Challenge Use this diagram to review events of meiosis chromosomes duplicated metaphase I anaphase I first division metaphase II anaphase II 1 The Paradox of Sex Meiosis when it goes wrong Why sex NOTE please see updates to what you are expected to teach yourself about meiosis at the end of this lecture 2 Learning goal students will be able to explain how meiosis generates genetic diversity in offspring and why this is an evolutionary advantage over mitosis asexual reproduction Focus Mistakes in Meiosis the Paradox of Sex 3 n and ploidy Genome all of the unique genes in an organism n number of copies of all the unique genes in the genome number of sets A B C D E F G a b c d e f g a1 b1 c1 d1 e1 f1 g1 a2 b2 c2 d2 e2 f2 g2 a3 b3 c3 d3 e3 f3 g3 Diploid 2 before the end Triploid 3n 4 n and ploidy Genome all of the unique genes in an organism N number of copies of all the unique genes in the genome number of set A B C D E F G c a f b d g e Ploidy number of unique chunks chromosomes that make up a sets 5 How meiosis generates genetic diversity in gametes A B C D E F G a b c d e f g 1 Gametes have a 50 50 chance of receiving any given chromosome A B C d e f g equally possible Probability of any given combination a b C d e F G 2 ploidy 6 How meiosis generates genetic diversity in gametes A B C D E F G a b c d e f g 2 Crossover between homologous chromosomes creates nonparent combinations A A B B a b a b Crossover location random A B A b a B a b Possible combinations endless Using meiosis ensures all gametes are genetically unique 7 Meiosis generates genetic diversity over generations paternal grandparents gametes father Crossover mixes genes from different chromosomes gametes offspring crossover not represented maternal grandparents gametes mother Every offspring contains mix of DNA from 4 different organisms crossover not represented 8 Meiosis generates genetic diversity over generations gametes parent offspring Even with self fertilization offspring are genetically unique 9 Self fertilization differs from parthenogenesis self fertilization through meiosis parent gametes offspring fertilization parthenogenesis through mitosis offspring parent 10 You must learn the details of the process of meiosis from your textbook see notes on lecture outline NOTE while random mutations DO generate genetic diversity mutations are NOT part of the controlled process of meiosis Mutations can happen in any organism 11 Mistakes during Meiosis affect entire chromosomes Gene dosage the number of working genes for a given protein The minimum normal dosage of most genes is 2 because we are diploid organisms amount of protein made from that gene Males 1 2 3 copies of a gene 4 have only one X and one Y Females turn off one X For many genes the number of copies present determines the amount of protein that will be made 12 Mistakes during Meiosis affect entire chromosomes Gene dosage The minimum normal dosage of genes on sex chromosomes is ONE amount of protein present Males have only one X and one Y 1 2 3 copies of gene Fun fact not all genes on the X Y chromosomes are sex specific 4 Females turn off one X 13 Altering one gene s dose can cause a phenotype amount of B protein present example flower pigments Phenotype die to no working copies for white BB bb Bb 0 1 2 copies of wild type gene Phenotype due to gene dosage Haploinsufficiency for pink 14 Altering one gene s dose can cause a phenotype Gene dosage the number of working genes for a given protein normal phenotype amount of protein present mutant phenotype BBB BB 2 3 copies of gene Duplication of a single gene can produce a phenotype even if it s a normal WT allele 15 Missing or duplicated chromosomes alter gene dosage of thousands of genes Gene dosage the number of working genes for a given protein amount of protein present missing chromosome extra chromosome 1 2 3 copies of all genes on chromosome this is usually fatal 16 Nondisjunction leads to gametes with extra or missing chromosomes nondisjunction can occur during anaphase I or anaphase II 17 Nondisjunction leads to zygotes with Aneuploidy incomplete sets normal gamete n fertilization resulting zygotes 18 Describing errors of meiosis Aneuploidy 2n 1 A B a b C D E F G d e f g Monosomy 2 Aneuploidy 2n 1 A B C D E F G a b c d e f g F G Trisomy 4 19 chromosomes duplicated metaphase I anaphase I occurs normally first division metaphase II anaphase II nondisjunction in one cell 20 Challenge Use this diagram to see predict effects of other kinds of nondisjunction on gametes Ex nondisjunction of BOTH chromosomes during metaphase I chromosomes duplicated metaphase I anaphase I occurs normally first division metaphase II anaphase II 21 Fate of Zygote Usually Some monosomies and trisomies are survivable only if it s a sex chromosome it s a small chromosome only one chromosome is involved 22 Asexual reproduction is more efficient Asexual Less energy investment Sexual More energy investment Yet sexual reproduction is the predominant method of reproduction among multicellular organisms why go through all this effort 23 Asexual reproduction is more efficient but sex predominates Asexual Sexual The Paradox Mathematically sexual populations should outnumber sexual populations 24 Sexual reproduction gives a population a Asexual Sexual Meiosis generates genetic diversity 25 Meiosis generates genetic diversity over generations paternal grandparents gametes father gametes offspring crossover not represented maternal grandparents gametes mother crossover not represented 26 Meiosis generates genetic diversity over generations gametes parent offspring Even with self fertilization offspring are 27 Self fertilization differs from parthenogenesis self fertilization through meiosis parent gametes offspring fertilization parthenogenesis through mitosis offspring parent 28 1 Sexual reproduction allows Purifying Selection Asexual A deleterious bad mutation is passed on to ALL offspring always Sexual A deleterious mutation is only passed on to 50 offspring sometimes less 29 2 A genetically diverse population is an advantage when there are environmental challenges Rapid changes in conditions Introduction of a pathogen 30 What you should know about Meiosis you have not yet read about mitosis so you are not expected to know about it yet You are expected to teach yourself the details of meiosis There are dozens of resources if you get stuck and an exercise worksheet posted with this lecture When is meiosis used and under what