EOC Biology Genetics

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.

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

Two heterozgyous tall pea plants are crossed. What is the expected phenotypic outcome for the offspring?

• 100% tall

• 50% tall, 50% short

• 75% tall, 25% short

• 100% short

Answer explanation

When two heterozygous tall pea plants are crossed, the expected phenotypic outcome for the offspring is 75% tall and 25% short due to the 3:1 phenotypic ratio predicted by Mendel's laws of inheritance.

Tags

NGSS.HS-LS3-1

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.

Tags

NGSS.HS-LS3-1

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 Texas Longhorn cattle, coat coloration is an inherited trait. What is the genetic basis of coat-color variation in Texas Longhorn cattle?

• Differences in the nucleotide sequences of genes

• Differences in the numbers of chromosomes in cells

• Differences in the diets of individual cattle

• Differences in the environmental conditions of different geographic areas

Answer explanation

The genetic basis of coat-color variation in Texas Longhorn cattle is differences in the nucleotide sequences of genes, which determine the expression of specific coat color genes.

Tags

B.6(A)

Some angelfish colors are determined by codominance. Possible phenotypes and genotypes of angelfish colors are shown.

Which table shows the expected phenotypes of offspring resulting from a cross between a black angelfish and a black-lace angelfish?

• 
• 
• 
• 

Tags

B.6(F)

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.

Tags

NGSS.HS-LS3-1

NGSS.HS-LS3-2

Coat color in cats is inherited by X-linked genes, with alleles for black and orange-brown. The alleles and phenotypes are as given below. A cross between an orange-brown male and a homozygous black female produce four kittens. What is the phenotypic probability of the offspring?

• 50% black female and 50% black male

• 50% calico female and 50% black male

• 50% orange-brown female and 50% black male

• 50% calico female and 50% orange-brown male

Answer explanation

The cross involves an orange-brown male (heterozygous) and a homozygous black female, resulting in 50% calico females (black and orange-brown) and 50% black males.

Tags

NGSS.HS-LS3-1

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.

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.