for dark
hair & straightening every morning → straight dark hair)
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