mastering genetics ch 5. linkage and mapping

3 or greater

A lod score is a statistical value that represents the probability of genetic linkage between human genes. What lod score is associated with a significant likelihood of linkage?

Ltr / lTR

A wild-type trihybrid soybean plant is crossed to a pure-breeding soybean plant with the recessive phenotypes pale leaf l, oval seed (r), and short height (t). The results of the three-point test cross are shown in the table. Traits not listed are wild type. Pale 648 Pale, oval 64 Pale, short 10 Pale, oval, short 102 Oval 6 Oval, short 618 Short 84 Wild type 98 What is the genotype of the wild-type trihybrid soybean plant? Use L, R, and T to represent dominant alleles and l, r, and t for recessive alleles. (part a)

0.269

Calculate the interference value for these data. (part e)

0.133

Calculate the recombination fraction between T and L pair of genes. (part c)

0.101

Calculate the recombination fraction between T and R pair of genes. (part d)

Recombination fraction 0.035

Calculate the recombination fraction between the Cl-Sh gene pair. (part c)

Recombination fraction .219

Calculate the recombination fraction between the Cl-Wx gene pair (part e)

Recombination fraction .184

Calculate the recombination fraction between the Sh-Wx gene pair. (part d)

0.2 The coefficient of coincidence is 0.01/0.0125 = 0.8, so the interference is 1 - 0.8 = 0.2.

For linked genes A, B, and C, the map distance A-B is 5 map units and the map distance B-C is 25 map units. If there are 10 double crossover events out of 1000 offspring, what is the interference?

Ae___, aE___, AE___, ae___ 370,370,130,130

Genes A, B, C, D, and E are linked on a chromosome and occur in the order given. The test cross Ae / aE × ae / ae indicates the genes recombine with a frequency of 26%. If 1000 progeny are produced by the test cross, determine the number of progeny in each outcome class.

0.3465 0.3465 0.0385 0.0385 0.1035 0.1035 0.0115 0.0115

Genes A, B, and C are linked on a chromosome and found in the order A-B-C. Genes A and B recombine with a frequency of 10%, and genes B and C recombine at a frequency of 23%. For the cross a + b + c/abc + × abc/abc, predict the frequency of progeny. Assume interference is zero. Predict the frequency of a+b+c progeny. Predict the frequency of abc+ progeny. Predict the frequency of a+ bc+ progeny. Predict the frequency of ab+c progeny. Predict the frequency of a+b+c+ progeny. Predict the frequency of abc progeny. Predict the frequency of a+bc progeny. Predict the frequency of ab+c+ progeny.

AH/ahCc-purple hairy cut AH/ahcc-purple hairy potato ah/ahCc-green hairless cut ah/ahcc-green hairless potato Ah/ahCc-purple hairless cut Ah/ahcc-purple hairless potato aH/ahCc- green hairy cut aH/ahcc-green hairy potato

Give the genotypes of progeny plants in this experiment. (part b)

Two-strand double crossover

If a and b are linked, which type of crossover between them will produce a parental ditype (PD) tetrad?

1:1:1:1:1:1:1:1 The law of independent assortment states that each pair of alleles segregates independently of all other pairs of alleles during gamete formation. The three Punnett squares below show the predicted phenotypic ratios for each trait in the F2 offspring.

If two genes are found on different chromosomes, or if they are far enough apart on the same chromosome that the chance of a crossover between them is very high, the genes are considered to be unlinked. Unlinked genes follow Mendel's law of independent assortment. If, however, two genes tend to "travel together" because they are near one another on the same chromosome, they are said to be linked. Linked genes do not follow Mendel's law of independent assortment. In this tutorial, you will compare the inheritance patterns of unlinked and linked genes. A wild-type tomato plant (Plant 1) is homozygous dominant for three traits: solid leaves (MM), normal height (DD), and smooth skin (PP). Another tomato plant (Plant 2) is homozygous recessive for the same three traits: mottled leaves (mm), dwarf height (dd), and peach skin (pp). In a cross between these two plants (MMDDPP x mmddpp), all offspring in the F1 generation are wild type and heterozygous for all three traits (MmDdPp). Now suppose you perform a testcross on one of the F1 plants (MmDdPp x mmddpp). The F2 generation can include plants with these eight possible phenotypes: solid, normal, smooth solid, normal, peach solid, dwarf, smooth solid, dwarf, peach mottled, normal, smooth mottled, normal, peach mottled, dwarf, smooth mottled, dwarf, peach Assuming that the three genes undergo independent assortment, predict the phenotypic ratio of the offspring in the F2 generation. (part a)

1:1:1:1 If the genes are unlinked, then they will assort independently in meiosis and test-cross progeny will be produced in a 1:1:1:1 ratio. If the two genes are linked, then more than 50% of the progeny will display parental phenotypes and less than 50% of the progeny will display recombinant (nonparental) phenotypes.

In a dihybrid test cross involving unlinked genes, what phenotypic ratios would be expected from a cross between a dihybrid female and a homozygous recessive male?

20 map units

In a three‑point mapping experiment for the genes y‑w‑ec, the following percentages of events are observed: NCO events: 65%; SCO events between y and w: 15%; SCO events between y and ec: 17%; DCO events: 3% What is the map distance between y and ec?

The tall, peach fuzz, round plant will produce TpR gametes. The pure-breeding dwarf, smooth, oblong plant will produce tPr gametes.

In tomatoes, the allele T for tall plant height is dominant to dwarf allele t, the P allele for smooth skin is dominant to the p allele for peach fuzz skin, and the allele R for round fruit is dominant to the recessive r allele for oblong fruit. The genes controlling these traits are linked on chromosome 1 in the tomato genome, and the genes are arranged in the order and with the recombination frequencies shown. T-P-R 0.04-.18 A pure-breeding tall, peach fuzz, round plant is crossed to a pure-breeding plant that is dwarf, smooth, oblong. What are the gamete genotypes produced by each of these plants? (part a)

All eight possible phenotypes could occur, but a greater proportion of the offspring would have the parental phenotypes Because all three genes are linked, it is more likely that the parental allele combinations would stay together rather than be recombined through a crossover event. That is why a greater proportion of the offspring would have parental phenotypes. Nevertheless, some crossing over would likely occur, which is why a small proportion of the offspring would have recombinant phenotypes.

Now, suppose that the three tomato genes from Part A did not assort independently, but instead were linked to one another on the same chromosome. Would you expect the phenotypic ratio in the offspring to change? If so, how? Which statement best predicts the results of the cross MmDdPp x mmddpp assuming that all three genes are linked? (part b)

L-T-R

Place the alleles in their correct gene order. (part b)

The chi-square value is 10,649. P value is below 0.01, which indicates that the difference between the expected and observed results is highly statistically significant.

Researchers cross a corn plant that is pure-breeding for the dominant traits colored aleurone (C1), full kernel (Sh), and waxy endosperm (Wx) to a pure-breeding plant with the recessive traits colorless aleurone (c1), shrunken kernel (sh), and starchy (wx). The resulting F1 plants were crossed to pure-breeding colorless, shrunken, starchy plants. Counting kernels from about 30 ears of corn yields the data shown in the table Colored, shrunken, starchy 116 Colored, full, starchy 601 Colored, full, waxy 2538 Colored, shrunken, waxy 4 Colorless, shrunken starchy 2708 Colorless, full, starchy 2 Colorless, full, waxy 113 Colorless, shrunken, waxy 626 Perform a chi-square test to determine if these data show significant deviation from the expected phenotype distribution. (part a)

offspring with red, round eyes resulted from fertilization of eggs containing recombinant X chromosomes

Stern observed all of the following results EXCEPT _______ in his experiment. (part b)

m-d 12 cM d-p 5 cM m-p 17 cM The recombination frequencies between genes can be used to construct a linkage map, as you have just done. The closer two genes are to each other on the same chromosome, the less likely they are to be separated by a crossover event, resulting in a lower recombination frequency. To calculate the distance between m and p, you would add the map distances between m and d and between d and p (12 cM + 5 cM = 17 cM). You probably noticed that the recombination frequency between m and p is slightly less than that sum. This is because of double crossover events--the times that crossovers occur both between m and d and between d and p. In a double-crossover event, the second crossover effectively "cancels out" the first, reducing the number of recombinants between m and p that are observed, while contributing to the number of recombinants between each of the other two pairs of genes. Therefore, adding the smaller map distances to calculate larger distances avoids inaccuracies due to double-crossover events that produce non-recombinant genotypes.

Suppose that you perform the cross discussed in Part B: MmDdPp x mmddpp. You plant 1000 tomato seeds resulting from the cross, and get the following results: solid, normal, smooth 420 solid, normal, peach 21 solid,dwarf,smooth 2 solid, dwarf,peach 52 mottled, normal smooth 62 mottled, normal, peach 4 mottled , dwarf, smooth 23 mottled, dwarf, peach 416 Drag the labels onto the chromosome diagram to identify the locations of and distances between the genes. Use the blue labels and blue targets for the genes; use the white labels and white targets for the distances. Gene m has already been placed on the linkage map. (part c)

394 each-tall peach fuzz round dwarf smooth oblong 16 each- tall smooth oblong dwarf peach fuzz round 86-tall peach fuzz oblong dwarf smooth round 4 each-tall smooth round dwarf peach fuzz oblong

The F1 are test-crossed to dwarf, peach fuzz, oblong plants, and 1000 test-cross progeny are produced. What are the phenotypes of test-cross progeny, and what number of progeny is expected in each class? (part d)

AH/ah Cc × ah/ah cc

The cross of a purple, hairy, cut plant heterozygous at each gene to a green, hairless, potato plant produces the following progeny: Purple, hairy, cut 21 Purple, hairy, potato 21 Green, hairless, cut 21 Green, hairless, potato 21 Purple, hairless, cut 4 Purple, hairless, potato 4 Green, hairy, cut 4 Green, hairy, potato 4 In tomato plants, purple leaf color is controlled by a dominant allele A, and green leaf by a recessive allele a. At another locus, hairy leaf H is dominant to hairless leaf h. The genes for leaf color and leaf texture are separated by 16 m.u. on chromosome 5. On chromosome 4, a gene controlling leaf shape has two alleles: a dominant allele C that produces cut-leaf shape and a recessive allele c that produces potato-shaped leaf. Give the genotypes of parental plants in this experiment. (part a)

it allowed cytological detection of physical exchange between the chromosomes The differences in structure between the two chromosomes allowed Stern to track the inheritance of recombinant and nonrecombinant X chromosomes.

The discernible difference in length between the two X chromosomes of the female fruit fly was important in Stern's experiments because _______. (part a)

genetic recombination is a result of physical exchange between homologous chromosomes Whenever recombinant phenotypes occurred, the cytological markers indicated that a physical exchange between the X chromosomes had also occurred.

The results of the Stern experiment supported the general idea that _______. (part c)

false To construct a mapping cross of linked genes, it is important that the genotypes of all of the gametes produced by the heterozygote can be deduced by examining the phenotypes of the progeny, taking into consideration that the homozygote produced only recessive gametes. Gametes and their genotypes can never be observed directly.

To construct a mapping cross of linked genes, it is important that the genotypes of some of the gametes produced by the heterozygote can be deduced by examining the phenotypes of the progeny.

genes that are located on the same chromosome

What are syntenic genes?

39.36%TpR, 39.36%tPr, 1.64%TPr, 1.64%tpR, 8.64%Tpr, 8.64%tPR, 0.36%TPR, and 0.36%tpr.

What are the genotypes of gametes produced by the F1, and what is the predicted frequency of each gamete? (part c)

1% recombinant products of meiosis

What is the definition of a map unit?

The F1 are tall, smooth, round and have the genotype TpR/tPr.

What is the genotype and phenotype of the F1 progeny of this cross? (part b)

Interference value 0.861

What is the interference value for this data set? (part f)

haplotype

What is the name given to the specific array of alleles in a set of linked genes on a single chromosome?

The gene order is Cl-Sh-Wx.

What is the order of these genes in corn? (part b)

Genetic linkage results in the production of significantly more parental gametes, and significantly fewer nonparental (recombinant) gametes than expected by chance

Which of the following statements about genetic linkage is generally true?

Alfred Sturtevant

Who is generally credited with creating the first genetic linkage map?

1/8 If the three genes are unlinked, then the expected frequency of each phenotypic class among the test-cross progeny would be 1/8. (table saved)

[Table 5.3] If the three genes in the crosses described in Table 5.3 were unlinked, what proportion of the test-cross progeny would be expected to display phenotypic class 4 (yellow, glossy, variable)?

phenotypes 3 and 6 The rarest classes of test-cross progeny are the products of double crossover events (table saved)

[Table. 5.3] By inspection (without performing any calculations), identify which phenotypic classes in Table 5.3 are the products of double crossover events.