Biology - Mendelian Genetics (Ch. 14)
Terms in this set (44)
The prevailing genetic hypothesis in the mid-1800s. The idea that genetic material contributed by two parents mixes in a manner analagous to how blue and yellow paint mixes to make green. Predicts that over time, a freely mating population will give rise to a uniform population of individuals.
Alternative to the blending hypothesis: Parents pass on discrete heritable units - genes - that retain their separate identities in offspring. Mendel came up with this idea.
A heritable feature that varies among individuals (i.e., flower color)
Each variant for a character (i.e., purple or white color for flowers)
Over several generations of self-pollination, parents produce the same variety as the parents
Mating (crossing) of two true-breeding varieties
First filial (offspring) generation
Second filial (offspring) generation
Law of Segregation
The two alleles for a heritable character segregate (separate) during gamete formation and end up on different gametes
Alternative versions of a gene for a specific trait
Specific place along a particular chromosome
The allele that determines the organism's appearance (regardless of whether hetero- or homozygous)
If heterozygous, recessive allele has no noticeable effect on organism's appearance and dominant allele determines appearance (phenotype). If homozygous for recessive allele, recessive allele determines organism's appearance.
Diagrammatic device for predicting the allele composition of offspring from a cross between individuals of a known genetic makeup.
When an organism has an identical pair of alleles for a character, it is said to be homozygous for the gene controlling that character.
An organism is heterozygous for a gene if it has two different alleles for a gene (these individuals are not true-breeding).
Breeding an organism of unknown genotype with a recessive homozygote - doing this can reveal the genotype of the unknown
Heterozygous for one character
Heterozygous for two characters
Law of Independent Assortment
Each pair of alleles segregates independently of each other pair of alleles during gamete formation
Determine the probability that two or more independent events will occur in some specific combination by multiplying the probability of one event by the probability of the other event.
Determine the probability that one of two or more mutually exclusive events will occur by adding their individual probabilities. (Use the results from the multiplication rule.)
The phenotype of the heterozygote and dominant homozygote are indistinguishable.
When F₁ hybrids have a phenotype somewhere in between those of the two parental varieties.
The two alleles affect the phenotype in separate, distinguishable ways.
When a gene has multiple phenotypic effects (one gene affects multiple characteristics of an organism)
A gene at one locus alters the phenotypic expression of a gene at a second locus.
Characters that vary along a continuum (i.e., skin color)
An additive effect of two or more genes on a single phenotypic character, usually a quantitative character. Example: skin color.
Norm of reaction
Phenotypic range of a genotype, the range is affected by the environment. (i.e., blood count) Norms of reaction are broadest for polygenic characters.
Many factors, both genetic and environmental, influence phenotype.
Pedigree (of a family)
A family tree describing the traits of parents and children across the generations
Individuals who are heterozygous for an inherited disorder; they are usually phenotypically normal but can transmit the recessive allele to their offspring
Mendel's Model (4 characteristics)
1) Alternative versions of genes account for variations in inherited characters
2) For each character, an organism inherits two alleles, one from each parent
3) If the two alleles at a locus differ, then one, the dominant allele, determines the organism's appearance; the other, the recessive allele, has no noticeable effect on the appearance
4) law of segregation: the two alleles for a heritable character segregate (separate) during gamete formation and end up on different gametes
Discrete heritable unit
When the experimenter is performing a cross to look at only one trait.
When the experimenter is performing a cross to look at two traits.
The ratio that shows the outcomes you can get from a genetic cross in terms of observable traits (phenotype).
The ratio that shows the outcomes you can get from a genetic cross in terms of actual genes for that trait.
When the same gene exists in two or more alleles within a population.
The proportion of total phenotypic variance at the population level that is contributed by genetic variance.