Male long-haired white (Wwll) × Female short-haired colored (wwLl)
Two genes control cat coat traits
Each gene has two versions called alleles — one dominant (uppercase), one recessive (lowercase). The dominant allele always wins when present.
Gene 1 — Coat color (W gene)
W
Dominant
White masking — solid white fur
w
Recessive
No masking — colored fur
Gene 2 — Fur length (L gene)
L
Dominant
Short hair
l
Recessive
Long hair
Key rule: A dominant allele always "wins" over a recessive one. You only see a recessive trait when BOTH alleles are recessive — for example, ww = colored fur, ll = long hair.
📚 Section explanation — What are alleles?
Every living thing has genes — instructions inside their cells that control their traits. For each gene, a cat inherits two copies (called alleles): one from mom and one from dad.
Think of alleles like a voting system. If one allele is dominant (uppercase letter), it always wins — no matter what the other allele says. You only see the recessive trait (lowercase letter) if the cat has two recessive copies with no dominant one to override it.
In this problem there are two separate genes being tracked at the same time — this is called a dihybrid cross ("di" = two). That is why genotypes have 4 letters like Wwll — the first two letters (Ww) describe the color gene, and the last two (ll) describe the fur-length gene.
Quick examples:
WW = two dominant W alleles → white fur | Ww = one W one w → still white (W wins) | ww = two recessive → colored fur
LL = two dominant L alleles → short hair | Ll = one L one l → still short (L wins) | ll = two recessive → long hair
Father (male)
Wwll
Long-haired cat with white fur
Ww → has W (dominant) → white fur
ll → both recessive → long hair
His gametes: Wl and wl (50% each)
Mother (female)
wwLl
Short-haired cat with colored fur
ww → both recessive → colored fur
Ll → has L (dominant) → short hair
Her gametes: wL and wl (50% each)
What is a gamete? When cats reproduce, each parent contributes only HALF their alleles — one from each gene pair. This half-set is called a gamete (egg or sperm). The Punnett square shows every possible gamete combination.
📚 Section explanation — Understanding the parents
Before we can fill in the Punnett square, we need to know what gametes (egg and sperm cells) each parent can produce. A gamete carries exactly ONE allele from each gene — so each gamete has 2 letters total (one for color, one for length).
Father (Wwll): For coat color he has W and w — so he can pass either W or w. For fur length he has l and l — he can only pass l. This gives him two possible gametes: Wl (50% chance) and wl (50% chance).
Mother (wwLl): For coat color she has w and w — she can only pass w. For fur length she has L and l — she can pass either. This gives her two possible gametes: wL (50% chance) and wl (50% chance).
Why does the father appear as Wwll and not WwLL?
The problem tells us the father has long hair. Long hair only appears when both fur-length alleles are recessive (ll). That confirms his fur-length genotype must be ll. He has white fur, which only requires ONE dominant W — so he could be WW or Ww. The problem says his genotype is Wwll, meaning he is heterozygous for color.
4×4 Punnett square
Each cell = one dad gamete + one mom gamete. Click any cell to see what that kitten looks like.
Father (Wwll) gametes →
Wl
Wl
wl
wl
Mother (wwLl) gametes ↓
wL
wL
wl
wl
White + short hairWhite + long hairColored + short hairColored + long hair
Phenotype ratios (what we see)
Out of 16 cells in the Punnett square, each phenotype appears exactly 4 times — a 1:1:1:1 ratio.
4/16
White + short hair WwLl
4/16
White + long hair Wwll
4/16
Colored + short hair wwLl
4/16
Colored + long hair wwll
Each phenotype has a 25% probability. This 1:1:1:1 ratio happens because both parents are heterozygous for different genes — neither has the same two dominant alleles for both traits.
"If this cross produces 20 offspring, what is the most likely number of long-haired kittens with colored fur?"
4/16
Probability per kitten
= 25%
Chance for each kitten
5
Most likely out of 20
Step 1: Find colored + long-hair cells in Punnett square → wwll = 4 out of 16 cells
The answer is 5 kittens. The phrase "most likely" means we use probability to calculate the expected value. In real life the count could vary, but statistically 5 is the most probable outcome out of 20 offspring.
