Genetics Chapter 4

Genes that "travel" together from one generation to the next more often than not exhibit _____________________ ______________________.

genetic linkage

Genes that "travel" together from one generation to the next more often than not exhibit _____________________ ______________________.

genetic linkage

A probability test that measures "goodness of fit" between observed and predicted results is a __________ ________________ test

chi square test

A hypothesis that predicts no linkage between genes is called the ______________ hypothesis

null hypothesis

Genes that can serve points of reference on a chromosome are useful as genetic markers while cytologically visible abnormalities that also make it possible to keep track of chromosomes are called ________________________ markers

physical

The movement of chiasmata toward the end of a chromosome is called _____________________.

teminalization

One percentage point of recombination or recombination frequency is a unit of measure called either centimorgan or ___________ _____________

map unit

Crossovers do not occur independently and the occurrence of one crossover reduces the likelihood of another occurring elsewhere on the chromosome this is called __________________________ __________________________.

chromosomal interference

A tetrad that contains four recombinant class haploid cells is known as a ____________________ ditype.

non-parental ditype

A tetrad that carries four kinds of haploid cells: two different parental and two different recombinant class spores is referred to as ________________________.

tetratype

Mistakes in mitosis during development often result in ______________________ organisms containing tissues of different genotypes

mosaic

The R/r and S/s genes are linked and 10 map units apart. In the cross Rs/rS rs/rs what fraction of the progeny will be RS/rs?

A)5%

If the map distance between genes A and B is 10 map units and the map distance between genes B and C is 25 map units what is the map distance between genes A and C?

C) Either 15 map units or 35 map units, depending on the order of the genes.

In Drosophila singed bristles (sn) and cut wings (ct) are both caused by recessive X-linked alleles. The wild type alleles (sn+ and ct+) are responsible for straight bristles and intact wings respectively. A female homozygous for sn and ct+ is crossed to

C)25 m.u.

The following information applies to problems 14 & 15. In Drosophila singed bristles (sn) and carnation eyes (car) are both caused by recessive X-linked alleles. The wild-type alleles (sn+ and car+) are responsible for straight bristles and red eyes respe

c)2.0

What is the p value from this test? (Pick the most accurate choice.)

A)p>.5

Suppose the L and M genes are on the same chromosome but separated by 100 map units. What fraction of the progeny from the cross LM/lm lm/lm would be Ll/lm?

B)25%

The pairwise map distances for four linked genes are as follows: A-B = 22 m.u.: B-C = 7 m.u.: C-D = 9 m.u.: B-D = 2 m.u.:A-D = 20 m.u.: A-C = 29 m.u. What is the order of these four genes?

B)ADBC

The zipper-like connection between paired homologs in early prophase is known as a:

C)synaptonemal complex.

The measured distance between genes D and E in a two point test cross is 50 map units. What does this mean in physical terms?

E)either a or c

The following information applies to problems 21 & 22. In humans the genes for red-green color blindness (R=normal: r=color-blind) and hemophilia A (H=normal: h=hemophilia) are both X-linked and only 3 map units apart.Suppose a woman has four sons and two

21: D)Hr/hR. 22. E).015

The following information applies to problems 24-27. In fruit flies the recessive pr and cn mutations cause brown and bright-red eyes respectively (wild-type flies have brick-red eyes). The double mutant pr cn combination has orange eyes. A female who has

A)wild-type and orange. C)pr+cn/prcn+

The mother of these progeny resulted from a cross between two flies from true breeding lines. What are the genotypes of these two lines?What is the map distance between the pr and cn genes?

C)pr+prcn+cn and prprcncn.

What is the map distance between the pr and cn genes?

C)4 m.u.

A dihybrid test cross is made between genes H and I. Four categories of offspring are produced: HI: Hi: hI: and hi. You wish to use the chi test to test the hypothesis that the H and I genes are unlinked. How many degrees of freedom would there be in this

C)3

Which of the following processes can generate recombinant gametes?

D)b and c

Crossing over takes place in paired bivalents consisting of ______ chromatids and involves _______ of the chromatids.

C)4 and 2

In Drosophila the genes y (yellow body) and car (carnation eyes) are located at opposite ends of the X chromosome. In doubly heterozygous females (y+ car+/y car) a single chiasma is observed somewhere along the X chromosome in 90% of the examined oocytes.

C)45%

Genes Q and R are 20 map units apart. If a plant of genotype QR/qr is selfed what percentage of the progeny will be rs in phenotype?

C)16%

The map of a chromosome interval is Q 10 R 40 S. Which interval would likely show the higher ratio of double to single chiasmata?

B)R-S

The map of a chromosome interval is A 10 B 40 C. From the cross Abc/aBC abc/abc how many double crossovers would be expected out of 1000 progeny?

D)40

The cross Lpq/lPQ lpq/lpq is carried out the L gene is found to be in the middle. What would be the genotypes of the double crossover gametes in this cross?

A)LPQ and lpq

Suppose a three-point testcross was conducted involving the genes X Y and Z. If the most abundant classes are XYz and xyZ and the rarest classes are xYZ and Xyz which gene is in the middle?

B)Y

In Drosophila the genes b c and sp are linked and in the order given the distances being b-c = 30 m.u. and c-sp = 20 m.u. These intervals exhibit 90% interference. How many double crossovers would be recovered in a three-point cross involving b c and sp o

B)6

In tetrad analysis the criterion for linkage of two genes is:

D)PD > NPD.

In tetrad analysis NPD asci result from:

E)a or b

In tetrad analysis second-division segregations result from:

C)single crossovers between a gene and a centromere.

Tetrad analysis shows that crossing over occurs at the four-strand stage (i.e. after replication) because when two genes are linked

B)T > NPD

The following information applies to problems 42 & 43. Consider a pair of homologous chromosomes heterozygous for three genes (e.g. ABC/abc) during prophase I of meiosis. Let the sister chromatids of one homolog be numbered 1 and 2; and the sister chromat

D)1 & 3 or 1 & 4 or 2 & 3 or 2 & 4

Assume a double crossover occurs in this pair of chromosomes that results in chromatids of the genotype AbC and aBc. If the first crossover (the one between A and B) involves chromatids 1 & 4 which chromatids could be involved in the second crossover?

D)1 & 3 or 1 & 4 or 2 & 3 or 2 & 4

Sturtevant's detailed mapping studies of the X chromosome of Drosophila established what genetic principle?

A)That genes are arranged in a linear order on the chromosomes.

The map of a chromosome is A 40 B 10 C 10 D 40 E. Suppose an investigator were to conduct two trihybrid crosses cross 1: ACE/ace ace/ace and cross 2: BCD/bcd bcd/bcd with the purpose of comparing the levels of crossover interference between the two cros

A)cross 1

Suppose an individual is heterozygous for a pair of alleles (e.g. A/a). Under what conditions would a crossover in a somatic cell of this individual lead to a clone of cells homozygous for a? (Pick the most precise answer.)

A)The crossover would have to occur between the A locus and the centromere and involve two homologous (non-sister) chromatids.

Suppose an individual is heterozygous for two linked pairs of alleles on the same chromosome arm Ab/aB such that the A locus is closer to the centromere than the B locus. Under what conditions would a crossover in a somatic cell generate a twin spot i.e.

A)The crossover would have to occur between the A locus and the centromere locus and involve two homologous (non-sister) chromatids.

Individuals heterozygous for the RB+ and RB- alleles can develop tumors as a result of:

A)a mitotic crossover that leads to homozygosity for both RB+ and RB-.B)a somatic mutation in the RB+ allele that leads to homozygosity for RB-=E)a and b

What happens physically during the process of crossing over?

C)Two homologous chromatids break and rejoin at precisely the same site along the chromosome so that there is no loss or gain of material on either product.

Here is a list of events during meiosis I. It is not in the correct order. What is the correct order of these events. A) Homologous chromosomes are roughly aligned but not physically linked.B) Homologous chromosomes segregate to opposite poles. C) Homolog

C)EACDB

Some of the larger human chromosomes typically contain multiple chiasmata during meiotic prophase. If you were to carefully study the distribution of these chiasmata what would you find?

D)Chiasmata are spaced along a chromosome arm more regularly than would be expected by chance.

Recombination due to crossing over occurs only rarely in mitosis.

Ans: True

Two genes are considered linked when F2 progeny more commonly show the recombinant genotype.

Ans: False

When considering the chi-square test a p-value of 0.05 is often considered significant but is actually an arbitrary assignment of significance.

Ans: True

Chiasmata are structures of cross over between sister chromatids of homologous chromosomes.

Ans: False

Chiasmata can be seen through a light microscope and are sites of recombination.

Ans: True

Three-point crosses are more tedious and less accurate than two-point crosses.

Ans: False

Chromosomal interference is not uniform and may significantly vary within a region of a single chromosome.

Ans: True

Genetic mapping distance calculated for a chromosome is directly related to physical distance along that chromosome.

Ans: False

Genes chained together by linkage relationships are known collectively as a linkage group.

Ans: True

Ascospores are haploid cells that can germinate, replicate by mitosis, and survive as haploid individuals.

True