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Unit 1: Understanding Biological Inheritance Bio 40S Words – What do you think they mean? • • • • • Genetics DNA Mitosis Meiosis Evolution • • • • • • Bacteria Species Ecosystem Biodiversity Global Warming Mutation WHMIS Workplace Hazardous Materials Information System Mitosis Vocabulary • Chromosomes – thread-like structures in nucleus that contain genetic information. • Chromatin – material in chromosomes composed of DNA and protein. • Chromatid – one of two distinct strands that make up each chromosome. • Cytoplasm – liquid area between the nucleus and the cell membrane of a cell. • DNA – (Deoxyribonucleic acid) - stores and transmits genetic information - codes for proteins. More vocabulary • Gametes: reproductive cells – sex cells (eggs and sperm); haploid cells ( ½ the number of chromosomes: in humans – 23 chromosomes). • Somatic Cells: regular body cells with full chromosome content (diploid cells); in humans: 46 chromosomes. • Centromere: the structure that holds the chromatids together. • Centriole: spindle fibre involved in cell division. What is Mitosis? 1. Cell division in eukaryotic cells 2. Separates chromosomes into two identical sets 3. Followed by cytokinesis - divides the nuclei, cytoplasm, organelles & cell membrane into two equal shares 4. result 2 daughter cells (identical to each other and to parent cell). 5. http://www.youtube.com/watch?v=ZEwddr9ho-4 Part of the Cell Cycle 2. Different phases of mitosis. Interphase: the time between cell division. at least 4 things happen: 1. Cell grows (small cell big cell) 2. ATP is made (NRG) 3. DNA replication 4. protein synthesis (enzymes) Steps of cell division 1) Prophase Chromatin condenses into chromosomes (46 in humans). Nuclear envelop disintegrates. 2) Metaphase (M for middle) Chromosomes align at the equatorial plate. 3) Anaphase Chromosomes split apart. Sister chromatids separate. Centromere divides. 4) Telophase Chromatin expands. Cytoplasm divides (cytokinesis). Two identical daughter cells are formed. Significance of Mitosis • 1. Development and growth: multicellular organisms • 2. Cell replacement e.g. cells of skin & digestive tract, RBCs have short life span (~ 4 months) • 3. Regeneration: e.g. starfish regenerate lost arms • 4. Asexual reproduction: e.g. hydra (fresh water animal) reproduces by budding • - vegetative propagation in plants • Review… • http://www.stolaf.edu/people/giannini/flashanimat/celldivision/crome3.swf Binary Fission • Cell division of Prokaryotic cells • e.g. Bacteria cells • http://www.youtube.com/watch?v=hOyUcjqc GpQ&feature=related Meiosis…What is it used for? • cell division of sex-cells • No meiosis … too many chromosomes!! (92) • halves # of chromosomes ~ new generations receive correct # of chromosomes • the egg (23) + the sperm (23) = baby (46) = Meiosis…What is it used for? • It allows for genetic variation which is important for survival of the species – we are all not identical to each other (and so a disease will not wipe all of us out at once). • Leads to Evolution. Meiosis 1. What is meiosis and what is it used for? • Meiosis is the process of cell division that results in the formation of gametes (sperm and egg cells). • Remember that gametes have only ½ the number of chromosomes than other cells in the body (somatic cells). • Somatic cells (human) – 46 chromosomes (diploid) • Sex cells (human) – 23 chromosomes (haploids) • Meiosis takes care to ensure that all gametes are different (and that you’re not the same as your siblings!). 2. Name and explain the different phases of meiosis. Meiosis is composed of 2 stages (Cell divisions) Meiosis I • Interphase I: chromosomes duplicate into sister chromatids (DNA replication) • Prophase I: chromosomes contract, nuclear membrane disintegrates, chromosomes partner up Crossing Over Sometimes during prophase, the chromotids of each pair of homologus chromosomes may wind around each other and pieces of chromosomes or pairs of sister chromatids are exchanged. This is called CROSSING OVER. • Metaphase I: the homologus chromosomes line up a the centre of the cell in pairs, the centromeres attach to the spindle fibers that run the length of the cell. • Anaphase I: after all chromosomes are aligned, one of each pair begins to move to opposite poles of the cell (sister chromatids remain connected to one another). *This is the stage where the chromosome # is reduced by half.* • Telephase I – cytoplasm divides 2 haploid cells result. Meiosis II (may begin with a short resting phase, called interphase II) • Prophase II – chromosomes begin to move to the cell’s equator (happens at the same time for all cells). Each chromosome still has 2 sister chromatids joined at a centromere. • Metaphase II – centromeres for each chromosome are attached to spindle fibers and are lined up at the cells equator. • Anaphase II – sister chromatids are pulled apart toward opposite poles of the cell. Each sister chromatid takes part of the centromere with it. • Telephase II – cytoplasm splits for each cell resulting in 4 haploid gametes. Sperm = spermatogenesis; Egg = Oogenesis • http://www.youtube.com/watch?v=D1_-mQS_FZ0&feature=related Meiosis ~ Gametogenesis - “creation of gametes.” • Spermatogenesis (the formation of sperm) • Male testes have tiny tubules diploid cells spermatogonium (diploid cells) • these mature to become sperm (haploid cells) • each one spermatogonium becomes 4 sperm • Starting at puberty, a male will produce literally millions of sperm every single day for the rest of his life. Spermatogenesis • http://www.youtube.com/watch?v=POpbN6R HOO0 Oogenesis • formation of haploid cells from an original diploid (primary oocyte. • The female ovaries contain the primary oocytes. • Two major differences between the male and female production of gametes. • 1. Oogenesis only leads to the production of one final ovum (large egg cell) – three come out much smaller than the final ovum. These are called polar bodies – they eventually disintegrate, leaving only the larger ovum. • 2. The production of one egg cell via oogenesis normally occurs only once a month, from puberty to menopause. Oogenesis Part One http://www.youtube.com/watch?v=VPezOuOnq1g Part Two http://www.youtube.com/watch?v=pK7qjcgIox0&feature=relmfu • Meiosis ensures that: • The chromosome # remains constant from one generation to the next. • That each sexually reproduced offspring will receive 2 complete sets of genetic instructions. • Allows for genetic diversity. Remember - chromosomes are found in the cell nucleus. - chromosomes contain genes (segments of DNA that control heredity traits). - chromosomes occur in pairs (homologus pairs) More Information! Extra Information • n = # of chromosomes in a gamete cell • 2n = # of chromosomes in a diploid cell • Synapsis – is when Homologus chromosomes pair up Meiosis Videos • http://www.youtube.com/watch?v=35ncSrJO wME&feature=related • http://www.youtube.com/watch?v=JKXAdwCi bsA&feature=related • http://www.youtube.com/watch?v=_IzfJSxauA&feature=related Unit 1: Genetics Understanding Biological Inheritance Genetics is… • The study of heredity. • Heredity is the transmission of traits from parents to offspring. • Genes are particular segments of DNA molecules that determine the inheritance and expression of a particular character, e.g. eye colour. • Alleles are two or more alternative forms of a gene, e.g. Tall (T) vs. short (t); alleles occupy the same locus on homologus chromosomes. More vocabulary • Genotype: the genetic composition of an organism – the combination of alleles, e.g. Bb. • Phenotype: The physical appearance of the individual based on their genotype, e.g. brown eyes. • Punnett square: A chart that shows possible genotype/phenotype of offspring. • Homozygous: Two copies of the same allele/gene, e.g. BB or bb • Heterozygous: Two different alleles for the same trait, e.g. Bb. More vocabulary • Purebred: The same as homozygous; used in breeding circles. • Hybrid: Same as heterozygous. • Dominant traits: Expressed in both homozygous and heterozygous forms (alleles denoted by capital letters, e.g. B) • Recessive traits: Expressed in only the homozygous form (alleles denoted by lowercase letters, e.g. b) • Carrier: Someone who carries the recessive allele but doesn’t show it. Recessive vs. Dominant • When the dominant allele is present in the genotype, it is always expressed in the phenotype. • When the recessive allele is present in the genotype, it is only expressed in the phenotype if it is paired with another recessive allele for the same trait. • Example: Brown eyes (B) are dominant to blue eyes (b). – BB = homozygous dominant (brown eyes) – Bb = heterozygous (brown eyes) – bb = homozygous recessive (blue eyes) Mendel • Gregor Mendel (1822 – 1884) is considered the “Father of Genetics” – He was the first to study how traits were passed from one generation to the next. – Studied garden pea plants in an Austrian monestary. – Pea plants were ideal to study heredity because they self-pollinate the sperm fertilizes the ovule in the same plant. – In a pea plant, the gene for producing seed shape may occur in two alternative forms: R = round; r = wrinkled Questions on Gregor Mendel 1. What were the 7 traits that Mendel studied in pea plants? 2. Which were the dominant of these traits? (Name all 7) 3. Which were the recessive of these traits? (Name all 7) 4. What is self-pollination? 5. What is cross-pollination? 6. What is purebred? 7. What is hybrid? 8. What is segregation? Generations • Parent Generation (P): The parents used for the first cross represent the parent generation. • F1 generation: The progeny (product) produced from a cross between two parents. • F2 generation: The progeny resulting from selfhybridization or inbreeding of F1 individuals. • Inbreeding: When individuals of a progeny are allowed to cross with each other (e.g. 2 individuals from F1) Mendel’s Pea-Plant Traits Trait Phenotype Genotype (dominant, recessive) Seed shape Round, wrinkled Seed colour Yellow, green Seed coat colour White, grey Pod shape Smooth, wrinkled Pod colour Green, yellow Flower position Axial, terminal Plant height Tall, short RR, Rr, rr YY, Yy, yy WW, Ww, ww NN, Nn, nn GG, Gg, gg AA, Aa, aa TT, Tt, tt Punnett Squares The segregation and combination of the male and female cells (gametes) produced as a result of meiosis can be expressed using a simple matrix. This checkerboard diagram is used to illustrate the possible results of a cross between the gametes of two individuals. • Test Cross: involves crossing a F1 offspring with a homozygous recessive individual. Used to determine whether or not the F1 offspring is purebred or not. Punnett Squares • Shows what type of offspring could be, given the genotypes of the parents. Probability (predictions) of offspring genotypes/phenotypes. • Mendel’s plants Tall = TT or Tt; short = tt • If a heterozygous tall pea plant (Tt) was crossed with a homozygous recessive short pea plant (tt), what will the offspring’s genotypes be? What would the phenotypes be? t t Genotypes Phenotypes T Tt Tt t tt tt 2 Tt : 2 tt ratio 2 tall : 2 short ratio 50% probability that the offspring will be tall or short. Males vs. Females What is the difference between boys and girls? • Both males and females have 44 autosomes (non-sexlinked chromosomes), and 2 sex-linked chromosomes. Sex-linked chromosomes (2 each) • The males have an X chromosome and a Y chromosome. • The females have two X chromosomes. How much of our DNA is the same as another human of the same sex? • 99%. One percent of our DNA is different. A Karyotype of a Human’s Chromosomes - Male or female? Mendel’s Laws Law #1: Law of Gene Character Genetic characters are controlled by unit factors (genes) that exist in pairs in individual organisms and are passed from parents to their offspring. When two organisms produce offspring, each parent gives the offspring one of the factors from each pair. Law #2: Law of Dominance When two unlike factors responsible for a single character are present in a single individual, one factor can mask the expression of another factor. That is, one factor is said to be dominant to the other, which is said to be recessive. Law #3: Law of Segregation (also known as The Principle of Segregation) During the formation of gametes, the paired factors separate (segregate) randomly so that each gamete receives one factor or the other. Law #4: Law of Independent Assortment (also known as The Principle of Independent Assortment) • During gamete formation, segregating pairs of factors assort independently of each other. (In humans, that’s a mixture of 30,000 genes!) • The inheritance of a pair of alleles affecting one characteristic occurs independently of alleles affecting any other characteristic. • i.e. The gene that controls one trait has no influence on the inheritance of a gene with a different trait. e.g. The gene that controls if a seed is round or wrinkled is NOT linked to the gene that determines if the seed if yellow or green (the genes are not on the same chromosome). Laws of Segregation and Independent Assortment on Wikipedia BIG Punnett Square (Di-hybrid Cross) • P-Generation – Cross a homozygous Tall, Green plant (dominant traits) with a short, yellow (recessive) plant. What will the offspring look like? T = Tall tt = short G = Green gg = yellow Cross TTGG (homozygous dominant) with ttgg (homozygous recessive) What are the genotypes of the gametes for each plant in the cross? (Remember, offspring inherit one allele from each parent.) “Male” plant gametes = TG, TG, TG and TG “Female” plant gametes = tg, tg, tg and tg tg tg tg tg TG TtGg TtGg TtGg TtGg TG TtGg TtGg TtGg TtGg TG TtGg TtGg TtGg TtGg TG TtGg TtGg TtGg TtGg • F1 generation – All genotypes are TtGg – All phenotypes are 100% Tall and Green – Each offspring produced will have the same genotype and phenotype. • Now cross two members of the F1 generation to interbreed and work out the geno and phenotype combinations. How many will be Tall and Green? – What are the genotypes of each parent plant? – What are the genotypes of each parent plant’s gametes (list all combinations). – Test cross. – Find the genotype and phenotype ratios. TtGg x TtGg “Male” gametes = TG, Tg, tG and tg “Female” gametes = TG, Tg, tG and tg TG TG Tg tG tg Tg tG tg TTGG TTGg TtGG TtGg TTGg TTgg TtGg Ttgg TtGG TtGg ttGG ttGg TtGg Ttgg ttGg ttgg Genotypic ratio 1 TTGG : 2 TTGg : 2 TtGG : 4 TtGg : 1 TTgg : 2 Ttgg : 1 ttGG : 2 ttGg : 1 ttgg Phenotypic ratio 9 Tall, Green plants 3 Tall, yellow plants 3 Short, Green plants Short, Yellow plants Genotypic ratio 1 TTGG : 2 TTGg : 2 TtGG : 4 TtGg : 1 TTgg : 2 Ttgg : 1 ttGG : 2 ttGg : 1 ttgg Phenotypic ratio 9 Tall, Green plants 3 Tall, yellow plants 3 Short, Green plants 1 Short, Yellow plant All Heterozygous Dihybrid Crosses will give this 9:3:3:1 ratio. Exceptions to Mendel’s Laws • We know today that there are many exceptions to Mendel's laws (i.e. not every gene has alleles that are strictly dominant or recessive). Does this mean that Mendel was "wrong"? NO, it means that we know more today about disesase, genes, and heredity than we did 150 years ago! Exceptions to Mendel’s Laws Exceptions to Mendel’s Laws 1) Co-dominance – Both alleles are dominant and expressed. e.g. A red flower crossed with a white flower = red and white striped flowered plants. RR = red flowers WW = white flowers RW = red and while striped flowers What would the phenotopic ratio be if we crossed 2 RWs? R W R RR RW W RW WW Genotypic ratio -- 1 RR : 2RW : 1 WW Phenotypic ratio – 1 red : 2 striped : 1 white 2) Incomplete dominance – Both alleles are blended and expressed. e.g. Cross a red flower and a white flower = pink flowers. RR = red flowers WW = white flowers RW = pink flowers What would the phenotopic ratio be if we crossed 2 RWs? R W R RR RW W RW WW Genotypic ratio -- 1 RR : 2RW : 1 WW Phenotypic ratio – 1 red : 2 pink : 1 white 3rd Exception – Lethal Alleles • Sometimes the phenotype that results from an allele is death. • These usually occur as mutations with essential genes (genes you need to survive). • Both dominant and recessive lethal alleles exist. Lethal Genes e.g. Huntington’s Disease – caused by a dominant and lethal gene – HH and Hh – homozygous and heterozygous – person lives long enough (usually in their 30s) so they can pass along the lethal gene onto their offspring. e.g. Cystic Fibrosis – caused by a recessive and lethal gene – life expectancy is 5 years without medical treatment – this genetic disorder exists only in the homozygous state (cc), This occurs when both parents are carriers (Cc). e.g. Dwarfism - dominant (A) – lethal only in the homozygous state (AA) – Spontaneous abortion – in the heterozygous state, dwarf only. • • • AA (die early) Aa (dwarf) aa (normal) • What is the probability that two dwarfs have a normal child? More Exceptions 4) Polygenic Traits – traits controlled by a number of different genes. – These genes may be on the same or on different chromosomes. – Each gene contributes a small but equal increment to the trait being expressed – a blending result. – Examples include skin colour, height, eye colour, hair colour and intelligence. Is this an Exception to Mendel? 5) Multiple Alleles – three or more alleles of the same gene but only 2 alleles required to express the trait. e.g. blood groups • 3 alleles • 4 different blood types • Determined by the presence or absence of antigens in the blood. Genotype Phenotype IAIA Type A Blood Iai Type A Blood IBIB Type B Blood IBi Type B Blood IAIB Type AB Blood ii Type O Blood What are the genotypes/phenotypes from the cross between 2 AB parents? A B A AA AB B AB BB Genotypes: 1 AA, 2 AB, 1 BB Phenotypes: 25% Type A, 50% Type AB, 25% Type AB Show the cross between IAi and Ibi. Mendel’s 6th Exception Sex-linked Traits (X-linked) • Many genes are located on the X chromosome (some on the Y). X is a BIG chromosome, Y is a smaller chromosome. • In humans there are 46 chromosomes, and only 2 of these are sex chromosomes (X and Y). Females – XX and males – XY. The other 44 are autosomes. • In meiosis, each egg (female) gives an X chromosome. • In meiosis, each sperm (male) give either an X or a Y chromosome (50 : 50). At fertilization (XX cross XY) X X X XX XX Y XY XY Geno: 2 XX and 2 XY Pheno: 50% girl, 50% boy • Because the Y chromosome carries less DNA than the X, the Mendelian ratio does not occur if the genes are on the X chromosome and are recessive. Fruit Flies • Thomas Morgan (scientist) experimented with Drosophilias (fruit flies). He found that there were more white-eyed males than white-eyed females. Red-eyed fruit flies were dominant. R = Red, r = white Genotypes Phenotypes XRXR female, red eyes XRXr female, red eyes X rX r female, white eyes XRY male, red eyes X rY male, white eyes Cross a homozygote red-eyed female with a white-eyed male. XRXR cross with XrY XR XR Xr XR Xr XR Xr Y XRY XRY Geno ½ X RX r ½ XRY Pheno ½ female carrier ½ red-eyed male All the offspring will have red eyes; no whiteeyed children. • Morgan showed that in his experiments with fruit flies that some off-spring had combinations different from either parents these new individuals are called RECOMBINANTS – e.g. In fruit flies body colour and wing size are linked most of the time, but not always. This can be explained by crossing over that takes place during the first meiotic division when the homologus chromosomes are paired. Colourblindness • A recessive sex-linked disorder. Most common is red-green colourblindness. B = normal, b = colourblind • XBXB cross XB XB Xb XBXb XBXb How many of the children b XY will be colourblind? Y XBY XBY Geno 2 XBXb, 2 XBY Pheno 50% Normal males 50% Female carriers Other diseases on X-chromosome – hemophilia, muscular dystrophy. Can a female carrier have a colourblind girl? Chromosomal Mutations • These occur when segments of chromosomes, entire chromosomes or even complete sets of chromosomes are involved in genetic change. Effects are due to chromosome arrangement. A. Changes in chromosome # -- Non-disjunction. • • This is a failure of chromosomes to separate during meiosis, resulting in an abnormal number of chromosomes. A gamete with +/- 1 chromosome may still fuse with an egg or sperm. Some survive, but most are spontaneously aborted. Common Non-Disjunction Disorders 1. Down Syndrome, “Trisonomy 21” The individual is born with 47 chromosomes. The frequency of this disorder increases with increasing maternal age. 50% of individuals die by 4 yars old, most live to approximately 30 years. Mental retardation, epicanthic folds of the eye, short stature, cardiac deformities. 1. Turner Syndrome (XO) 45 chromosomes, short stature, webbed neck, may have slight retardation, immature genitals, sterile, occurs 1 in 2500 conceptions. 2. Kleinfelters Syndrome (XXY) 47 chromosomes, tall, female-like breasts, some mental retardation, (50%), normal male, small testes, produce little to no sperm. It doesn’t matter how many X-chromosomes a person has, it is the presence of the Y chromosome that makes an individual a male. The Y chromosome has a “testis determining factor” that stimulates growth of male reproductive organs. Chromosomal Mutations (cont’d) B. Changes in chromosomal structure (3 types) i. Deletions: due to loss of a chromosome segment after breakage. e.g. Cri-du-chat Syndrome – deletion of portion of the arm of chromosome 5, severe retardation, cry resembles cat. ii. Duplication: due to an increase in the amount of genetic material carried by a chromosome, usually not problematic and may actually provide genetic variation. iii. Inversions, Shifts and Translocations: when a portion of the chromosome breaks and it may rotate 180° and reattach on the same/original chromosome (inversion), if it becomes inserted in a different region on the same chromosome (shift), or may be inserted on a different/non-homologous chromosome (translocation). These all may be fatal to the zygote. “Boy With an Extra X” • Read story. Answer these questions in your notebook (complete sentences). 1. Did Tom have all the Kleinfelter’s Syndrome symptoms? Which symptoms did he have? 2. What is a good idea to have genetic testing done? Why? 3. How would you feel if you found out you had a genetic disorder? What would you do about it? 4. Likewise if you were to have a child with a genetic difference. How would you feel? What would you do? Pedigrees • A geneticist’s way of charting the passage of a trait from one generation to the next. • In a pedigree chart, the darkening of squares/circles indicates the presence of the Pedigree Legend trait under study. How to Draw a Pedigree Draw a pedigree for a family with a husband and wife and 4 children – 2 girls and 2 boys (in that order). The father is colour-blind (a recessive, sex-linked disorder) and the two girls are carriers. I II Xd Y XD XDXd XDY XD XDXd XDY Draw a pedigree of the following family showing the genotypes of all the individuals (place these under the individuals in the pedigree). Make a legend! The inability to roll one’s tongue is recessive to the ability to roll one’s tongue. It is not sexlinked. A man who can roll his tongue marries a woman who cannot roll her tongue. They have three children: a daughter followed by two sons. The oldest and youngest children are able to roll their tongues, but their middle child cannot. The daughter marries a man who is able to roll his tongue, but their son cannot. The middle son marries a woman who is able to roll her tongue. The youngest child marries a woman who is unable to roll her tongue, but they have no children. Pedigree Activities • • • • Pedigree Studies Applied Genetics Baby Pierre Queen Victoria Heredity vs. Environment • “Nature vs. Nurture” • Environment can affect the expression of a gene. – e.g. 1) height genes determine approximate height of a person, but environment (i.e. nutrition may or may not allow the individual’s potential to be reached (poor diet shorter ; poor posture shorter) – e.g. 2) intelligence affected by prenatal environment (alcohol – FAS – or nutrition), as well as early years environment (stimulating environment helps mental development). – e.g. 3) high blood pressure: predisposition inherited, but influenced by diet, exercise, stress, smoking. – e.g. 4) coat colour in siamese cats: dark legs, face and tail result because the black fur gene can only be expressed at cool temperatures; fur at extremities darkens, fur close to warm body stays light. Karyotypes • The “picture” of the arrangement of all homologus pairs of chromosomes in an individual. • Karyotypes can be studied to identify the presence of a genetic disorder, and pinpoint the chromosome responsible for the disorder. Normal Karyotype (Male) Down Syndrome (Trisonomy 21) in a Female Klinefelter Syndrome (XXY)