Heredity
the biological process whereby genetic factors are transmitted from one generation to the next
Genetics
the scientific study of heredity. Began in 1860's by Gregor Mendel (Augustinian monk)
Mendel
Mendel stressed that the heritable factors (genes) retain their individual identities generation after generation, no matter how they are mixed up or temporarily masked.
Character
heritable feature that varies among individuals
trait
variant of a character
true-breeding
describes organisms or genotypes that are homozygous for a specific trait and thus always produce offspring that have the same phenotype for that trait
hybrids
The offspring of crosses between parents with different traits
P generation
parental generation, the first two individuals that mate in a genetic cross
F1 Generation
the first offspring from a cross of two varieties in the parental (P) generation
f2 generation
the second generation of offspring, obtained from an experimental cross of two organisms; the offspring of the F1 generation
f if for filial
latin for son or daughter
why was the the development of true-breeding pea plant varieties critical to Mendel's work?
True-breeding varieties allowed Mendel to predict the outcome of specific crosses and therefore to run controlled experiments.
monohybrid cross
mating of two organisms that differ in only one character
homozygous
having two identical alleles for a trait
heterozygous
having two different alleles for a trait
dominant allele
an allele whose trait always shows up in the organism when the allele is present
recessive allele
an allele that is hidden whenever the dominant allele is present
law of segregation
Mendels' first law. The Law of Segregation states that the two alleles of a given gene will be separate from one another during gamete formation (meiosis).
punnett square
a chart that shows all the possible combinations of alleles that can result from a genetic cross
phenotype
physical characteristics of an organism
genotype
genetic makeup of an organism
loci
point on the chromosome where the gene is found
Genes come in different versions called______. If both of these are the same, the individual is_____. If they are different, the individual is the ______ and the version expresses is called_____.
alleles;homozygous; heterozygous;dominant
How can 2 plants that have different genotypes for flower color be identical in phenotype?
One could be homozygous for the dominant allele, while the other is heterozygous.
you carry two alleles for every trait. Where did these alleles come from?
one is from your father via his sperm, and one is from your mother via her egg.
dihybrid cross
A cross between two individuals, concentrating on two definable traits.
law of independent assortment
Mendel second law that states that allele pairs separate independently during the formation of gametes. (inheritance of one character has no effect on the other)
test cross
mating of an individual of unknown genotype but dominant phenotype with a homozygous recessive individual
rule of multiplication
A statistical rule stating that the probability of two independent events occuring together is the product of their individual probabilities.
wild-type traits
traits most commonly found in nature
pedigree
ancestry of a purebred animal
carriers
a human reservoir. the person carries and spreads the disease with out necessarily having symptoms
cystic fibrosis
most common lethal genetic disease in the US. Excess mucus in lungs, digestive tract, liver: increased susceptibility to infections;death in early childhood unless treated.
Huntington's disease
a degeneration of the nervous system that usually does not begin until middle age.
incomplete dominance
one allele is not completely dominant over the other allele
hypercholesterolemia
An inherited human disease characterized by an excessively high level of cholesterol in the blood
ABO blood groups
Genetically determined classes of human blood that are based on the presence or absence of carbohydrates A and B on the surface of red blood cells; phenotypes, also called blood types, are A, B, AB, and O.
codominance
situation in which both alleles of a gene contribute to the phenotype of the organism
pleiotropy
A single gene having multiple effects on an individuals phenotype
sickle-cell disease
(example of pleitropy) A human genetic disease caused by a recessive allele that results in the substitution of a single amino acid in the hemoglobin protein; characterized by deformed red blood cells that can lead to numerous symptoms.
polygenic inheritance
process by which several genes interact to produce a certain trait; responsible for most important traits
chromosome theory of inheritance
A basic principle in biology stating that genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns.
linked genes
genes located on the same chromosome that tend to be inherited together in genetic crosses.
recombination frequency
percentage of recombinants, meaning percentage of of offspring that had traits from crossover. recombination frequencies are lower when alleles are closer together.
linkage map
a genetic map based on the frequencies of recombination between markers during crossing over of homologous chromosomes
sex-linked gene
gene located on a sex chromosome
most sex linked genes are found on what chromosome?
the X chromosomes because it contain many more genes.
red-green colorblindness
A category of common, sex-linked human disorders involving several genes on the X chromosome; characterized by a malfunction of light-sensitive cells in the eyes; affects mostly males but also homozygous females.
The genetic makeup of an organism is called its__________ while the physical traits of an organism is called its_______.
genotype,phenotype
which of Mendel's law is represented by "alleles of each homologous pair seperate independently during gamete formation?
law of independent assortment
which of the Mendel's law is represented by "alleles segregate during gamete formation; fertilization creates pairs of alleles once again?
law of segregation
whether an allele is dominant or recesive depends on ?
whether it or another allele determines the phenotype when both are present.