6. Chromosomal Variation

A person has a WT chromosome with the following segments. A B C • D E F G H. Which of the following shows how the chromosome would look after an paracentric inversion?

A person has a WT chromosome with the following segments. A B C • D E F G H. Which of the following shows how the chromosome would look after a pericentric inversion?

From the following list, identify the types of chromosome changes you expect to show phenotypic consequences.

Pericentric inversion

Inversions are said to 'suppress crossing over.' Is this terminology technically correct? If not, restate the description accurately.

Contrast the genetic composition of gametes derived from tetrads of inversion heterozygotes where crossing over occurs within a paracentric versus a pericentric inversion.

A normal chromosome and its homolog carrying a paracentric inversion are shown here. The dot (·) represents the centromere.

Normal    ABC • DEFGHIJK

Inversion  abc • djihgfe

Assume a crossover takes place in the region between A and B. Identify the gametes that are formed by this crossover event, and indicate which, if any, gametes are viable.

A normal chromosome and its homolog carrying a paracentric inversion are shown here. The dot (·) represents the centromere.

Normal    ABC • DEFGHIJK

Inversion  abc • djihgfe

Assume a crossover takes place in the region between F and G. Identify the gametes that are formed following this crossover, and indicate which, if any, gametes are viable.

The outcome of a single crossover between nonsister chromatids in the inversion loop of an inversion heterozygote varies depending on whether the inversion is of the paracentric or pericentric type. What differences are expected?

A couple planning their family are aware that through the past three generations on the husband's side a substantial number of stillbirths have occurred and several malformed babies were born who died early in childhood. The wife has studied genetics and urges her husband to visit a genetic counseling clinic, where a complete karyotype-banding analysis is performed. Although the tests show that he has a normal complement of 46 chromosomes, banding analysis reveals that one member of the chromosome 1 pair (in group A) contains an inversion covering 70 percent of its length. The homolog of chromosome 1 and all other chromosomes show the normal banding sequence. Would you advise the woman that she will have to bring each pregnancy to term to determine whether the fetus is normal? If not, what else can you suggest?

A couple planning their family are aware that through the past three generations on the husband's side a substantial number of stillbirths have occurred and several malformed babies were born who died early in childhood. The wife has studied genetics and urges her husband to visit a genetic counseling clinic, where a complete karyotype-banding analysis is performed. Although the tests show that he has a normal complement of 46 chromosomes, banding analysis reveals that one member of the chromosome 1 pair (in group A) contains an inversion covering 70 percent of its length. The homolog of chromosome 1 and all other chromosomes show the normal banding sequence. What can you predict about the probability of abnormality/normality of their future children?

A couple planning their family are aware that through the past three generations on the husband's side a substantial number of stillbirths have occurred and several malformed babies were born who died early in childhood. The wife has studied genetics and urges her husband to visit a genetic counseling clinic, where a complete karyotype-banding analysis is performed. Although the tests show that he has a normal complement of 46 chromosomes, banding analysis reveals that one member of the chromosome 1 pair (in group A) contains an inversion covering 70 percent of its length. The homolog of chromosome 1 and all other chromosomes show the normal banding sequence. How would you explain the high incidence of past stillbirths?

In the tomato, Solanum esculentum, tall (D−)(D−) is dominant to dwarf (dd) plant height, smooth fruit (P−) is dominant to peach fruit (pp), and round fruit shape (O−) is dominant to oblate fruit shape (oo). These three genes are linked on chromosome 1 of tomato in the order dwarf–peach–oblate. There are 12 map units between dwarf and peach and 17 map units between peach and oblate. A trihybrid plant (DPO/dpo) is test-crossed to a plant that is homozygous recessive at the three loci (dpo/dpo). The accompanying table shows the progeny plants. Identify the mechanism responsible for the resulting data that do not agree with the established genetic map.

A pair of homologous chromosomes in Drosophila has the following content (single letters represent genes):

Chromosome 1RNMDHBGKWU

Chromosome 2RNMDHBDHBGKWU

How does the pairing diagrammed in part (b) differ from the pairing of chromosomes in an inversion heterozygote?