character
an observable feature of an organism ex) eye color
trait
different versions of a character
ex) brown eye color
there are genes and alleles for
genes: characters
alleles: traits
2 basic conditions in diploid organisms
homozygous: identical alleles for a character are present
heterozygous: different alleles for a character are present
each allele is on one of the homologous chromosome
there terms dont apply to haploid cells
genotype
the genetic makeup of an organism
phenotype
the traits in an organism
wild type
the most common trait or phenotype found in a population
genotype influence phenotype but
individuals with different genotype can have the same phenotype
(because in some cases only one of the pair of alleles is expressed)
rules of heredity
discovered by gregor mendel in the 1860’s but ignored until 1900’s
his results relied probabilities
mechanisms of meiosis were not understood
he used pea plants which can be
a) can bred in a controlled fashion
b) have true breeding lines
c) have large number of varieties
d) have character that are discrete
e) have a short generation
f) the character have the same traits regardless of the environmental conditional
in many organisms the phenotype
is a result of the genotype and environment conditions
mendel found:
- when peas with different traits are crossed, all the offspring (hybrids) show only one trait
- the offspring of self fertilization hybrids show both traits in a 3:1 ratio
mendels hypotheses
- inheritance of genetic material is particulate, not blending
- there are alternative forms of genes (alleles)
- organisms receive genes from both egg and sperm cells
- organisms contain 2 copies of a gene, gametes only have one copy
- when gametes form, the 2 copies of a gene are separated
- if both dominant and recessive alleles are present in an organism, only the dominant allele is expressed
explanation of mendels results
true breeding plants are homozygous (all gametes have the same allele)
crosses between homozygous plants that have different alleles produce heterozygous individuals
self pollination in heterzygous indivdials produce offspring that are either:
-homozygous with the dominant allele
-heterzygous
-homozygous with the recessive allele
homozygous dominant individual look the same as hetro people
determining offspring genetypes from parent genotypes
- each gamete has equal probability of containing either allele present in the parent
- each egg has an equal probability of being fertilized by each sperm
determining genotypes from phenotypes
- organisms expressing a recessive trait
a) are homozygous recessive
b) have parents who each have at least one recessive allele - organisms that express a dominant trait are either:
homozygous dominant
or heterozgous
