Exam 5: Pedigree Analysis, Applications, and Genetic Testing

Genetic testing is used to screen newborns for genetic diseases, detect persons who are heterozygous for recessive diseases, detect disease-causing alleles in those who have not yet developed symptoms of the disease, and detect defective alleles in unborn babies. Preimplantation genetic diagnosis combined with in vitro fertilization allows for the selection of embryos that are free from specific genetic diseases. -How does preimplantation genetic diagnosis differ from prenatal genetic testing?

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Question 1

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Preimplantation genetic diagnosis determines the presence of disease-causing genes in an embryo at an early stage, before it is implanted in the uterus and initiates pregnancy. Prenatal genetic diagnosis determines the presence of disease-causing genes or chromosomes in a developing fetus.

Y-linked traits appear only in males and are passed from a father to all his sons. -What features of a pedigree would distinguish between a Y-linked trait and a trait that is rare, autosomal dominant, and sex-limited to males?

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Question 2

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If the trait were Y linked, an affected male would pass it on to all his sons, whereas, if the trait were autosomal and sexlimited, affected heterozygous males would pass it on to only half of their sons on average.

Autosomal dominant traits appear in both sexes with equal frequency. An affected person has an affected parent (unless the person carries new mutations), and the trait does not skip generations. Unaffected persons do not transmit the trait. -When might you see an autosomal dominant trait skip generations?

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It might skip generations when a new mutation arises or the trait has reduced penetrance.

Autosomal recessive traits appear with equal frequency in males and females. Affected children are commonly born to unaffected parents who are carriers of the gene for the trait, and the trait tends to skip generations. Recessive traits appear more frequently among the offspring of consanguine matings. -Autosomal recessive traits often appear in pedigrees in which there have been consanguine matings, because these traits

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Question 4

Higher concordance for monozygotic twins compared with that for dizygotic twins indicates that genetic factors play a role in determining differences in a trait. Low concordance for monozygotic twins indicates that environmental factors play a significant role. -A trait exhibits 100% concordance for both monozygotic and dizygotic twins. What conclusion can you draw about the role of genetic factors in determining differences in the trait?

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Question 5

Rare X-linked recessive traits appear more often in males than in females and are not passed from father to son. Affected sons are usually born to unaffected mothers who are carriers of the gene for the trait; thus X-linked recessive traits tend to skip generations. -How can you distinguish between an autosomal recessive trait with higher penetrance in males and an X-linked recessive trait?

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Question 6

X-linked dominant traits affect both males and females. Affected males must have affected mothers (unless the males possess a new mutation), and they pass the trait on to all their daughters. -A male affected with an X-linked dominant trait will have what proportion of offspring affected with the trait?

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Question 7

Similarities between adopted persons and their genetically unrelated adoptive parents indicate that environmental factors affect a particular characteristic; similarities between adopted persons and their biological parents indicate that genetic factors influence the characteristic. -What assumptions underlie the use of adoption studies in genetics?

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Question 8

Dizygotic twins develop from two eggs fertilized by two separate sperm; they have, on average, 50% of their genes in common. Monozygotic twins develop from a single egg, fertilized by a single sperm, that splits into two embryos; they have 100% percent of their genes in common. -Why are monozygotic twins genetically identical, whereas dizygotic twins have only 1/2 of their genes in common on average?

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Question 9

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Y-linked traits appear only in males and are passed from a father to all his sons. -What features of a pedigree would distinguish between a Y-linked trait and a trait that is rare, autosomal dominant, and sex-limited to males?

Introduction to Genetics, Chromosomes and Cellular Reproduction

Basic Principles of Heredity

Sex Determination and Sex-Linked Characteristics

Extensions and Modifications of Basic Principles

Linkage, Recombination, and Eukaryotic Gene Mapping

Bacterial and Viral Genetic Systems

Chromosome Variation

DNA: The Chemical Nature of the Gene

Chromosome Structure and Transposable Elements

DNA Replication and Recombination

Transcription

RNA Molecules and RNA Processing

The Genetic Code and Translation

Control of Gene Expression in Prokaryotes

Control of Gene Expression in Eukaryotes

Gene Mutations and DNA Repair

Molecular Genetic Analysis and Biotechnology

Genomics and Proteomics

Organelle DNA

Developmental Genetics and Immunogenetics

Cancer Genetics

Quantitative Genetics

Population Genetics

Evolutionary Genetics

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