Unit 5: Patterns of Inheritance

Trait

• heritable physical/ behavioral characteristics

Genotype

• the set of alleles an individual has

Gene

• the sequence of DNA that provides instructions to make a protein (specific)

  • each has 2 alleles (one from each parent)

Alleles

• version of a gene

  • ex: allele X on a gene Y can make protein Z

  • each gene has 2 alleles (one from each parent)

Model Organism

• non-human species a scientist uses to study a particular biological process to apply the discoveries to other organisms

  • must be ideal for process…

• GOOD for studying inheritance?

  • short generation time (see many generations)

  • lots of offspring per generation (larger sample size)

  • distinct, countable traits (objectivity)

  • easy to control mating

Phenotype

• the observable trait of an individual

  • what one looks/ acts like

True-breeding

• organism will never give rise to offspring with different phenotype

  • homozygous

    • ONLY carries instructions for one phenotype

Self-fertilization

• Fusion of male and female gametes produced by same organism

  • humans also can act as “pollinator” to fuse sperm + egg of specific flowering plants

• process undergone by F1 to produce F2

P Generation

• = Parental generation

  • 1st generation of organism (usually true-breeding)

  • each parent possesses 2 versions of instructions (alleles) for each trait

    • passes on genes *instructions) to children

F1 Generation

• Filial Generation 1

  • 1st generation of offspring from parents

• counted to measure trait variance

F2 Generation

• Filial Generation 2

  • 2nd generation of offspring from parents

• counted to measure trait variance

Dominant Allele

• phenotype exhibited/ visible

  • heterozygotes MUST have dominant allele

• responsible for Punnet Square naming

Recessive Allele

• phenotype not exhibited/ invisible

  • if you see recessive allele phenotype, means 2 RECESSIVE ALLELES ARE PRESENT

Punnett Square

• used to predict genotype + phenotype ratios of the offspring of parents w/ known genotypes

  • must know dominant genotype

    • phenotype ratio

    • genotype ratio

• STEPS + RULES

Homozygous

• an individual has 2 sets of the SAME alleles for a particular gene

Heterozygous

• an individual has 2 sets of DIFFERENT alleles for a particular gene

  • heterozygotes MUST have dominant allele

One-trait Cross

• breeding experiment that focuses inheritance of one specific trait controlled by a single gene

Complete Dominance

* dominant allele completely hides the effect of a recessive allele in a heterozygous individual

1. Discovery

• controlled mating of true-breeding plants

  • plants that only carry instructions for one gene

• count offspring w/ each trait variant

  • P → F1 → F2

• allow F1 to self-fertilize to produce F2

• observe traits of offspring F2 + count

  • information for one gene may be HIDDEN (not destroyed)

2. Observations + Ideas

• parents pass on instructions (genes)

  • instructions may/ may not be visibly in use by offspring

• each parent possesses 2 versions (alleles) of instructions for each trait

  • these versions can be same or different

• presence of one version of instructions does NOT alter/ destroy another version (DOMINANT ALLELE)

  • still available to be used/ passed on

• presence of one version of instructions does NOT guarantee that it will be used (RECESSIVE ALLELE)

  • can have information that does not affect phenotype