Chapter 14: Mendel and the Gene Idea Flashcards
Character
Observable heritable feature that may vary among individuals
True-Breeding
Referring to organisms that produce offspring of the same variety over many generations of self-pollination
Hybridization
In genetics, the mating, or crossing, of two true-breeding varieties
P Generation
True-breeding (homozygous) parent individuals from which F1 hybrid offspring are derived in studies of inheritance
F1 Generation
First filial, hybrid (heterozygous) offspring arising from a parental cross
F2 Generation
Offspring resulting from interbreeding (or self-pollination) of the hybrid F1 generations
Allele
Any of the alternative versions of a gene that may produce distinguishable phenotypic effects
Dominant Allele
Allele that is fully expressed in the phenotype of a heterozygote
Recessive Allele
Allele whose phenotypic effect is not observed in a heterozygote
Law of Segregation
- Mendel’s first law
- States that the two in a pair segregate into different gametes during gamete formation
Punnett Square
Diagram used in the study of inheritance to show the predicted genotypic results of random fertilization in genetic crosses between individuals of known genotype
Homozygous
Having two identical alleles for a given gene
Heterozygous
Having two different alleles for a given gene
Phenotype
- Observable physical and physiological traits of an organism
- Determined by genetic makeup
Genotype
Genetic makeup, or set of alleles, of an organism
Testcross
- Breeding an organism of unknown genotype with a homozygous recessive individual to determine the unknown genotype
- Ratio of phenotypes in the offspring reveals the unknown genotype
Monohybrid
Organism that is heterozygous with respect to a single gene of interest
Monohybrid Cross
Cross between two organisms that are heterozygous for the character being followed (or the self-pollination of a heterozygous plant)
Dihybrid
Organism that is heterozygous with respect to two genes of interest
Dihybrid Cross
Cross between two organisms that are heterozygous for both of the characters being followed (or self-pollination of a plant that is heterozygous for both characters)
Law of Independent Assortment
- Mendel’s second law
- States that each pair of alleles segregates, or assorts, independently of each other during gamete formation
- Applies when two genes for two characters are located on different chromosomes
Multiplication Rule
Rule of probability stating that the probability of two or more independent events occurring together can be determined by multiplying their individual probabilities
Addition Rule
Rule of probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities
Complete Dominance
Situation in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable
Incomplete Dominance
Situation in which the phenotype of heterozygotes is intermediate between the phenotypes of individuals homozygous for either allele
Codominance
Situation in which the phenotypes of both alleles are exhibited in the heterozygote because both alleles affect the phenotype in separate, distinguishable ways
Tay-Sachs Disease
- Human genetic disease caused by a recessive allele for a dysfunctional enzyme
- Leads to an accumulation of certain lipids in the brain
- Seizures, blindness, and generation of motor and mental performance usually manifest a few months after birth
- Death within a few years
Pleiotropy
Ability of a single gene to have multiple effects
Epistasis
Type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited
Quantitative Character
Heritable feature that varies continuously over a range rather than in an either-or fashion
Polygenic Inheritance
Additive effect of two or more genes on a single phenotypic character
Multifactorial
Referring to a phenotypic character that is influenced by multiple genes and environmental factors
Pedigree
Diagram of a family tree showing the occurrence of heritable characters in parents and offspring over multiple generations
Carrier
- In genetics, an individual who is heterozygous at a given genetic locus for a recessively inherited disorder
- Heterozygote is generally phenotypically normal for the disorder but can pass the recessive allele to offspring
Cystic Fibrosis
- Human genetic disorder caused by a recessive allele for a chloride channel protein
- Characterized by an excessive secretion of mucus and consequent vulnerability to infection
- Fatal if untreated
Sickle-Cell Disease
Recessively inherited human blood disorder in which a single nucleotide change in the beta-globin gene causes hemoglobin to aggregate, changing red blood cell shape and causing multiple symptoms in afflicted individuals
Huntington’s Disease
- Human genetic disease caused by a dominant allele
- Characterized by uncontrollable body movements and degeneration of the nervous system
- Usually fatal 10 to 20 years after the onset of symptoms
Amniocentesis
- Technique of prenatal diagnosis
- Amniotic fluid, obtained by aspiration from a needle inserted into the uterus, is analyzed to detect certain genetic and congenital defects in the fetus
Chorionic Villus Sampling (CVS)
- Technique associated with prenatal diagnosis
- Small sample of the fetal portion of the placenta is removed for analysis to detect certain genetic and congenital defects in the fetus
