Studied by 10 people
Gregor Mendel
father of genetics who discovered the basic principles of heredity by breeding garden peas
trait
specific characteristic that varies from one individual to another (ex: purple flower color)
Advantages of pea plants
many variations, mating of the plants can be controlled, and produce many offspring in a short period time
True-breeding
organisms that produce offspring identical to themselves if allowed to self-pollinate (homozygous)
Hybridization
mating or crossing of two, contrasting true-breeding varieties
P generation
true breeding parents
F1 generation
hybrid offspring of the P generation
F2 generation
self pollination of F1 individuals
Alleles
alternate versions of a gene
Dominant allele
allele that determines the organism’s appearance
Recessive allele
allele that has no noticeable effect on the organism’s appearance
Law of segregation
the two alleles for a heritable character separate from each other during gamete formation and end up in different gametes
Four concepts of Mendel’s model
1) alternative versions of genes (alleles) account for variation in inherited characters 2) for each character, an organism inherits two versions of each gene, one from each parent 3) if two alleles at a locus differ, there will be one dominant and one recessive allele 4) law of segregation
punnet square
a chart that shows all the possible combinations of alleles that can result from a genetic cross
homozygote
an organism that has a pair of identical alleles for a gene
heterozygote
an organism that has two different alleles for a gene
phenotype
an organism’s appearance or observable traits
genotype
an organism’s genetic makeup
test cross
breeding an organism of an unknown genotype with a recessive homozygote to reveal its genotype
If you do a test cross and the offspring of an organism with an unknown genotype displays the recessive phenotype, what is the genotype of the unknown parent?
heterozygous
monohybrids
individuals that are heterozygous for one character
monohybrid cross
mating of heterozygotes
complete dominance
occurs when phenotypes of the heterozygote and dominant homozygote are identical (Pp=PP)
incomplete dominance
occurs when neither allele is completely dominant and the hybrids are a blend of their parents
codominance
two dominant alleles affect the phenotype in separate, distinguishable ways
what effect does dominant alleles have on recessive alleles?
dominant alleles masks the other effect
tay-sachs disease
human genetic disease caused by a recessive allele for a dysfunctional enzyme, leading to accumulation of certain lipids in the brain, resulting in seizures, blindness, and degeneration of motor and mental performance
polydactyl
condition in which a rare dominant allele causes babies to be born with extra fingers or toes
three possible alleles for ABO blood group in humans
IA, IB, and i
pleiotropy
one gene that effects phenotype in many ways
sickle cell disease
recessive hereditary disease caused by a change in one amino acid in beta hemoglobin which causes the red blood cell to make a crescent shape, and thus the cell cannot carry enough oxygen
quantitative characters
characters that vary in a population along a continuum
polygenic inheritance
an additive effect of two or more genes on a single phenotype (ex: skin color)
multifactorial
many factors, both genetic and environment, collectively influence phenotype
why are humans not good subjects for genetic research?
generation time is too long, produce few offspring, and unethical
pedigree
family tree that describes the interrelationships of parents and children across generations (help make predictions about future offspring)
recessive genetic disorders examples
albinism, cystic fibrosis, and sickle cell disease
recessively inherited disorders
occur only in individuals homozygous for the allele
carriers
heterozygous individuals who carry the recessive allele but are phenotypically normal
cystic fibrosis
a recessive genetic disorder in which the lungs and pancreas are clogged with large quantities of abnormally thick mucus
dominantly inherited disorders
caused by dominant alleles
dominantly inherited disorders examples
Achondroplasia and Huntington’s disease
Achondroplasia
a form of human dwarfism caused by a single dominant allele (the homozygous condition is lethal)
huntington’s disease
genetic disorder that causes degeneration of brain cells, caused by a dominant allele (symptoms do not appear until the age of 30 or so)
aminocentesis
liquid that bathes the fetus is removed by inserting a needle in the amniotic sac to check genetic health and development of a fetus
chronic villus sampling (CVS)
a sample of the placenta is removed and tested to detect fetal abnormalities
gene idea
the model that says parents pass on discrete heritable unit-genes that retain their separate identities in offspring
law of independent assortment
during gamete formation, different pairs of alleles segregate independently of each other
epistasis
a gene at one locus alters the phenotypic expression of a gene at a second locus
