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Mendel inheritance
biol 1210
| Question | Answer |
|---|---|
| Define heredity & trait | Heredity: the transmission of traits from parents to their offspring. Trait: any characteristic of an individual |
| Blending hypothesis & why rejected | Parental traits blend so their offspring have intermediate traits. Mendel proved not all offspring have intermediate traits - some r dominant, & If blended, over time = no diversity, but we have diversity |
| Inheritance of acquired characteristics hypothesis | Parental traits are modified thru use & then passed on . Mendel proved that hereditary determinants of traits (genes) do not change thru use - they r discrete & unchanging particles |
| Particulate hypothesis | Parents pass on discrete heritable units (genes), documented by Mendel |
| Why did Mendel choose peas? | Inexpensive & easy to grow, short generation time, produce large #s of seeds, can control which parents involved in mating (cross-fert & self-fert), have several polymorphic traits |
| Polymorphic traits | Trait that commonly appears in 2+ different forms ex. Purple vs. white flowers |
| How did Mendel control pea plant mating? | Peas have female & male reproductive organs on same flower - may self-fertilize, or Mendel could prevent self-pollination by removing an organ, or cross-pollinate by bringing pollen from one flower to another |
| Define pure lines | The parental (P) generation that produces offspring identical to themselves when self-fertilized |
| Define hybrids | The result of mating two different pure lines that differ in one or more traits (F1 generation) |
| Mendel’s F2 generation | The result of self-pollinating parents from F1 generation |
| Dominant v. Recessive trait | A dominant trait is one whose genetic determinant is always expressed if it is present (RR, Rr). Recessive traits are overtaken by dominant traits and only expressed if there is no dominant gene (rr) |
| Particulate inheritance hypothesis | Hereditary determinants (genes) do not blend or change thru use - act as discrete, unchanging particles. Each individual has 2 copies (alleles) of each gene; dif. versions of a gene are alleles; dif. alleles cause variation in traits |
| law/principle of segregation | 2 members of each gene pair must separate into gamete cells during formation of eggs & sperm (meiosis - paternal & maternal chromosomes split) |
| Homozygous v. Heterozygous | Homozygous: individuals w 2 copies of the SAME allele (RR or rr). Heterozygous: individuals w 2 DIFFERENT alleles (Rr) |
| How to choose letters for indicating genes & alleles | The letter chosen should represent the dominant trait (ex. R/r for round, not P/p for pea), Capital = Dominant gene is expressed, double lowercase = recessive gene expressed |
| Monohybrid cross & ratios | Mating btwn 2 parents that are BOTH heterozygous for ONE gene. Phenotypic ratio: 3 dominant:1 recessive, genotypic: 1AA:2Aa:1aa. Basic punnet square in quarters. |
| recessive v. dominant inherited disorders in humans | recessive: associated w recessive allele, disorder develops if individual carries both alleles (homozygous recessive) ex. albinism. Dominant: dominant allele, disorder develops if individual carries min. ONE dominant allele ex. polydactly |
| dihybrid cross & mendel | mendel used it to determine whether alleles of different genes segregate together or independently. Dihybrid cross: mating btwn parents that are both heterozygous for TWO traits |
| independent assortment v. dependent assortment | independent: alleles of dif. genes are transmitted independently of each other. Dependent: transmission of one allele depends on the transmission of another. Mendel's results supported independent assortment |
| phenotypic & genotypic ratios of dihybrid cross | phenotypic: 9 dominant of both:3 heterozygous of one parent:3 heterozygous of other parent:1 homozygous recessive. Genotypic: 9 A_B_:3 A_bb:3 aaB_:1 aabb |
| law of independent assortment | alleles of different genes are transmitted independently of one another (on non-homologous chromosomes) |
| test cross | a homozygous recessive parent is mated with a parent that has the dominant phenotype but an unknown genotype. The genotype of the unknown parent can be inferred from the results. Work with monohybrid and dihybrid cross |
| how do the results of test cross help determine genotype of unknown parent? | if unknown genotype parent is heterozygous - offspring have 1:1:1:1 phenotypic ratio. If parent is homozygous dominant, all offspring will have dominant phenotype |
| in a test cross, if the test individual is homozygous, the progeny will have a 3:1 ratio. T/F | F. they would have no ratio - all dominant phenotype |
| if an individual is homozygous for an allele, each of its gametes only contain one copy of that allele. T/F | T. Thru meiosis |
| genetic linkage | the tendency of genes to be inherited together bc they r close together on the same chromosome (autosome or sex chromosome) (a lack of independent assortment) |
| recombinant offspring | offspring represented by fewer #s of progeny (uncommon) and have traits different from their parents. Result from the crossover of homologs when recombinant chromosomes mix up characteristics and create gametes w dif. DNA than parents |
| nonrecombinant offspring | offspring that consist of genotypes found in one of the parents and make up larger #s of progeny (more common) |
| frequency of recombination | measure of the distance btwn linked genes. 2 genes on same chromo, may be very far apart or very close |
| likeliness of crossing over | on the same chromosome, crossing over occurs frequently btwn genes that are far apart on the same chromosomes, rarely occurs btwn genes that are close bc crossing over occurs a small # of times btwn homologs |
| how to calculate the frequency of recombination | # of recombinant offpsring (phenotype dif. from parents) / total # of offspring x 100 (for % answer). Higher % = genes farther apparent, recombination/crossing over likely & vice versa |
| genetic recombination of unlinked genes | unlinked genes (2 genes on separate chromosomes) = expected 1:1:1:1 for recombinant & nonrecombinant gametes (1:1:1:1 phenotypic ratio for offspring) |
| compare monohybrid & dihybrid inheritance based on: # of genes involved, # of chromosomes involved, # of alleles involved, phenotypic ratio in F2 gen, mendelian law that explains it | monohyrid: 1 gene, 2 chromosomes, 2 alleles, 3:1 F2 gen. ratio, Law of Segregation. Dihybrid: 2 genes, 4 chromosomes, 4 alleles, 9:3:3:1 F2 gen. ratio, Law of Independent Assortment |
| multiplication rule | the probability that 2+ independent events will occur together is the product their individual probabilities |
| rule of addition | the probability that any one of 2+ exclusive events will occur is calculated by adding together their individual probabilities |
| In the genetic cross, AaBbCcDdEE x AaBBCcDdEe, what proportion of the offspring will be heterozygous for all of the genes (AaBbCcDdEe)? Assume all genes are unlinked and the alleles show simple dominance. | answer in notes |
| what organism did Mendel choose for his experiments and why? | peas bc they were inexpensive & easy to grow, have short generation time, produce large amounts of seeds, have several polymorphic traits and he could control which parents were involved in a mating (cross-fertilization or self-fertilization) |
| examples of traits Mendel studied | Mendel's peas differed in 7 easily recognizable traits: seed shape & colour, pod shape & colour, flower colour, flower & pod position, & stem length |
| why was it important Mendel started with true-breeding plants? | True-breeding plants would allow him to create verifiable hybrids that he could then self-fertilize to study the transmission of traits |
| true-breeding plants | plants that are homozygous for one/all genes |
| draw a 2n = 6 cell with genotype YyRr at the end of metaphase I, meiosis I, metaphase II and meiosis II, tracking the alleles through the drawings | see notes |
| why, in humans, many recessives traits like albinism "skip" generations while dominant traits do not? | recessive traits can be carried by heterozygous individuals - recessive trait is not expressed but still present in the genome and may be passed onto the offspring. If the other parent also carrier, offspring could exhibit the disorder (homozygous recessi |
| why is Mendel's law of indep. assortment only valid for genes located on dif. chromosomes or far apart on the same chromosome? | Genes on different chromosomes can orient separately during metaphase I, genes far apart on the same chromosome are likely to crossover & therefore migrate to separate chromosomes. Genes close together unlikely to cross over; genetically linked |
| results in the F2 generation of a dihybrid cross if dependent assortment is assumed? | transmission of one allele depends on the transmission of the other, so alleles will stay together when gametes form. Ex. RrYy parents make only RY and ry gametes = same results as monohybrid cross if dep. assortment |
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AntBanana
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