Module 3 - Genetics Flashcards
(91 cards)
1
Q
Reproduction types
A
- asexual, one organism needed
- sexual, two organisms needed
2
Q
Asexual reproduction definition
A
- adult creates new version of herself with complete copy of entire genome
- advantageous if stable environment as quick and efficient
- disadvantageous if environment highly variable as no diversity
3
Q
Asexual reproduction types
A
- budding - growth of organism off side of parent
- fragmentation - break into different parts that become new organism
- fission - split into equal parts
- gemmulation - cell that can become anything
- regeneration - cut off pieces, regenerate parts missing to create new organism
- self-fertilization - produces sperm and egg
- pathogenesis - eggs not fertilized, become clone of adult
4
Q
Sexual reproduction
A
- requires two separate halves of genome
- each half comes from one adult via sex cells
- sex cells fuse to form new, smaller version of parents, zygote
- adv = genetic recombination + diversity
- disadv = struggle to find mate
5
Q
Sexual life cycles
A
adult with germline cells –> meiosis –> sperm + egg –> fertilisation –> zygote –> mitosis –> baby with somatic and germline cells –> mitosis –> adult with germline cells
6
Q
Germline cells
A
gonads which give rise to haploid gametes
7
Q
Fertilisation
A
produces diploid zygote with paternal and maternal homologue
8
Q
Meiosis definition
A
cell division that causes number of chromosomes in newly formed cell to be reduced by half
9
Q
Stages overview
A
- interphase
- cell division I
- cell division II
- two divisions with one round of replication
10
Q
Interphase (2n)
A
- DNA replication
- duplicate into two sister chromatids joined at centromere to form pair of chromosomes
- one maternal and one paternal = homologous
11
Q
Prophase I (2n)
A
- synapsis - maternal and paternal chromosomes line up and fuse together
- crossing over - exchange of information resulting in new genetic combinations and non-identical chromatids
12
Q
Metaphase I (2n)
A
- homologue pair align randomly on metaphase plate
13
Q
Anaphase I + telophase I (n)
A
- centromere does not divide
- homologous chromosomes separate, sister chromatids remain together
- result = 2 genetically different haploid cells
14
Q
Meiosis II (1n x 2)
A
- no replication
- chromosomes align
- sister chromatids separate
- 4 genetically different haploid cells
15
Q
Location meiosis occurs
A
germline cells
16
Q
Spermatogenesis
A
4 sperm, testis
17
Q
Oogenesis
A
- 1 egg and 3 degenerate polar bodies
- begins in embryo but arrest in prophase I until puberty
- at ovulation, resume meiosis and arrest at metaphase II until fertilization
- if fertilization, meiosis resumed and ovum + 3 polar bodies produced
18
Q
Ways genetic variation created in meiosis
A
- crossing over, recombination, prophase I
- random distribution of chromosomes, anaphase I
- mixing of maternal and paternal genomes when zygote formed
19
Q
Meiosis vs mitosis
A
meiosis:
- gametogenesis
- pairing of homologues
- 2 divisions
- centromere does not divide in meiosis I
- 4 cells
- diploid to haploid
- genetically different
mitosis:
- somatic cells
- no pairing
- 1 division
- centromere divides
- 2 cells
- retain diploidy
- genetically identical
20
Q
Gametogenesis
A
formation of gametes from diploid germ cell
21
Q
Why Mendel chose garden pea for experiments
A
- self-fertilizes, pure breeding
- conspicuous external features that vary –> flower color, seed color, seed texture
- grew garden pea in monastery garden
22
Q
Gregor Mendel
A
- father of genetics
- discovered laws describing how genes inherited
- led way to discovery of the gene
23
Q
Cross-fertilization process of pea plants
A
- parent line - cross fertilized plant with yellow seeds and plant with green seeds
- F1 gen - all yellow seeds, F1 then self fertilized
- F2 gen - 3:1 ratio of yellow to green seeds
24
Q
Mendel’s explanation
A
- seed color determined by inheritable factor with 2 forms
- each plant carries two forms of the factor, can be same or different
- each plant passes on one form to each gamete, gametes receive one or other with equal probability
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Modern explanation
- seed color is determined by inheritable gene with two alleles
- each plant carries two alleles which can be homozygous or heterozygous
- meiosis independently assorts alleles randomly into gametes
- combination of alleles is the genotype and the physical expression is the phenotype
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F2 monohybrid ratio
3:1
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Mendel's First Law
- principle of segregation
- two alleles segregate during gamete formation so half of gametes carry one member of the pair and the other half carry other member
- alleles rejoined at random, one from each parent, during fertilization
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Incomplete dominance
- phenotype is intermediate
- 1:2:1 ratio
- snapdragons: produce pink phenotypes, halfway between red and white
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Codominance
- both alleles expressed simultaneously
- 1:2:1 ratio
- cattle: red and white produce roan with both colorings in coat
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Test cross
- reveals unknown genotypes
- cross dominant phenotype to recessive homozygote
- equal proportions = heterozygote parent
- all one trait = homozygous dominant parent
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F2 dihybrid ratio
- two traits - seed color and texture
- 9:3:3:1
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Mendel's second law
- independent assortment
- segregation of different allele pairs are independent
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Two point test cross
- cross double heterozygote to double recessive homozygote
- confirms independent assortment
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Chromosome theory of inheritance
- genes carried on chromosomes
- each gene has one or more loci
- each locus has one allele
- diploid = 2 of each chromosome so 2 alleles at each loci
- during meiosis, alleles from one homologue can swap to other at equivalent locus
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Inheritance of sex
- inheritance of traits follows inheritance of chromosomes
- XX, homogametic, female
- XY, heterogametic, male
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Inheritance of eye color in Drosophila
- mutant, white-eyed male discovered
- crossed white-eyed male with red-eyed female
- F1 gen = all red but heterozygous
- F2 gen = females red, males 50% white, 50% red
- males inherit X chromosome from mother
- gene that controls eye color on X chromosome
- heterozygous female gives 50% male offspring recessive white trait
- allele inherited from mother, determines phenotype in males
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Continuous variation
many different genes influence one phenotypic trait, phenotype continuous e.g. height
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Pleiotropy
one gene affecting more than one phenotypic trait at same time
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More than two alleles
two or more at given gene e.g. blood type
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Epistasis
effect of one gene depends on effect of another e.g. labrador pigment only expressed if E gene present
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Phenotypic plasticity
same genotype produces different phenotypes depending on environmental conditions e.g. within individuals - tyrosinase activity in siamese cats, among individuals - temperature-dependent sex determination
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Evolution
change in genetic composition of population across generations
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Microevolution
genetic change in gene pools
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Macroevolution
change above species level
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Darwinian theory
- evolution: descent with modification
- natural selection: Darwin's mechanism for evolutionary change
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Mendelian genetics
predicts proportions of different genotypes from particular mating
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Genotypic frequency
proportion of individuals in a population with a given genotype
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Allelic frequency
proportion of each allele within a gene pool
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frequencies
P = f(AA)
H = f(Aa)
Q = f(aa)
P + H + Q = 1
p = f(A) = P + 0.5H
q = f(a) = Q + 0.5H
p + q = 1
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Hardy-Weinberg equilibrium
p^2 + 2pq + q^2
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Assumptions of Hardy-Weinberg equilibrium
1. random mating
2. no mutation
3. no migration
4. no selection
5. large population
- if assumptions not met and frequencies do not conform, evolutionary forces are acting on the population
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Nonrandom mating
- positive assortative mating: tendency for like individuals to mate
- negative assortative mating: tendency for unlike individuals to mate
- changes genotypic proportions but not allele frequencies
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Inbreeding
- most common type of mating
- positive assortative mating for relatedness
- self-fertilization: each gen, number of heterozygotes reduces by half until all genotypes are homozygotes
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Mutation
- ultimate source of variation
- weak cause of genetic change in populations
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Migration (gene flow)
- make populations more similar
- reduces genetic divergence while maintaining variation
- higher mobile species = fewer genetic differences among populations
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Genetic drift
- random changes in allele frequencies from one generation to the next
- caused by random sampling of gametes from gene pool
- more susceptible if small population
- results in fixation - one allele available
- change in allele frequencies and loss of genetic variation
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Importance of random drift
- conservation genetics - loss of genetic variation in small populations close to extinction, more susceptible to genetic drift
- evolution - potential for rapid evolutionary change without selection if negative allele chosen
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Natural selection
- most complex evolutionary force affecting genetic makeup of populations
- variation exists --> traits inherited --> differential survival and reproductive success
- alleles with greater survival success increase in frequency the next generation
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Fitness
- average contribution by a particular genotype to subsequent generations
- response to selection determined by variation in fitness
- individual with highest number of offspring = 1 fitness
- environment dependent
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Disruptive selection
selection for small and large individuals, midsized selected against, two peaks form e.g. finch with small and large peaks being the two peaks
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Directional selection
selection for larger individuals, peak shifts in direction favored by selection e.g. salmon with selective fishing for large salmon resulting in decrease in size of fish as allele for large fish depleted
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Stabilizing selection
selection for midsize individuals, peak gets narrower e.g. humans with intermediate body weight = lowest infant mortality
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Secondary sexual characteristics
- characteristics have function during reproduction but not necessary for breeding e.g. peacock trains
- reduce survival but compensated by increased advantage in reproduction, more alleles passed onto next generation
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Theory of sexual selection
advantage which certain individuals have over other individuals of same sex and species in exclusive relation to reproduction
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Intrasexual competition
members of one sex compete with each other for members of other sex
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Intersexual competition
members of one sex choose mates
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Example of intrasexual selection - sperm competition
- testis size in fishes
- mullet = mass spawning, high sperm competition, testis = large amount of body weight
- seahorses and pipefish = female inserts egg into male's pouch, no sperm competition, small amount of body weight
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Mate choice
- direct benefits = parental care, provide food and protection
- indirect benefits = attributes of mate inherited by offspring
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Handicap hypothesis
- males either have genes that confer higher quality or lower quality
- males with handicap have good genes = females mate preferentially to have offspring with good genes
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Ways of defining species
- morphological species concept: morphologically alike
- recognition species concept: common mate recognition system
- evolutionary species concept: lineage with common ancestry
- ecological species concept: shared ecological attributes
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Biological species concept
groups of interbreeding individuals that are reproductively isolated from other such groups
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Limitations of biological species concept
- does not consider asexual species and fossils
- overlooks common causes of hybridization between species
- morphological diversity and reproductive isolation do not go hand-in-hand
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Speciation requirements
divergence and reproductive isolation
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Allopatry
populations do not overlap
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Sympatry
populations occur in the same place
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Allopatric speciation
- geographic barrier splits population
- two populations diverge over time
- form two species that cannot interbreed
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Types of geographic barriers
- birds migrating to new islands
- mountains, rivers forming
- continuous distribution = wipes out intermediate population so individuals separated
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Distribution of rock wallabies
- allopatric speciation
- each rocky outcrop = different species
- separate environment allows species to diverge
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Ring species
- allopatric speciation
- desert splits individuals
- diverge and adapt to own environment
- at end of desert, species converge but cannot interbreed
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Sympatric speciation
new species arises within distribution of original species, no geographic barrier needed
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Apple maggot fly
- lays eggs on hawthorns and domestic apples
- when apple introduced, some flies moved over
- genetic divergence, no gene flow as grew up, looked for mates and laid eggs on respective fruits
- genetic difference in <200 years
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Examples of sympatric speciation in lakes
- crater lakes in Cameroon = many species, smooth lake bottom, sympatric
- Lake Victoria = fish diversified to exploit different micro niches but not pure sympatric speciation as mini lakes form
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Polyploidy
- two species with different sets of chromosomes produce infertile offspring with odd number of chromosomes so cannot produce gametes
- hybrid with copying error doubled chromosomes so could make gametes and reproduce itself
- not compatible with parent generation so new species
84
Post-zygotic barriers
- zygote dies early during embryogenesis, not enough matching information for embryo to work
- hybrids survive but are sterile - can produce gametes but less fertile or can't produce gametes
- cannot be direct result of natural selection, must be due to genetic drift or mutation
85
Pre-zygotic barriers
- ecological: species occupy same geographic area but do not hybridize because occupy separate habitats e.g. forest margins and central forest
- temporal: differences between species in timing of reproduction e.g. Banksia species
- behavioral - differences between species in courtship behaviors
- mechanical - physical restrictions to mating
- gametic - gametes of different species do not interact, lock and key mechanism
- can be incidental result of genetic change or direct result of natural selection
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Reinforcement
- natural selection to prevent formation of maladaptive hybrids
- Drummond's phlox - red phenotype expressed in sympatry, butterflies have preference, prevents hybrids from occurring
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Adaptive radiation
- rapid evolutionary diversification of single lineage
- increase in morphological and ecological diversity
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Example of adaptive radiation
- Darwin's finches
- difference in beak structure due to diet
- single ancestor made it to other islands and evolved to exploit different resources and fill niches
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Model of adaptive radiation on island archipelagos
- ancestral species flies from mainland to colonize one island
- ancestral species spreads to different islands
- populations on different islands adapt to conditions and evolve to become different species
- species evolve different adaptations in allopatry
- colonization of islands with different species on same island
- species evolve different adaptations to minimize competition with other species = character displacement
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Character displacement
- differences among species accentuated in regions where they co-occur
- minimized or lost where species distributions do not overlap
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Examples of character displacement
- WA stygofauna = beetles started at different sizes and character displacement exaggerate sizes so beetles could use different resources in the same area
- Hawaiin Drosophila = new islands formed, flies colonize and adapt to fill niches, undergo adaptative radiation and character displacement
