Genetics Flashcards
Differentiation
development of a cell
Genetics
based on Fact #5 of Darwainian Scenaria, much variation is heritable
Mitosis
- cell division to produce more cells, growth of bodies and repair
- 46 structures in each adult cell
- all offspring come from one cell called zygote
Zygote
First cell produced by fertilization
Fertilization
Biological process when the sperm and eggs cell are fused together
Chromosomes
- large bodies composed of one long strand of DNA wrapped around proteins called histones and are super coiled
- only seen when the cell is actively dividing
Chromatin
- partially coiled DNA (with histones), normal state of DNA when not dividing
DNA
- deoxyribonucleic acid
- large polymore (special molecule) that carries info about species and individual traits
- 2 m long, exists partially folded in nucleus
Genes
- length of DNA that code protein structures
- proteins give us characteristics
- normally 2 letters
Allele
- Alternative form of a gene
- normally 1 letter
Asexual Reproduction
- one parent needed
- produces genetically identical daughter cells
- cell division by mitosis, identical to parent
- if environment changes they show less variation
Sexual Reproduction
- uses meiosis
- two parents needed, each have 46 chromosomes
- producing sex cells that are not identical to parents
- egg and sperm
- MAJOR SOURCE OF VARIATION FOR EVOLUTION
Haploid
- One copy of each gene (has 23 chromosomes)
- produced at the end of Meiosis 1
Diploid
- a cell that has all 46 chromosomes, adult cells are diploids
Gametes
- sex cells produced
- a mature haploid male or female cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote.
Meiosis
- the combination of genes you have from parents determines how it related to a sibling you are
- cell division used to produce sex cells
- sexual recombination is the source of variation in offspring
- explains why genetic inheritance behaves the way that it does
Interphase (before Meiosis)
- cell prepares for division, building up energy, chromatid doubles
Prophase 1
- chromosomes become visible because DNA goes from a chromatin state to being all coiled up in a chromosome state
- to pull these chromosomes apart we need to lose the nuclear membrane (that structure is in the way) so it starts to breakdown
- chromosomes line up to the middle in homologous pairs
- crossing over (a unique characteristic that only happens in meiosis) chromosomes will come so close to each other that’s they will overlap and enzymes will split the parts of the chromosomes and swap parts of the DNA (this offers more gentic variation)
Synapsis
Homologous chromosomes pair up, grouping of four chromatids that have similar genes
Tetrad
Pair of chromosomes (aka bivalent) cross over between chromatids at locations called chiasma
Methaphase 1
- moved to the center, spindle fibers attached to chromosomes
- microtubules attached and pull them apart
Anaphase 1
- homologous chromosomes are being pulled apart by breakdown of microtubules and pulled to either side of the cell
- sister chromatids remain attached
Telophase 1
- chromosomes lie at pole
- cells divide into two cells making haploids
Meiosis II
Same as mitosis but in two cells at the same time
Prophase II
- chromosomes are duplicated
Metaphase II
Chromosomes line up in middle
Anaphase II
Chromatids now splits to opposite cell poles
Telophase II
New nuclei formed and there are now 4 daughter cells
Homlogous Chromosomes
Chromosomes, one from each parent
Spindle
Fibers that are composed microtubules to pull chromosomes to opposite poles
Principles Idea
Mendel revolutionized understanding of how organisms and inherit traits from generations. After his experiment he proposed laws but are now known as principles because they are generally true but not universal.
Principle of Segregation
In adults, genes exist in pairs which separate pairs of alleles when gametes are formed and recombine into pairs at fertilization.
Principle of Dominance
If an individual is heterozygous (has 2 different versions of same gene) you one version will be dominant and the other will recede (be hidden). The recessive version of the gene will only appear when an individual inherits two copies of recessive/ becomes homozygous recessive.
Genotype
The number of combinations of genes
Phenotype
trait/physical appearance
Hybrid
used when referring to a population with a gene of 2 different alleles
Pure Breed
used when referring to a population with a gene of 2 of the same alleles
Homozygous
2 of the same alleles (dominant or recessive)
Heterozygous
2 different alleles
Monohybrid Cross
crossing for 1 gene between 2 heterozygous
Principle of Independent Assortment
- each pair of alleles separates independently
- all possible combinations of factors can occur in the gametes in roughly equal proportions
- Genes are found on separate chromosomes or very far apart on the chromosomes
Dihybrid Cross
- testing different genes being produced together
- the alleles travel independently so that there are more possible combinations in the gametes
Incomplete Dominance
When the two traits from pure strains appeared to blend in the hybrids, they referred to the phenomenon as “incomplete dominance”. We use lower case letters with superscripts for incompletely dominant alleles.
Three phenotypes (one per genotype) and the third one looks like a blend.
ex: red and white flower produced pink
Co-Dominance
When the two traits from parents appeared to be expressed side by side in the same individual, they referred to the phenomenon as “co-dominance”. Co-dominant alleles are given capital letters with superscripts.
Three phenotypes (one per genotype) and the third one is a combination of the other two
Purebreed Cross
1 gene cross between 2 nomozygous
Homologous Chromosomes
The cell has two sets of each chromosome; one of the pair is derived from the mother and the other from the father. The maternal and paternal chromosomes in a homologous pair have the same genes at the same loci, but possibly different alleles.
Spindle
Protein structure that divides the genetic material in a cell, made up of microtubles
Test Cross
To assess the genotype of an individual with a dominant trait, we can perform a Test Cross, in which we cross such an individual with a
known double recessive.
Carrier
a heterozygous person possessing a recessive gene for a trait, and not expressing the trait
Loci
position of a gene on a chromosome
Multi-alleic genes
A pair of genes with more than 2 alleles
Epistatic Genes
When a trait is determined by more than 1 pair of genes
Autosomal
chromosomes 1-22 (don’t determine the gender)
Population
Group of individuals from the same species in a given area
Gene pool
total number of alleles at all gene loci in the population, all alleles present in population
Allelic frequency
proportion or percentage of a certain allele of a specific gene in the population
- frequency of dominant allele (A)
- frequency of recessive allele (a)
Genotypic frequency
frequency of a specific genotype in a population
- frequency homozygous dominant (AA)
- frequency homozygous recessive (aa)
- frequency heterozygous (Aa)
Microevolution
change of allelic frequency in a population in a short period of time
Speciation and macroevolution
Evolution over a long period of time. Microevolution over time may lead to formation of new species (speciation) from a common ancestor.
p
frequency of dominant allele in the gene pool
q
frequency of the recessive allele
genotypic structure of the population
p2 + 2pq + q2 = 1
Frequency
how often something occurs
Phenotypic frequency
- frequency of dominant phenotype
- frequency of recessive phenotype
Hardy Weinberg Equilibrium
As long as certain conditions are met, allele frequencies will remain constant and population will not evolve. This is important as it serves as a control. We can find out how strongly different factors affect rate of evolution.
HW Conditions
- Very large popultaion- sampling errors could change population if it were small
- No immigration or emmigration- alleles can not enter or leave
- No mutations- alleles do not change spontaneously
- No Natural Selection- no allele is favoured relative to any other allele
- Random mating- individuals have equal chances of mating with eachother, so alleles get fully mixed
p2
frequency of homozygous dominant indivuals
2pq
frequency of heterozygous individuals
q2
frequency of homozygous recessive individuals
Bottleneck Effect
population contracts to a significantly smaller size over a short period of time due to some
random environmental event
Violation #1
Small Populations
Genetic Drift (2nd most powerful)
- random chance events that results from smapling errors in small populations
- random events have large impact on small pop. vice versa
- results a change in evolution but is Non-Adaptive (doesn’t help or benefit in their environment)
Founder Effect
special case of a population bottleneck, occurring when a small group in a population splinters off from the
original population and forms a new one
Violation #2
Mutations
- to cause changes in the gene pool by creating new alleles
- changes allele frequency but not rapid enough to cause change in population
- NON ADAPTIVE
Violation #3
Immigration/Emmigration
Gene Flow (result of immigration)
- movement or changes of allele frequencies based on the fact that members can leave/enter
- tend to make pop more homogenous
- can change allele structre, can cause evolution
- NON ADAPTIVE
Violation #4
Random Mating
Non random mating (not same as unequal mating)
- does not change allelic frequencies, changes distributio of those alleles in genotypes
Assortive Mating- like choses like, higher homozygosity
Dissortive Mating- opposites attract, increased heterozygosity
Directional Selection
- fitness is lower at arrow, Darwinian NS
Stabilizing Selection
- both extremes are being selected against
- heterozygous advantage, prevents change
Diruptive Selection
- sides have highest fitness
- can cause speciation if both ends become so different
- favours most extreme phenotype
Sexual selection
- ties into NS and non-random mating
- drives evolution of most extreme characteristics in population
- competition between 1 gender competeing for other gender
Handicap Principal
- sexual selection
- males are using elaborate displays to demonstrate the high quality genes they have, drive by testosterone
Sexy son hypothesis
- sexual selection
- males could false advertise genes, as long as females are willing to mate, characteristics will stay in population
Speciation
- process of formation of species
- process by which an existing population gives rise to a new population that no longer has the potential to recombine with it as a single gene pool
Biological Species Concepet
- Ernst Mayer
one or more populations of individuals that can interbreed under natural conditions and produce fertile offspring that are reproductively isolated from other such populations.
Reproductive Isolation
prezygotic, postzygotic
diff species, same area, can not breed together
Postzygotic Isolation
hybrids formed, reduced fitness
Prezygotic
prevents formation of hybrid in first place
Gametic Isolation
The sperm and egg cannot unite to form a zygote
-protein or signal incompatibilities
Mechanical isolation
some sort of physical barrer through the delivery of sperm to egg, physically can’t mate
Temporal Isolation
- Human fertility is year long
- certain times of year species will breed, some don’t mate at same time
Behavioural Isolation
certain traits or characterisice that they do to advertise themselves to opposite gender of species, not all signals are recognized by all populations
Habitat (ecological) Isolation
of something live in water and something lives on land, they will not get oppurtunities to mate
Allopatric Speciation
Speciation requires reproductive isolation.
The standard model of speciation is the allopatric model
(allo = other, patria = land) in which geographic separation is prerequisite to evolutionary change.
Sympatric (sym = same) speciation, when new species evolve from a single ancestral species while inhabiting the same geographic region.
Allopatric Model
The standard model of speciation assumes that a gene pool must be physically split before the two sub-populations can diverge enough to speciate.
