Ch. 6 Concept Check & Comprehension Questions Flashcards
Genetic linkage occurs because..
Genes that are close together on the same chromosome tend to be transmitted together to offspring
In the experiment by Bateson and Punnett, which of the following observations suggested linkage in the sweet pea?
Both b and c suggested linkage
- a 9:3:3:1 ratio was not observed in the F2 offspring
- an unusually high number of F2 offspring had phenotypes of the parental generation
With regard to linked genes along the same chromosome, which of the following statements is false?
Crossing over is needed to produce nonrecombinant offspring
Morgan observed a higher number of recombinant offspring involving eye color and wing length (401+318) than recombinants for body color and eye color (17+12). These results occurred by..
The genes affecting eye color and wing length are farther apart on the X chromosome than are the genes affecting body color and eye color
In a chi square analysis involving genes that may be linked, which of the following statements is correct?
An independent assortment hypothesis is proposed because it allows you to calculate expected numbers of offspring
Parental generation: true-breeding flies with red eyes and long wings were crossed with white eyes and miniature wings. All F1 offspring had red eyes and long wings.
The F1 females flies were then crossed to males with white eyes and miniature wings. The following results were obtained for the F2 generation:
129 red eyes, long wings
133 white eyes, miniature wings
71 red eyes, miniature wings
67 white eyes, long wings
What is/are the phenotypes of the recombinant offspring of the F2 generation?
Red eyes, long wings and white eyes, miniature wings
Parental generation: true-breeding flies with red eyes and long wings were crossed with white eyes and miniature wings. All F1 offspring had red eyes and long wings.
The F1 females flies were then crossed to males with white eyes and miniature wings. The following results were obtained for the F2 generation:
129 red eyes, long wings
133 white eyes, miniature wings
71 red eyes, miniature wings
67 white eyes, long wings
The recombinant offspring of the F2 generation were produced by crossing over that occurred..
During spermatogenesis in the F1 males
Parental generation: true-breeding flies with red eyes and long wings were crossed with white eyes and miniature wings. All F1 offspring had red eyes and long wings.
The F1 females flies were then crossed to males with white eyes and miniature wings. The following results were obtained for the F2 generation:
129 red eyes, long wings
133 white eyes, miniature wings
71 red eyes, miniature wings
67 white eyes, long wings
What is the map distance between these two genes?
34.5mu
An ascus called an octad is the product of..
One meiotic division followed by one mitotic division
One yeast stain is lys+ and arg+, whereas another strain is lys-3 and arg-2. The two strains were crossed to each other and an ascus obtained from this cross has four spores with the following genotypes: lys+ arg+, lys+ arg-2, lys-3 arg+, and lys-3 arg 2. This ascus is a..
Tetratype
The process of mitotic recombination involves the..
Exchange of chromosomal regions between homologs during then division of somatic cells
An experiment of Bateson and Punnett with sweet peas, showing that independent assortment does not always occur
Which types of offspring are found in excess based on Mendels law of independent assortment?
The offspring found in excess are those with purple flowers, long pollen, and red flowers, round pollen.
Consequences of crossing over during meiosis
If a crossover began in the short region between gene A and the tip of the chromosome, would this event affect the arrangement of the A and B alleles?
No, such a crossover would not change the arrangements of these alleles.
Morgans three-factor crosses involving three X-linked traits in Drosophila
Of the eight possible phenotypic combinations in the F2 generation, which ones are the product of a single crossover?
A single crossover can produce offspring with: gray body, red eyes, miniature wings; gray body, white eyes, miniature wings; yellow body, red eyes, long wings; and yellow body, white eyes, long wings.
Morgan’s explanation for nonrecombinant and recombinant offspring.
Why are the nonrecombinant offspring more common than the recombinant offspring?
When genes are relatively close together, a crossover is relatively unlikely to occur between them. Therefore, the nonrecombinant offspring are more common.
Morgans explanation for different proportions of recombinant offspring.
(b) crossover between eye color and wing length genes, fairly common
(C) crossover between body color and eye color genes, uncommon
Why are the types of offspring described in part (b) more numerous than those described in part (c)?
The reason is because the w and m genes are further apart than the y and w genes
Crossing over between abnormal and abnormal chromosome 9 in corn
In this experiment, what two types of characteristics can crossing over change? Hint: one type is seen only with a microscope, whereas the other type can be seen with the unaided eye.
Crossing over can change the combination of kernel phenotypes and also it can change the morphologies of the chromosomes compared to the parental chromosomes
A simplified genetic linkage map of Drosophila melanogaster.
List five reasons why genetic maps are useful.
- to understand the complexity and genetic organization of a species
- understand the underlying basis of inherited traits
- clone genes
- understand evolution
- diagnose and treat diseases
- predict the likelihood of a couple having offspring with genetic diseases
- agricultural breeders of livestock and crops
Use of a testcross to distinguish between recombinant and nonrecombinant offspring.
When and in which fly or flies did crossing over occur in order to produce the recombinant offspring?
Crossing over occurred during oogenesis in the female parent of the recombinant offspring
Relationship between the percentage of recombinant offspring in a testcross and the actual map distance between genes.
What phenomenon explains why the maximum percentage of recombinant offspring does not exceed 50%?
Multiple crossovers prevent the maximum percentage of recombinant offspring from exceeding 50%.
Mitotic recombination in Drosophila that produces twin spotting.
Does mitotic recombination occur in a gamete or in a somatic cell?
Mitotic recombination occurs in somatic cells.
