Week 10 Notes (Chapters 11, 12)
Week 10 Notes (Chapters 11, 12) Bio 1510
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This 13 page Class Notes was uploaded by Nausheen Zaman on Sunday November 8, 2015. The Class Notes belongs to Bio 1510 at Wayne State University taught by Dr. Nataliya Turchyn in Summer 2015. Since its upload, it has received 66 views. For similar materials see (LS) Bas Life Mch in Biology at Wayne State University.
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Date Created: 11/08/15
Chapter 11 (cont) ● Meiosis I vs. Mitosis ○ Meiosis II ■ Homo chromosomes come together in synapsis → tetrad ■ Crossing over occurs with exchange of genetic material ■ Nuclear envelope breaks apart ■ Metaphase 1 ● Mitotic spindle brings homo chromosomes in the middle on the metaphase plate, kinetochore microtubules attached to kinetochores of ONLY one half of chromatids ■ Anaphase 1 ● synaptonemal complex destroyed, cohesins still present, homo chromatids come apart (nonidentical sister chromatids bc of crossing over) ■ Daughter cells haploid, nonidentical ○ Mitosis ■ Nuclear envelope is intact ■ Homo chromosomes don’t come together, no synapsis → no tetrad ■ No crossing over ■ Metaphase ● kinetochore microtubules are attached to kinetochores of ALL chromatids, individual chromosomes are aligned on metaphase plate ■ Anaphase ● cohesins destroyed, move to opposite side of cells when kinetochore micros become shorter, polar micros become longer ■ Daughter cells diploid, identical ○ Telophase 1/Telophase ■ mitotic spindle disassembles, chromos decondences (condensins become destroyes) nuclear envelope reassembles around new chromatids ○ Cytokinesis separates one cell → two identical cells ○ Haploid human cells (n) = 23 chromosomes ○ Both ALWAYS function with diploid parent cells (human diploid 46 chromosomes) ● Meiosis II ○ Very similar to mitosis ○ Metaphase 2 ■ chromosomes align on metaphase plate, kinetochore microtubules attached to kinetochores of all chromatids, each chromosome consists of two nonidentical sister chromatids attached by cohesin ○ Anaphase 2 ■ cohesins destroyed to allow sister chromatids to come apart ○ Telophase 2 ■ mitotic spindle disassembles, chromos decondence, 4 nuclear envelopes reform, 4 haploid nonidentical sister chromatids are formed Chapter 12: Patterns of Inheritance ● Mendel was first to record how traits were passed from gen to gen (came up with ‘Laws of Heredity’) ● Each person has one of two alleles for a trait ● Why Do We Look a Little Bit Like Our Parents? ○ Events that occur during meiosis determine how much we will ‘look’ like the rest of our family ○ Laws of Heredity ■ 1st Law: Principle of Segregation ● Two versions (alleles one from mom, one from dad) for a gene segregate during gamete formation ● Rejoined at random, one from each parent during fertilization ● Principle works in Anaphase 1 (synaptonemal complex formed during Prophase 1 is destroyed, allowing chromosomes to come apart ● Cohesins then destroyed in Meiosis 2 to allow sister chromatids to come apart ● No crossing over takes place ● Two alleles for a gene are rejoined at random, one from each parent during fertilization ■ 2nd Law: Principle of Independent Assortment ● Alleles of two different genes sort into gametes independently of each other ○ The two different genes MUST be on different chromosomes in order for this to work ● This step occurs in Metaphase 1 when different homologous chromosomes align on the metaphase plate ● How did Gregor Mendel Figure Out the Way Alleles are Inherited? ○ Used pea plants for testing ○ Why Pea Plants? 1. Short generation time 2. Fertilization (syngamy) can be controlled 3. Several easily observed traits (colors, height, pod color/shape, etc.) ● Monohybrid cross = mating between 2 organisms that are similar in everything except one trait ○ Mono (one), hybrid (mix), cross (to mate) ● True breeding/purebred organism – mendel created purebred white and purple flowering plants by crossing them with their respective colors ● P = purple (Dominant), p = white (recessive) st ○ 1 gen – all heterozygous because all flowers have white allele, but also have dominant purple allele ● Dominant vs. Recessive ○ Dominant trait shows up in every generation ○ Recessive skips one/more generations ○ Purple flower – dominant (it keeps showing up in each generation) ○ white flower – recessive (skips one/two generations and reappears) ■ White was NOT lost, masked by the purple in f1 gen ● Punnett Square ○ A way to determine the probability/chance of certain traits being expressed in the offspring ○ Hearing = dominant trait; deafness = recessive trait ○ Dominant allele = hearing (D); recessive allele = deafness (d) ○ Phenotype = physical appearance of an organism (e.g., hearing and deafness) ○ Genotype = genetic makeup of an organism; total set of alleles the organism contains ■ homozygous dominant = 2 dominant alleles (DD) ■ heterozygous = 1 dominant and 1 recessive alleles (Dd) ■ homozygous recessive = 2 recessive alleles (dd) ○ Alleles can be dominant or recessive, every person has two alleles for each trait ○ Homo (same), Zygous (zygote/fertilized egg) – example of genotype ○ Hetero (other), Zygous (zygote/fertilized egg) ■ Homozygous dominant/recessive known as ‘truebreeding/purebred’ genotype ■ No such thing as heterozygous dominant/recessive ○ In monohybrid cross (only one trait differs between two organisms) between heterozygous organisms , phenotypic ratio is 3:1 (75% normal, 25% affected) + genotypic ratio is 1:2:1 (1 homodominant: 2 hetero: 1 homorecessive) ● How Can We Figure Out What is ‘Dominant’ in Humans? ○ Pedigree shows inheritance of a family trait through multiple generations ■ Squares – males ■ Circles – females ■ Horizontal line – mating ■ Vertical line – offspring ■ Shaded – affected with disease ■ Unshaded – not affected with the disease ○ Juvenile glaucoma (a disease that causes degeneration in optic nerve, causing blindness) is a dominant trait (shows up in every generation of the family) ○ Recessive pedigree when recessive trait skips one/more generations ■ Halfshaded = carriers (one Dom, one recess allele) ● Carriers stereotypically normal as dominant allele (normal allele) prevents recessive allele (albinism) from being expressed ○ Only true for recessive disorders ■ Unshaded = unaffected ■ Completely shaded = affected ■ Doubleline = mating between first cousins ○ Albinism a conditions where the pigment melanin is not produced ● What is Recessive in Humans? ● What is Dominant in Humans? ● Can One Gene Affect how Another Gene is Inherited? ○ Dihybrid cross mating between 2 organisms that are similar in everything except 2 traits ■ Di (two) ○ Gene that controls seed color has dominant (yellow; Y) and recessive (green; y) alleles ○ Gene that controls seed texture also has dominant (round; R) and recessive (wrinkled; r) alleles ■ Seed color – Yellow = dominant (YY), Green = recessive (yy) ■ Seed texture – Round = dominant (RR), wrinkled = recessive (rr) ○ Homodominant plants (round yellow) were crossed with homorecessive plants (wrinkled green) ○ F1 = round yellow seed (hetero for 2 different traits) ○ Hetero organism go through meiosis to produce gametes with 4 different types of gametes with different allele combos ○ Under normal conditions, you will never get 2 alleles within the same gene in one gamete ■ Against the rule of segregation – alleles segregate during gamete formation because synapto complex is destroyed between pat and mat chromosomes during anaphase 1 of meiosis 1 ○ Alleles for round seeds will not always be inherited together with alleles for green seeds; it can be inherited together with alleles for yellow seeds ■ rule of independent assortment – two alleles of two different genes sort into gametes independently of each other, bc of independent assortment of chromosomes on metaphase plate during metaphase 1 ○ F2 gen made by crossing f1 gen plants together (phenotypic ratios) ■ 9/16 – round yellow seeds ■ 3/16 – round green seeds ■ 4/16 – wrinkled seeds ■ 1/16 – wrinkled green seeds ○ In case of dihybrid cross between two hetero organisms: ■ Phenotypic ratio of 9:3:3:1 is generated ■ Monohybrid hetero phenotype cross – 3:1 ■ Mono hetero genotype cross – 1:2:1 ○ If organism is hetero for 2 diff traits, 4 diff gametes can be produced ● How can you Test Whether you have a ‘Purebred’? ○ Testcross cross used to determine whether you have a homozygous dominant (purebred) or heterozygous (mutt) organism ○ Cross individual with unknown genotype (Ll/LL) with homozygous recessive (ll) ALWAYS ○ In testcross between hetero and homorecessive organisms, phenotypic and genotypic ratios are the same (1:1 – 50% longfur, 50% shortfur [pheno]; 50% hetero, 50% homorecessive [geno]) ● Incomplete Dominance ○ Heterozygous genotype produces an intermediate phenotype between phenotypes of homozygous dominant (red) and homozygous recessive (white) (e.g., pink flowers in four o’clock plants) ○ In pea plants, purple allele is truly dominant and formation of purple flowers is an example of complete dominance ○ Red allele in four o’clock plants is not truly dominant, it cannot completely mask the white recessive allele ○ Pheno and geno ratio – 1:2:1 in cases of incomplete dominance between two hetero organisms ● Incomplete Dominance in Humans ○ (hh) 600 mg – very high blood cholesterol level (hypercholesterolimic) They are also homorecessive for LDL receptors ○ (HH) 400 mg – normal blood cholesterol levels and have normal amount of LDL receptors (homodominant) ○ (Hh) 300400 mg – Twice as much blood cholesterol levels ● Codominance ○ Two different alleles of a single gene are both expressed, they don’t overpower each other in the phenotype, and heterozygote shows some aspects of the phenotypes of both homozygotes (e.g., AB blood type in humans) A B ○ Gene has 3 different al,I, and i ■ I and are dominant tbut codominant to each other