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Bio 321 F13 lecture 2 v2

For the principle of independent assortment

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Unformatted text preview: has one allele from each parent (except for sex- linked traits which were discovered later - see below) •  •  2. The seven traits show a system of dominance •  - one allele is dominant •  - the other is recessive •  - hybrids between (homozygous - see below) dominant and recessive individuals have the dominant allele's phenotype 3. At any gene alleles segregate randomly during gamete formation (later we will talk about genetic linkage = nonindependent segregation of two genes) Terminology Trait - inherited character (pea plant height) Gene - basic unit of inheritance (this comes to have different shades of definition in the molecular era) i.e. a gene for plant height (there are typically many genes determining complex traits) a gene is a segment of DNA on a chromosome Alleles - variant forms of a gene (e.g. tall and dwarf alleles for pea plant height) -differ in some way in the DNA sequence of the gene gene7c conven7ons •  Capital and lower case leRers to indicate two different alleles –  A, a •  Genotypes: –  Aa or A/a •  If mul7ple alleles –  superscripts or subscripts •  A1A2 •  C1C3 gene7c conven7ons: mul7ple loci •  genotype: A1 B2 C4 ___________ A4 B4 C1 separate different chromosomes by semicolon A1 B2 C4 C4 E1 F1 ___________ ; __________ A4 B4 C1 C1 E1 F1 gametes are generated by meiosis •  remember: –  mitosis is cell replica7on/prolifera7on during growth •  one diploid (2N) cell replicates its genome and gives rise to two iden7cal diploid (2N) cells •  meiosis –  diploid premeio7c cell (2N) replicates to become 4N and then undergoes two divisions - >2N - >1N •  gives rise to 4 haploid (1N) gametes –  typically four sperm in males, 1 egg + 3 polar bodies in females one locus illustrated on one chromosome (in this case, A/a heterozygote; “monohybrid A a replication pre-meiotic cell (2N) A a 1st division 4N A a a 2nd A division 25% a 2nd division 25% 50% 25% A 25% A a 50% Punne= Square method for a cross (we will return to this concept for popula7ons, HW equilibrium) e.g. cross between two Aa heterozygotes AA, Aa, aa EGGS 50% A 50% a AA, Aa, aa Reginald Crundall Punnett (1875-1967) 50% A 25% Aa 50% a SPERM 25% AA 25% Aa 25% aa Ra5o of genotypes in progeny: 1 : 2 : 1 AA : Aa : aa Punnett could be played by Will Patton Punne= square http://s3.amazonaws.com/criterionproduction/images/2177ae0a97b2ab10cff8e133dc5627...
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