March 6 2014 Today s topics and readings Meiosis Pg 248 260 Genetics The study of heredity and heritable variation Fig 12 1 Review cell cycle and mitosis End product involves two genetically identical daughter cells compared to the parent Meiosis and Sex Meiosis cell division that produces haploid cells Meiosis has similarities to mitosis but several crucial differences Meiosis is required for sexual reproduction Asexual vs Sexual Reproduction What are the differences genetically speaking Asexual clone offspring such as bud off of a plant such organisms can employ this technique but can also engage in sexual reproduction to mix up genes Bdelloid rotifers have not had sex in 40 million years integrates DNA from other organisms Sexual produces new combination of genes Life Cycle Stages in reproductive history of an organism fig 13 5 13 6 Includes haploid n stage and Diploid 2n states Time spent in n or 2n varies Some multicellular haploid stages Haploid or Diploid cells can divide by mitosis Only diploid cells can undergo meiosis 13 5 Human Lifecycle Gonads produce the only haploids in the body through meiosis 2 gametes 23 n from both parents come together through fertilization to form a diploid zygote 13 6 comparison sexual life cycles Terminology Chromosome Sister chromatid 2 chromosomes connected by centromere that are genetically identical Centromere Homologous chromosomes pair of chromosomes 1Mom 1Pop with same length centromere position and genetic content differs a little Autosomes everything but sex chromosomes pairs 1 22 Sex Chromosomes X and Y pair number 23 Gamete Zygote Fig 13 3b Human karyotype 13 4 Meiosis Purpose to create haploid cell Only occurs at gonad region in the body Occurs only at the adult stage Fig 13 7 Interphase Meiosis 1 Separation of homologous chromosome pairs Prophase 1 Synapsis homologous chromosomes pair up Cross over homologous chromosomes exchange DNA Chiasmata location where crossing over occurred Fig 13 8 Metaphase 1 line up in the middle Anaphase 1 splitting up Telophase 1 cleavage No chromosome replication Straight to Meiosis Meiosis 2 Sister chromatids separate Prophase II Metaphase II Anaphase II Telophase II Four daughter cells that are haploid Fig 13 9 Genetic variation one of the benefits of sex Crossing over during Prophase 1 Independent assortment during Metaphase 1 Random fertilization Fig 13 12 Terminology for next lecture True breeding Hybridization P generation F1 generation F2 generation Allele Dominant trait Recessive traits March 18 2014 March 20 2014 Use Laws of Probability to sove complex genetics problems Probability Scale 0 1 Rules All chances add to 1 o Each even unaffected by other events Multiplication Determine allele Figure 14 9 for segregation of alleles and fertilization are chance events What is the probability that a SSYYaa offspring is produced from the cross SsYyAa x SsYyAa USE PUNNETT SQUARES FOR INDIVIDUAL TRAITS SsxSs YyxYy AaxAa 1 4 X X 1 164 CHAPTER 14 PAGES 271 283 Modifications to Mendel How do the alleles segregate during gamete formation LiGgX LiGg Dihybrid cross must have 2 different types of alleles IG Ig iG ig both sperm egg The parent was heterozygous for BOTH traits so 4 different possibilities for gametes are possible If 400 seeds are planted from this cross predict how many offspring would have constricted yellow pods both recessive iigg X 1 16 X400 25 would have that 9 3 3 1 1 9 3 3 1 1 16 Or ii x gg 1 16 1 16 of 400 25 Mendel s Principles extended o Multiple alleles affecting phenotype of one character Complete dominance Fig 14 5 More of one pigment than the other One allele dominates phenotype Heterozygote and homozygote dominant are indistinguishable Must do test cross with recessive homozygous to figure out genotype of that one Incomplete dominance Fig 14 10 Both alleles produce the same pigment Snapdragons can be red or white if red or white they are true breeding individuals One allele shows partial dominance F2 intermediate phenotype Heterozygote and homozygote dominate ARE distinguishable Red genes white genes PINK F1 generation F2 generation WILL have some pink but will also have some red and white appear Co dominance Fig 14 11 Multiple alleles of a single gene Concept one word can have different spellings ex Color us colour uk couleur france Source from mutation change in DNA Examples hair color in rabbits blood groups in humans A B or O o A B O refers to sugars o OR blood type refers to protein on outside of blood cell you have it you don t Epistasis Fig 14 12 One gene altering or controlling phenotypic expression of another gene Example if you and your sister are frosting cookies and you have a certain frosting color and she has the knife If yall don t work together that cookie will not get frosted if yall both have frosting and knives it works better additive effect BbCc C is the ability to make pigment so C is controlling epistatic to B Polygenetic inheritance Fig 14 13 Additive effect of two or more genes on a single phenotypic character Example basic skin color white tan brown black 3 different genes control skin color o AaBbCc Pedigree Analysis Pedigree collection of information about family history for a particular trait charted on to a family tree Fig 14 15 pedigree symbols o Square male o Circle female o Genotype Ww o Phenotype what is seen widows peak no widows peak March 25 2014 Genetic Disorders o Recessively inherited disorders fig 14 16 Recessive allele produces little to no functional protein Ex sickle cell cystic fibrosis tay sachs albinism Usually inherited from carriers Severe and can lead to death o Carriers Phenotypically normal genotypic heterozygous carry recessive allele o Dominantly inherited disorders fig 14 17 Dominant allele causes disorder Ex huntington s disease polydactyly more than 5 fingers achondroplasia a form of dwarfism How are lethal dominant alleles maintained in populations Lethal condition but it does not effect you until AFTER you have reproduced so you ve already passed the trait down Why don t most humans have more than 5 digits Just because something is dominant does not mean there is a lot of it within a population Chapter 15 pages 286 294 and 297 302 Chromosomal basis of inheritance Pages 303 304 8th edition 1 4 11 or 9th edition 1 3 5 7 PRACTICE PROBLEMS Sex determination in mammals o Sex chromosomes XY system fig 15 6 o Sex linked genes SRY gene sex determining region of Y chromosome DAX gene dosage sensitive gene on X chromosome Figure
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