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 geneis 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

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 macaroniwheat, 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.