Chapter 12: Mendel and Inheritance

blending hypothesis

idea that genetic material contributed by two parents mixes in a manner analogous to the way blue and yellow paints blend to make green

particulate hypothesis

alternative hypothesis to the blending model where parents pass on discrete heritable units or genes

gregor mendel

scientist who documented a particulate mechanism of inheritance through his experiments with garden peas

scientific approach

what method did mendel use to identify the two laws of inheritance

why mendel worked with peas

-there are many available varieties

-can be strictly control which plants mated with which

-you can eat peas

character

a heritable feature

trait

a variant of a character

mendel experiment

-mating 2 true-breeding varieties of different colored peas

-removed stamens (male parts) from flower and transferred sperm bearing pollen from stamens of white flower to carpel (female part) to pollinate pea plants

either-or

what type of character did mendel track in his experiment

P generation

the true breeding parents (ie: white x white = white offspring)

hybridization

mating two contrasting, true breeding varieties

self-hybridization

when plants are able to generate offspring without external interference

filial (F1) generation

the hybrid offspring of the P generation

F2 generation

what generation is the result of F1 organisms self-pollinating

recessive

the gene that is not visible in the presence of dominant contrasting genes

alternative versions of genes

concept that accounts for variations in inherited characters

alleles

one of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome

two

how many alleles do organisms inherit from their parents

twice

how many times are genetic locii represented

law of segregation

two alleles for a heritable character separate during gamete formation and end up in different gametes

metaphase I of meiosis

when does the law of segregation occur

punnett square

method that we can determine the genetic makeup of generations of organisms

phenotype

appearance/physical traits of an organism

genotype

genetic makeup of an organism

homozygous

when an organisms has a pair of identical alleles for that particular gene

exhibits true breeding

heterozygous

when an organism has a pair of alleles that are different for that particular gene

testcross

a method that allows us to determine the genotype of an organism with the dominant phenotype but an unknown genotype

crosses an individual with the dominant phenotype with an individual that is homozygous recessive for a triat

P_ x pp

monohybrids

when organisms are heterozygous for one character

law of independent assortment

each pair of alleles segregates independently from others during gamete formation

dihybrid cross

method that illustrates the inheritance of 2 characters

4

how many phenotypes are produced in the F2 generation

laws of probability

what statistical principle governs mendelian inheritance

multiplication rule and addition rule

two statistical rules applied to monohybrid crosses

multiplication rule

law that states that the probability that two or more independent events will occur together is the product of their individual probabilities

addition rule

law that states that the probability that any one of two or more exclusive events will occur is calculated by adding togethre their individual probabilities

complete dominance

what occurs when the phenotypes of the heterozygote and dominant homozygote are identical

codominance

two dominant alleles affect the phenotype in separate but distinguishable ways

incomplete dominance

the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties

relationship between dominant and recessive alleles

-do not interact

-leads to synthesis of different versions of a protein that produces a phenotype

dominant allele misconception

not more common in populations than recessive alleles

in more than two allelic forms

how do most genes exist in populations

pleiotropy

allele that has multiple phenotypic effects

epistasis

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

quantitative characters

human characters that vary in the population along a continuum

quantitative variation

additive effect of two or more genes on a single phenotype

sickle cell disease

whats a common example of pleiotropy

multifactorial characters

characters influenced by both genetic and environmental factors

norm of reaction

phenotypic range of a particular genotype that is influlenced by the environment

laws of segregation and independent assortment

what two genetic rules still apply in complex inheritance patterns

chromosome theory of inheritance

-mendelian genes have specific loci on chromosomes

-chromosomes undergo segregation and independent assortment

thomas hunt morgan

scientist who provided convincing evidence that chromosomes are the location of mendel’s heritable factors

morgan experiment

worked with fruit flies and noted that wild type phenotypes are common in flu populations

wild type

another name for normal phenotype

mutant phenotype

traits alternative to the wild type

organisms’ sex

inherited phenotypic character determined in large part by the presence or absence of certain chromosomes (X and Y)

sex determining region Y

gene required for testicular development

sex-linked gene

gene located on either sex chromosom