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 traitsMarch 18, 2014March 20, 2014Use Laws of Probability to sove complex genetics problems- Probability Scale: 01- Rules: All chances add to 1o Each even unaffected by other events- Multiplication- Determine allele Figure 14-9 for segregation of alleles and fertilization are chance eventsWhat 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 ¼ X ¼ = 1/164CHAPTER 14 PAGES 271-283 Modifications to MendelHow 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 ¼ X ¼ = 1/16 X400= 25 would have that 9:3:3:1= 1/(9+3+3+1)= 1/16Or ¼ ii x ¼ gg = 1/16 1/16 of 400 = 25- Mendel’s Principles-extendedo 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 sugarso + 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 coloro AaBbCc… Pedigree Analysis- Pedigree: collection of information about family history for a particular trait charted on to a family tree- Fig 14-15 pedigree symbolso Square-maleo Circle- femaleo Genotype- Wwo Phenotype- what is seen (widows peak, no widows peak)March 25, 2014- Genetic Disorderso 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 deatho Carriers Phenotypically normal, genotypic heterozygous, carry recessive alleleo Dominantly inherited disorders (fig 14-17)
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