Principles of Genetics

Blending hypothesis

Blending hypothesis

the idea that genetic material from the two parents blends together

Particulate hypothesis

the idea that parents pass on discrete heritable units (genes) o Mendel documented a particulate mechanism through his experiments with garden peas

Character

Heritable feature that varies among individuals ▪ Ex. Flower color

Trait

Each variant for a character ▪ Ex. Purple or white color for flowers

Short generation time ▪ Large numbers of offspring ▪ Mating could be controlled

Why did Mendel use peas as the subject?

Hybridization

process of mating two contrasting, true-breeding varieties

P - generation

the true breeding parents

F1 generation

hybrid offspring of the P generation

F2 generation

offspring of F1 individuals that self-pollinate or cross-pollinate with other F1 hybrids

Law of Segregation

each individual that is a diploid has a pair of alleles (copy) for a particular trait

all purple flowers were yield in the f1 gen

(Mendel experiment) crossing the true breeding parents yield what type of f1 gen of hybrids?

purple and white flowers in the f2 gen

(Mendel experiment) he then cross the purple f1 gen flowers ; the f2 gen showed what type of flowers

3 : 1 ratio (purple to white flowers)

(Mendel experiment) what is the ratio of the f2 gen flowers

the purple flower color is a dominant trait, while white is recessive trat

(Mendel Experiment) what does the amount of purple and white flowers tell us?

Gene

heritable factor is also known as

Flower color, seed color, seed shape, pod shape, pod color, flower position, and stem length

What characteristics did Mendel observe in his experiment?

Punnett square

can show possible combinations of sperm and egg

Dominant allele

capital letter represents what allele

Recessive allele

lowercase letter represents what allele

Homozygous

An organism with 2 identical alleles for a character

Heterozygous

An organism that has 2 different alleles for the gene controlling that character

Phenotype

physical appearance

Genotype

genetic makeup

Testcross

dominant phenotype could be either homozygous dominant or heterozygous

Monohybrid Cross

cross between heterozygotes following one trait only (ex. seed color)

Dihybrid Cross

cross following two traits at the same time (ex. seed color and seed shape)

Law of Independent Assortment

the alleles of two (or more) different genes get sorted into gametes independently of one another

Dihybrid cross (between F1 dihybrids)

this cross can determine whether two characters are transmitted to offspring as a package or independently

Complete Dominance

Occurs when phenotypes of the heterozygote and dominant homozygote are identical

Incomplete Dominance

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

Codominance

Two dominant alleles affect the phenotype in separate, distinguishable ways

multiple alleles

Most genes exist in populations in more than two allelic forms (ex. blood type)

Pleiotropy

Most genes have multiple phenotypic effects called (ex. Sickle Cell Disease)

Epistasis

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

Polygenic Inheritance

An additive effect of two or more genes on a single phenotype (ex. skin color of humans)

Pedigree Analysis

a family tree that describes the inter-relationships of parents and children across generations ; can predict the future offspring

Recessively Inherited Disorders

Show up only in individuals homozygous for the allele ; genetic disorders that are inherited in a recessive manner

Carriers

are heterozygous individuals who carry the recessive allele but are phenotypically normal

Albinism

a recessive condition characterized by a lack of pigmentation in skin and hair

Dominantly Inherited Disorders

human disorders are caused by dominant alleles

Achondroplasia

is a form of dwarfism caused by a rare dominant allele

Multifactorial Disorders

Many diseases, such as heart disease, diabetes, alcoholism, mental illness, and cancer have both genetic and environmental components (lifestyle and genotype are the factors for diseases)

Thomas Hunt Morgan

provided the first solid evidence associating a specific gene with a specific chromosome came in the early 20th century

Female

a person with two x chromosomes is

Male

a person with one x and y chromosome is

Sex- linked gene

gene that is located on either sex chromosome

Linked genes

Genes located on the same chromosome that tend to be inherited together

Parental Types

Offspring with a phenotype matching one of the parental phenotypes are called

Recombinants / Recombinant types

Offspring with non-parental phenotypes (new combinations of traits) are called

crossing over of homologous chromosomes

genes can be linked, but the linkage was incomplete, because some recombinant phenotypes were observe ; this mechanism is called

Deletion, Duplication, Inversion , Translocation

Breakage of a chromosome can lead to four types of changes in chromosome structure

Down Syndrome

is an aneuploid condition that results from three copies of chromosome 21

Klinefelter syndrome

the result of an extra chromosome in a male, producing XXY individuals

Monosomy X, / Turner Syndrome,

produces X0 females, who are sterile; it is the only known viable monosomy in humans

cri du chat (“cry of the cat”)

specific deletion in chromosome 5 ; A child born with this syndrome is severely intellectually disabled and has a catlike cry; individuals usually die in infancy or early childhood

chronic myelogenous leukemia (CML)

cancer caused by translocations of chromosomes