Transcript alleles: t
Genetics – Part I Spring 2013 - Althoff Reference: Mader & Windelspecht Ch. 11) • Mendel’s Laws • Beyond Mendel’s Laws • Sex-Linked Inheritance • Inheritance of Linked Genes Lec 15 3 Basic Terms…for starters • _______— the unit of heredity…passed on to offspring. 1) Each gene has a specific location on a chromosome. 2) Each gene contains the code for specific traits to be expressed 3) Genes come in “pairs”…each pair is known as an allele • _______— an allele is alternative form of a gene at a particular location • ______________— contains genes…rod-like structures in the nucleus observed during cell division ALLELES of a GENE at a gene locus CHROMOSOMES SISTER CHROMATIDS HAVE IDENTICAL ALLES DUPLICATED CHROMOSOMES SISTER CHROMATIDS The Pea Picker… _____________ An Austrian monk who developed the ___________________________ Pea Traits • • • • • • • Stem length Pod shape Seed shape Seed Color Flower position Flower color Pod color Dominant • • • • • • • Tall Inflated Round Yellow Axial Purple Green Recessive • • • • • • • Short Constricted Wrinkled Green Terminal White Yellow Mendel in his garden….. Pea Traits • • • • • • • Stem length Pod shape Seed shape Seed Color Flower position Flower color Pod color Dominant Recessive _____ Mendel • Most animal and plant breeders agreed that both sexes contributed equally to a new individual • Same folks had not been able to account for the presence of definite ___________ (i.e., differences) among members of a family…generation after generation. • Mendel’s MODEL OF HEREDITY does account for such ___________ Model of Heredity….consider this! • This model is compatible with the THEORY OF EVOLUTION which states that various combinations of traits are __________ by the environment, and those combinations that lead to _________________ are the ones passed on. or….”all living things have a __________ ancestor, but each is adapted to a particular way of life”. • For the record, the ________________ was formulated by Charles Darwin in the 1830s but not published until 1844 and 1859, so his perspectives did not influence Mendel (remember: no internet, little publishing, long-turn around time on exchange of information). Some key terms…. • __________ – some expressed “quality” or “structure” • __________ trait – exerts “quality/structure” in heterozygous allele pairing • __________ trait – exerts “quality/structure” only in homozygous allele pairing Some more key terms…. • __ generation: original parents • __ generation: first generation offspring • __ generation: second generation offspring • _______: haploid sex cell (____________) • ________ –exact combination of alleles • ________—exact ___________ (i.e, physical appearance) One-trait Inheritance…and the Punnett Square F 1 Sperm gametes ♀ ♂ Eggs T t T t ALLELES: T = tall plant t = short plant Results from this Punnett Square F2 ____________________ 3 Tall (T) : 1 Short (t) Translation: with this combination of alleles, There is a ____ chance of the F2 generation individual being tall and ____ chance it will be short. The One-Trait Testcross lead to: ______________________ • Each individual has __________ (alleles) for each _______ • The factors (alleles) segregate during the formation of gametes • Each gamete contains only one factor (allele) from each pair of factors (alleles) • ______________ gives each new individual two factors (alleles) for each trait Mendel’s _______ law of inheritance Genotype vs. Phenotype using the One-trait Inheritance for pea plant height Genotype (alleles) Genotype description Phenotype TT Homozygous dominant Tall Tt Heterozygous Tall tt Homozygous recessive short Another One-Trait Testcross F1 gametes ♀ ♂ Eggs R r Sperm R r ALLELES: R = round seed r= wrinkled seed A Two-Trait Testcross F1 gametes Sperm ♂ Eggs ♀ TR Tr tR tr TR TTRR TTRr TtRR TtRr Tr TTRr TTrr TtRr Ttrr tR TtRR TtRr ttRR ttRr tr TtRr Ttrr ttRr ttrr ALLELES: T = tall plant ALLELES: R = round seed Phenotypic Ratio Tall, round (TTRR, TTRr, TtRr) Tall wrinkled (TTrr, Ttrr) Short, round (ttRR, tt,Rr) Short, wrinkled (ttrr) t = short plant r= wrinkled seed The Two-Trait Testcross lead to: _________________________ __________________ • Each pair of factors (traits) ________________ independently of the other pairs • All possible combinations can occur in the gametes Mendel’s ____________ law of inheritance A few things to consider… Remember PHENOTYPE refers to _____________ “trait”…not the ______________ unless….. A recessive trait is expressed—because a recessive trait will only appear (i.e., be expressed) if ______ ________ are recessive. ex. AA and Aa genotypes result in same PHENOTYPE …as long as one dominant (A) allele is present vs aa –then recessive trait expressed and therefore we also know the genotype. Examples: Dominant – Recessive EE or ee Ee • Earlobes WW or Ww • Widow’s Peak SS • Straight/Bent Thumb or Ss • Cheek dimples DD or Dd PRESENT ss ABSENT dd Beyond Mendel’s Laws • Incomplete Dominance “intermediate” phenotype possible” Beyond Mendel’s Laws • ____________________ “more than 2 alleles involved” • ABO Blood Types: 3 alleles __________ Beyond Mendel’s Laws • __________________ “trait governed by two or more sets of alleles” • In this example, trait is controlled by 3 genes (i.e., Aa, Ba, Cc). Only those combinations represented by capital letters contribute to the ________________ Mader, p197, Fig. 11.16 ______________ & Phenotype • Ex. Temperature impact on phenotype for the Himalayan rabbit….homozygous for allele ch, which is involved in ____________ production. Encoded (gene) enzyme is active only at low temperatures….when activated it results in _______ hair (and, yes…hare!) being produced What are the advantages to the individual for such a trait? Snowshoe hare winter summer-fall