Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement

Klug - Essentials of Genetics 10th Edition

Klug10th EditionEssentials of GeneticsISBN: 9780135588789당신이 사용하는 게 아니라요?교과서 변경

Klug 10th Edition

Ch. 6 - Chromosome Mutations: Variation in Number and Arrangement

문제 19b

6장, 문제 19b

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?

검증된 단계별 안내

Understand that the husband carries a large paracentric inversion on one chromosome 1, meaning a segment of the chromosome is reversed but the overall chromosome number remains normal (46 chromosomes).

Recall that during meiosis, homologous chromosomes pair and undergo crossing over. In individuals heterozygous for an inversion, the inverted segment forms a loop to align properly with the normal homolog.

Recognize that crossing over within the inversion loop can produce abnormal chromatids with duplications and deletions, which often lead to inviable gametes or zygotes with developmental abnormalities.

Note that because the inversion covers 70% of the chromosome length, the chance of crossover within this large inverted segment is relatively high, increasing the risk of producing unbalanced gametes.

Conclude that the couple's future children have a significant risk of chromosomal abnormalities or miscarriage due to unbalanced gametes from the father's inversion, but some gametes will be normal or carry the inversion without imbalance, so normal offspring are also possible.

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이 영상 해법은 위 문제에 도움이 된다고 튜터들이 추천한 것입니다.

영상 길이:

주요 개념

질문에 올바르게 답하기 위해 반드시 이해해야 하는 핵심 개념들은 다음과 같습니다.

Chromosomal Inversions

A chromosomal inversion occurs when a segment of a chromosome breaks off, flips, and reinserts in the reverse orientation. Inversions can be pericentric (including the centromere) or paracentric (excluding the centromere). While carriers often have a normal phenotype, inversions can disrupt gene function or cause problems during meiosis, leading to abnormal gametes.

Meiotic Consequences of Inversions and Recombination

During meiosis, homologous chromosomes pair and exchange genetic material via crossing over. In inversion heterozygotes, crossing over within the inverted segment can produce unbalanced gametes with duplications or deletions, increasing the risk of miscarriages, stillbirths, or congenital abnormalities in offspring.

Genetic Counseling and Risk Prediction

Genetic counseling uses family history and chromosomal analysis to assess reproductive risks. In cases of large inversions, counselors estimate the likelihood of producing abnormal gametes and offspring. Although the carrier may be phenotypically normal, the risk of abnormal children depends on inversion size, location, and recombination frequency.

관련 실천

교과서 질문

A woman who sought genetic counseling is found to be heterozygous for a chromosomal rearrangement between the second and third chromosomes. Her chromosomes, compared to those in a normal karyotype, are diagrammed to the right.

Using a drawing, demonstrate how these chromosomes would pair during meiosis. Be sure to label the different segments of the chromosomes.

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교과서 질문

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?

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교과서 질문

What kind of chromosomal aberration is shown?

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교과서 질문

Having correctly established the F₂ ratio in Problem 18, predict the F₂ ratio of a 'dihybrid' cross involving two independently assorting characteristics (e.g., P₁ = WWWWAAAA x wwwwaaaa).

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교과서 질문

How would you explain the high incidence of past stillbirths?

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