Chapter 14 - Mendel and the Gene

character

a heritable feature that varies among individuals

trait

each variant for a character

true-breeding plants

over many generations of self-pollination, these plants has produced only the same variety as the parent plant

blending hypothesis

the idea that genetic material from the two parents blends together

law of segregation

Mendel's law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete

test cross

breeding an organism of unknown genotype with a recessive homozygote

law of independent assortment

the law that states that genes separate independently of one another in meiosis

multiplication rule

to determine the probability of one event and the other occurring, we multiply the probability of one event by the probability of another event

addition rule

the probability that any one of 2 or more mutually exclusive events will occur is calculated by adding their individual probabilities

complete dominance

phenotypes of the heterozygote and the dominant homozygote are indistinguishable

incomplete dominance

Situation in which one allele is not completely dominant over another allele

codominance

A condition in which both alleles for a gene are fully expressed

multiple allelelism

more than 2 alleles exist

pleiotropy

The ability of a single gene to have multiple effects

epistasis

the phenotypic expression of a gene at one locus alters that of a gene at a second locus

polygenic inheritance

combined effect of two or more genes on a single character

Explain the evidence against a blending hypothesis of inheritance

When Mendel crossed two different homozygous plants, the offspring only looked like the homozygous dominant one

Multiple Allelism v. Polygenic Inheritance

Multiple Alleles all involve the same DNA strand

Polygenic Inheritance involves multiple DNA strands

incomplete penetrance

not all individuals who carry the mutation are affected by the disease, when an individual with a particular phenotype does not express the expected phenotype

quantitative effects

polygenic traits (controlled by many genes) are impacted by environmental effects that alter the phenotypic state of an individual