Genetics Question Bank for Unit 2

Review Questions for Unit-2 Test

Key Definitions

• Maternal Effect: The phenomenon whereby the genotype of the mother directly affects the phenotype of her offspring, independent of the offspring's genotype.

• Epigenetic Inheritance: Non-genetic factors that influence the gene expression and phenotype. It involves changes that do not alter the DNA sequence but affect how genes are expressed.

• Dosage Compensation (Lyon Hypothesis): The process that equalizes the expression of X-linked genes between males (XY) and females (XX) by inactivating one of the X chromosomes in females.

• X-Chromosome Inactivation (Barr Bodies): Randomly inactivation of one X chromosome in females leading to the formation of a Barr body, making females functionally hemizygous for X-linked genes.

• Genomic Imprinting: A mechanism where genes are expressed in a parent-of-origin-specific manner, affecting the phenotype depending on whether the allele is inherited from the mother or father.

• Monoallelic Expression: The expression of only one of the two alleles of a gene, which can be influenced by genomic imprinting.

• DNA Methylation: A biochemical process that inhibits gene expression through the addition of methyl groups to the DNA molecule, often leading to gene silencing.

• Extranuclear Inheritance (Cytoplasmic Inheritance): Transmission of genetic material independent of nuclear DNA, such as the inheritance of traits through mitochondrial or chloroplast DNA.

• Mitochondrial DNA and Chloroplast DNA: Genetic material found in mitochondria and chloroplasts, respectively; inherited maternally.

• Heteroplasmy: The presence of multiple types of organellar genomes within a cell or individual, leading to variable expression of traits.

• Endosymbiosis Theory: A theory that explains the origin of mitochondria and chloroplasts as a result of ancient symbiotic events between host eukaryotic cells and engulfed prokaryotes.

• Synteny: Conservation of blocks of genes on chromosomes of different species.

• Genetic Linkage: The tendency of genes close to each other on a chromosome to be inherited together.

• Two Factor Cross: A genetic cross that examines the inheritance of two different traits.

• Three Factor Cross: A genetic cross that examines the inheritance of three different traits simultaneously.

• Recombinant or Nonparental Offspring: Offspring that exhibit new combinations of traits not found in the parents, resulting from crossing over in meiosis.

• Non-Recombinant Offspring: Offspring that possess the same combinations of traits as their parents.

• Positive Interference: The concept that one crossover event reduces the likelihood of a second crossover event happening nearby.

• Karyotype: The number and appearance of chromosomes in the nucleus of a eukaryotic cell, often used in genetic diagnosis.

• Deletion: Loss of a chromosome segment, potentially leading to genetic disorders.

• Duplication: A chromosome segment is duplicated, resulting in extra genetic material.

• Inversion: A segment of a chromosome is reversed end to end, which can disrupt gene function.

• Translocation: A piece of one chromosome breaks off and attaches to another chromosome, which can lead to genetic disorders.

• Paralogs: Genes related by duplication within a genome that may evolve new functions.

• Cri du Chat Syndrome: A genetic disorder caused by a deletion on chromosome 5, characterized by a distinctive cry of affected infants.

• Down Syndrome: A genetic disorder caused by trisomy 21, resulting in developmental and physical challenges.

• Robertsonian Translocation: A chromosomal rearrangement that involves the fusion of two acrocentric chromosomes, leading to structural abnormalities.

• Semisterility: A condition in which an individual can produce only some fractions of viable gametes due to chromosomal abnormalities.

• G banding: A technique used to stain chromosomes, revealing characteristic patterns for identification and analysis.

• Aneuploidy: An abnormal number of chromosomes, which can lead to developmental disorders.

• Euploidy: The presence of multiple sets of chromosomes; organisms with a complete set of chromosomes are classified as euploid.

• Polytene Chromosome: An oversized chromosome formed by repeated DNA replication without cell division, commonly seen in certain tissues such as salivary glands in fruit flies.

• Nondisjunction: The failure of chromosome pairs to separate properly during cell division, leading to an abnormal distribution of chromosomes in the daughter cells.

• Haplodiploid: A sex determination system where males are haploid and females are diploid, commonly observed in bees.

• Autopolyploidy: A form of polyploidy involving the duplication of chromosome sets within a single species.

• Alloploidy and Allopolyploidy: Polyploidy resulting from the hybridization of two different species, leading to increased genetic variation.

Genetics Problems and Solutions

• Genotypic Offspring from Matings:

  • A. Cross with nn mother results in all Nn offspring being small body phenotype.

  • B. Cross with NN mother results in all Nn offspring having normal body phenotype.

  • C. Cross with Nn mother results in genotypic ratios of 1 NN : 2 Nn : 1 nn, showing functional dominance from the N allele.

• Genetic Disorders and Maternal Effects:

  • The disorder in offspring is caused by a dominant allele (M) passed through maternal influence controlling the expression of the phenotype.

  • If the female is Mm (normal appearance), she can produce M and m eggs, but the phenotype is determined by her genotype due to maternal effects.

Cloning Process in Mammals

• Mammalian Cloning Technique: Involves introducing a diploid nucleus from a somatic cell into an enucleated egg (egg without a nucleus) to produce a clone of the original organism.

Inheritance Patterns in Mice

• Trait Inheritance: When normal-tailed and long-tailed true-breeding strains are crossed:

  • F1 from normal females x long males shows full long tail phenotype.

  • F1 from long females x normal males results in normal tails.

  • Cross F1 females with normal males results in all normal tails, indicating dominance and lack of recessive phenotype expression.

  • F1 males crossed with long-tailed females results in 50% normal and 50% long tails, indicating a Mendelian inheritance pattern.

Snail Genotype Determination

• Determining Genotype of a Female Snail:

  • Use test cross with known Dd males. Possible results:

    • All offspring red (female is DD).

    • Half red and half left-coiling (female is Dd).

    • All left-coiling (female is dd).

Testcross Limitations

• Testcross Explanation: A testcross cannot yield more than 50% recombinant offspring due to the nature of gene linkage.

  • A 50% result indicates independent assortment of genes or a unlinked scenario.

Genetic Linkage Example in Peas

• Calculating Map Distance: Given a cross of orange and green pods (orp and Orp), an F2 offspring distribution helps calculate the linkage distance between the two genes, yielding specific ratios indicating their genetic distance.

Recombination Frequencies Calculation

• Three Linked Genes: Calculating recombination frequencies between v, m, and s genes provides insights into genetic distances and crossover events.

  • Coefficient of Coincidence and Interference are calculated to understand the suppression of double crossover events.

Chromosomal Conditions in Humans

• Chromosomal Counts: Understanding lethal conditions like Trisomy 22 and Monosomy 11 helps determine total chromosome numbers and characteristics of euploidy and aneuploidy, stressing the importance of chromosome number in genetic disorders.

Types of Inversions

• Chromosomal Inversions: Identifying whether a given inversion is pericentric or paracentric and analyzing the alignment of chromosomes during meiosis is essential for understanding genetic variations.

Crossover Outcomes in Inversion Heterozygotes

• Crossover Products: Analyzing the products of crossover events in an inversion heterozygote helps clarify genetic outcomes in meiosis.

Chromosomal Complications in Drosophila

• Chromosomal Counts in Drosophila: Calculating chromosome number in various conditions (tetraploid, trisomy, monosomy, etc.) emphasizes the diversity of genetic compositions.

Unique Cases of Trisomy

• Trisomy's Viability: Speculating on the survivability of certain trisomies against lethal conditions and their implications in human genetics reveal underlying reasons for tolerance.

Familial Down Syndrome and Karyotyping

• Karyotype Observations: Understanding variations in chromosome numbers among siblings and parents facilitates insights into genetic heritability and chromosomal abnormalities.

Meiotic Nondisjunction and its Mechanisms

• Meiotic Nondisjunction: Identification of mechanisms behind nondisjunction events during meiosis emphasizes the necessity of proper chromosomal segregation for healthy organismal development.

Unusual Events in Honeybee Spermatogenesis

• Spermatogenesis in Honeybees: The unique haploid condition and its impact on sperm production, highlighting meiotic adaptations in haplodiploid organisms.