Questions and Answers
What is the difference between a locus and an allele?
Locus = place on chromosome that a gene is located; Allele = version of a gene that encodes a specific trait.
How did Mendel know that each of his pea plants carried two alleles encoding a characteristic?
Traits for both alleles appeared in the F2 progeny.
Which of the following factors did not contribute to Mendel's success in his study of heredity? a) Using the pea plant b) Study of plant chromosomes c) Adoption of experimental approach d) Use of mathematics
How are the principles of segregation and independent assortment similar and different?
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What causes the genetic variation seen in offspring produced by sexual reproduction?
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How does the heterogametic sex differ from the homogametic sex? a) Het is male, homo is female b) Het gametes have different sex chromosomes; homo gametes have the same sex chromosomes c) Het gametes all contain Y chromosome; homo gametes all contain X
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How do chromosomal, genic, and environmental sex determination differ?
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What is the phenotype of XXXY? a) Klinefelter syndrome b) Turner syndrome c) Poly-X syndrome
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How many Barr bodies will a male with XXXYY chromosomes have in each of his cells?
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How does incomplete dominance differ from incomplete penetrance?
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A cross between two green corn plants yields 2/3 green and 1/3 yellow progeny. What is the genotype of the green progeny? a) WW b) Ww c) ww d) W_
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How does gene interaction differ from dominance between alleles?
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How do sex-influenced and sex-limited characteristics differ from sex-linked characteristics?
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What type of epigenetic mark is responsible for genomic imprinting?
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Autosomal recessive traits often appear in pedigrees in which there have been consanguineous matings, because these traits: a) tend to skip generations b) appear only when both parents carry a copy of a gene for the trait, which is more likely when the parents are related c) usually arise in children born to parents who are unaffected d) appear equally in males and females
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When might you see an autosomal dominant trait skip generations?
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How can you distinguish between an autosomal recessive trait with higher penetrance in males and an X-linked recessive trait?
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A man with an X-linked dominant trait will have what percentage of offspring affected by the trait?
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What features of a pedigree would distinguish between a Y-linked trait and a trait that is a rare, autosomal dominant, and sex-limited to males?
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A trait exhibits 100% concordance for both monozygotic and dizygotic twins. What conclusion can be drawn?
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Study Notes
Genetics Fundamentals
- Locus vs. Allele: A locus is the specific location on a chromosome where a gene resides, while an allele denotes the variant of a gene that determines a specific trait.
- Mendelian Experimentation: Mendel inferred that each pea plant carried two alleles due to the presence of both traits in the F2 progeny.
- Factors in Mendel's Success: Significant elements include usage of pea plants, experimental approach, and mathematical analysis; however, lack of knowledge about chromosomes did not hinder his findings.
Genetic Principles
- Segregation and Independent Assortment: Both processes occur during anaphase I of meiosis; segregation refers to alleles separating, while independent assortment involves separation of alleles from different loci without influence on one another.
- Role of Meiosis: The process of meiosis is responsible for genetic variation in offspring produced through sexual reproduction.
Sex Determination
- Heterogametic vs. Homogametic Sex: Heterogametic sex (typically males) has two different sex chromosomes (X and Y), while homogametic sex (typically females) carries identical sex chromosomes (XX).
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Sex Determination Types:
- Chromosomal: Distinct chromosomes determine male and female.
- Genic: Similar-looking chromosomes with gene-based sex determination.
- Environmental: Sex influenced by environmental factors.
Genetic Anomalies and Traits
- Phenotypes of XXXY: Presence of a Y chromosome denotes male; XXXY corresponds to Klinefelter syndrome.
- Barr Bodies: A male with XXXYY chromosomes will have two Barr bodies, representing inactivated X chromosomes.
- Incomplete Dominance vs. Incomplete Penetrance: Incomplete dominance results in a heterozygote showing an intermediate phenotype, while incomplete penetrance can lead to individuals not expressing the expected phenotype.
Genetic Crosses and Interactions
- Corn Plant Cross Result: A cross of two green corn plants producing 2/3 green (Ww) and 1/3 yellow progeny indicates the presence of a lethal allele affecting the survival of WW and ww individuals.
- Gene Interaction vs. Dominance: Gene interaction happens between different genes, while dominance is the relationship between alleles at a single gene locus.
Autosomal and X-Linked Traits
- Autosomal Recessive Traits: Often appear more frequently in offspring from consanguineous matings because both parents having a gene copy increases likelihood of expression.
- Autosomal Dominance: Traits may skip generations if new mutations occur or if penetrance levels drop.
- X-Linked Recessive Traits: Distinguishable as they cannot be inherited from father to son, unlike traits with higher penetrance affecting males.
Pedigree Analysis
- X-Linked Dominant Traits: All daughters of an affected male will display the trait, while sons will not, due to chromosomal inheritance patterns.
- Y-Linked vs. Autosomal Dominant Traits: Y-linked traits are passed to all sons, whereas an autosomal dominant, sex-limited trait might only be passed to half of the sons from a heterozygous male.
Twin Studies and Genetic Concordance
- Genetic Concordance: A trait exhibiting 100% concordance in both monozygotic and dizygotic twins suggests a strong genetic influence on the trait's expression.
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Description
Test your knowledge on the basics of genetics, including key concepts like loci, alleles, and Mendelian principles. This quiz will cover important topics such as segregation, independent assortment, and the role of meiosis in genetic variation. Perfect for students looking to solidify their understanding of genetic principles!
