Mendelian Genetics

gene idea

the model that says that parents pass on discrete heritable unit-genes-that retain their separate identities in offspring

Gregor Mendel

Augustinian monk and botanist whose experiments in breeding garden peas led to his eventual recognition as founder of the science of genetics (1822-1884)

character

a heritable feature that varies among individuals (color)

trait

specific characteristic that varies from one individual to another (purple)

true-breeding

term used to describe organisms that produce offspring identical to themselves if allowed to self-pollinate

hybridization

the act of mixing different species or varieties of animals or plants and thus to produce hybrids

P generation

Parental generation, the first two individuals that mate in a genetic cross.

F1 generation

the first generation of offspring obtained from an experimental cross of two organisms

F2 generation

the second generation of offspring, obtained from an experimental cross of two organisms; the offspring of the F1 generation

law of segregation

Mendel's first law, stating that each allele in a pair separates (segregates) into a different gamete during gamete formation.

Mendel's model

1. Alternative versions of genes account for variations in inherited characters.

2. For each character an organism inherits two copies of a gene, one from each parent.

3. If two alleles at the locus differ, then the dominant allele determines the organism's appearance, the recessive has no noticeable effect.

4. Law of segregation

alleles

alternative versions of a gene that produce distinguishable phenotypic effects

dominant allele

one whose trait always shows up in the organism when the allele is present

recessive allele

an allele that has no noticeable effect on the phenotype of a gene when the individual is heterozygous for that gene.

Punnett square

a chart that shows all the possible combinations of alleles that can result from a genetic cross

homozygous

term used to refer to an organism that has two identical alleles for a particular trait

heterozygous

an organism that has two different alleles for a trait

phenotype

The physical traits that appear in an individual as a result of its gentic make up.

genotype

the genetic makeup, or set of alleles, of an organism

testcross

the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype

monohybrid

genetic cross that involves one trait

monohybrid cross

mating of two organisms that differ in only one character

dihybrid

Crosses between individuals that differ in two traits

dihybrid cross

A cross in which two characteristics are tracked.

law of independent assortment

each pair of alleles segregates independently of each other pair of alleles during gamete formation

multiplication rule

to determine the probability, we multiply the probability of one event by the probability of another

addition rule

A rule of probability stating that the probability of any one of two or more mutually exclusive events occurring can be determined by adding their individual probabilities.

complete dominance

A type of inheritance in which the phenotypes of the heterozygote and dominant homozygote are indistinguishable.

incomplete dominance

production of a phenotype that is intermediate between the two homozygous parents

codominance

A phenotypic situation in which the two alleles affect the phenotype in separate, distinguishable ways

Tay-Sacks disease

A human genetic disease caused by a recessive allele for a dysfunctional enzyme, leading to accumulation of certain lipids in the brain. Seizures, blindness, and degeneration of motor and mental performance usually become manifest a few months after birth, followed by death within a few years.

polydactyly

pertaining to having more than the normal number of fingers and toes

pleiotropy

A single gene having multiple effects on an individuals phenotype (more than one phenotypic expression)

epistasis

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 (in gradations)

polygenic inheritance

An additive effect of two or more gene loci on a single phenotypic character.

norm of reaction

The range of phenotypes produced by a single genotype, due to environmental influences.

multifactorial

many factors, both genetic and environmental, influence phenotype

pedigree

A diagram of a family tree showing the occurrence of heritable characters in parents and offspring over multiple generations.

carrier

individual who has one copy of the allele for a recessive disorder and does not exhibit symptoms

consanguineous mating

mating between biological relatives

cystic fibrosis

a genetic disorder in which the lungs and pancreas are clogged with large quantities of abnormally thick mucus

sickle-cell disease

Caused by a change in one amino acid in Beta Hemoglobin. Causes the red blood cell to make a crescent shape. The cell can't carry enough oxygen.

achondroplasia

A form of human dwarfism caused by a single dominant allele; the homozygous condition is lethal

Huntington's disease

genetic disorder that causes progressive deterioration of brain cells. caused by a dominant allele. symptoms do not appear until the age of 30 or so

amniocenteses

A diagnostic medical procedure that removes a sample of amniotic fluid by inserting a needle in the amniotic sac. A way to check genetic health & development of a fetus.

chorionic villus sampling

sampling of placental tissue for microscopic and chemical examination to detect fetal abnormalities