Genetics

1
Genetics

• Instructor Dr. Jihad Abdallah
• Lecture 1
• Cells and chromosomes

2
Animal Cell
3
Plant Cell
4
Cell Boundaries (animal cells)

• Plasma Membrane
• An outer covering that defines the cell boundary
• Controls the movement of material such as gases,
  nutrients and waste products into and outside the
  cell
• Cell Coat
• Consists of glycogen and polysaccharides
• Provides biochemical identity at the surface of
  cells (molecular recognition)
• Various antigens are part of the cell coat as for
  example the MN and AB antigens on red blood cells
• Receptor molecules are integral components of the
  cell surface (recognition sites)

5
Nucleus

• Contains the genetic material. Consists of
• - Nuclear membrane with nuclear pores
• - Nucleolus site for synthesis of ribosomal
  RNA (rRNA).
• The areas of DNA encoding rRNA are collectively
  known as the Nucleoler Organizer Region (NOR)
• Note that prokaryotes (like bacteria) do not have
  a nucleus. In bacteria, the genetic material is
  present as a long, circular DNA molecule that is
  compacted in an area called the nucleoid region.

6
The Cytoplasm and Organelles

• The cytoplasm consists of a colloidal material
  referred to as the Cytosol which surrounds the
  various organelles
• An extensive system of tubules and filaments
  comprising the cytoskeleton provides a lattice of
  support structures within the cytoplasm. This
  system consists of
• - Tubulin-derived microtubules
• - Actin-derived microfilaments

7

• Endoplasmic Reticulum (ER)
• 1. Smooth ER serve as the site for the
  synthesis of fatty acids and phospholipids
• 2. Rough ER studded with ribosomes which
  serve as sites for the translation of mRNA into
  proteins.
• Mitochondria
• - Are the sites of oxidative phases of cell
  respiration ? chemical reactions generate large
  amounts of ATP
• - Contain a type of DNA distinct from that in
  the nucleus
• - Can duplicate themselves and transcribe and
  translate their own genetic information

8

• Centrosome
• Also called the "microtubule organizing center",
  is an area in the cell where microtubles are
  produced.
• Within an animal cell centrosome there is a pair
  of small organelles, the centrioles, each made up
  of a ring of nine groups of microtubules.
  Centerioles are associated with organization of
  spindle fibers in mitosis and meiosis.
• Plant cells have centrosomes that function much
  like animal cell centrosomes but they do not have
  centrioles.

9
Genetic material and Chromosomes

• The genetic material is composed of the nucleic
  acid DNA (Deoxyribonucleic Acid)
• A molecule of DNA contains many units called
  genes. The gene is defined as the fundamental
  physical unit of heredity and is a sequence of
  DNA which occupies a certain location (called
  locus) on the chromosome
• The DNA is found associated with protein. During
  non-division phases of the cell cycle this
  DNA/protein complex exists in uncoiled, dispersed
  state called chromatin. During mitosis and
  meiosis it coils up and condenses into structures
  called chromosomes.

10

• The chromosomes serve as the vehicle for the
  transmission of genetic information
• Chromosomes are most easily visualized during
  cell division and take distinctive lengths and
  shapes.
• Each chromosome contains a condensed or
  constricted region called centromere to which the
  spindle fibers attach during cell division.
• Two arms extend from each side of the centromere
• - p arm (short arm) ? above the centromere
• - q arm (long arm) ? below the centromere

11
The chromatin material just before cell division
forms into chromosomes. Each chromosome is made
up of two longitudinal strands called sister
chromatids.
12
Classification of chromosomes

• 1) Sex and Autosomal chromosomes
• Sex chromosomes X and Y (humans and animals) or
  W and Z (in birds) ? males XY and ZZ , females
  XX and ZW
• Autosomal chromosomes (autosomes) chromosomes
  other than the sex chromosomes

13

• 2) Chromosomes are classified based on the
  position of the centromere into
• Metacentric centromere location is in the middle
  of the chromosome. The chromosome is V-shaped
  during anaphase
• Submetacentric centromere location is between
  the middle and the end of the chromosome. The
  chromosome gets an L shape during anaphase .
• Acrocentric centromere location is close to the
  end of the chromosome. The chromosome is J-shaped
  during anaphase
• Telocentric centromere location is at the end of
  the chromosome. The chromosome is I-shaped during
  anaphase

14
(No Transcript)
15
3) Human chromosomes are classified based on size
and shape into 8 groups
Large, metacentric
Large, submetcentric
small
Karyogram of a human male.
16

• Karyotype is the complete set of all chromosomes
  of a cell of any living organism. Often used to
  refer to the arrangement of metaphase chromosomes
  in a sequence according to length and position of
  the centromere.
• The pectorial representation of the karyotype is
  called a Karyogram

17
Haploids and Euoploids

• Haploid a cell or organism having one set of
  unpaired (single) chromosomes (1n) ? like yeasts
  and molds and germ cells (gametes) of animals and
  humans.
• Euoploid a cell or organism whose cells have a
  chromosome number that is an exact multiple of a
  basic chromosome set (2n, 3n, 4n, ..etc) ?
• - Diploid 2n (have two sets of chromosomes
  present in pairs and called homologous
  chromosomes like somatic cells of humans and
  animals)
• - Polyploid (3n, 4n, .,etc) ? more than two
  basic chromosome sets like some plants
• - Triploid (3n)
• - Tetraploid (4n)
• - Pentaploid (5n)
• - Hexaploid (6n)

18
Polyploidy in animals

• Examples in animals are more common in the
  'lower' forms such as flatworms, leeches, and
  brine shrimp.
• Polyploid animals are often sterile, so they
  often reproduce by parthenogenesis. Polyploid
  lizards are also quite common and
  parthenogenetic.
• Parthenogenesis is an asexual form of
  reproduction found in females where growth and
  development of embryos or seeds occurs without
  fertilization by a male.
• The offspring produced by parthenogenesis are
  always female in species that use the XY
  sex-determination system but they will be male if
  two like chromosomes determine the male sex (such
  as the ZW sex-determination system).

19
Polyploidy in plants

• Polyploidy is common in plants and some estimates
  suggest that 30-80 of living plant species are
  polyploid.
• Polyploid plants can arise spontaneously in
  nature by several mechanisms including meiotic or
  mitotic failures and fusion of unreduced (2n)
  gametes.
• Polyploid plants tend to be larger and better at
  flourishing in the field.
• In some situations polyploid crops are preferred
  because they are sterile. For example many
  seedless fruit varieties are seedless as a result
  of polyploidy. Such crops are propagated using
  asexual techniques such as grafting.
• Polyploidy in crop plants is most commonly
  induced by treating seeds with the chemical
  colchicine.

20
Examples of Polyploid Crops

• Triploid crops banana, apple, watermelon, citrus
• Tetraploid crops durum or macaroni wheat, maize,
  cotton, potato, cabbage, tobacco, peanut.
• Hexaploid crops bread wheat, triticale, oat,
  kiwifruit
• Octaploid crops strawberry, sugar cane
• Some crops are found in a variety of ploidy.
  Apples, tulips and lilies are commonly found as
  both diploid and as triploid. Daylilies cultivars
  are available as either diploid or tetraploid.

21
Autopolyploidy

• Autopolyploids are polyploids with multiple
  chromosome sets derived from a single species.
• Autopolyploids can arise from a spontaneous,
  naturally occurring genome doubling (for example,
  the potato).
• Others might form following fusion of 2n gametes
  (unreduced gametes).
• Bananas and apples can be found as triploid
  autopolyploids.
• Autopolyploid plants are often infertile and
  propagated clonally

22
Allopolyploidy

• Allopolyploids are polyploids with chromosomes
  derived from different species.
• Precisely it is the result of doubling of
  chromosome number in an F1 hybrid.
• Triticale is an example of an allopolyploid,
  having six chromosome sets, four from wheat
  (Triticum turgidum) and two from rye (Secale
  cereale). Triticale is essentially a
  self-fertilizing (naturally inbred) crop.

23
Chromosome numbers (2n) in some animals and
insects
24
Chromosome numbers (total number) in some plants
25
Some chromosomal Aberrations

• Chromosomal aberrations are disruptions in the
  normal chromosomal content of a cell, and are a
  major cause of genetic conditions in humans
• Some chromosome abnormalities do not cause
  disease in carriers, such as translocations
  (rearrangement of parts between non-homologous
  chromosomes ), or chromosomal inversions (a
  chromosome rearrangement in which a segment of a
  chromosome is reversed end to end) , although
  they may lead to a higher chance of birthing a
  child with a chromosome disorder.

26

• Down's syndrome caused by an extra copy of
  chromosome 21 (trisomy 21). Is the most common
  trisomy.
• Edwards syndrome, which is the second-most-common
  trisomy. It is a trisomy of chromosome 18.
• Klinefelter's syndrome (XXY). Men with
  Klinefelter syndrome are usually sterile, and
  tend to have longer arms and legs and to be
  taller than their peers. Boys with the syndrome
  are often shy and quiet, and have a higher
  incidence of speech delay
• Turner syndrome (X instead of XX or XY). In
  Turner syndrome, female sexual characteristics
  are present but underdeveloped. People with
  Turner syndrome often have a short stature
• XYY syndrome. XYY boys are usually taller than
  their siblings. Like XXY boys and XXX girls, they
  are somewhat more likely to have learning
  difficulties.
• Triple-X syndrome (XXX). XXX girls tend to be
  tall and thin.