Practice Exam (Lessons 1-3) Flashcards
When your friend tells you about the rat problem in his building, you kindly offer to help him (and use this as an opportunity to do a little genetics on the side). From his building you isolate two true-breeding lines, one has a straight tail, the other has a curly tail. When you cross a pure-bred straight-tailed parent with a pure-bred curly-tailed parent all the offspring have wavy tails which are neither completely straight nor completely curly. When you allow these wavy-tailed rats to breed with each other their offspring occur in a ratio of 1 straight : 2 wavy : 1 curly. What is the mode of inheritance?
a) one gene pair with straight dominant to curly
b) one gene pair with incomplete dominance
c) two gene pairs with duplicate genes
d) one gene pair with codominance
e) two gene pairs with recessive epistasis
Why?
- Incomplete dominance is a type of genetic inheritance where the heterozygous phenotype is an intermediate blend of the two homozygous phenotypes. In this case, the wavy-tailed rats exhibit a phenotype that is neither completely straight nor completely curly when the pure-bred straight-tailed and pure-bred curly-tailed rats are crossed. The 1:2:1 ratio of straight:wavy:curly in the second generation supports the idea of incomplete dominance.
Organisms who determine their sex using the XX–XO system have the following:
a) female offspring have one X chromosome, and it is inherited from their mother.
b) male offspring have one X chromosome, and it is inherited from their father.
c) male offspring have two X chromosomes, one inherited from each parent.
d) female offspring have one X chromosome, and it is inherited from their father.
e) male offspring have one X chromosome, and it is inherited from their mother.
Why?
- In the XX–XO system, females have two X chromosomes (XX), and males have only one X chromosome (O represents the absence of a second sex chromosome). Female offspring inherit one X chromosome from their mother.
In mammals XX sex chromosomes determine sex in females and XY sex chromosomes determine sex in males. You are studying a particular mammal with a total of 12 chromosomes (2n = 12) in their diploid somatic cells. If you were to look at cells from that species during metaphase I of meiosis, what would be the total number of chromosomes you would observe?
a) 12
b) 6
c) 72
d) 96
e) 24
Black hair in elves is an X-linked recessive trait. Silver is the dominant hair color. An elf woman with silver hair has a father who had black hair. The woman has a child with an elf man with silver hair. Which phenotype is MOST expected?
a) a silver-haired male or a black-haired female
b) a black-haired male
c) a black-haired female
d) a silver-haired female
e) a silver-haired male
During the evolution of the human Y chromosome, all of the following are assumed to have occured EXCEPT
a) the original chromosome was an autosome that eventually evolved into the Y chromosome.
b) one of the early events in the evolution of the Y chromosome was the acquisition or evolution of a gene somewhat similar to the current human SRY gene.
c) many of the genes on the early X chromosome that were responsible for critical cellular functions got moved to the evolving Y chromosome.
d) several regions of chromosomal inversion evolved or were acquired and are now present on the Y chromosome.
e) many of the genes on the original ancestral chromosome suffered mutations and became inactive during the evolution of the Y chromosome.
Axial flowers (A) are dominant to terminal flowers (a), and green pods (G) are dominant to yellow pods (g). A plant of unknown genotype is testcrossed to a true-breeding plant with terminal flowers, and yellow pods. The offspring produced were 97 green and axial, 91 yellow and axial, 100 yellow and terminal, and 93 green and terminal. What is the likely genotype of the parent in question?
a) AAGg
b) AAGG
c) AaGG
d) AaGg
e) aagg
c) AaGG
Color blindness is an X-linked recessive trait. A man who is not color-blind marries a woman who is also typical for color vision, whose father was color-blind. They have a color-blind daughter with Turner syndrome (XO). What is the BEST explanation for this result?
a) mitotic nondisjunction in the first division of the zygote
b) two sperm fertilizing the same egg simultaneously
c) nondisjunction at meiosis II in the mother
d) nondisjunction at meiosis I or meiosis II in the father
e) nondisjunction at meiosis I in the mother
You discover a new mutation that causes curled wings in Drosophila. When a male fly with this mutation is crossed to a homozygous normal female, the F1 are all wild-type phenotypically. The F2 flies consist of 1/2 phenotypically normal females, 1/4 phenotypically normal males, and 1/4 males with curled wings. What is the MOST likely explanation for the new mutant allele?
a) It is autosomal and recessive.
b) It is X linked and dominant.
c) It is X linked and recessive.
d) It is autosomal and dominant.
e) It is Y linked.
Consider two loci that control flower characteristics. For the first gene, the allele m that causes a scalloped margin is recessive to the allele M for a whole margin. For the second gene, the dominant O allele causes orange colour while the recessive allele o makes yellow flowers. Since these genes assort independently, what fraction of gametes produced by an MMOo individual are likely to have an Mo genotype?
a) 1 (100%)
b) 1/2
c) 1/4
d) 9/16
e) 1/16
In goats, black coat color is dominant to grey. Suppose that a black goat is mated with a grey one and the offspring are twins, one black and one grey. What can you conclude about the genotype of the black parent?
a) The genotype cannot be determined from these data.
b) The genotype must be bb.
c) The genotype must be Bb.
d) The genotype could be either BB or Bb.
e) The genotype must be BB.
In llamas, buck teeth (B) are dominant over straight teeth (b), and a shaggy coat (S) is dominant over short hair (s). A cross between a buck toothed, shaggy female and a buck toothed, shaggy male produces only buck toothed, shaggy offspring. This same female was then mated with a straight toothed, short-haired male. Half of the offspring from this cross were buck toothed and shaggy, and half of the offspring were buck toothed and short-haired. What is the genotype of the female?
a) bbss
b) BbSs
c) BBSS
d) BBSs
e) BbSS
A mother of blood type A gives birth to a child with blood type O. Which of the following could NOT be the blood type of the father?
a) B
b) AB
c) O
d) Any of these is a possible blood type of the father.
e) A
In a cross between PpQqRrSstt and PpQqRrssTt, what proportion of the offspring would be expected to be heterozygous for all five traits (P, Q, R, S & T).
a) 1/32
b) 1/64
c) 1/128
d) 1/8
e) 1/16
Why?
- the probability of being heterozygous for each trait is 1/2 because the parent individuals are heterozygous for each trait.So, for each trait (P, Q, R, S, and T), the probability of being heterozygous is 1/2. Since these traits assort independently, you multiply these probabilities together:
(1/2) * (1/2) * (1/2) * (1/2) * (1/2) = 1/32
Hair color is determined in Charolais cattle by alleles at the B and E loci. A dominant allele B encodes black pigment, whereas a recessive allele b encodes tan pigment. Alleles at a second locus affect the deposition of the pigment in the shaft of the hair; dominant allele E allows dark pigment (black or tan) to be deposited, whereas recessive allele e prevents the deposition of dark pigment, causing the hair to be white. A black female Charolais was mated with a white male. Half of the calves born were black, and half were white. If the pigment genotype of the black female parent was Bb, then what was the genotype of the other parent?
a) BB ee
b) Bb ee
c) BB EE
d) bb EE
e) bb ee
Bob B. has determined that in racing tortoises, an allelic series helps to determine muscle twitch speed: t (slow), ta (average), tf (fast), and top (overpowered). The top allele is dominant to all others, tf is dominant to ta and t, ta is dominant to t, and t is recessive to all the other alleles. To help Bob with his breeding program, indicate the phenotypic ratios expected of tortoises from the following cross topta × tft .
a) 2 overpowered : 1 fast : 1 average
b) 3 overpowered : 1 fast
c) 1 overpowered : 1 fast : 1 average : 1 slow
d) 1 overpowered : 1 fast
e) 1 fast : 1 average
