Question

A new human species was found on a distant planet, whose genetic inheritance and process of reproduction is identical to that of humans on earth, however, their phenotypes are much different. You are tracking two phenotypes in this new species: eye shape and tail size. The single gene that controls eye shape (gene E) is unlinked from the single gene that controls tail size (gene T). Square eyes is the dominant eye shape and round eyes is the recessive eye shape. Long tail is the dominant tail size and short tail is the recessive tail size.

1. An individual of this new species is heterozygous for gene E and heterozygous for gene T. What is their genotype and phenotype? (Note, the ‘ / ‘ symbolizes the genotype of the two different homologs for a given chromosome, for example chromosome 5 homolog / chromosome 5 homolog, and ' ; ' separates different chromosomes for example 'chromosome 5 ; chromosome 8)
a. E/E ; T/T – square eyes and long tail
b. e/e ; t/t – round eyes and short tail
c. E/e ; T/t – round eyes and short tail
d. E/e ; T/t – square eyes and long tail
e. e/e ; T/T – round eyes and long tail
f. E/T ; E/T– square eyes and long tail
2. Two individuals, who are both heterozygous for eye shape and tail size, mate. Which of the following is a correct statement about the phenotype ratios expected for their offspring?
a. 9/16 will have square eyes and short tails
b. 9/16 will have round eyes and short tails
c. 3/16 will have round eyes and long tails
d. 3/16 will have round eyes and short tails
e. 1/16 will have square eyes and long tails
3. From the mating described in question ABOVE, what proportion of ALL of the offspring in will be heterozygous for both traits?
a. 1/4
b. 1/16
c. 1/8
d. 1/9
e. 3/16
f. 9/16

Answer 1

1. E/e ; T/t ⇒ Square eyes and long tail (Option D)
2. 3/16 will have round eyes and long tails (Option C)
3. 1/4 of the progeny will be heterozygous for both traits (Option A)

Step-by-step explanation:

Available data:

• Two diallelic unlinked genes
• Gene E controls eye shape: Dominant allele E expresses square eyes, and recessive allele e expresses round eyes.
• Gene T controls the tail size. Dominant allele T expresses long trail, and recessive allele t expresses short tail.

Genotypes Phenotypes

EETT, EeTT, EETt, EeTt Square eyes and Long tail

eeTT, eeTt Round eyes and Long tail

EEtt, Eett Square eyes and Short tail

eett Rounf eyes and short tail.

1. An individual of this new species is heterozygous for gene E and heterozygous for gene T. What is their genotype and phenotype?

The heterozygous individual is E/e ; T/t, expressing square eyes and a long tail.

2. Two individuals, who are both heterozygous for eye shape and tail size, mate. Which of the following is a correct statement about the phenotype ratios expected for their offspring?

Cross: between two heterozygous individuals

Parentals) EeTt x EeTt

Gametes) ET, Et, eT, et

ET, Et, eT, et

Punnett square) . ET Et eT et

ET EETT EETt EeTT EeTt

Et EETt EEtt EeTt Eett

eT EeTT EeTt eeTT eeTt

et EeTt Eett eeTt eett

F1) Genotype:

• 1/16 EETT
• 2/16 EETt
• 1/16 EEtt
• 2/16 EeTT
• 4/16 EeTt ⇒ 1/4 EeTt
• 2/16 Eett
• 1/16 eeTT
• 2/16 eeTt
• 1/16 eett

Phenotype

• 9/16 E-T-, Square eyes and Long tails
• 3/16 E-tt, Square eyes and short tails
• 3/16 eeT-, Round eyes and Long tails
• 1/16 eett, round eyes and short tail

Phenotypic ratio 9:3:3:1

3. From the mating described in question ABOVE, what proportion of ALL of the offspring in will be heterozygous for both traits?

4/16 = 1/4 = 25% of the progeny are expected to be heterozygous for both traits, EeTt.