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Chapter 5: Problem 44

Which of the following statements describes an example of a phenocopy? Explain your reasoning. a. Phenylketonuria results from a recessive mutation that causes light skin as well as intellectual disability. b. Human height is influenced by genes at many different loci. c. Dwarf plants and mottled leaves in tomatoes are caused by separate genes that are linked. d. Vestigial wings in Drosophila are produced by a recessive mutation. This trait is also produced by high temperature during development. e. Intelligence in humans is influenced by both genetic and environmental

Short Answer

Expert verified
Option d describes a phenocopy. High temperature mimics the genetic trait of vestigial wings in Drosophila.

Step by step solution

01

Understand the Concept of Phenocopy

A phenocopy is when an environmental factor induces changes in an individual such that it mimics the phenotype of a different genotype. Essentially, the phenotype of an organism is altered by environmental conditions to imitate a genetic mutation.
02

Analyze Option a

Phenylketonuria is a genetic disorder caused by a recessive mutation that results in certain symptoms such as intellectual disability. This is strictly genetic and not an environmental mimic, so it is not a phenocopy.
03

Examine Option b

Human height is a polygenic trait influenced by multiple genes, as well as environmental factors, but it does not involve a phenotype mimicking a genetic condition solely through environmental influence. This does not demonstrate phenocopy.
04

Assess Option c

Dwarf plants and mottled leaves in tomatoes are caused by linked genes. There's no evidence of an environmental factor mimicking these genetic conditions, so this is not a phenocopy.
05

Review Option d

Vestigial wings in Drosophila can be produced by a recessive genetic mutation as well as by environmental factors like high temperature during development. The environmental factor mimics the phenotype of the genetic condition, defining it as a phenocopy.
06

Inspect Option e

Intelligence in humans is a multifactorial trait influenced by both genetics and environment, but it doesn鈥檛 demonstrate environmental factors mimicking a single genetic trait. Therefore, it is not a phenocopy.
07

Final Decision

Based on the previous analysis, option d accurately describes a phenocopy because an environmental factor leads to a phenotype that mimics a genetically-induced condition.

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Key Concepts

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

Environmental Factors
Environmental factors play a crucial role in shaping the physical characteristics, or phenotypes, of organisms. For instance, temperature, nutrition, light, and chemicals are common factors that can influence development. These factors do not change the organism's genetic code but may alter the way genes are expressed.

Important points about environmental effects:
  • They are external influences, not inherited traits.
  • They can cause an organism to develop traits similar to those caused by genetic mutations.
  • They can be temporary or permanent influences on an organism's phenotype.
Understanding the interaction between these factors and genetics is essential in studying phenocopies, where environment-induced appearances mimic genetic conditions.
Genetic Mutation
Genetic mutations are changes in the DNA sequence that can lead to changes in an organism's phenotype. These mutations can be spontaneous or induced by external factors like radiation or chemicals. Mutations can have various effects, including beneficial, neutral, or harmful changes to an organism.

Key aspects of genetic mutations include:
  • They are stable changes to the genetic material.
  • They can be passed down to the next generation if they occur in germ cells.
  • They can result in new traits or diseases.
In cases of phenocopy, an organism's phenotype resembles a mutation-induced phenotype due to environmental influences, without any actual change to the DNA sequence.
Phenotypic Changes
Phenotypic changes refer to alterations in the observable traits of an organism, which may occur due to genetic mutations or environmental influences. These changes can range from differences in physical features to physiological functions. It's important to note that phenotypic changes do not always correlate with changes in the organism's DNA.

In the context of phenocopy, phenotypic changes arise due to:
  • Alterations in environmental conditions, such as temperature.
  • Nutritional differences or exposure to certain chemicals.
  • Stress or other external stimuli that affect gene expression.
Understanding phenotypic changes is key in distinguishing between those caused by genetic variations and those induced by the environment.
Drosophila Vestigial Wings
Drosophila, a genus of small flies often referred to as fruit flies, is a popular model organism in genetic research. One interesting trait observed in these flies is the development of vestigial wings. Vestigial wings can arise due to a recessive genetic mutation that affects wing development, but they can also be induced by specific environmental conditions, such as high temperature during the flies' development.

In the case of Drosophila:
  • The vestigial wings due to mutation result in reduced wing size, affecting the fly's ability to fly.
  • High-temperature exposure during critical developmental stages can mimic this mutant condition without a genetic change.
  • Such instances where environment mimics mutation exemplify the concept of a phenocopy.
Studying this phenomenon helps scientists understand how environmental factors can influence phenotypic traits in organisms, even leading to complex traits mirroring those caused by genetic mutations.

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Most popular questions from this chapter

What is genomic imprinting?

A variety of opium poppy (Papaver somniferum L.) with lacerate leaves was crossed with a variety that has normal leaves. All the \(\mathrm{F}_{1}\) had lacerate leaves. Two \(\mathrm{F}_{1}\) plants were interbred to produce the \(\mathrm{F}_{2}\). Of the \(\mathrm{F}_{2}, 249\) had lacerate leaves and 16 had normal leaves. Give genotypes for all the plants in the \(\mathrm{P}, \mathrm{F}_{1},\) and \(\mathrm{F}_{2}\) generations. Explain how lacerate leaves are determined in the opium poppy.

When a Chinese hamster with white spots is crossed with another hamster that has no spots, approximately 12 of the offspring have white spots and 12 have no spots. When two hamsters with white spots are crossed, 23 of the offspring possess white spots and 13 have no spots. a. What is the genetic basis of white spotting in Chinese hamsters? b. How might you go about producing Chinese hamsters that breed true for white spotting?

Mu Tatuo Aida investigated the genetic basis of color variation in the medaka (Aplocheilus latipes), a small fish found in Japan (T. Aida. 1921. Genetics \(6: 554-573\) ). Aida found that genes at two loci \((B, b\) and \(R, r)\) determine the color of the fish: fish with a dominant allele at both loci \(\left(B_{-} R_{-}\right)\) are brown, fish with a dominant allele at the \(B\) locus only \(\left(B_{-} r r\right)\) are blue, fish with a dominant allele at the \(R\) locus only \(\left(b b R_{-}\right)\) are red, and fish with recessive alleles at both loci \((b b r r)\) are white. Aida crossed a homozygous brown fish with a homozygous white fish. He then backcrossed the \(\mathrm{F}_{1}\) with the homozygous white parent and obtained 228 brown fish, 230 blue fish, 237 red fish, and 222 white fish. a. Give the genotypes of the backcross progeny. b. Use a chi-square test to compare the observed numbers of backcross progeny with the number expected. What conclusion can you make from your chi-square results? c. What results would you expect for a cross between a homozygous red fish and a white fish? d. What results would you expect if you crossed a homozygous red fish with a homozygous blue fish and then backcrossed the \(\mathrm{F}_{1}\) with a homozygous red parental fish?

A summer-squash plant that produces disc-shaped fruit is crossed with a summer-squash plant that produces long fruit. All the \(\mathrm{F}_{1}\) have discshaped fruit. When the \(\mathrm{F}_{1}\) are intercrossed, \(\mathrm{F}_{2}\) progeny are produced in the following ratio: 916 disc-shaped fruit : 616 spherical fruit : 116 long fruit. Give the genotypes of the \(\mathrm{F}_{2}\) progeny.
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