Chapter 8Chapter 8Section 1: The Origins of Genetics

Grade 10 BiologySpring 2011

Bell RingerBell RingerMake a list of 5 characteristics

that are passed on in familiesName one characteristic that

may also be inherited but that is also influenced by behavior or environment

ObjectivesObjectivesIdentify the investigator whose

studies formed the basis of modern genetics

List characteristics that make the garden pea a good subject for genetic study

Summarize the three major steps of Gregor Mendel’s garden pea experiments

Relate the ratios that Mendel observed in his crosses to his data

Mendel’s Studies of Mendel’s Studies of CharactersCharactersHeredity: the passing of

characters from parents to offspring

Mendel’s Breeding Mendel’s Breeding ExperimentsExperimentsGregor Mendel: grandfather of

geneticsCarried out experiments with the

garden pea plant Genetics: the branch of biology

that focuses on heredity

Mendel’s Breeding Mendel’s Breeding ExperimentsExperimentsT.A. Knight

◦Crossed a variety of the garden pea that had purple flowers with a variety that had white flowers

◦All of the offspring of Knight’s crosses had purple flowers

◦When 2 of the purple flowered offspring were crossed, their offspring showed both white and purple flowers

◦White trait had reappeared

Mendel’s Breeding Mendel’s Breeding ExperimentsExperimentsMendel’s experiments differed

because he counted the number of each kind of offspring and analyzed the data

Useful Features in PeasUseful Features in PeasSeveral characters of the garden

pea exist in two clearly different forms◦Character = inherited

characteristic, such as flower colour ◦Trait = refers to single form of a

character, such as purple flowers

Useful Features in PeasUseful Features in PeasMale and female parts of a

garden pea plant are enclosed within the same flower◦Can control mating

Small, grows easily, matures quickly, and produces many offspring

Traits Expressed as Simple Traits Expressed as Simple RatiosRatiosMonohybrid cross: cross that

involves one pair of contrasting traits True breeding: all of offspring

would display only one form of the character ◦Done by allowing a variety of peas to

self pollinate for several generationsP Generation: first two individuals

that are crossed in a breeding experiment

Traits Expressed as Simple Traits Expressed as Simple RatiosRatiosF1 Generation: the offspring of

the P generation F2 Generation: the offspring of

the F1 generation

Mendel’s ResultMendel’s ResultF1 generation showed only

one form of the trait F1 generation allowed to self-

pollinate Missing trait reappeared in the F2

generation

Mendel’s ResultMendel’s ResultF2 Generation:

◦705 purple◦224 white ◦705:224 or 705/224◦Reduced = 3:1

He found the same results for each of the other 7 traits he studied