selective breeding
a practice whereby animal or plant breeders choose which individual animals or plants will be allowed to mate based on the traits (such as coat color or body size) they hope to produce in offspring. animals or plants that dont have the desirable traits ar
before the mid nineteenth century, what was the most common belief about traits
traits seen in offspring resulting from the blending of parental traits
what did Mendel's background lead him to invesigate
how physical traits, such as color and height, could be expressed in plant hybrids
hybrids
offspring of parents who differ from each other with regard to certain traits or certain aspects of genetic makeup; heterozygotes
what did the results of the pea experiment suggest
that different expression of a trait were controlled by discrete units (we would call them genes), which occurred in pairs, and that offspring inherited one unit from each parent
Mendel's Principle of Segregation (first principle of inheritance)
genes (alleles) occur in pairs because chromosomes occur in pairs. during gamete formation, the members of each pair of alleles separate, so that each gamete contains one member of each pair. (meiosis explains this)
recessive
describing a trait that isnt expressed in heterozygotes; also refers to the allele that governs the trait. for a recessive allele to be expressed, an individual msut have two copies of it )i.e., the individual must be homozygous).
-the expressiont hat is
dominant
describing a trait governed by an allele thats expressed in the presence of another allele (i.e., in heterzygotes). dominant alleles prevent the expression of recessive alleles in heterzygotes. (this is the definition of complete dominance).
-the expresse
locus
the position on a chromosome where a given gene occurs. the term is frequently used interchangeably with gene. at many genetic loci, there are more than one possible form of the gene, and these variations of genes at specific loci are called alleles.
alleles
alternate forms of a gene. alleles occur at the same locus on both members of a pair of chromosomes, and they influence the same trait. but because theyre slightly different from one another, their action may result in different expressions of that trait.
homozygous
having the same allele at the same locus on both members of a pair of chromosomes
heterozygous
having different alleles at the same locus on members of a pair of chromosomes
genotype
the genetic makeup of an individual. genotype can refer to an organism's entire genetic makeup or to the alleles at a particular locus
-ex. (TT, Tt, tt)
punnett square
shows the different ways alleles can be combined and shows all the genotypes that are possible in the new generation. also shows the proportions of phenotypes
phentoypes
the observable or detectable physical characteristics of an organism; the detectable expressions of genotypes, frequently influenced by environmental factors
what is the only way a recessive allele can be expressed
if it occurs with another recessive allele, that is, if the individual is homozygous recessive at the particular locus in question
principle of independent assortment
the distribution of one pair of alleles into gametes does not influence the distribution of another pair. the genes controlling different traits are inherited independently of one another
random assortment
the chance distribution of chromosomes to daughter cells during meiosis, along with recombination, a soruce of genetic variation (but not new alleles) from meiosis.
medelian traits
characteristics that are influenced by alleles at only one genetic locus. exs include many blood types, such as ABO; many genetic disorders, including sickle cell anemia, and tay sachs disease; are also medelian traits.
(also called discrete traits)
where is the most comprehensive listing of mendelian traits in humans
Mendelian Inheritance in Man
also online lists 20,000 human characteristics known or believed to be inherited according to mendelian principles
antigenes
large molecules found on the surface of cells. several different loci govern various antigens on red and white blood cells. (foreign antigens provoke an immune response)
codominance
the expression of two alleles in heterozygotes. in this situation, neither allele is, dominant or recessive, so they both influence the phenotype.
ex. of a blood type being AB
polygenic
referring to traits that are influenced by genes at two or more loci. exs include stature, skin color, eye color, and hair color. many (but not all) polygenic traits are influenced by environmental factors such as nutrition and exposure to sunlight
-conti
mendelian traits are described as discrete, or discontinuous, because....
their phenotypic expressions dont overlap; instead, they fall into clearly defined categories.
mendelian traits dont show continuous variation
pigment
in reference to polygenic inheritance, molecules that influence the color of skin, hair, and eyes
what is influenced by the genetic-environemntal interaction
many aspects of phenotype. genotypes set limits and potentials for development
are mendelian traits less or more likely to be influenced by environmental factors
less likely
in regards to mtDNA, how might certain genetic disorders arise
since mtDNA is subject to mutations, and some mutations cause certain genetic dirsorders that result from impaired energy conversion. because mtDNA is inherited from one parent (mother), meiosis and recombination dont occur. this means that all the variat
modern synthesis
realized in late 20s and early 30s. realized that mutation and natural selection werent opposing processes, both contributed to biological evolution. in this modern perspective, we define evolution as a two-stage process
what are the 2 stages of the modern synthesis
1. the production and redistribution of variation (inherited differences among orgs)
2. natural selection acting ont his variation, wherby inherited differences, or variation, among individuals differentially affect their ability to successfully reproduce
variation (genetic)
inherited differences among individuals; the basis of all evolutionary change
evolution
change in allele frequency from one generation to the next
allele frequency
indicators of the genetic makeup of a population. in a population, the percentage of all the alleles at a locus accounted for by one specific allele
population
within a species, a community of individuals where mates are usually found
gene pool
all of the genes shared by the reproductive memebrs of a population
microevolution
small changes occurring within species, such as changes in allele frequencies
macroevolution
changes produced only after many generations, such as the appearance of a new species
point mutation
the substitution of one single DNA base for another, can cause the allele to change
when mutation is combined with natural selection, what happens
evultionary changes not only can occur, but they can occur more rapidly
gene flow
exchange of genes between populations
genetic drift
evolutionary changes, or changes in allele frequencies, that are produced by random factors in small populations. genetic drift is a result of small population size.
-drift occurs solely because the population is small
founder effect
a type of genetic drift in which allele frequencies are altered in small populations that are taken from, or are remnants of, larger populations
colonization isnt the only way founder effect can happen. what is the other way
small founding groups maybe the survivord of a larger group that was mosttly wiped out by some disaster. the small group of survivors ebcomes a founder pop, possessing only a sample of all the alleles that were present in the original population
genetic bottleneck
the loss of genetic diversity, and the effects can be very detrimental to a species
what does evidence suggest abotu genetic bottleneck regarding humans
that in the last 100 thousand to 200 thousand years, our species experienced a genetic bottleneck that considerably influenced the pattern of genetic variation seen in all human populations today
what happens when paired chromosomes exchange DNA and why is it importnat
genes find themselves in different genetic environments. this is important because the functions of some genes can be influenced simply by the alleles theyre close to. thus, recombination not only changes the composition of part of chromosomes but also ca
what is the one factor that can cause directional change in allele frequency relative to specific environmental factors (some alleles consistently becoming more common, while others less common)
natural selection. if there are long term environmental changes in a consistent direction, then allele frequencies should also shift gradually each generation
sickle-cell anemia
a severe inherited hemoglobin disorder in which red blood cells collapse when deprived of oxygen. it results from inheriting two copies of a mutant allele. this allele is caused by a single base substitution in the DNA.
sickle-cell trait
people who have one copy of each allele, although some of their hemoglobin in abnormal, enough of it is normal to allow them to function well under most circumstances