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Genetics
Mitosis & Meiosis
• Review p 45-47• A. The Cell Cycle• 1. The dividing cell goes through a cycle of events
known as the cell cycle• 2. Cycle divided into interphase and mitosis• B. Interphase• 1. Period of DNA replication in preparation of
nucleus dividing• 2. Divided into 3 periods, G1 (1st growth or gap
period), S (synthesis), and G2 (2nd growth or gap period)
Mitosis• C. Mitosis• 1. Terms• a. Mitosis = division of the nucleus• b. Cytokinesis = division of the cytoplasm• c. Meristem = regions in plants where mitosis occurs (growing site)• 2. Prophase• a. Chromosomes become shorter, thicker and double move toward
equatorial plate• 1) Chromatids• • double threads of chromosomes• 2) Centromeres• • hold chromatids together• 3) Kinetochore• • near centromere, spindle fibers attach here• 4) Other constrictions may occur on individual chromosomes• • called satellites• b. Nucleolus and nuclear envelope disappear• c. Centrioles and asters form (only in algae, fungi, and animal cells)
• 3. Metaphase• a. Spindle forms• b. Chromosomes become aligned at the equatorial plate and connect to
spindle fiber at the kinetochore (part of the centromere)• 4. Anaphase• a. sister chromatids separate• b. once separated, daughter chromosomes are pulled by the kinetochore
along spindle fibers to opposite poles • 5. Telophase• a. Each group of daughter chromosomes becomes surrounded by a new
nuclear envelope• b. Daughter chromosomes become longer and thinner• c. New nucleoli appear• d. Phragmoplast appears• e. Cell plate forms• 1) Vesicles from the Golgi fuse to form the cell plate• 2) Plasmodesmata form as ER becomes trapped in cell plate
Phragmoplast
Alternation of Generations review • A. Terminology: n and x• B. Sporophyte Phase (2n)• 1. Diploid (2x)• 2. Meiosis takes place in special spore mother cells (meiocytes)• C. Gametophyte Phase (n)• 1. Haploid (x)• 2. Meiospores begin this phase• 3. Meiospores develop by mitosis into multicellular
gametophyte• 4. Gametes are produced which upon fertilization produce the
zygote, the first cell of the new sporophyte (2n) phase• D. Many Plant Species Are Polyploid• E. Six Rules Pertaining to Alternation of Generations
Six Rules Pertaining to Alternation of Generations (from the book)
• 1. the first cell of any gametophyte generation is normally a spore (sexual spore or meiospore), and the last cell is normally a gamete
• 2. any cell of a gametophyte generation (n) is usually haploid (x)
• 3. the first cell of any sporophyte generation is normally a zygote, and the last cell is normally a sporocyte (meiocyte)
• 4. any cell of a sporophyte generation (2n) is usually diploid (2x)
• 5. the change from a sporophyte to a gametophyte generation occurs as a result of meiosis
• 6. the change from a gametophyte to a sporophyte generation occurs as a result of fertilization (fusion of gametes) which is also called syngamy
Meiosis
• First meiosis• Interphase: replication of DNA and
chromosomes• Prophase I: chromosomes of diploid nucleus
becomes visible as long thin threads (each consists of 2 chromosomes)– Example: 2 chromosomes with 4 chromotids– 2 homologous pairs of chromosomes
Prophase cont.
– Prophase I cont: 2 chromosomes with 4 chromotids
– 2 homologous pairs of chromosomes – N = 2
Prophase cont.
• Homologues chromosomes pair up (synapses); each chromosome now with 4 chromatids (tetrad) and there is ½ the original number of chromosomes
• ========o==========• ========o==========• Above is a tetrad
Prophase cont.• Chromosomes condense as homologous
chromatids exchange parts (crossing over)
Prophase cont.
• Nuclear membrane disappears• Nucleolus disappears• Homologous chromatids separate at the
centramers but remain attached by schismatic
Metaphase I• Paired chromosomes move to equatorial
plane• Centromeres of paired chromosomes line up
on opposite sides of the equatorial plate
Anaphase I
• See above• Homologues chromosomes separate and
move toward poles• Two sister chromatids comprise each
chromosome• Homologues separate (not the sister
chromatids)• Homologs differ because of crossing over
Telophase I
• Chromosomes at each pole relax and become elongate and indistinct
• Nuclear envelope forms• Nucleoli appear• Each of the two new nuclei have ½ of the
original chromosome number• Reduction completed• Cytokinesis may occur or nuclei may proceed
immediately to the second division of meiosis
Meiosis II
• No additional duplication• Prophase II: nuclear envelope disappears• nucleolus disappears• Metaphase II: chromosomes line up at equator
plate• Anaphase II chromatids separate and move to
opposite poles• Telophase II: new nuclear envelope and
nucleolus reappear
Review
• Stop here Wednesday, 7 November 2012
Mendelian Genetics
• A. Mendel’s Studies• 1. Austrian monk, born 1822• 2. Scientific and mathematical studies• 3. Experiments with pea plants• a. Crosses between tall and
short plants• b. Crosses between plants with
smooth seeds and wrinkled seeds• c. Determination of factors
4. Law of Unit Characters
• factors which always occur in pairs, control the inheritance of various characteristics
• Paired factors now known as gene "alleles"
5. Law of Dominance
• in any given pair of factors (alleles), one may suppress or mask the expression of the other
• Dominant allele: the expressed factor• Recessive allele: the factor not expressed• Phenotype: what something looks like (pink flowers, wide
leaves)• Genotype:• 1) Homozygous: both alleles of a pair are identical (e.g.,
YY or yy)• 2) Heterozygous: allele pair is composed of contrasting
alleles (e.g., Yy)• Incomplete dominance:
• 6. Law of Segregation• • members of allele pairs become separated
during meiosis• 7. The Monohybrid Cross• a. F2 genotype ratio is 1:2:1
• b. F2 phenotype ratio is 3:1• 8. The Dihybrid Cross• a. Law of independent assortment• b. Punnett square• c. F2 genotype ratio is 1:2:2:4:1:2:1:2:1
• d. F2 phenotype ratio is 9:3:3:1
• 9. The Backcross• • between homozygous recessive
parent and F1 offspring• 10. Incomplete Dominance• 11. Interactions Among Genes• 12. How Genotype Controls Phenotype• 13. Polyploidy in plants
Incomplete Dominance
How Genotype Controls Phenotype
Polyploidy in plants
Polyploidy in agricultural plants
• Science 25 April 2008: Vol. 320 no. 5875 pp. 481-483
• AT SCHOOL: go to Google and put the above into the search line. Print out the article and bring it to class.
• We will make plans
Hardy-Weinberg Law
• We will go into this in lab.
DNA and RNA
• Two kinds of nucleic acids– 1. RNA = ribose nucleic acid– 2. DNA = deoxy ribo nucleic acid
nucleotides
Sugars
D-Ribose 5-phosphate
DNA & RNA
• A. Structure of DNA• 1. Nucleotides• a. Nitrogenous base• b. 5-carbon sugar• c. Phosphate group• 2. Nitrogenous bases• a. Purines, adenine and guanine (2 linked
rings)• b. Pyrimidines, cytosine and thymine
(single ring)
DNA Structure
• B. DNA Functions• 1. Storage of Genetic Information• a. A “Gene” molecular unit of of heredity of a living
organism• b. Codons and amino acids (see table)• 2. Replication (Duplication) of Information• a. Semi-conservative replication would produce two copies
that each contained one of the original strands and one new strand.• b. DNA polymerase• 3. Expression of Information• a. Transcription• b. Translation• 4. Mutation
Codons
DNA polymerase
Transcription
• 1. DNA unzips and RNA polymerase enzyme binds to one strand of DNA.
• 2. RNA polymerase makes an elongating chain of RNA nucleotides, each new RNA nucleotide is complementary to the DNA nucleotide.
• 3. The completed mRNA molecule is released from RNA polymerase - DNA complex and can begin translation. In eukaryotic cells this means first moving from the nucleus into the cytoplasm.
Translation
• 1. the ribosome binds to mRNA at a specific area (promoter region)
• 2. the ribosome starts matching tRNA anticodon sequences to the mRNA codon sequence
• 3. each time a new tRNA comes into the ribosome, the amino acid that it was carrying gets added to the elongating polypeptide chain
• 4. the ribosome continues until it hits a stop sequence, then it releases the polypeptide and the mRNA
• 5. the polypeptide forms into its native shape and starts acting as a functional protein in the cell
Mutations
• Somatic: occurs in a body cell and will occur in all cells produced by mitosis
• 1. source of new types of horticultural plants• Germ line: occurs in tissue that will produce
gametes.• 1. passed on to future generations• 2. important for the genetic improvement of
plants (example very sweet corn)
Little Review
• DNA– 1. must carry genetic material from cell to cell and
form generation to generation. Must carry a great deal of information
– 2. must be able to self replicate with great precision– 3. must be able to be modified or changed (mutation)– 4. must have mechanism to read stored information
and transfer it into the living system to be used to carry out activities
• DNA replication – semi conservative– 1. each strand has ½ of the original strand– 2. after replication both strands are the same 3.
occurs in s phase of mitosis • DNA strand is very long to have all of the
information– 1. carried on triplicate sequences of DNA– 2. begin reading on a specific sequence– 3 There are 16 combinations of those same 4 bases
Little Review
• RNA• Three kinds of RNA– 1. tRNA– 2. rRNA – structural portion, rough ER– 3. mRNA – carries sequences of triplet codes
• Codon: triplet sequence on mRNA• Anticodon sequence on tRNA
DNA mRNA tRNA
ATG
UAC
AUG
END