BIOL239 Lecture Notes - Lecture 1: Numbers Game, Mendelian Inheritance, Selective Breeding
14 May 2018
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Introduction
-Artificial selection: purposeful mating
- eg domestication (genetic process)
- as opposed to taming (merely behavioural; nature vs nurture)
- dogs and their breeds - same genes (same species) b/w dogs and wolves, just
different variations
- genetically close enough that their offsprings would be fertile; wouldn’t
naturally breed together
- human civilization is based on the genetics of our food supply
Set 1: Mendelian Genetics
Pages 16-31, 40-41 (2.1-2.2)
●Advantages to Mendel’s use of garden peas:
oEasy to cross-fertilize
oLarge numbers of offspring (numbers game)
oShort growing season
oClear-cut alternative forms of particular traits – alternative phenotypes
(observable and measurable)
▪ purple vs white flowers, yellow vs green peas; round vs wrinkled peas
oEstablishment of pure-breeding (true-breeding) lines
▪offspring carry parental traits that remain constant (always express the
same phenotype) from generation to generation
oCarefully controlled breeding – use of reciprocal crosses and self-fertilization
oSelf- vs Cross-fertilization (cross pollination)
▪ self: can be self reproduced, has ovules and anthers in one
▪ cross: anthers removed to prevent self-fert; another male pollen (ex
purple) added to female stigma (ex white) → when you examine the seeds
that form, you can see how each male and female dominates and later on
the germination (outcome)
●each seed is genetically different (~ fraternal twins; diff colour
corn)
●see dominance and recessiveness
o⇒ observed consistent pattern of inheritance…
●Phenotype = observable characteristic (largely determined by genotype)
o commonly referred to as a trait
o can be influenced by environment
●Genotype = genetic makeup; underlying description of the genetic information carried by
an individual
●Theories prior to Mendel:
oOne parent contributes most to an offspring’s inherited features – disproved
through reciprocal crosses (esp male, bc they are bigger and stronger)
oParental traits become mixed and forever changed in the offspring (disproved
through reappearance of recessive traits) → cannot be reversed
●Monohybrid crosses (differ in only one trait)
oP → F1 → F2 (refers only to inbreeding, no outcrosses)
o y x g ⇒ all yellow in first filial → (self-fert) lost green reappeared in 2nd filial
(always 3:1 ratio)
▪ why? bc the F1 has both traits from P (even though they only express the
dominant trait), so they would express either of the traits in the 3:1
dominant/recessive ratio when self fertilization
●Alleles: discrete units of inheritance; alternative forms of a gene – different DNA
sequences
o Hypothetical example… although irl it is more complicated
▪ Gene for trait = eye pigment, skin pigment, height, hair texture
▪ Allele = brown or blue, albino or pigmented, tall or short
Document Summary
Each seed is genetically different (~ fraternal twins; diff colour corn) See dominance and recessiveness: observed consistent pattern of inheritance . Phenotype = observable characteristic (largely determined by genotype) o o commonly referred to as a trait can be influenced by environment. Genotype = genetic makeup; underlying description of the genetic information carried by an individual. Polymorphic gene may have several alleles that normally occur in a population not one as dominant, can easily find variations (eg. gene for blood type) o. Monomorphic gene has only one allele that is normally present in a population (other alleles are very rare) Gamete = reproductive cells o pollen/ovules = sperm/eggs. Mendel"s law of segregation : the two alleles for each trait separate (segregate) during gamete formation, then unite at random, one from each parent, at fertilization: describes how alleles of one gene behave, punnett square - shows possibilities. 3:1 phenotypic ratio simple dominant and recessive traits; cross between monohybrids: predictive.
