AP Biology Chapter 14 Study Guide

Blending Hypothesis

The idea that genetic material from 2 parents blend together

-Blue + Yellow = Green

Particulate Hypothesis

The idea that parents pass on discrete heritable units (genes)

-Mendel documented this mechanism with garden peas

Gregor Mendel

-Discovered the basic principles of heredity

-Studied pea plants

Benefits of Pea Plants + Fruit Flies

-Short generation time

-Large numbers of offspring

-Mating could be controlled (plants could self-pollinate or cross-pollinate)

Character

A heritable feature

-Flower color

Trait

A variant of a character

-Purple colored flower or white colored flower

True-Breeding

Plants that produce offspring of the same variety when they self-pollinate

-Example: YY x yy = 100% Yy (All the same phenotype)

Hybridization

The mating of 2 true-breeding (homozygous) varieties

-Mendel would do this

P Generation

True-Breeding Parents

-Parents

F1 Generation

-Hybrid offspring of the P generation

-Kids

F2 Generation

-Hybrid offspring of the F1 generation

-Grandkids

Mendel's Results

P Generation: PP X pp (Purple X White)

F1 Generation: All Pp (All Purple)

F2 Generation: 1 PP : 2 Pp : 1 pp (3 Purple : 1 White)

-For each character, organisms inherit 2 alleles, one from each parent

-Alleles at same locus may be identical (homologous) or different (heterozygous)

-Dominant alleles always determines appearance

Law of Segregation

2 alleles for a heritable character separate (segregate) during meiosis (gamete formation) and end up in different gametes

-SINGLE gene

-Egg or sperm only have 1 allele from the 2 that the organism possesses

Dominant Trait

A trait that is dominant over another and if existent, will be expressed

Recessive Trait

A trait that is recessive and is only expressed if no dominant trait is present

Gene

-A character: Flower Color

-Mendel called it a "heritable factor"

-Alternative versions of genes account for variation in inherited characters

-Resides at a specific locus on a specific chromosome

Allele

Alternative version of a gene

-The specific flower color (purple or white)

Homozygous

2 identical alleles for the gene controlling that character

Heterozygous

2 different alleles for the gene controlling that character

-Not true-breeding

Phenotype

An organism's physical appearance

-Example: Purple

Genotype

An organism's genetic makeup

-Example: PP

Testcross

Determining genotype by crossing the dominant unkown with a homozygous recessive

-P? X pp

Monohybrid

A cross involving one character

Monohybrid Cross

-Cross between monohybrid heterozygotes

-Pp X Pp

Dihybrid

A cross involving 2 characters

Dihybrid Cross

-Cross between dihybrids

Example: PpSsXppss

Law of independent assortment

-Each pair of alleles segregates during meiosis

-Only applies to genes on different, nonhomologous chromosomes

-Different genes

Multiplication Rule

-AND rule

-States that the probability that 2 or more independent events will occur together is the product of their individual probabilities

• 1/4*1/4=1/16

Addition Rule

-OR rule

-States that the probability of 1 of 2+ exclusive events will occur is calculated by adding together their individual probabilities

-This OR this

Complete Dominance

Gregor Mendel

-Occurs when phenotypes of heterozygote and dominant homozygote are identical

-Either or

-Purple or white

Incomplete dominance

-Results in a intermediate phenotype (mixed color)

-Occurs when the phenotype of F1 hybrids is between the phenotypes of the 2 parental varieties

Example: C^RC^R x C^WC^W = C^R C^W (Pink)

Codominance

-Both colors are expressed in a way

Example: BB x bb = 4 Bb, both are still shown (spots, etc)

Multiple Alleles

-Most genes exist in populations in more than 2 allelic forms

-Blood groups have 3 alleles: I^A, I^B, i (6 possible genotypic combinations)

Pleiotropy

• 1 gene -> Multiple phenotypes

-1 gene affects multiple phenotypic characters

Example: Cystic fibrosis & sickle-cell disease

-Sickle-cell disease leads to other negative side effects from the one gene

Epistasis

• 2 genes -> 1 gene affects the other

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

Example: Labrador coat color, Bb (Black or brown color) & E (Color) or e (no color)

-The gene "sits on top of" another gene, if ee is present, then the dog is neither black or brown, it is beige

Polygenic Inheritance

• 2+ genes affect 1 phenotype

-Additive effect of 2+ genes on 1 phenotype

Example: Skin color, (trihybrid cross), 3 genes control is AaBbCc

Nature and Nurture

-Genes and the environment effect the phenotypic results of an organism

Multifactorial

Traits that are dependant on multiple genes + environmental influences

Example: Pp leads to pink in basic soil and blue in acidic soil

Humans as genetic research

-Not good genetic testing subjects

-Generation time is too long

-Parents produce relatively few offspring

-Breeding experiments are unacceptable

Pedigree

Family tree

-Dominant Trait: one of the parents MUST have it

-Recessive Trait: Parents are dominant but don't have it

-Can make predictions about future offspring

Recessive Disorders (aa)

-Albinism (lack of pigmentation in skin and hair, albino)