Genetics. PART I: Mitosis & Meiosis prerequisites for inheritance. A. Mitosis. Review: A closer look inside of the nucleus: DNA: chromatin:

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1 Genetics PART I: Mitosis & Meiosis prerequisites for inheritance A. Mitosis Review: A closer look inside of the nucleus: DNA: chromatin: chromosome: parts: chromatid: centromere: telomere: 1

2 Mitosis & the cell cycle: STAGES OF MITOSIS & THE CELL CYCLE: Interphase: Prophase: 2

3 Metaphase: Anaphase: Telophase: Cytokinesis: RESULTS OF MITOSIS (& CELL CYCLE): 3

4 Q: How does mitosis differ between plant an animal cells? 2. Meiosis Some important information about chromosomes: somatic cells: homologous chromosomes: diploid cells: sketch: haploid cells: sketch: 4

5 Meiosis I: 1. Prophase I: EARLY: - a parent with a distinct nucleus, nucleolus, cytoplasm & centrioles is present - chromosomes replicate LATE: - each pair of chromosomes lines up with its homologous pair - each group of four chromosomes is called a tetrad - nuclear membrane disappears; spindle fibers form - sometimes crossing over occurs 2. Metaphase I: - tetrads line up at the middle & attach to fibers at the centromeres - the chromosomes that are attached to the same centromere are called sister chromatids 3. Anaphase I: - tetrads separate so that sister chromatids move to opposite poles (disjunction) - chromosomes haploid but double stranded 4. Telophase I: - cytoplasm divides, nuclear membranes reappear & two daughter cells result - Sometimes a short interphase exists between meiosis I and II RESULT AFTER MEIOSIS I: 5

6 Meiosis II: 1. Prophase II: - each daughter cell forms spindle fibers - the double stranded chromosomes begin to move to the centre 2. Metaphase II: - centromeres of the chromosomes attach to the spindle fibers at the centre of the cell 3. Anaphase II: - centromeres of chromosomes divide and sister chromatids separate, moving to opposite poles of the cell - there are now 4 individual chromosomes, one in each daughter cell 4. Telophase II: - both daughter cells divide to form 4 haploid cells - nuclear membranes reappear - in each cell, chromosomes return to the interphase stage RESULT AFTER MEIOSIS II (end of meiosis): 6

7 7 BIO 30 - REGIER

8 PART II An Introduction to Inheritance 1. Mendelian Genetics What is genetics? Gregor Mendel - - Mendel s Experimental Design Q: Why did Mendel use peas? Q: What did Mendel do in his experiments? (3 main points) 8

9 Mendel s conclusions: : When an organism is hybrid for a pair of contrasting traits (ie: carries a copy of each trait), only the dominant trait can be seen in the hybrid. ex: when only yellow-seeded plants turned up after a cross between a pure-breeding yellow and a pure-breeding green plant, Mendel concluded that the characteristic for yellow seeds was dominant - Factors (genes) that occur in pairs are separated from one another during gamete formation (ie: sperm & egg production) and are recombined at fertilization (ie: when sperm and egg meet during sexual reprod n). : During meiosis, factors (genes) for different traits will be separated & distributed to gametes (sperm or egg) independent of one another. * this is not always true because of. Learning the terms.. 1. gene: 2. allele: 3. locus: 4. homozygous: 5. heterozygous: 9

10 6. dominant: 7. recessive: 8. genotype: 9. phenotype: Genetics Problem Solving Using the Punnett Square Q: What is a punnett square? a) Monohybrid Cross: Ex #1: 10

11 ex #2: What are the results (in terms of plant height) after crossing two offspring of the previous parent plants? ex #3: In peas, yellow seed color is dominant over green seed color. The genotypes of the parents are both Yy. State the genotypic and phenotypic ratios of the offspring. 11

12 Q: When not given the genotypes, how does one know if an individual showing a dominant trait is pure for the trait (homozygous) or hybrid (heterozygous)? 12

13 b) Dihybrid Cross: ex #1: Mendel considered both seed color & shape when crossing pea plants. He started with plants that were homozygous for these traits. Perform the following cross: YYRR x yyrr P 1 alleles Y = yellow y = green R = round r = wrinkled 13

14 ex #2: Perform an F1 cross. State the genotypic & phenotypic ratios of the offspring. 14

15 ex #3: Brown hair is dominant over red hair. Green eyes are dominant over blue. Describe the phenotypes of the F1 generation knowing that both parents are heterozygous for both traits. (Note: Hair color & eye color are governed by multiple genes..this question simplifies the inheritance!) Ex #4: Find the results of a cross between a homozygous tall, heterozygous yellow-seeded plant & a short, heterozygous yellow-seeded plant. 15

16 2. Other Concepts in Genetics A. Incomplete Dominance ex #1: snapdragon plant trait flower color alleles R red W white RW pink cross red flower x white flower RR WW ex #2: Try pink flower x pink flower 16

17 B. Codominance ex#1: trait coat color in horses (C) alleles cross homozygous red-coated horse x homozygous white-coated ex #2: Students try this one. Two roan colored horses mate. What is the probability that their foal will be white in color? 17

18 C. Multiple Alleles Ex of inherited trait with multiple alleles: ABO blood typing system GENOTYPES PHENOTYPES (blood type) Ex #1: Billy, type O blood, and Betty, heterozygous for type A blood, have a daughter, Betsy. What is the probability that Betsy will have type A blood? 18

19 ex #2: Johnny is curious as to whether or not he is adopted. His mother has type A blood and his father has type B blood. Johnny has type O blood. Could he be their child? ex #3: Gerald (heterozygous type A blood) and Georgetta (heterozygous type B blood) plan to have 3 children. What is the probability that all three children will have type O blood? 19

20 D. Polygenic Inheritance Examples include: 3. Chromosomal Inheritance Thomas Hunt Morgan a) Sex Chromosomes autosomes: sex chromosomes: During the fertilization of the egg. 20

21 sex-linked traits: examples of x-linked: examples of y-linked: ex #1: trait red-green color blindness (X-linked recessive) allele C color blind gene (found on X) * write in superscript* cross normal father x carrier mother ex #2: A father with hemophilia marries a woman who is a carrier of hemophilia. What is the probability that a son of theirs will have hemophilia? What is the probability that a daughter of theirs will have hemophilia? 21

22 b) Gene linkage c) Crossing Over & Recombination A LOOK BACK AT PART II: An Intro to Inheritance. 1. Mendelian genetics - Mendel s experimental design, experiment & conclusions - learning genetics terms - genetic crosses involving the punnett square a) monohybrid b) dihybrid 2. Other concepts in genetics A. Incomplete dominance B. Codominance C. Multiple Alleles D. Polygenic Inheritance 3. Chromosomal Inheritance a) Sex chromosomes & sex-linked traits b) Gene linkage c) Crossing over & recombination 22

23 PART III: A Closer Look At Genetics 4. The Genetic Material - A review of DNA.. nucleotide: base pairing rules (bonding): - Hershey & Chase (1952) - - Watson & Crick (& Rosalind Franklin) (1953) - 23

24 DNA Replication (How it Copies Itself ) The Ingredients: The process: STEP 1: STEP 2: STEP 3: 24

25 FINAL RESULT: From Gene to Protein STEP A Transcription The purpose: The ingredients: The process (4 steps): 25

26 The product: STEP B Translation The ingredients: The process: STEP #1: trna (transfer RNA) carries amino acids from the cytoplasm to the ribosomes by binding with them. Each trna combines with only one type of amino acid (aa). The trna is in the shape of a cloverleaf with an aa attachment site at one end and an anticodon (made of three bases) at the other end. Each trna has a different anticodon (see #4 in diagram). STEP #2: When protein synthesis is about to begin, a ribosome moves along an mrna. At the same time, a trna approaches with its amino acid. The anticodon of the trna recognizes and joins with only a particular codon of the mrna. ex: an anticodon CGC must join with a GCG mrna codon The trna with its aa remains temporarily attached to the mrna 26

27 STEP #3: The ribosome moves to the next triplet codon; the appropriate trna comes with its aa and joins the mrna. The new aa is attached to the previous aa by a peptide bond and the first trna can leave. STEP #4: This process continues until the ribosome reads a terminating codon (see #2 in diagram) which instructs the trna to stop. The aa chain (polypeptide chain) (see #5 in diagram) that has been created detaches & moves away. The mrna may be read again or it will go back to the nucleus & dismantle. The products: Q: What is the overall significance of DNA replication, transcription & translation? 27

28 5. Variation & Mutations Q: Why are variations among individuals important? 28

29 Q: What are the sources of these variations? Mutation a) chromosomal mutation: nondisjunction polyploidy b) gene mutation: 29

30 6. Some Human Genetic Disorders see handout Q: How can genetic disorders be detected? a) : cell undergoing mitosis is photographed, chromosomes in photograph are cut out and arranged in pairs. Anomalies are detected through a study of the appearance of the chromosomes. b) : used for genetic testing of growing fetus - sample of amniotic fluid, which contains cells of the fetus, is tested - tests may include an examination of the appearance of chromosomes or testing for an enzyme c) : : cells of part of the placenta in a pregnant mother are tested for genetic disorders of fetus 30

31 2. Pedigree Charts Example: The pedigree below is studying the incidence of blonde hair in a family. In humans, dark hair (B) is dominant to blonde hair (b). In this case, individuals who are shaded in are homozygous recessive. Individuals who have clear circles and squares have at least one dominant gene. What are the genotypes of persons A through F below? 31

32 8. Selective Breeding, Genetic Engineering & Recombinant DNA Selective breeding: list some examples: Genetic engineering: Q: What is the purpose of producing recombinant DNA? How genetic engineering is done.. Genetic engineering can be done for many purposes. Often, it is used to make more of a desired protein in drug production. This would be done as follows: 1. DNA is cut up into fragments by using enzymes (often isolated from bacteria) that recognize specific sequences of nucleotides & cut the DNA there. 32

33 2. The fragments of DNA are then combined with another DNA molecule to make the recombinant DNA. Often the fragments of DNA are combined with small, ring-shaped DNA called plasmids. These are found outside of the main chromosome set of many bacteria, some viruses & some yeasts. 3. The altered plasmids are exposed to a host cell (usually a bacterium or virus) which takes them in. The host cell then produces the protein specified by the inserted gene. The host cell is cloned so that more of the desired protein will be produced. Ethical concerns? 33

34 9. Population Genetics The genes of an individual.. The genes of a population. gene pool: population genetics: Hardy-Weinberg Law: Conditions of the law (4): 34

35 Q: Why is a law that can never be fulfilled important to study? genetic drift: Founder effect: LOOKING BACK I: Mitosis & Meiosis II: An Introduction to Inheritance 1. Mendelian Genetics - Mendel s experiments; terminology; punnett squares (mono & dihybrid crosses) 2. Other Concepts in Genetics A. Incomplete dominance C. Multiple Alleles B. Codominance D. Polygenic Inheritance 3. Chromosomal Inheritance a) sex chromosomes b) gene linkage c) crossing over & recombination III: A Closer Look at Genetics 4. The Genetic Material - history & structure; DNA replication, transcription, translation 5. Variation & Mutations - chromosomal & gene mutations 6. Human Genetic Disorders 7. Pedigree Charts 8. Selective Breeding, Genetic Engineering & Recombinant DNA 9. Population Genetics 35