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Ch 14, Ch 15 - Coggle Diagram
Ch 14
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Inheritance
Gregor Mendel
- discovered the basic principles of heredity by breeding garden peas
- Began with true-breeding (when plants that produce offspring identical to themselves over generations. plants)
- Started breeding peas to study inheritance in 1857
Reason why peas were useful
- Many varieties with distinct traits
- Short generation time
- Large number of offspring per mating
- Can strictly control mating
Terms:
Generational
- P generation — true-breeding parents
- F₁ generation — first filial generation (hybrids of P cross)
- F₂ generation — offspring of F₁ self-pollination or cross-pollination
- Hybridization — mating of two true-breeding contrasting varieties
Mendel’s Flower Color Experiment
- P was purple × white
- F₁ was all purple (not pale) → disproved blending hypothesis
- F₂ was 3 purple : 1 white
- Dominant trait: expressed when present (purple)
- Recessive trait: masked in F₁, reappears in F₂ (white)
Conclusion:
- Individuals have two alleles for each gene
- Alleles separate (segregate) during gamete formation
- Each gamete gets one allele only
- F₁ plants carry both alleles but show only dominant trait
- Recessive allele reappears in F₂
- Explains consistent 3:1 ratio in F₂
- Pattern repeated with six other characters (seed shape, stem length, pod color, etc.)
Law of Segregation
- Two alleles separate during gamete formation
- Each gamete gets only 1 allele
- Segregation: separation of homologous chromosomes in meiosis
- If alleles identical --> all gametes receive same allele --> true-breeding
- If alleles differ: 50% gametes = dominant allele 50% = recessive allele
Law of Independent Assortment
- alleles for diff genes sort independently of one another during gamete formation
- Monohybrid Cross: Cross involving 1 character
- Dihybrid Cross Setup: 2 traits followed simultaneously (eg: seed color & seed shape)
Mendel's Model
Alleles: Alternative versions of genes
- Genes vary in nucleotide sequence → different alleles
- Alleles account for variation in inherited characters
- e.g: flower color
- Purple allele = produces pigment
- White allele = no pigment
- Locus: location of gene on chromosome
- DNA variation at a locus --> variation in protein --> variation in trait
Organisms Inherit 2 Alleles Per Gene
- Organisms get 1 allele from each parent
- Diploid organisms have two chromosome sets
- Genetic locus represented twice (one on each gene or chromosome that is related to another through descent from a common ancestor aka, homolog)
- Alleles can be:
Dominant vs Recessive Alleles
- If alleles differ:
- Dominant allele determines appearance
- Recessive allele has no visible effect
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Ch 15
Behavior of Chromosomes
Terms:
- wild type: phenotype for a character most commonly observed in natural populations
Choosing Experimental Organisms
- Major biological discoveries often came from choosing the "right organism".
- Successful research depends on: variety availability, ease of breeding, generation time, observable traits
Sex-linked Genes
- Sex: anatomical/physiological traits; often chromosomal.
- Gender: personal identity; not the same as chromosomal sex.
Human Sex Chromosomes:
- X chromosome: Large, ~1,100 genes
- Y chromosome: smaller, 78 genes → ~25 proteins
Sex-Linked Genes: Gene located on either sex chromosome
- X-linked genes: on X chromosome, fathers pass X-linked alleles to all daughters, to no sons. Mothers pass X-linked alleles to both sons and daughters
- Y-linked genes: on Y chromosome, very few, passed from father to all sons
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