What is meant by “pure-breeding stock”?
Individuals that consistently produce offspring with the same phenotype when self-fertilized or crossed within the same line
What’s the mechanism of inheritance?
How traits are passed from parents to offspring
What are the three major historical hypotheses about inheritance?
- Blending inheritance – parental traits mix into an intermediate form.
- Particulate inheritance (haploid) – offspring inherit one unchanged “particle” per trait.
- Particulate inheritance (diploid) – offspring inherit two particles (alleles) per trait that segregate during reproduction.
If inheritance were blending, what would F1 offspring look like from dark × light parents?
All medium-colored
If inheritance were blending, what would the F2 offspring look like?
All medium-colored (variation would disappear)
If inheritance were particulate, haploid, what would we expect in the F1 generation?
Offspring would resemble one parent or the other, not intermediates
If inheritance were particulate, diploid, what would we expect in the F1 generation?
All offspring would appear the same, but traits of both parents could reappear in F2
Why were F2 results crucial for distinguishing among hypotheses?
Only the diploid particulate model predicted re-emergence of the original parental forms in specific ratios
According to Mendel’s model, how is hereditary information carried?
By genes, which exist in different versions called alleles
How many copies of each gene does an individual carry?
Two — one inherited from each parent
What happens to alleles during gamete formation?
They segregate, so each gamete carries one allele
What do the genetic terms dominant and recessive mean?
They describe the phenotype of heterozygotes: the dominant allele determines the phenotype when paired with a recessive allele
Why is it misleading to think of dominance as a property of alleles themselves?
Because dominance/recessiveness only describe allele interaction, not inherent qualities of the alleles
What gametes are produced by parents with genotype PP?
Only gametes carrying P
What gametes are produced by parents with genotype Pp?
Gametes with either P or p
What gametes are produced by XRXr parents?
Gametes with XR or Xr
What gametes are produced by A1A2 parents?
Gametes with A1 or A2
What gametes are produced by S+S parents?
Gametes with S+ or S
What is a gamete?
A sex cell (sperm or egg) that carries only one copy of each gene. Gametes are haploid.
What is an allele?
A version of a gene. Different alleles produce variation in traits (e.g., purple vs. white flowers).
What does haploid (n) mean?
A cell with one set of chromosomes (one copy of each gene).
Example: gametes (sperm/egg).
What does diploid (2n) mean?
A cell with two sets of chromosomes (two copies of each gene, one from each parent).
Example: most body cells in humans and plants.
What is a zygote?
The first cell formed when two gametes fuse at fertilization; it is diploid, carrying one set of chromosomes from each parent.
