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Chapter 18: Problem 49

To determine whether radiation associated with the atomic bombings of Hiroshima and Nagasaki produced recessive germ-line mutations, scientists examined the sex ratio of the children of the survivors of the blasts. Can you explain why an increase in germ-line mutations might be expected to alter the sex ratio?

Short Answer

Expert verified
Germ-line mutations could change the sex ratio by affecting embryo viability differently for males and females.

Step by step solution

01

Understanding Sex Ratio

The sex ratio generally refers to the number of males compared to females in a population. In humans, the typical sex ratio at birth is slightly biased towards males, typically about 105 boys to 100 girls.
02

Germ-line Mutations Impact

Germ-line mutations are changes in genes that can be passed from parents to offspring. These mutations can affect reproduction and the development of embryos.
03

Link Between Mutations and Sex Ratio

If a particular mutation affects factors such as embryonic viability or the chance of conception for one sex over another, this might alter the usual sex ratio at birth.
04

Mutation Induced by Radiation

Radiation from atomic bombings can increase the rate of germ-line mutations. If these mutations selectively affect one sex, for example by decreasing the survival rate of male embryos more than females, we would see a shift in the sex ratio.
05

Conclusion on Altered Sex Ratio

Therefore, an increase in radiation-induced germ-line mutations might skew the sex ratio if those mutations disproportionately affect the viability or reproductive success of embryos of one sex.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Sex Ratio
The sex ratio is a figure that indicates the number of males per females in a population. In humans, this ratio at birth typically skews slightly towards males. For every 100 girls, about 105 boys are born according to global averages. This disparity is due to several factors, including different chromosomal contributions during reproduction.
  • Males have one X and one Y chromosome, while females have two X chromosomes.
  • The presence of the Y chromosome influences the development of male characteristics.
  • Factors like stress, environmental influences, and mutations can alter this delicate balance.
An altered sex ratio can provide insights into environmental effects, genetic mutations, and changes in reproductive processes.
Radiation Effects
Radiation, a form of energy emitted from radioactive substances, can have significant health impacts. In the context of atomic bombings, exposure to high levels of radiation can lead to severe biological damage.
  • Radiation can break chemical bonds within DNA molecules, leading to cell damage and mutations.
  • High radiation doses are linked to increased cancer risks and genetic alterations.
  • It can particularly influence cells during their division, making rapidly dividing cells, like germ-line cells, highly susceptible.
Understanding radiation effects helps us comprehend its potential to cause genetic changes, including mutations that might influence the sex ratio.
Embryonic Viability
Embryonic viability refers to an embryo's ability to survive and develop successfully during gestation. Factors affecting viability are closely monitored in reproductive health.
  • The genetic makeup of an embryo can greatly influence its viability.
  • External influences such as toxins, environmental stresses, and radiation can affect the critical early stages of development.
  • Germ-line mutations can influence embryos differently, depending on their genetic characteristics.
Radiation-induced mutations, if affecting embryonic viability, can potentially influence whether more male or female embryos survive, thus altering the sex ratio.
Genetic Mutations
Genetic mutations are alterations in the DNA sequence that can lead to changes in physical traits or biological functions. These can occur naturally or be induced by external factors, such as radiation.
  • Mutations can be harmless, beneficial, or harmful depending on their nature and location in the genome.
  • They can affect any part of the organism's biology, including growth, reproduction, and physical characteristics.
  • When mutations occur in germ-line cells, they can be passed to the next generation, potentially causing variations in traits such as the sex ratio.
The study of these mutations gives insights into how they might result in skewed sex ratios, should they affect one sex more than the other.
Reproduction
Reproduction is the biological process by which new offspring are produced from their parents. This process involves both genetic inheritance and cellular processes.
  • Sex determination in humans is influenced by the chromosomal contributions from each parent (XX for females, XY for males).
  • Any genetic mutations in the germ-line can influence reproductive success and embryo development.
  • Environmental factors, like radiation, can impact reproduction by inducing mutations that affect embryo viability or development.
By understanding reproduction and its nuances, we better grasp how changes, like those from radiation-induced mutations, could influence outcomes such as the birth sex ratio.

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Most popular questions from this chapter

Achondroplasia is an autosomal dominant disorder characterized by disproportionate short stature: the legs and arms are short compared with the head and trunk. The disorder is due to a base substitution in the gene, located on the short arm of chromosome \(4,\) for fibroblast growth factor receptor 3 (FGFR3). Although a chondroplasia is clearly inherited as an autosomal dominant trait, more than \(80 \%\) of the people who have achondroplasia are born to parents with normal stature. This high percentage indicates that most cases are caused by newly arising mutations; these cases (not inher ited from an affected parent) are referred to as sporadic. Studies have demonstrated that sporadic cases of achondroplasia are a lmost always caused by mutations inherited from the father (paternal mutations). In addition, the occurrence of achondroplasia is higher among older fathers; approximately \(50 \%\) of children with achondroplasia are born to fathers older than 35 years of age. There is no association with maternal age. The mutation rate for achondroplasia (about \(4 \times 10^{-5}\) mutations per gamete) is high compared with those for other genetic disonders. Explain why most spontaneous mutations for achondroplasia are paternal in origin and why the occurrence of achondroplasia is higher among older fathers.

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