1. Lecture 1&2 Genetics Dr. Heba Al-Fares
AN-NAJAH NATIONAL UNIVERSITY
Cell and Chromosome
Lecture 1&2
Genetics
Dr. Heba Al-Fares 1

2. Introduction
Genetics is the study of how cells and whole organisms resemble and differ from the cell and organisms that give rise to them. It is the study of genes.
Gene is defined as a hereditary unit that occupies a specific position (locus) within the genome or chromosome. 2

3. Introduction
The genome is the complete set of sequences in the genetic material of an organism.
The study of genetics and the study of how cells work are closely related.
The process of passing genetic material from one generation to the next depends completely on how cells grow and divide. 3

4. Cell structure
Cell is the basic functional unit in the living organisms.
Parts of cell and their functions
Component of cell that involve directly or indirectly with the genetic material (nucleolus, ribosome, and centriole)
Mitochondria and chloroplast contain their own unique genetic information. 4

5. There are two basic kinds of organisms:
Prokaryotes: Organisms whose cells lack a nucleus and therefore have DNA floating loosely in the liquid center of the cell
Eukaryotes: Organisms that have a well-defined nucleus to house and protect the DNA
A nucleus is a compartment filled with DNA surrounded by a membrane called a nuclear envelope. 5

6. Prokaryotes Cell and Eukaryotes Cell6

7. Prokaryotic cells
Prokaryotes are the most common forms of life on earth.
All bacteria, regardless of nature, are simple, one-celled prokaryotic organisms.
None have cell nuclei, and all are small cells with relatively small amounts of DNA 7

8. Prokaryotic cells
The exterior of a prokaryotic cell is encapsulated by a cell wall that serves as the bacteria’s only protection from the outside world.
Bacterial cell have cell wall, but chemical composition is a complex macromolecule called a peptidoglycan 8

9. DNA, usually in the form of a single circular-shaped piece
A plasma membrane (membranes are thin sheets or layers) regulates the exchange of nutrients, water, and gases that nourish the bacterial cell.
DNA, usually in the form of a single circular-shaped piece
The liquid interior of the cell is called the cytoplasm 9

10. Prokaryotes divide, and thus reproduce, by simple mitosis
DNA not associated extensively with protein.
During cell division chromosome compacted into nucleoids.
In bacteria no distinct nucleolus, but do contain genes that specify rRNA. 10

11. Eukaryotic Contain organelles surrounded by membranes
Most living organisms
Plant
Animal 11

12. Eukaryotic cells
Eukaryotes range in complexity from simple one-celled animals and plants all the way to complex multicellular organisms like human.
Eukaryotic cells are fairly complicated and have numerous parts.
Like prokaryotes, eukaryotic cells are held together by a plasma membrane, and sometimes a cell wall surrounds the membrane (plants, for example have cell walls). But that’s where the similarities end. 12

13. Cell structure and function of eukaryotes
Cell is surrounded by a plasma membrane
functions
(1) defines the cell boundary, and protects the cell from its immediate environments
(2) Controls the movement of materials such as gases, nutrients, and waste products in to and out of the cell.
Plant have outer covering cell wall
Primary composed of a polysaccharide called cellulose 13

14. Eukaryotic cells
The most important feature of the eukaryotic cell is the nucleus
The nucleus protects the DNA from damage during day-to-day living. 14

15. Eukaryotic chromosomes are usually long, string-like segments of DNA instead of the circular-shaped ones found in prokaryotes.
Another feature of eukaryotes is the way the DNA is packaged:
Unlike prokaryotes, eukaryotes have all sorts of cell parts, called organelles found in the cytoplasm, that help carry out the metabolism of living. 15

16. Eukaryotic cells Two of the most important organelles are:
Mitochondria: The powerhouses of the eukaryotic cell, mitochondria pump out energy by converting glucose to ATP (adenosine triphosphate).Both animals and plants have mitochondria.
Chloroplasts: These organelles are unique to plants. They process the energy of sunlight into sugars that then are used by plant mitochondria to generate the energy that nourishes the living cells.
DNA differ than that in nucleus.
Can be duplicate themselves, transcribe and translate their genetic information similar to prokaryotic cells 16

17. Cell structure and function in plants and animals
Plants and animals have a nuclear envelope and membranous organelles
In mitosis DNA is coiling and chromosome are visible 17

18. Nucleolus is composed of RNA and protein
It is associated with specific chromosomal region
The region contain DNA that codes for rRNA
rRNA + specific protein ---- mature ribosome 18

19. Cell structure and function in plants and animals
The reminder of the cell is enclosed by the plasma membrane and excluding the nucleus is composed of cytoplasm.
Cytoplasm nonparticular colloidal material cytosol
Cytosol surrounded and encompasses the numerous type of cellular organelles 19

20. Extensive system of tubules and filaments comprising the cytoskeleton ----provide support maintains cell shape facilitate cell mobility and anchors the various organelles. 20

21. Cell structure and function in plants and animals
Endoplasmic reticulum (ER)
Compartmentalizes the cytoplasm
Increase the surface area available for biochemical synthesis
Type of ER
Smooth ER site for synthesis of fatty acids and phospholipids
Rough ER it is studied with ribosomes
As ER Synthetic activity
Ribosomes
Function: translation of the genetic information contained in mRNA into protein. 21

22. Cell structure and function in plants and animals
Centrioles is cytoplasmic bodies contain in special region in the centrosome.
Function:
Organization of these spindle fibers that function in mitosis and meiosis 22

23. Type of cells in eukaryotic
In most multicellular eukaryotes, cells come in two basic varieties: body cells (called somatic cells) or sex cells .
The two cell types have very different functions and are produced in very different ways.
Somatic cells are produced by simple cell division called mitosis.
Sex cells are specialized cells that are used for reproduction. Produced by meiosis 23

24. Chromosome Structure
DNA is long and thin and fragile: needs to be packaged to avoid breaking.
First level is the nucleosome, 200 bp of DNA wrapped twice around a core of 8 histone proteins (small and very conserved in evolution). A string of beads.
The nucleosomes coil up into a 30 nm chromatin fiber. This level of packaging exists even during interphase. 24

25. Chromosome Structure
During cell division, chromatin fibers are attached in loops of variable size to a protein scaffold. The DNA probably attaches at specific AT-rich areas called scaffold attachment regions.
The loops may be functional units: active vs. inactive in transcription.
Further coiling gives the compact structures we see in metaphase.
The centromere is the attachment point for the spindle.
Telomeres are the DNA sequences at the ends of chromosomes. 25

26. 26

27. Chromosomes Eukaryotic Prokaryotic Linear Circular Fairly long
Very small
1 chromosome per cell
Some enzymes and proteins are associated with the DNA.
Not housed in a nucleus.
Eukaryotic
Linear
Fairly long
Several chromosomes per cell.
Histone proteins package DNA Same in all eukaryotes
Housed in a nucleus.
Nucleosome—2 loops of DNA wrapped around 8 histone proteins. 27

28. Classification of chromosomes
Main features to identify and classify chromosomes
1. Size: large, medium and small and sex chromosomes
2. Location of the centromeres:
Metacentric: centromere in the middle, with arms of equal length.
Telocentric: centromere at one end, with only 1 arm.
Acrocentric: centromere near one end, with arms of very different lengths
Sub-metacentric: centromere near the middle, with arms of slightly different lengths. 28

29. Classification of chromosomes Location of the centromeres:29

30. Chromosome numbers haploid and euploid
Chromosome numbers can get a bit confusing.
Humans are diploid, meaning we have two copies of each chromosome.
Some organisms (like bees and wasps) have only one set of chromosomes (cells with one set of chromosomes are referred to as haploid); others have three, four, or as many as sixteen copies of each chromosome! 30

31. Variation In Chromosome Number
Euploidy
Normal variations of the number of complete sets of chromosomes
Chromosomes number are multiples of some basic number (n)
N: number of chromosome in one nuclear genome (haploid) that is 1xn=n, diploid 2n that is 2xn=2n, and so on
N is called the haploid chromosome number.
2n is called diploid.
3n, 4n, and so on are called polyploid.
Haploid, Diploid, Triploid, Tetraploid, etc… 31

32. Variation In Chromosome Number
Aneuploidy
Variation in the number of particular chromosomes within a set
Aneuploidies: changes in part of chromosome sets
A change from euploid number
Monosomy, trisomy, tetrasomy 32

33. Polyploidy v Aneuploidy33

34. Euploidy Variations Plants commonly exhibit polyploidy
30-35% of ferns and flowering plants are polyploid
Many of the fruits & grain are polyploid plants
Polyploid strains often display desirable agricultural characteristics
wheat
cotton
strawberries
bananas 34

35. Euploid Number can Naturally Vary
Most animal species are diploid
Polyploidy in animals is generally lethal
Some naturally occurring euploidy variations
bees - females are diploid.
Bees male are monoploid 35

36. Benefit of Odd Ploidy-Induced Sterility
Seedless fruit
watermelons and bananas
asexually propagated by human via cuttings
Seedless flowers
Marigold flowering plants
Prevention of cross pollination of transgenic plants 36

37. Chromosomal aberrations
Substantial changes in chromosome structure
Typically affect multiple genes (loci)

38. Variation In Chromosome Structure
Amount of genetic information in the chromosome can change
Deficiencies/Deletions
Duplications
The genetic material remains the same, but is rearranged
Inversions
Translocations

39. Categories of Chromosomal Aberrations
Inversions
Normal A B C D E F
Pericentric – inversion about the centromere
A D C B E F
Paracentric – inversion not involving the centromere
A B C E D F

40. Inversions
A segment of chromosome that is flipped relative to that in the homologue
Centromere lies within inverted region
Centromere lies outside inverted region
Figure 8.11

41. Inversions No loss of genetic information Break point effect
Many inversions have no phenotypic consequences
Break point effect
Inversion break point is within regulatory or structural portion of a gene
Position effect
Gene is repositioned in a way that alters its gene expression
separated from regulatory sequences, placed next to constitutive heterochromatin

42. Deletions
Loss of a region of a chromosome

43. Cri-du-chat Syndrome
Symptom: cat-like cry, short stature, and facial abnormality.

44. Deficiencies Phenotypic consequences of deficiency depends on
Size of the deletion
Functions of the genes deleted
Phenotypic effect of deletions usually detrimental

45. Duplication
Duplications result from doubling of chromosomal segments, and occur in a range of sizes and locations.
a. Tandem duplications are adjacent to each other.
b. Reverse tandem duplications result in genes arranged in the opposite order of the original.
c. Tandem duplication at the end of a chromosome is a terminal tandem duplication.

46. Fig. 17.5 Duplication, with a chromosome segment repeated

47. Forms of chromosome duplications are tandem, reverse tandem, and terminal tandem duplications

48. Duplications
Phenotypic consequences of duplications correlated to size & genes involved
Duplications tend to be less detrimental

49. Translocations
When a segment of one chromosome becomes attached to another
Exchange or joining of regions of two non-homologous chromosomes
In reciprocal translocations two non-homologous chromosomes exchange genetic material
Usually generate so-called balanced translocations
Usually without phenotypic consequences.

50. Fig. 8.13b(TE Art) Nonhomologous chromosomes 1 1 7 7 Crossover between
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 8.13b(TE Art)
Nonhomologous chromosomes 1 1 7 7
Crossover between
nonhomologous
chromosomes 1 7
Reciprocal
translocation
Nonhomologous crossover

51. Fig. 8.13a(TE Art) 22 22 Environmental agent 2 2 causes 2 chromosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Fig. 8.13a(TE Art) 22 22
Environmental agent
causes 2 chromosomes
to break. 2 2
Reactive ends
DNA repair enzymes
recognize broken ends
and connect them.
Chromosomal breakage and DNA repair

52. Example: Familial Down Syndrome
In simple translocations the transfer of genetic material occurs in only one direction
These are also called unbalanced translocations
Unbalanced translocations are associated with phenotypic abnormalities or even lethality
Example: Familial Down Syndrome
In this condition, the majority of chromosome 21 is attached to chromosome 14