BIO 1305 Chapter 14: Mendel and the Gene Idea

Gene

A heritable unit composed of DNA that encodes for a specific detail.

Character (Gene)

A heritable feature that varies among individuals.

Trait (allele)

Each variant for a character.

Allele

Different versions of a gene.

True-breeding/homozygous

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

Hybridization

Medel mater two contrasting, true breeding varieties, a process called ___________________.

P generation

The true-breeding parents.

F1 generation

The hybrid offspring of the P generation.

F2 generation

Fi individuals were allowed to self-pollinate or were cross-pollinated with other F1 individuals to produce the __________________.

purple

In Mendel's experiment, the ________________ flower color was dominant.

white

In Mendel's experiment, the _______________ flower color was recessive.

heritable factor

What Mendel called a "________________" is what we now call a gene.

Alleles

Alternate versions of the same gene.

2

For each gene, organism inherit _______ alleles from the mom and the dad.

homozygous

Two alleles at a particular locus may be identical, or _______________, like the P generation.

heterozygous

Two alleles may be different, or ___________________, like the F1 generation.

Dominant allele

Determines the organism's appearance if the two alleles at a locus differ; it is expressed.

Recessive allele

Has no noticeable effect on the organism's appearance; it is hidden.

Law of segragation

The two alleles for a heritable character (gene) separate during gamete formation and end up in different gametes.

homologous chromosomes

This segregation of alleles corresponds to the distribution of _______________________ to different gametes in meiosis.

Punnett square

Shows the possible combinations of sperm and egg.

Homozygote

An organism with two identical alleles for a gene.

Heterozygote

An organism with two different alleles for a gene.

Phenotype

An organism's physical appearance.

Genotype

An organism's genetic makeup; the total set of alles an individual contains.

homozygous recessive

In a testcross, breed/cross the unknown individual with a _______________________ individual.

Monohybrid cross

A cross between individuals that were heterozygous for one gene.

Dihybrid cross

Cross between F1 dihybrids; is used to determine whether two traits are transmitted to offspring as a unit (together) or independently.

Law of independent assortment

States that each pair of alleles segragates independenly of any other pair of alleles during gamete formation.

different nonhomologous, far apart

The law of independent assortment only applies to genes on __________________________ chromosomes or those ____________________ on the same chromosome.

Multiplication rule

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

1/2

Segregation in meiosis results in each gamete has a ______ chance of having a dominant allele and a _______ chance of having a recessive allele.

Addition rule

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

Rule of addition

The _____________________ can be used to figure out the probability that an F2 plant from a monohybrid cross will be heterozygous or homozygous.

Multicharacter cross

Is equivalent to two or more independent monohybrid crosses occurring simultaneously.

seperately; multiplied

In calculating the chances for various genotypes, each character is considered __________________, and then the individual probabilities are ________________.

complex patterns of inheritance

The basic principles of segregation and independent assortment apply even to more ___________________________.

Complete dominance

Occurs when phenotypes of heterozygote and dominant homozygote are identical.

Incomplete dominance

The phenotype of F1 hybrids is somewhere between phenotypes of the parentals.

Codominance

Two dominant alleles affect the phenotype in separate, distiguishable ways.

enzyme

In the case of pea shape, the dominant allele code for an ________________ that converts and unbranched form of starch in the seed to a branched form.

defective form

The recessive allele codes for a _____________________ of the enzyme, which leads to an accumulation of unbranched starch.

Multiple alleles

A gene that has more than two alleles.

more than 2

For most genes, there are ______________________ alleles in a population.

Human blood type

An example of a of multiple alleles that has 3 alleles (IA, IB, i); gene encodes enzyme that attaches A or B carbohydrates to red blood cells.

A, B, O, AB

For blood types, there are 4 phenotypes: _____, ______, ______, _______.

Pleiotropy

A property where a gene has multiple phenotypic effects.

Epistasis

One gene affects the phenotype of another due to interaction of their gene products.

Polygenic inheritance

Multiple genes independently affect a single trait.

epistasis

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

Quantitative characters

Characters that vary in the population along a continuum.

polygenic inheritance

Quantitative variation usually indicates ____________________, an additive effect of two or more genes on a single phenotype.

Multifactorial traits

Traits that depend on multiple genes combined with environmental influences.

Pedigree

A family tree that describes the inheritance of a trait across generations.

predicitions

Pedigrees are used to make _____________________ about future offspring.

recessive

Many, but not all, genetic disorders are inherited in a ___________________ manner.

homozygous

For genetic disorders, an individual must be _______________ to have the disorder.

heterozygotes

For genetic disorders, _________________ are carriers. They can pass on the disorder to offspring.

Cystic fibrosis allele

Results in defective or absent chloride transport channels in plasma membranes, leading to a buildup of chloride ions outside the cell.

Sickle-cell disease

Genetic disorder that is caused by the substitution of a single amino acid in the hemoglobin protein in red blood cells.

mutation

Dominant alleles that cause a lethal disease are rare and arise by _________________.

Achondrioplasia

A form of dwarfism caused by a rare dominant allele.

Huntington's disease

A degenerative disease of the nervous system that has no obvious phenotypic effects until the individual is about 35 to 40 years of age.

Multifactorial diseases

Diseases such as heart disease, cancer, alcoholism, and mental illnesses that have both genetic and environmental components.

genotype

Each child represents an independent event in the sense that its __________________ is unaffected by that of older siblings.