Genetics 101
Define gene
A gene: an instruction for making a protein molecule.
What does it mean to inherit a trait?
To receive genes from a parent (passed from parent to offspring)
Name the type of reproduction where one parent produces genetically identical offspring.
Asexual reproduction.
If a homozygous dominant (TT) is crossed with a homozygous recessive (tt), what are the genotypes of the offspring?
All offspring genotype: Tt (100% heterozygous).
What is an allele?
Allele: a specific form of a gene that provides instructions for making a particular protein molecule.
Describe the difference between heterozygous and homozygous.
Heterozygous: having gene versions that are different. Homozygous: having gene versions that are the same.
What is sexual reproduction? Give its main genetic outcome in one sentence.
Sexual reproduction: process in which two parents pass on their genes to create offspring, typically producing genetic variation.
Cross a homozygous dominant female (AA) with a heterozygous male (Aa). What fraction of offspring will show the dominant phenotype?
Offspring genotypes: AA,Aa (50% AA, 50% Aa); fraction showing dominant phenotype = 100%.
Give the terms for an organism's genetic makeup and its physical appearance.
Genotype, phenotype
Why can siblings from the same parents look different? (Two-sentence explanation)
Sexual reproduction mixes genetic information from two parents, creating new combinations of alleles.
Give two plant traits that help increase successful reproduction (one structural, one behavioral- think how they reproduce).
Structural: bright petals (attract pollinators). Behavioral: producing nectar (attracts pollinators).
Cross two heterozygous tongue-rollers (Rr × Rr). What is the genotypic ratio?
Genotypic ratio for Rr×RrRr×Rr: 1 RR:2 Rr:1 rr
What is a mutation? Provide a short example that could change a trait.
Mutation: a random change to a gene; example: a change causing white fur instead of brown.
Explain how a change in a single gene can be beneficial, harmful, or neutral.
A mutation changes a gene’s sequence; it may change a protein’s structure/function and thus be harmful, beneficial, or neutral depending on effect.
What is artificial selection (selective breeding)? Give an example.
Offspring will be genetically identical to the parent.
For a cross Rr × Rr, what is the phenotypic ratio assuming R is dominant?
Phenotypic ratio for Rr×RrRr×Rr with R dominant: 3 roller:1 non−roller
Explain how a protein molecule connects genes to traits.
Genes code for proteins; proteins build structures or perform functions that produce observable traits.
How does sexual reproduction increase genetic variation compared to asexual reproduction?
Sexual reproduction combines half the genes from each parent, producing offspring with genetic variation; asexual reproduction produces genetically identical offspring.
Describe one human technology that changes how humans influence inheritance of traits (use a real example).
Example: inserting a pest-resistance gene into corn (genetic engineering / transgenic crops).
A plant with unknown genotype shows dominant phenotype. Describe a test cross and explain how results would reveal if it is homozygous dominant or heterozygous.
Test cross: cross the unknown dominant-phenotype plant with a homozygous recessive (aa). If any offspring show recessive trait, the unknown was heterozygous (Aa). If all offspring show dominant trait, the unknown is likely homozygous dominant (AA).