BIOL 1107: Test 4
118 Cards in this Set
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heredity
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transmission of traits from one generation to the next
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Genes
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coded information that specifies specific traits
specific DNA sequences tell cells to make enzymes and proteins that lead to different traits
located along chromosomes and can be tagged with dye
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Gametes
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reproductive cells (egg and sperm) that transmit genes to the next generation
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somatic cells
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other body cells besides gametes
each species has a certain number of chromosomes in somatic cells; humans have 46 (23 from each parent)
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diploid
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cells with 2 copies of each chromosome (2n)
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haploid
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cells with only one copy of each chromosome (n)
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locus
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the location of a specific gene on a chromosome
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Asexual reproduction
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one parent produces offspring that are exact genetic copies of the parent
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sexual reproduction
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two parents produce offspring that have a unique combination of both parents' genes
offspring are different from the parents and each other
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karyotype
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ordered display of all the chromosomes
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Homologs or Homologous chromosomes
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genes that are the same length, etc. and carry genes controlling the same traits
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sex chromosomes
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X and Y chromosomes
females have XX, males have XY
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Autosomes
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chromosomes other that sex chromosomes
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fertilization
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when sperm and egg join and their nuclei fuze
2 haploid cells -> diploid
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zygote
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Fertilized egg, diploid cell
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Meiosis
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Special cell division that produces haploid sperm and eggs
only diploid cells undergo meiosis
involves duplication of chromosomes and two cell divisions: meiosis I and II
produces 4 haploid daughter cells
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Meiosis I
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homologous chromosomes separate
crossing over
ends with 2 haploid cells, each chromosome is still 2 sister chromatids
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Prophase I
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chromosomes condense and homologs become physically connected
crossing over happens
spindles form and nucleus is disassembled
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Crossing over
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the exchanging of DNA segments between non sister chromatids
makes recombinant chromosomes that carry genes from both parents
1-3 crossovers happen per chromosome pair in humans
recombinant chromatids can be oriented different ways in metaphase II and assort independently again
the fu…
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Metaphase I
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homologous chromosomes line up along the center
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Anaphase I
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homologous chromosomes separate and move to poles
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Telophase I and cytokinesis
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2 haploid cells form
each chromosome is still 2 sister chromatids
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Meiosis II
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sister chromatids separate
4 genetically distinct haploid daughter cells are formed
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Prophase II
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spindle forms
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Metaphase II
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chromosomes line up in the center
chromosomes are not identical because of crossing over in meiosis I
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Anaphase II
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Sister chromatids move to poles
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Telophase II and cytokinesis
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nuclei reform
chromosomes de-condense
4 genetically distinct haploid daughter cells are formed
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Alleles
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different versions of a gene
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Independent Assortment of chromosomes
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homologous chromosomes are oriented randomly in metaphase I
the maternal chromosome and parental chromosome could be pulled to either pole of the cell
number of possibilities is 2^n
component of genetic variation
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Random fertilization
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any combination of genes in a sperm can fertilize an egg with any possible combination of genes
component of genetic variation
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Fitness
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producing offspring
individuals with combinations of genes best suited to their environment are more likely to survive and reproduce and thus pass those genes on: survival of the fittest
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traits
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variants on a characteristic
studied by Mendel
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True breeding plants
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with self pollination, it produces the same variety as the parent plant over and over
P is used to refer to the true breeding parents, and F1 is used to me the first generation of offspring, F2 for the next, and so on
This is the reason why Mendel's studies had such success
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Dominant and recessive traits
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Dominant traits appear to cover up recessive ones when one dominant and one recessive allele are inherited and when two dominant alleles are inherited
recessive traits appear when two recessive alleles are inherited
dominant traits are dominant because they code for enzymes or proteins…
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Law of Segregation
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the two alleles for a characteristic segregate (separate) during formation of gametes and end up in different gametes
an egg or sperm only gets 1 of the 2 alleles for a trait that end up in the diploid cell
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heterozygous
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having two different alleles for a trait
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homozygous
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having 2 of the same allele for a trait
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phenotype
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an organism's appearance or observable trait
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genotype
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and organism's genetic makeup
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test cross
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breeding an organism of an unknown genotype with a homozygous recessive organism to determine its genotype
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monohybrid
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heterozygous for the particular characteristic being studied in a cross
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monohybrid cross
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breeding 2 organisms heterozygous for a trait
leads to a 3:1 dominant to recessive phenotypic ratio
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Dihybrid
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heterozygous for 2 characteristics being studied in a cross
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dihybrid cross
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breeding 2 organisms heterozygous for the 2 traits being studied
leads to a 9:3:3:1 phenotypic ratio (dominant & dominant; dominant & recessive; recessive & dominant; recessive & recessive)
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Law of Independent Assortment
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each pair of alleles segregates independently of each other pair of alleles during gamete formation
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Probability and Mendel
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use multiplication to find the probability of one thing happening AND another thing happening (probability of the first event x probability of the second event)
use addition to find the probability of one thing happening OR another thing happening (probability of first event + probabilit…
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Mendel and Simple inheritance
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inheritance is usually more complex than the simple traits Mendel studied
Mendel studied traits controlled by one gene with one allele totally dominant and one allele completely recessive; complete dominance
Mendel's studies focused on characteristics with only 2 alleles; most characte…
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incomplete dominance
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hybrids have a phenotype somewhere in between the phenotypes of the parents
Ex: red flower + white flower = pink flower; heterozygotes make less red pigment than the red homozygotes
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Co-dominance
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when both phenotypes are being expressed by heterozygotes
ex: MN blood type has M and N proteins on blood cells
dominant traits are dominant because they code for enzymes or proteins that control a trait. Either it's present or it isn't, if it's present, the dominant trait is displayed
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pleiotropy
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when one gene controls multiple phenotypic characteristics
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Epistasis
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when the expression of one gene alters the expression of another unrelated gene
ex: black and brown fur in labs is determined by B and b alleles, with black being dominant. Another gene determines whether pigment is deposited in the fur or not with E (disposition) being dominant and e (n…
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polygenic inheritance
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many genes additively affect on phenotypic characteristic
ex: skin color
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Environment and phenotype
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sometimes phenotype depends on environment and genotype
ex: skin darkens with exposure to the sun
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pedigree
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family tree describing traits of parents and children over generations
females are circles and males are squares
people who have the trait that is being studied are shaded in
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carrier
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a person who is heterozygous for a certain disorder or trait and carries a recessive allele that could be passed on to offspring
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Chromosome theory of inheritance
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the idea that genes have specific positions on chromosomes and undergo independent assortment and segregation
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Morgan and inheritance
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studied flies
most had red or "wild type" eyes. One male, though, had white eyes: a mutation in the wild type allele
white eyes is recessive and lies on the X chromosome (sex linked trait)
a male only has to inherit one white eye allele to have white eyes, a female has to inherit 2 wh…
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Sex-linked trait
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a trait whose gene is located on a sex chromosome (X or Y)
females have two X chromosomes, males have an X and Y
ex: colorblindness is a recessive sex-linked trait in humans
The Y chromosome is much smaller than the X and only short segments at either end of the Y are homologous with c…
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hemizygous
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since males have an X and Y, a male only has to inherit one white eye allele to have white eyes
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Barr body
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because females have two X chromosomes, most of the second one is redundant, so those parts are inactivated and condense into a compact Barr body
Either the X from the mother of the X from the father can be the active on in any given cell, so about half of the females cells have the mat…
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Linked genes
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genes located near each other on the same chromosome that are usually, but not always, inherited together
with linked genes, offspring usually show a higher proportion of parental phenotypes than would be expected if they assorted independently (called parental types)
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genetic recombination
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production of offspring that have combinations of traits that are different from either parent (these offspring are recombinant types)
this happens because of crossing over
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Evolution
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descent with modification
changes in genetic compostion from one generation to the next
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adaptations
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inherited characteristics of organisms that help them survive and reproduce in specific environments
ex: finches that Darwin observed; different beak sizes/shapes based on diet and readily available food
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homologous structures
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underlying skeletons of arms, forelegs, flippers, wings, etc. that represent variations of a structure that was present in a common ancestor
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Natural selection
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individuals with certain inherited traits survive and reproduce at higher rates than other individuals because they have those certain traits.
these traits are passed onto offspring, making them more frequent in the subsequent generations, etc.
organisms produce more offspring than the…
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Artificial selection
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humans selectively modifying other species by selecting and breeding individuals with desirable traits
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Microevolution
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individual organisms do not evolve
microevolution is the change in allele frequencies in a population over generations and is caused by natural selection, genetic drift and gene flow
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genetic drift
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the change in allele frequencies due to chance events
more pronounced in smaller populations
leads to a loss of genetic variation in a population and could cause harmful alleles to be fixed in a population
Founder effect and Bottleneck effect
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gene flow
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the transfer of alleles between populations
ex: emigration
tends to reduce genetic differences between populations and can also transfer alleles that allow the populations to better adapt to local conditions
increasingly important for humans as global travel and contact between differe…
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genetic variation
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differences between individuals in their DNA/genes
a species can vary based on their geographic location
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population
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group of individuals of the same species that live in the same area and interbreed
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gene pool
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all copies of every type of allele in all members of a population
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mutations
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new alleles can come to be due to mutations
mutations aren't usually helpful and usually aren't passed on to offspring (has to be in a gamete to be passed on)
on rare occasions, can be helpful to an organism
changing gene number and position can sometimes be positive, too
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allele frequencies
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each allele has a given frequency (proportion or percentage of all alleles) in a population.
for diploid organisms, p and q are used to represent to 2 alleles
to find the allele frequency for an allele, count the number of that allele and divide by the total number of alleles
If there …
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Hardy Weinberg principle
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if the frequencies of alleles aren't changing from generation to generation, the population is evolving (Hardy-Weinberg equilibrium)
if the allele frequencies do change, evolution is happening.
the equation p² + 2pq + q² = 1 is used to figure out in what proportion the three genotypes w…
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Hardy Weinberg conditions
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no mutations
random mating
no natural selection
extremely large population size
no gene flow
these conditions are never actually met in real life, buut Hardy-Weinberg still lets us make close estimates about real populations
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Founder effect
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if a few individuals are isolated from a population, they may establish a new population whose gene pool is different from the original populations
can account for high frequencies of certain inherited disorders in isolated human populations
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Bottleneck effect
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a sudden environmental change or disaster can cause a severe drop in population size
by chance, certain alleles are over or under represented in the remaining population
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relative fitness
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contribution an individual makes to the gene pool of the next generation relative to the contribution of other individuals; having more offspring
natural selection is determined by relative fitness
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Directional selection
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conditions favor one or the other extreme of a phenotype, so a population shifts in that direction
happens when an environment changes
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disruptive selection
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conditions favor both extremes of a phenotype, so a population shifts toward the extremes and against individuals with an intermediate phenotype
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stabilizing selection
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conditions favor the intermediate phenotype, so a population shifts toward the middle and against individuals with extreme phenotypes
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sexual selection
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individuals with certain inherited characteristics are more likely than others to obtain mates and reproduce
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Sexual dimorphism
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differences between sexes in characteristics like behavior, size, color, etc.
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intrasexual selection
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Individuals of one sex compete for members of the opposite sex
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Intersexual selection
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individuals of one sex (usually females) are choosy in selecting mates from the pool of members of the opposite sex
this evolved from female preference for male traits the indicate "good genes"
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diploidy
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recessive alleles are hidden from selection because they aren't expressed in a phenotype and are still passed down
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balancing selection
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natural selection maintains 2+ forms in a population
heterozygote advantage and frequency-dependent selection
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heterozygote advantage
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individuals that are heterozygous have greater fitness than both zygotes
ex: heterozygous for sicle cell anemia; safe from malaria and don't have disease
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frequencey-dependent selection
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fitness of phenotype depends on how common it is in population
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Speciation
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process by which one species splits into 2+ species
when this happens, the new species share common characteristics because they descended from a common ancestor
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Biological Species Concept
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a species is a group of populations whose members can interbreed in nature and produce fertile offspring but don't produce fertile offspring with members of other species
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reproductive isolation
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existence of biological barriers that keep members of 2 species from interbreeding and producing fertile offspring
required for the formation of a new species
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hybrids
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offspring produced from interspecific mating
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Prezygotic barriers
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block fertilization from happening by keeping different species from being able to mate, preventing attempted mating from being completely successful, or hindering fertilization if mating is successful
habitat isolation
temporal isolation (species breed at different times)
behavioral i…
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postzygotic barriers
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reduced hybrid viability
reduced hybrid fertility
hybrid breakdown (hybrid offspring are feeble or unstable)
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Biological species concept doesn't always apply...
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organisms that reproduce asexually all or most of the time -- many pairs of species have gene flow between them
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Morphological species concept
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characterizes species based on body shape and other structural features
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Ecological species concept
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species is determined by how its members interact with nonliving and living parts of the environment
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Phylogenetic species concept
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species is defined as smallest group of individuals that share a common ancestor
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punctuated equilibria
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fossil records show new species appearing, living unchanged, then disappearing
punctuated patterns indicated that speciation occurred quickly
other species changed more gradually and speciation occurs over time
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Once speciation starts
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...it can be completed quickly
extensive genetic changes can happen over a short period.
On average, millions of years pass before a new species gives rise to another species
The time it takes new species to for widely varies, so speciation begins only after gene flow between populatio…
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Evolving reproductive isolation
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rarely due to a change in one gene, ex: gene that determines direction that snail shells spiral
in other organisms, large numbers of genes and gene interactions have to be changed
as speciations pile up and certain groups of organisms increase by producing more new species, the cumulati…
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Populations can expand greatly when resources are abundant
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it can be explained by the equation: change in population = births + immigrants entering - deaths - emigrants leaving.
simplifying, change in number (ΔN) / change in time (Δt) = B - D (births - deaths)
rewritten accounting for per capita: ΔN/Δt = rN
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per capita birth rate
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number of offspring produced per unit time by an average population member.
using this birth rate (b), B = bN can be used to find the expected number of births for a population
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per capita death rate
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m
D = mN
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per capita rate of increase
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r
r = b - m
if r is greater than zero, the population is growing.
if r is less than zero, the population is declining
if r equals zero, there is zero population growth
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Exponential population growth
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growth under unlimited resources and reproduction at capacity
graph of this is a J-shaped curve; population accumulates more individuals per unit time when it is large than when it is small
characteristic of populations rebounding after disasters, etc.
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Carrying capacity
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since resources are never unlimited, as populations increase, each individual has access to fewer resources
thus, there is a limit to how many individuals can live in a habitat - carrying capacity (K)
Many factors influence, like energy, shelter, water, nesting sites, etc.
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Logistic population growth
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per capita rate of increase approaches zero as carrying capacity is reached.
If r(max) is the maximum per capita rate of increase, the equation becomes dN/dt = r(max)N ((K - N) / K)
the graph of this is an s-shaped curve leveling off at K
when N is small compared to K, (K - N) / K is…
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In real populations...
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there are delays between overshooting carrying capacity and population decrease, etc.
Also, some populations show an Allee effect: individuals have s harder time surviving and reproducing if the population is too small
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Organisms whose offspring are subject to high mortality rates...
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produce lots of small offspring (ex: sea turtles, mice)
in other organisms, parents invest a little extra in them for a few years; important in high population density areas
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K-selection
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selection for traits that are favored at high population densities
selection based on being near carrying capacity
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r-selection
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selection for traits that maximize reproductive success when population is low
selection base on maximizing reproduction rate when not near carrying capacity
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density independent
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birth or death rate doesn't change with population density
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density dependent
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a death rate that rises as population density rises or a birth rate that falls when population density rises
mechanisms of regulation: competition for resources, predation, toxic wastes, intrinsic factors, territoriality, and disease; show how increased density can cause growth rates to …
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population dynamics
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fluctuations in population size from year to year or place to place
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BIOL 1107: Test 4