Question

1. in horses, black is dependent upon a dominant gene (b) and chestnut upon its recessive allele (b).

the trotting gait is due to a dominant gene (t) and the pacing gait to its recessive allele (t).
a homozygous black pacer is mated to a homozygous chestnut trotter. give the genotypic and
phenotypic ratios.

p1 genotype________ p1 gametes __, __, __, ____
p2 genotype________ p2 gametes __, __, __, ____

Explanation:

Step1: Define parental genotypes

P1 (homozygous black pacer): $BBtt$
P2 (homozygous chestnut trotter): $bbTT$

Step2: Identify parental gametes

P1 gametes: All $Bt$
P2 gametes: All $bT$

Step3: Set up Punnett Square

	$Bt$	$Bt$	$Bt$	$Bt$
$bT$	$BbTt$	$BbTt$	$BbTt$	$BbTt$
$bT$	$BbTt$	$BbTt$	$BbTt$	$BbTt$
$bT$	$BbTt$	$BbTt$	$BbTt$	$BbTt$

Step4: Count genotypes/phenotypes

All offspring have genotype $BbTt$, phenotype black trotter.

Step5: Calculate ratios

Genotypic ratio: 1 (only $BbTt$)
Phenotypic ratio: 1 (only black trotter)

Answer:

Parental Information:

P1 Genotype: $BBtt$; P1 Gametes: $Bt, Bt, Bt, Bt$
P2 Genotype: $bbTT$; P2 Gametes: $bT, bT, bT, bT$

Offspring Counts:

Genotype	#	Phenotype	#

Ratios:

Genotype Ratio: 1:0 (only $BbTt$)
Phenotype Ratio: 1:0 (only black trotter)