Chapter 4 Flashcards
(16 cards)
Gain-of-function mutations are associated with being ________.
Dominant
Assume that a cross is made between two organisms that are both heterozygous for a gene that shows incomplete dominance. What phenotypic and genotypic ratios are expected in the offspring?
1:2:1, 1:2:1
Assume that a dihybrid cross for two different traits (AaBb × AaBb) is made in which the gene loci are autosomal, independently assorting, and incompletely dominant. How many different phenotypes are expected in the offspring?
9
Assume that a dihybrid cross for two different traits (AaBb × AaBb) is made in which the gene loci are autosomal, independently assorting, and both incompletely dominant. What phenotypic ratio would you expect from such a cross?
1:2:1:2:4:2:1:2:1
What is the difference between incomplete dominance and codominance?
In codominance, both phenotypes are expressed in heterozygotes. In incomplete dominance, the heterozygote shows a phenotype that is intermediate between the two homozygotes.
Which of the following statements is always true when mutations occur in genes whose products are essential to an organism’s survival?
A homozygote for a recessive lethal allele will not survive.
Why do multiple and lethal alleles often result in modifications of the classic Mendelian monohybrid and dihybrid ratios?
Multiple alleles mean that there are more than two alternatives of a gene at a given locus. A diploid organism has two homologous gene loci that may be occupied by different alleles of the same gene. This can result in many different phenotypes for traits, which may not follow typical Mendelian ratios.
When an essential gene is mutated, it can result in a lethal phenotype. In this case, classic Mendelian monohybrid and dihybrid ratios will not be observed.
A couple each with blood type AB and normal pigmentation have a child with AB blood type and albinism. What is the probability that their next child will have the same phenotype as the first child?
1/8
Typical ratios resulting from epistatic interactions in dihybrid crosses would be ________
9:3:4, 9:7
In the mouse, gene B can produce black pigment from a colorless precursor molecule. A mouse having at least one B allele can produce black pigment, whereas the homozygous recessive mouse (bb) cannot and is albino. The agouti locus (A) can convert the black pigment to brown in the presence of at least one dominant A allele, whereas the homozygous recessive (aa) cannot convert the black pigment to brown. What would be the probability of an albino mouse offspring if the parents were genotypes AaBb and AAbb?
1/2
Many of the color varieties of summer squash are determined by several interacting loci: AA or Aa gives white, aaBB or aaBb gives yellow, and aabb produces green. Assume that two fully heterozygous plants are crossed. Give the phenotype ratio of the offspring.
12 (white): 3 (yellow): 1 (green)
Comb shape in chickens represents one of the classic examples of gene interaction. Two gene pairs interact to influence the shape of the comb. The genes for rose comb (R) and pea comb (P) together produce walnut comb. The fully homozygous recessive condition (rrpp) produces the single comb. Assume that a rose-comb chicken is crossed with a walnut-comb chicken and the following offspring are produced: 17 walnut, 16 rose, 7 pea, 6 single. What are the probable genotypes of the parents?
Rrpp x RrPp
Individuals from two separate true-breeding strains of white deer mice are crossed yielding all grey offspring. White is recessive to gray color based on crossing mice from each strain with a grey mouse. Which of the following would best explain this result?
Complementation
Complementation analysis is used to determine __________.
whether two mutations that produce the same phenotype reside in the same or different genes
The phenomenon of a gene which has multiple phenotypic effects on an individual is referred to as ________
pleiotropy
Because of the mechanism of sex determination, males of many species can be neither homozygous nor heterozygous. Such males are said to be ________.
hemizygous
