Chapter 4 Flashcards
Selective Breeding
A practice where animals or plant breeders choose which individual animals or plants will be allowed to mate in order to pass on desired traits in future generations
What else can selective breeding do?
Can influence the frequency of desirable traits in mammals
hybrid
the offspring of parents who differ from each other with regard to certain traits or aspects of genetic makeup
Segregation
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. (the first principle of inheritance
Recessive
- describing a trait that isn’t expressed in heterozygotes; also refers to the allele that governs the trait, for a recessive allele to be expressed, an individual must have two copies of it
a trait governed by an allele that’s expressed in the presence of another allele
Dominant
prevent the expression of recessive alleles in heterozygotes.
Dominant alleles
having the same allele at the same locus on both members of a pair of chromosomes
homozygous
having different alleles at the same locus on members of a pair of chromosomes
heterozygous
Genotype
the genetic makeup of an individual
the observable or detectable physical characteristics of an organisms; the detectable expressions of genotypes, frequently influenced by environmental factors
Phenotype
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.
Principle of Independent Assortment-
the chance distribution of chromosomes to daughter cells during meiosis
random assortment
- characteristics that are influenced by alleles at only one genetic locus. Examples include many blood types, genetic disorders, etc.
Mendelian traits
discrete
do not overlap in expression
Antigens
large molecules found on the surface of cells, several different loci govern various antigens on red and white blood cells.
Codominance
the expression of two alleles in heterozygotes, both influence the phenotype.
Recessive Alleles have an influence on phenotype
Example- Tay-Sachs disease. Inability to produce an enzyme. Carriers don’t have the disease.
Pedigree chart
a diagram showing family relationships. It is used to trace a hereditary pattern of particular genetic traits.
Autosomal Dominant Traits
traits which are governed by dominant alleles located on autosomes. (ex- achondroplasia-dwarfism)
Autosomal Recessive Traits
influenced by loci on autosomes but show a different pattern of inheritance
Sex-linked traits
Sex-linked traits- controlled by genes located on the X and Y chromosomes.
Example- Hemophilia caused by a recessive allele on the X chromosome.
Polygenic
referring to traits that are influenced by genes at two or more loci (examples include height, skin color, eye color, and hair color, may be influenced by environmental factors)
Mitochrondria
contain around 40 genes that direct the conversion of energy within the cell
Pleiotropy
A situation where a single gene influences more than one characteristics (or phenotypic expressions)
Example- autosomal recessive disorder phenylketonuria- can lead to mental problems.
Mendelian traits are less likely to be influenced by
environmental factors
1920’s and 1930’s- biologists realized that mutation and natural selection were not opposing processes, they contributed to evolution. They decided evolution is a two stage process:
The production and redistribution of variation
Natural selection acted upon variation
Current Evolution Principle States What?
Evolution s a change in allele frequency from one generation to then next
Microevolution
small changes occurring within species such as changes in allele frequencies
Macroevolution
the long term effects through time of these small changes
Mutation
Point mutations- substitutions of one DNA to another
Must occur in sex cells if they are to have any evolutionary differences
Rare for evolution to take place solely because of mutation
Tandem repeats
short adjacent segments of DNA within a gene that are repeated several times
why are tandem repeats important?
Important because they have much higher mutation rates than single alleles do and therefore could have significant influence on the rate of evolution.
Gene Flow
The exchange of genes between populations
Only happens when migrants interbreed
Changes in allele frequencies can be influenced by long term patterns of mate selection
Genetic drift
Genetic drift- the random factor in evolution, a function of population size. It is evolutionary changes in allele frequencies that are produced by random factors in small populations.
Founder Effect
a type of genetic drift in which allele frequencies are altered in small populations that are taken from or are remnants of a larger population, results in a loss of genetic diversity
Recombination
When paired chromosomes exchange DNA genes sometimes find themselves in different genetic environments. This can influence the functions of some genes because of the closeness of alleles.
If the environment changes, then the selection pressures also change, such a shift is known as what?
adaptation
