Topic 13 - Patterns of Inheritance Flashcards
What was the significance of Mendel’s work?
Mendel’s experiments demonstrated that traits are transmitted from parents to offspring independently of other traits and in dominant/recessive patterns
Trait
Variation in the physical appearance of a heritable characteristic
Dominant trait
Trait which confers the same physical appearance whether an individual has 2 copies of the trait or one copy of the dominant trait and one copy of the recessive trait
Recessive trait
Trait that appears “latent” or non-expressed when the individual also carries a dominant trait for that characteristic; when present as two identical copies, the recessive trait is expressed
Allele
Gene variations that arise by mutation and exist at the same relative locations (loci) on homologous chromosomes
Phenotype
The observable traits expressed by an organism
Genotype
Underlying genetic makeup, consisting of both physically visible and non-expressed alleles, of an organism
Homozygous
Having two identical alleles for a given gene on the homologous chromosome
Heterozygous
Having two different alleles for a given gene on the homologous chromosome
True or false: each parent can donate one of two different alleles, which segregate randomly into gametes
True
Law of Dominance
In a heterozygote, one trait will conceal the presence of another for the same characteristic
Law of Segregation
Two alleles for a gene segregate during gamete formation and are rejoined at random, one from each parent, during fertilization
- Occurs during anaphase I of meiosis
Law of Independent Assortment
Each pair of alleles segregates into gametes independently of the other pairs, and every possible combination of alleles is equally likely to occur
- Occurs during metaphase I of meiosis
- Only true if pairs of alleles are on separate chromosomes
Product rule
The probability of two independent events occurring simultaneously can be calculated by multiplying the individual probabilities of each event occurring alone
- Compound event: when 2 or more independent events happen at the same time
- “and” = product rule
Sum rule
The probability of the occurrence of one event or the other event, or two mutually exclusive events, is the sum of their individual probabilities
- “or” = sum rule
Under what circumstances is the Law of Independent Assortment NOT true?
This principle only holds true when genes are located far away from one another on the same chromosome or when they are on different chromosomes entirely. Once genes are close to one another on the same chromosome, they become linked together and can no longer be independently inherited.
Explain the significance of linked genes.
While genes that are located on separate chromosomes will always sort independently, linked genes are more likely to be inherited as a pair because they are physically close together on the same chromosome
Incomplete dominance
In a heterozygote, expression of two contrasting alleles such that the individual displays an intermediate phenotype
Ex. some flowers (red + white = pink)
Codominance
In a heterozygote, complete and simultaneous expression of both alleles for the same characteristic
Ex. human blood types (AB)
Pleiotropic gene
Single gene that affects multiple characteristics
Ex. sickle-cell anemia
Epistasis
Gene at one locus alters gene at a second locus
Ex. coat color
Polygenic inheritance
Non-epistatic genes interact additively to influence a phenotypic trait
Ex. skin color
