Chapter 6 Flashcards
What is a synteny group?
A group of genes that are found in the same order on the chromosomes of different species.
What is genetic linkage or linkage groups?
A group of genes that are linked together because they are found on the same chromosome.
The number of linkage groups is equal to what?
The number of chromosome types.
Humans have how many autosomal linkage groups?
22
What other linkage groups do humans have?
x chromosome linkage groups
Y chormosome linkage group.
What did William Bateson and Reginald Punnett study in 1905?
How genes are not assorted independently.
What was Bateson and Punnett’s study?
On Sweet Pea plants and flower color and pollen shape. The F2 generation did not follow the 9:3:3:1 ratio. They had a greater proportion of the two phenotypes found in the parental generation. They determined that the two characteristics were coupled.
Which types of offspring are found in excess based on Mendel’s law of independent assortment in Bateson and Punnett’s study?
Purple flowers, long pollen, and red flowers, round pollen.
Genetic linkage occurs because
a. genes that are on the same chromsome may affect the same character.
b. genes that are close together on the same chromosome tend to be transmitted together to offspring
c. genes that are on different chromsomes are independently assorted.
d. none of the above.
b. 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?
a. a 9:3:3:1 ratio was observed in the F2 offspring
b. a 9:3:3:1 ratio was not observed in the F2 offspring
c. an unusually high number of F2 offspring had phenotypes of the parental generation.
d. both b and c suggested linkage.
d. both b and c suggested linkage.
Even though the alleles for different genes may be linked along the same chromosome, the linkage can be what?
Altered during meiosis.
What is crossing over?
A physical exchange of chromosome pieces that most commonly occurs during prophase of meiosis I.
What is a bivalent?
A structure in which two pairs of homologous sister chromatids have synapsed with each other.
If a crossover began in the short region between gene A and the tip of the chromosome, would this event affect the arrangment of the A and B alleles?
No, such a crossover would not change the arrangements of these alleles.
What is genetic recomination?
- The process in which chromosomes are broken and then rejoined to form a nove genetic combination
- The process in which alleles are assorted and passed to offspring in combinations that are different from the parents.
What are recombinant cells?
a. Combinations of alleles or traits that are not found in the parental generations.
b. DNA molecules that are produced by molecular techniques in which segments of DNA are joined to each other in ways that differ from their original arrangment in their native chromosomal sites.
What are recombinant offspring?
The offspring of haploid cells that were gamates that participated in genetic recombination.
What are nonrecombinant offspring?
Offspring that have inherited the same combination of alleles found in the chromosomes of their parents.
What did Thomas Hunt Morgan study in 1911?
The inheritance pattern of different characters that have been shown to follow an x-linked pattern of inheritance.
Fruit flies with red and white eyes.
Of the eight possible phenotypic combinations in the F2 generation, which ones are the product of a single crossover in Morgan’s Fruit fly study?
Single cross can produce: Gray body, red eyes, miniature wings
Gray body, white eyes, miniature wings;
Yellow body, red eyes, long wings;
yellow body, white eyes, long wings.
Why are the types of offspring described in part (b) involving crossover between eye color and wing length genes more numerous than those described in part (c) involving crossover between body color and eye color genes?
When genes are relatively close togehter, a corssover is relatively unlikely to occur between them. Therefore, nonrecombinant offspring are more common.
What determines the proportions of recombinant offspring?
The distance between the two genes.
Why are the nonrecombinant offspring more common than the recombinant offspring?
The w and m genes are farther apart than the y and w genes.
What are the seven reasons why genetic maps are useful?
- understand the complexity and genetic organixation of a species.
- understand the underlying basis of inherited traits.
- clone genes
- understand evolution
- diagnose and treat disases
- provide the likelihood of acouple having offspring with genetic diseases
- agricultural breeders of livestock and crops.
What can be used to determine if two genes are linked or independently assorted?
chi square test.
How do you begin determining whether genes are linked or indpendently assorted?
Begin with the hypothesis that the genes are not linked.
If the chi square value is low we cannot reject the null hypothesis, we infer that the genes are independently assorted. If the chi square value is high, then we accept the alternative hypothesis that the genes are linked.
What other factor could provide a false acceptance of linked genes?
Decreased viability of particular phenotypes is actually independent assortment
What are the steps for applying the chi square test?
Propose a hypothesis
Based on the hypothesis, calculate the expected value of each of the four phenotypes.
Apply the chi square formula, using the data for the observed values and the expected values that have been calculated.
Interpret the calculated chi square value.
In Creighton and McClintock’s experiement, involving the corsses of two linked genes to produce nonrecombinant and recombinant offspring, 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 chromsomes.
Creighton and McClintock began with what in their experiment?
A corn strain that carried an abnormal chromosome that had a knob at one end and a translocation at the other. It was Cwx
With regard to linked genes along the same chromosome, which of the following statements is false?
a. crossing over is needed to produce nonrecombinant offspring.
b. crossing over is needed to produce recombinant offsrping
c. corssing over is more likely to separate alleles if they are far apart on the same chromosome.
d. crossing over that separates inked alleles occurs during prophase of meiosis I.
a. 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 because
a. the genes affecting eye color and wing length are farther apart on the x chromsome than are the genes affecting body color and eye color.
b. the genes affecting eye color and wing length are closer together on the x chromosome than are the genes affecting body color and eye color.
c. the gene affecting wing length is not on the x chromosome.
d. the gene affecting body color is not on the x chromosome.
a. the genes affecting eye color and wing length are farther apart on the x chromsome 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?
a. an independent assortment hypothesis is not proposed because the data usually suggest linkage.
b. an independent assortment hypothesis is proposed because it allows you to calculate expected number of offspring.
c. a large chi square value suggests that the observed and expected data are in good agreement.
d. the null hypothesis is rejected when the chi square value is very low.
b. an independent assortment hypothesis is proposed because it allows you to calculate expected number of offspring.
What are the other names for Genetic mapping?
Gene mapping
Chromosome mapping
What is the purpose of genetic mapping?
To determine the linear order and distance of separation among genes that are linked to each other along the same chromosome.
What is locus?
The physical location of a gene within a chromosome.
Why is genetic mapping useful?
It allows geneticist to understand the overall complexity and genetic organization of a particular species.
It displays the inherited traits an organism displays
The locus of a gene can help molecular geneticists to clone that gene.
Useful for evolutionary understanding
Can help treat inherited diseases.
Genetic mapping is based on what?
The level of recombination that occurs in just one parent
When and in which fly or flies did corssing over occur in order to produce the recombinant offspring when dealing with fruit flies with long or short bristles and black or gray body color.
Crossing over occurs during oogenesis in the female parent of the recombinant offspring.
What is the map distance?
The relative distance between sites along a single chromsome.