Genetics and Inheritance Quiz

Which of the following statements incorrectly illustrates incomplete dominance?

• Red flowers crossed with white flowers produce pink flowers

• Dark brown fur crossed with white fur produces yellow fur

• Tall plants crossed with short plants produce medium height plants

• A black horse crossed with a white horse produces a mixture of white and black hair in a horse

Answer explanation

The statement about the black and white horse describes codominance, where both traits are fully expressed. Incomplete dominance would show a blending of traits, like pink flowers from red and white.

Which of the following statements illustrates codominance?

• Tall plants crossed with short plants produce medium height plants

• Individuals who are heterozygous for the sickle cell anemia allele are more resistant to malaria

• Red flowers crossed with white flowers produce pink flowers

• Grey heterozygous chickens have black and white feathers

Answer explanation

Codominance occurs when both alleles in a heterozygote are fully expressed. The statement about grey heterozygous chickens having black and white feathers illustrates this, as both feather colors are visible.

A black horse mated with a blue roan horse. Which of the following alternatives correctly identifies the phenotypic ratio of the offspring?

• 1 BB: 1 BW

• 1 black: 1 blue roan

• 1 white: 1 black

• 1 WW: 1 BB

Answer explanation

The black horse (BB) and blue roan horse (BW) produce offspring with a phenotypic ratio of 1 black (BB) to 1 blue roan (BW), as the blue roan is a mix of black and white genes.

An agouti rabbit (Cch) and a chinchilla rabbit (cchc) are crossed. What is the phenotype ratio of the offspring?

• 2 agouti: 1 chinchilla: 1 Himalayan

• 1 chinchilla: 1 Himalayan

• 1 agouti: 2 chinchilla: 1 Himalayan

• 1 agouti: 1 chinchilla: 1 Himalayan: 1 albino

Answer explanation

The cross between an agouti rabbit (Cch) and a chinchilla rabbit (cchc) produces 1 agouti (Cchcch), 2 chinchilla (cchc), and 1 Himalayan (CchCch). Thus, the phenotype ratio is 1 agouti: 2 chinchilla: 1 Himalayan.

A test cross was performed to determine the genotype of an agouti rabbit. Out of 32 offspring, 14 were Himalayan rabbits. What is the genotype of the agouti rabbit?

• Cc

• CC

• Cch

• Ccch

Answer explanation

The presence of 14 Himalayan rabbits indicates that the agouti rabbit must carry the recessive allele for the Himalayan trait. The genotype Ccch (heterozygous agouti with Himalayan allele) explains the offspring ratio observed.

Sarah and George have been married for 6 years. They had a daughter 5 years ago and her blood type is AB. Sarah had complications during her birth and was transfused with three pints of type A blood. The couple recently welcomed a new baby boy to their family. He has the blood type O. What are Sarah's and George's genotypes?

Answer explanation

Sarah's genotype is AO (since she can have an AB child) and George's is BO (to have an O child). This explains the blood types of their children: AB from Sarah and O from George.

Multiple alleles control the intensity of pigment in mice. The gene D1 designates full colour, D2 designates dilute colour, and D3 is deadly when homozygous. The order of dominance is D1>D2>D3. When a full colour male is mated to a dilute colour female, the offspring are produced in the following ratio: two full colour to one dilute to one dead. Indicate the genotypes of the parents.

• Male: D1D3, Female: D1D1
• Male: D1D1, Female: D2D2
• Male: D1D2, Female: D2D3
• Male: D2D2, Female: D3D3

Answer explanation

The full colour male must be D1D1 or D1D2, and the dilute female must be D2D2. The offspring ratio indicates the male is D1D2 (2 full colour: 1 dilute) and the female is D2D2, producing the expected ratios including dead offspring.

Palomino horses are known to be caused by the interaction of two different genes. The allele Cr in the homozygous condition produces a chestnut, or reddish colour, horse. The allele Cm produces a very pale cream coat colour, called cremello, in the homozygous condition. The palomino colour is caused by the interaction of both the chestnut and cremello alleles. Indicate the parent genotypes, and the expected ratios in the F1 generation from mating a palomino with a cremello.

Answer explanation

The palomino (CrCm) mated with a cremello (CmCm) results in F1 genotypes: 50% palomino (CrCm) and 50% cremello (CmCm). The expected ratio is 1:1 for palomino to cremello offspring.

List the gametes that would be produced by organisms having the following genotypes: a) AaBB b) aaBB c) AAbb d) AaBBCc

Answer explanation

Gametes are formed by combining alleles from each parent. a) AB, Ab; b) aB; c) Ab; d) ABC, ABc, AbC, Abc. Thus, the gametes for each genotype are listed.

For human blood type, the alleles for types A and B are codominant, but both are dominant over the type O allele. The Rh factor is separate from the ABO blood group and is located on a separate chromosome. The Rh+ allele is dominant to Rh-. Indicate the possible phenotypes from the mating of a woman, type O, Rh-, with a man type A, Rh+.

Answer explanation

The woman (O, Rh-) can only pass O and Rh- alleles. The man (A, Rh+) can pass A or O and Rh+ or Rh-. Possible phenotypes for their children are A Rh+, A Rh-, O Rh+, and O Rh-.