Genetics and Recombinant DNA BIT 120
Mitosis • 46 chromosomes • 23 pairs • 22 pairs autosomes (Chromosomes other than the X or Y sex chromosomes) • 1 pair sex chromosomes: XX and XY • Mitosis is the process that facilitates the equal partitioning of replicated chromosomes into two identical groups.
Stages of Mitosis • Prophase: The chromatin, diffuse in interphase, condenses into chromosomes. Each chromosome has duplicated and now consists of two sister chromatids. At the end of prophase, the nuclear envelope breaks down into vesicles. • Metaphase: The chromosomes align at the equitorial plate and are held in place by microtubules attached to the mitotic spindle and to part of the centromere. • Anaphase: The centromeres divide. Sister chromatids separate and move toward the corresponding poles. • Telophase: Daughter chromosomes arrive at the poles and the microtubules disappear. The condensed chromatin expands and the nuclear envelope reappears. The cytoplasm divides, the cell membrane pinches inward ultimately producing two daughter cells (phase: Cytokinesis).
Genes on Chromosomes • Definition of Gene: The functional and physical unit of heredity passed from parent to offspring. Genes are pieces of DNA, and most genes contain the information for making a specific protein • One gene one enzyme • One gene one peptide
Meiosis - The Genetics of Reproduction • Diploid – 2 chromosomes per pair • Haploid – set of one chromosome • The process of meiosis essentially involves two cycles of division, essentially involving a gamete mother cell (diploid cell) dividing and then dividing again to form 4 haploid cells. These can be subdivided into four distinct phases which are a continuous process
Meiosis II • Meiosis II is simply a mitotic division of each of the haploid cells produced in Meiosis I. There is no interphase between Meiosis I and Meiosis II and the latter begins with:
Summary: Meiosis Steps • Prophase - Homologous chromosomes in the nucleus begin to pair up with one another and then split into chromatids (one half of a chromosome) where crossing over can occur. Crossing offer can increase genetic variation explained soon. • Metaphase - Chromosomes line up at the equator of the cell, where the sequence of the chromosomes lined up is at random, increasing genetic variation via independent assortment explained soon.
Summary: Meiosis Steps • Anaphase - The homologous chromosomes move to opposing poles from the equator • Telophase - A new nuclei forms near each pole alongside its new chromosome compliment. • At this stage two haploid cells have been created from the original diploid cell of the parent.
Summary: Meiosis Steps • Prophase II - The nuclear membrane disappears and the second meiotic division is initiated. • Metaphase II - Pairs of chromatids line up at the equator
Summary: Meiosis Steps • Anaphase II - Each of these chromatid pairs move away from the equator to the poles via spindle fibres • Telophase II - Four new haploid gametes are created that will fuse with the gametes of the opposite sex to create a zygote.
Summary: Meiosis Steps • When Meiosis II is complete, there will be a total of four daughter cells, each with half the total number of chromosomes as the original cell. • Increases Genetic diversity
Crossing Over • During meiosis, when homologous chromosomes are paired together, there are points along the chromosomes that make contact with the other pair. This point of contact is deemed the chiasmata, and can allow the exchange of genetic information between chromosomes. This further increases genetic variation
Mendel’s Work • Gregor Mendel, an Austrian monk is most famous in this field for his study of the phenotype of pea plants, including the shape of the peas on the pea plants. • 2 laws: • Segregation • Independent Assortment
Mendel cont’d • Mendel's goal was to have a firm scientific basis on the relationship of genetic information passed on from parents to offspring • Did work with Pea plants - looked at traits for color and texture • For texture - showed more round than wrinkled; for color - more green than yellow
Mendel cont’d • Idea of Dominant and Recessive • Idea of alleles - alternate forms of the same gene • Monohybrid cross
Segregation • Mendel's First Law • "The alleles of a gene exist in pairs but when gametes are formed, the members of each pair pass into different gametes. Thus each gamete contains only one allele of each gene."
Independent Assortment • Genes affecting different traits will separate independently from one another during gamete formation. • Dihybrid cross - see example next slide • Can use to see how 2 or more genes will sort out
Dihybrid Cross Rr, round & wrinkled Yy, yellow and green
New convention for naming • See overhead • now would be Ww and Gg • Exceptions: • incomplete dominance • multiple alleles • linked genes
Sex Determination • XX females • XY males - not “truly” a homologous pair Arrows indicate genes on the X chromosome for which there is no complement on the Y chromosome
SRY gene - Sex Determining Region Y • Gene on Y chromosome that determines embryo will be a male • Produces TDF - testis determining factor Testis-determining factor
Sex-linked Genes • Some examples: • · Red-Green colour blindness • · Hemophilia - A condition which prevents the clotting of the blood • · DMD - muscular dystrophy • · Hypertension
Pedigree Analysis • Charts to look at inheritance pattern of genes in humans • http://www.blc.arizona.edu/courses/181gh/rick/human_genetics/pedigree.html • http://www.ndsu.nodak.edu/instruct/mcclean/plsc431/mendel/mendel9.htm
Chromosomal mutationshttp://www.people.virginia.edu/~rjh9u/chromdel.html • Gene deletion
Chromosomal mutationshttp://www.people.virginia.edu/~rjh9u/chromdup.html • Gene duplication
Chromosomal mutationshttp://www.people.virginia.edu/~rjh9u/chrominv.html • Gene inversion
Chromosomal mutationshttp://www.people.virginia.edu/~rjh9u/chromtran.html • Gene translocation
DNA-level mutation • Previous examples chromosomal level changes • changes can occur at DNA level • also can have deletion, insertion, inversion and substitution
DNA mutation 1.DeletionHere, certain nucleotides are deleted, which affects the coding of proteins that use this DNA sequence. If for example, a gene coded for alanine, with a genetic sequence of C-G-G, and the cytosine nucleotide was deleted, then the alanine amino acid would not be able to be created 2. InsertionSimilar to the effects of deletion, where a nucleotide is inserted into a genetic sequence and therefore alters the chain thereafter. This alteration of a nucleotide sequence is known as frameshift
DNA mutation 3.InversionWhere a particular nucleotide sequence is reversed, and is not as serious as the above mutations. This is because the nucleotides that have been reversed in order only affect a small portion of the sequence at large 4.SubstitutionA certain nucleotide is replaced with another, which will affect any amino acid to be synthesized from this sequence due to this change. If the gene is essential, i.e. for the coding of hemoglobin then the effects are serious, and organisms in this instance suffer from a condition called sickle cell anemia. - CAN BE SILENT MUTATION. CONSERVATION SUBSTITUTION, OR SUBSTITUTION
Other related topics • Polyploidy • Mutation Frequency
Recessive human genetic disorders • Brachydactly - first human genetic disorder characterized - short fingers and toes • Albinism - absence of pigmentation • Sickle cell anemia - inefficient oxygen transport due to abnormal shape red blood cells • PKU • Tay Sachs - neurodegenerative
Dominant Human genetic disorders • Huntington’s disease - progressive destruction of brain cells • Polydactly - extra fingers and toes
Intro to Recombinant DNA • Some unmet medical needs: • · invasive fungi infections • · drug resistant bacteria • · hepatitis virus • · new vaccines • · HIV • · Cancer
Recombinant DNA • Definition : DNA molecule produced artificially and containing sequences from unrelated organisms. • Genetic Engineering • Use of techniques involving recombinant DNA technology to produce molecules and/or organisms with new properties. • Biotechnology • All inclusive term for several technologies including but not limited to recombinant DNA. Refers to the use of technology in applications for solving fundamental problems in biology.
Restriction endonucleases • Also called restriction enzymes: digest DNA at specific sequences
Sequence Recognition -R.E. • · Restriction endonucleases -- cut double stranded DNA at specific sequences, protection against viruses in bacteria. • · Sequences often palindromes: a sequence which is the same when read in either direction. ”A man a plan a canal: Panama”