Chapter 10 Intro Genetics PDF

1 What traits could be inherited in plants? 2 Genetics ahead Warning 3  Objectives 1. Contrast the chromosome number of body cells and gametes 2. Summarize the events of meiosis 3. Contrast meiosis and m...

1 What traits could be inherited in plants? 2 Genetics ahead Warning 3  Objectives 1. Contrast the chromosome number of body cells and gametes 2. Summarize the events of meiosis 3. Contrast meiosis and mitosis 4. Explain the importance of meiosis in providing genetic variation 4 Introduction to Genetics Chapter 11 5 Many of your characteristics--or-- traits like... shape of your eyes Shape of your nose Hair color... resemble those of your parents 6  The passing of characters/traits from parent to offspring is called Heredity Her but ity Traits are inherited characteristics such as... 7 Every species has a certain number of chromosomes in each cell nucleus 46 Chicken 78 Monkey 48 Fruit fly 8 A body cell in an adult fruit fly has 8 chromosomes: 4 from the fruit fly's male parent, and 4 from its female parent These two sets or one pair of chromosomes are called homologous chromosomes 8 Each of the 4 chromosomes that came from the male parent has a corresponding chromosome from the female parent A cell that contains both sets of homologous chromosomes is said to be Ll oy d DIP Diploid 9 The number of chromosomes in a diploid cell is represented by the symbol 2n For Drosophila, the diploid number is 8, written as 2n=8 Fruit fly Gametes which are sex cells have half the number of chromosomes and therefore only a single set of chromosomes 10 These cells are called Haploid Ll oy d Haploid cells are represented by the symbol N For Drosophila, the haploid number is 4, Fruit fly which can be written as n=4 11 Haploid (N) a.k.a. gamete cells are produced from a diploid (2N) cell by the process of Meiosis meiosis I and Meiosis involves two divisions, meiosis II By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells 12 13  Meiosis Before Meiosis begins each chromosome is replicated Meiosis I Telophase I and 14 Cytokinesis  Prophase 1 Each chromosome pairs with its corresponding homologous chromosome to form a There are 4 chromatids in a tetrad Chromosome tetrad 15 When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing-over Crossing-over produces new combinations of alleles. 16 17 18  Metaphase Pairs or homologous chromosomes randomly line up along the middle of the cell by spindle fibers. This mixes up the chromosomal combinations. Human’s 23 pairs of chromosomes results in 223 or 8,388,608 possible combinations of chromosomes 19  Anaphase I The spindle fibers pull the homologous chromosomes of the tetrad toward opposite ends of the cell. The sister chromatids remain attached 20 MEIOSIS I Telophase I and Cytokinesis Nuclear membranes form The cell separates into two cells The two cells produced by meiosis I have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I 21  Meiosis II The two cells produced by meiosis I now enter a second meiotic division Unlike meiosis I, neither cell goes through chromosome replication Each of the cell’s chromosomes has 2 sister chromatids 22 Meiosis II 23 MEIOSIS II Metaphase II The chromosomes line up in the center of cell 24 MEIOSIS II Anaphase II The sister chromatids separate and move toward opposite ends of the cell 25 MEIOSIS II Telophase II and Cytokinesis Meiosis II results in four haploid (N) daughter cells 26 In male animals, meiosis results in four equal-sized gametes called sperm The sperm begins as a round cell and ends in a streamline cell with a flagellum tail DNA is tightly packed in its head 27  In many female animals, only one egg results from meiosis. The one egg receives most of the organelles, cytoplasm, and nutrients The other three cells, called polar bodies, are not involved in reproduction They are eventually broken down  How is meiosis different from mitosis? Mitosis results in the production of two genetically identical diploid cells Meiosis produces four genetically different haploid cells 29  Mitosis Cells produced by mitosis have the same number of chromosomes and alleles as the original cell Mitosis allows an organism to grow and replace cells Some organisms reproduce asexually by mitosis 30  Meiosis Cells produced by meiosis have half the number of chromosomes as the parent cell These cells are genetically different from the diploid cell and from each other Meiosis is how sexually reproducing organisms produce gametes 31 Quiz 32  Scientific study of heredity began with an Austrian monk named Gregor Mendel Mendel was the first to develop rules that accurately predicted patterns of heredity He achieved this by carrying out experiments with garden peas. 33 Mendel knew that: the male part of each flower produces pollen, (sperm, gamete) Male parts the female part of the flower produces egg cells, (gamete) Female parts 34 During reproduction, sperm and egg cells join in a process called Fertilization Fertilization produces a new cell. 35  Peas and most plants are self-pollinating Sperm cells in a plant fertilize the egg cells in the same flower The seeds that are produced by self-pollination inherit all of their characteristics from the single plant that bore them 36  Mendel had true-breeding pea plants self-pollinate plants that, would produce offspring identical to themselves. 37  Mendel wanted to produce seeds by joining male and female reproductive cells from two different plants. Male parts Female parts He cut away the pollen-bearing male parts of the plant and dusted the plant’s flower with pollen from another plant 38 This process is called cross-pollination Mendel was able to produce seeds that had two different parents This made it possible for him to cross-breed plants with different characteristics 39  Mendel studied different pea plant traits... seed shape and color, pod shape and color Flower position of the plant and Plant height each with two contrasting characters After crossing plants with contrasting characters he studied their offspring 40 Each original pair (of true breeding plants) is the P (parental) generation The offspring are called the F1, or “first filial,” generation 41 Each of the traits Mendel studied was controlled by one gene.... Seed shape Seed shape Wrinkled Round DNA Green Yellow Seed color Seed color...that occurred in two different versions (allele) that produced different characters for each trait 42 The offspring of crosses between parents with different traits are called hybrids Tulip The F1 hybrid plants all had the character of only one of the parents The trait from the other parent seemed to disappear 43  Mendel wanted to know what happen to the disappearing allele. Did it just disappear or was it still present in the F1 plants? Dominant Mendel allowed the F1 generation to self- P generation pollinate to produce the F2 (second filial) generation What is your prediction of the cross between F1 parents? F1 Generation 44  The traits controlled by the disappearing allele reappeared in one fourth of the F2 plants Mendel assumed that a dominant trait (allele) had masked the corresponding disappearing allele in the F1 generation Dominant P generation F1 Generation F2 Generation 45 Mendel developed a hypothesis to explain the 3:1 inheritance pattern he observed in F2 offspring Four related concepts make up this model These concepts can be related to what we now know about genes and chromosomes 46 The first concept is that alternative versions of genes account for variations in inherited characters Allele for purple flowers Homologous Locus for flower-color gene pair of chromosomes These alternative versions of a gene are now called alleles Allele for white flowers Each gene resides at a specific locus on a specific chromosome 47 The second concept is that for each character an organism inherits there are two alleles, one from each parent Dad True-breeding Flower color The two alleles at a locus on a chromosome Mom may be identical, as in the true-breeding plants of Mendel’s P generation Crossing non-true breeding the two alleles at a locus may differ, as in the Dad F1 hybrids F1 Flower color Mom 48 The third concept is that if the two alleles at a locus differ, then one (dominant allele) determines the organism’s appearance, Dad Flower color Mom and the other (the recessive allele) has no noticeable effect on appearance 49  The fourth concept, now known as the law of segregation, states that the two alleles for a heritable character separate (segregate) during gamete formation and end up in different gametes Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells of an organism gametes 50 Mendel repeated experiments with hybrid plants, each time the results were the same 3/4 of the offspring were like the dominate trait and 1/4 like the recessive trait 51  The likelihood that a particular event will occur is called probability There are two possible outcomes --- Heads or Tails The chance of heads in one flips would be 1 in 2 or 1/2 or 50% If you flip a coin three times in a row, what is the probability that it will be heads? Each coin flip is an independent event 1 1 1 1 X X = 8 2 2 2 52 Organisms that have two identical alleles for a particular trait are said to be Homozygous TT tt T t Homozygous organisms are true-breeding for a particular trait Organisms that have two different alleles for the same trait are Heterozygous Tt Heterozygous organisms are hybrid for a particular trait 53 The set of alleles that an individual has for a trait is called its Genotype TT Tt The physical appearance of a character / trait is called its Phenotype 54 55  A Punnett Square is a diagram that predicts the outcome of Law of segregation a genetic cross A capital letter represents the dominant allele for tall A lowercase letter represents the recessive allele for short 56 One third of the tall plants are dominate TT, while Two thirds of the tall plants are Tt The plants have different genotypes (TT and Tt), but they have the same phenotype (tall). 57 Indicate if it is heterozygous or homozygous BB homozygous B= brown hair b= green hair Bb heterozygous B b bb homozygous What is the phenotype? B BB Bb BB Brown hair b B b bb Bb Brown hair bb Green hair 58 All of the crosses we have done so far involved only a single trait. This is called Monohybrid crosses Crosses that examine the inheritance of two different traits is knows as dihybrid crosses 59 How many alleles per trait do individuals have? How many alleles per haploid per trait ? RrYy Genotype FOIL method Gametes-haploids RY Ry r Y r y RRY Y R R y Y r R Y Y rR y Y R Y RrYy R y Genotype r Y r y 60 In Mendel’s experiment, F1= RrYy × RrYy Phenotype of F1: Round and Yellow the F2 generation produced the following: 556 seeds some seeds were round and yellow 315 some seeds that were wrinkled and green 32 209 seed that did not look like the parents Recombinant Offspring that does not look like the parents some seeds that were round and green some seeds that were wrinkled and yellow 61  A Summary of Mendel's Principles Genes are passed from parents to their offspring If two or more alleles of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. 62 In sexually reproducing organisms, each adult has two copies of each gene. One from the female the other from the male. These genes are segregated from each other when gametes are formed 63 The alleles for different genes usually segregate independently of one another 64  Non-mendelian genetics Some alleles are neither dominant nor recessive, and some traits are controlled by multiple alleles or multiple genes When one allele is not completely dominant over another it is called Incomplete dominance In incomplete dominance, the offspring heterozygous phenotype is between the two homozygous dominant parent 65 Sometimes, both alleles of a gene are expressed completely When both traits are fully expressed it is called Codominance W W B BW BW B BW BW 66  In incomplete dominance, the offspring have Blend In Codominant alleles Both traits are expressed The flowers will have some red areas and some white areas 67 Genes that have more than two alleles are said to have Multiple alleles Individuals may have a combination of two alleles Often times this type is displays as co-dominance 69  An excellent example of multiple allele inheritance is human blood type. Blood type exists as four possible phenotypes: There are 3 alleles for the gene that determines blood type. IA I B i Remember: You have just 2 of the 3 in your genotype --- 1 from mom & 1 from dad 70  ALLELE CODES FOR The alleles are as follows: I A Type "A" Blood With three alleles we have a higher number Type "B" Blood IB of possible combinations in creating a i Type "O" Blood genotype. GENOTYPES PHENOTYPES I AI A Type A I Ai Type A I BI B Type B I i B Type B Universal recipient I AI B Type AB ii Type O Universal donor 71  The most common blood type is O+ 37% of US population are 0+ Which makes it in demand the most A+ is the second most frequently occurring blood type. 34% of US population are A+ AB negative blood type is the rarest, which is seen in just 0.6 percent of people followed by. 72  Traits controlled by two or more genes are said to be polygenic traits The genes for a polygenic trait may be scattered along the same chromosome or located on different chromosomes. Due to independent assortment and crossing-over during meiosis, many different combinations appear in offspring 73 Skin color in humans is a polygenic trait controlled by more than four different genes The End 75