Biology EOC Texas

If one allele for a trait is dominant and the other allele is recessive, which trait will be visible? The dominant allele or the recessive allele?

• Dominant will be visible because it is blocked by the recessive allele.

• Dominant will be visible because it hides or blocks the recessive allele.

• Recessive will be visible because it is blocked by the dominant allele.

• Recessive will be visible because it hides or blocks the dominant allele.

Answer explanation

Dominant will be visible because it hides or blocks the recessive allele.

Using the dihybrid cross and key provided, what is the probability of the offspring being tall and white?

• 9

• 2

• 3

• 6

Answer explanation

The probability of the offspring being tall and white is 3, as determined by the dihybrid cross and key provided.

In sheep, producing white wool (W) is dominant to black wool (w), and having brown eyes (E) is dominant to blue eyes (e). A cross of two heterozygous sheep is shown in the Punnett square below
Which of the following describes an outcome of this cross?

• 1/16 will have white wool and brown eyes

• 3/16 will have black wool and brown eyes

• 4/16 will have white wool and blue eyes

• 9/16 will have black wool and blue eyes

Answer explanation

The correct choice is 3/16 will have black wool and brown eyes because the Punnett square shows the possible genotypes and phenotypes resulting from the cross of two heterozygous sheep.

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The table below lists human blood group genotypes and phenotypes.

Why is the AB phenotype a result of codominance?

• Neither allele is expressed in the phenotype.

• Both alleles are equally expressed in the phenotype.

• One allele masks the expression of the other during expression of the phenotype.

• Both alleles blend together to form an intermediate phenotype during expression.

Answer explanation

The AB phenotype is a result of codominance because both alleles are equally expressed in the phenotype, leading to the presence of both A and B antigens on the red blood cells.

What is the term used to describe the movement of alleles between populations?

• Genetic drift

• Gene flow

• Natural selection

• Mutation

When red carnations are crossed with white carnations, the resulting flowers are pink. Pink carnations are an example of what type of inheritance pattern?

• incomplete dominance

• recessive alleles

• dominant alleles

• codominance

Answer explanation

The correct inheritance pattern is incomplete dominance, where the heterozygous genotype results in an intermediate phenotype, in this case, pink carnations.

Which explanation describes how the presence of a white flower color occurred in the offspring?

• Parents are homozygous for the dominant gene expressing red color.

• Parents are heterozygous for the dominant gene expressing red color.

• Parents are homozygous for the recessive gene expressing white color.

• Parents are heterozygous for the recessive gene expressing white color.

Answer explanation

The presence of a white flower color occurred in the offspring because the parents are heterozygous for the recessive gene expressing white color.

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This diagram shows a diploid cell with two pairs of homologous chromosomes.

Due to independent assortment, what is the possible genetic make-up of gametes produced by this organism?

• SsTt

• Ss, Tt

• S, s, T, t

• ST, St, sT, st

Answer explanation

The correct choice is 'ST, St, sT, st' because independent assortment allows for different combinations of alleles from homologous chromosomes to be present in gametes.

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Which of the following is a phenotype?

• Aa

• red hair

• heterozygous

• DNA

Answer explanation

The correct choice is 'red hair' because it is a visible trait or characteristic resulting from the interaction of an organism's genotype with the environment.

In guinea pigs, the allele for short hair is dominant. If all the guinea pigs are born short haired what are the possible genotypes of the parents? (There are two possible combinations.)

• Ss + Ss

• SS + SS

• SS + Ss

• ss + ss

Answer explanation

The possible genotypes of the parents for all short-haired guinea pigs are SS + Ss and SS + SS, as short hair is dominant and all offspring are short haired.

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