Ch 15: Mendelian Genetics Flashcards
T/F: Although Mendel’s work was not originally considered by his contemporaries to be groundbreaking, his principles of segregation and independent assortment were “rediscovered” nearly two decades after his death.
True
What made the plant hybridization studies performed by Mendel more successful than plant hybridization studies performed by others?
Mendel used true breeding plants that were carefully breeded to ensure the parents could be traced. He focused on traits that could be observed as phenotypes and used statistical analysis to study those phenotypes.
What were Mendel’s two key discoveries?
Segregation and Independent Assortment.
Genes that are _____ do not assort independently and are said to be _____.
close to each other in the same chromosome; linked
The _____ of an individual describes the combination of _____ present, and the _____ constitutes the expression of the _____.
genotype; alleles; phenotype; trait
You are given two populations of true-breeding tomato plants with two simple dominant/recessive traits that sort independently. Using the multiplication rule, how many different phenotypic combinations would you expect to see in the F2 generation? In what phenotypic ratio?
four; 9:3:3:1
Genes that modify the phenotypic expression of other genes show:
epistasis
A testcross involves crossing with _____ individual and is used to determine the _____ of the tested parent.
homozygous recessive; genotype
The cellular mechanism that determines the independent assortment of maternal and paternal chromosomes is:
separation of homologous pairs at anaphase I of meiosis.
Recall that alleles of a single gene will segregate from one another during anaphase I. When do alleles for two different genes—located in two different chromosomes—segregate?
anaphase I
A true-breeding black rabbit is crossed with a true-breeding white rabbit to produce an F1 generation of 16 individuals. If the black color trait is dominant, which answer option represents the expected phenotype of an F1 generation cross?
16 black rabbits
You are given two true-breeding groups of rabbits. The first group has floppy ears and white fur. The second group has straight ears and black fur. When you perform a cross of these two groups, your F1 rabbits all have floppy ears and gray fur. If each of these traits was determined by a single gene and underwent independent assortment, you would predict that 75% of your F2 generation rabbits have _____ ears and _____ of your rabbits have black fur.
floppy; 25%
For a trait such as flower color in snapdragons that is determined by two alleles with incomplete dominance, the offspring of true-breeding parents show an intermediate phenotype. This is also what would be expected of blending inheritance. The difference is that:
The trait with blending inheritance will lose variation over time.
Transmission Genetics
The discipline that deals with the manner in which genetic material is passed from generation to generation.
Trait
A characteristic of an individual.
Blending Inheritance
The now-discredited model in which heredity factors transmitted by the parents become intermingled in the offspring instead of retaining their individual genetic identities.
Hybridization
Interbreeding between two different varieties or species.
True Breeding
Describes a trait whose physical appearance in each successive generation is identical to that in the previous one.
P1 Generation
The parental generation in a series of crosses.
F1 Generation
The first filial, or offspring, generation.
Reciprocal Cross
A cross in which the female and male parents are interchanged.
Dominant
Describes an allele or trait that is expressed in heterozygotes. Only one dominant allele is needed to express the phenotype.
Recessive
Describes an allele or trait that is only expressed in homozygotes, and not expressed in heterozygotes. Two recessive alleles are needed to express the phenotype.
Allele
The different forms of a gene, corresponding to different DNA sequences in each different form.
Genotype
The genetic makeup of a cell or organism; the particular combination of alleles present in an individual.
Phenotype
The expression of a physical, behavioral, or biochemical trait; an individual’s observable phenotypes include height, weight, eye color, and so forth.
Homozygous
Describes an individual who inherits an allele of the same type from each parent, or a genotype in which both alleles for a given gene are of the same type.
Gamete
A reproductive haploid cell; gametes fuse in pairs to form a diploid zygote. In many species, there are two types of gametes: eggs in females, sperm in males.
Segregate
Separate; applies to chromosomes or members of a gene pair moving into different gametes.
Principle of Segregation
The principle by which half the gametes receive one allele of a gene and half receive the other allele.
Zygote
The diploid cell formed by the fusion of two gametes.
Heterozygote
Describes an individual who inherits different types of alleles from the parents, or genotypes in which the two alleles for a given gene are different.
Punnett Square
A worksheet in the form of a checkerboard used to predict the consequences of a random union of gametes.
Testcross
Any cross of an unknown genotype with a homozygous recessive genotype.
Incomplete Dominance
Inheritance in which the phenotype of the heterozygous genotype is intermediate between those of homozygous genotypes.
Probability
Among a very large number of observations, the expected proportion of observations that are of a specified type.
Addition Rule
The principle that the probability of either of two mutually exclusive outcomes occurring is given by the sum of their individual probabilities.
Multiplication Rule
The principle that the probability of two independent events occurring together is the product of their respective probabilities.
Principle of Independent Assortment
The principle that segregation of one set of alleles of a gene pair is independent of the segregation of another set of alleles of a different gene pair.
Epistasis
Interaction between genes that modifies the phenotypic expression of genotypes.
Pedigree
A diagram of family history that summarizes the record of the ancestor–descendent relationships among individuals.
Multiple Alleles
Two or more different alleles of the same gene, occurring in a population of organisms.
Incomplete Penetrance
The phenomenon in which some individuals with a genotype corresponding to a trait do not show the phenotype, either because of environmental effects or because of interactions with other genes.
Variable Expressivity
The phenomenon in which a particular phenotype is expressed with a different degree of severity in different individuals.
Genetic Test
A method of identifying the genotype of an individual.
