Question

A rabbit breeder wishing to breed only black-haired rabbits wants to know if the black rabbit it has carries the recessive allele for white fur. Both of the rabbit's parents had black fur.
Which of the following methods would be the best method for the breeder to use in order to determine if the rabbit will produce pure-breeding black-haired offspring?
A. Cross breed the rabbit back to its parents and see if any offspring have white fur
B. Breed the rabbit with another rabbit with black fur and see if any of the offspring have white fur
C. Examine the chromosomes from a hair cell from a black hair on the rabbit
D. Closely examine the rabbit’s fur to see if there are any white hairs embedded within
E. Cross breed the rabbit with a rabbit that has white fur, if the offspring are all black, the rabbit is pure breeding for black fur.

Answer 1

Hint: Mendel stated three fundamental laws which laid the base of genetics. He studied the genes characters and their inheritance into the offsprings. He conducted the experiments on pea in 1856 and established the laws in 1863.

Complete Answer:
Gregor Mendel was a scientist who is known for his Fundamental laws of Inheritance. He stated that the genes come in pairs and are inherited as individual units from each parent. He studied the traits being dominant and recessive in the offspring.
- His laws are- Law of dominance, the law of segregation and law of independent assortment.
- When there is cross-breeding, in the F1 generation homozygous alleles whether dominant or recessive will give the heterozygous trait.
- Whereas the heterozygous trait on crossing or selfing gives the heterozygous dominant and homozygous recessive traits.

Option A: Crossbreed the rabbit back to its parents and see if any offspring have white fur: Crossing black fur rabbit with another black fur rabbit will give either homozygous or heterozygous black fur rabbit.

Option B: Breed the rabbit with another rabbit with black fur and see if any of the offspring have white fur: Breeding the black fur rabbit with another black rabbit will give only black fur rabbit which can have the heterozygous or homozygous trait. So we will not come to know whether it has the recessive white allele or not.

Option C: Examine the chromosomes from a hair cell from a black hair on the rabbit: the colour of the hair depends on the alleles present in the chromosome which cannot be seen or examined. We can examine them only by cross-breeding or selfing.

Option D: Closely examine the rabbit’s fur to see if there are any white hairs embedded within: the genotype features depend on the alleles present for that particular trait.

Option E: Crossbreed the rabbit with a rabbit that has white fur, if the offspring are all black, the rabbit is pure breeding for black fur: crossing a homozygous black fur rabbit with homozygous white fur rabbit will give all black progenies. While the heterozygous black fur rabbit and white fur rabbit will give both black and white progenies. Thus we will come to know by this crossing whether the white allele is present in the fur colour trait or not.

So the answer is option E: Crossbreed the rabbit with a rabbit that has white fur, if the offspring are all black, the rabbit is pure breeding for black fur.

Note: Mendel studied the characters in seven aspects- seed shape, flower colour, seed coat, pod shape, flower location, plant height and unripe pod colour. Mendel’s mathematical and statistical skills helped him to figure out the whole process. Crossing over is all a biological process occurring during the fertilization to maintain the gene pool. These distinct characters lay the base of existence of an offspring.