Genetics flash card
Define: Variation
All of the differences found in a population due to the differences in individuals DNA/genes/alleles
Define: Genetic Boidiversity
the number and range of types of living things seen within a community or ecosystem
Define: Species
A group of organisms that are able to breed together and produce viable and fertile offspring
Define: Population
Members of the same species living in the same area at the same time
Define: Allele frequencey
The proportion of a particular allele in a gene pool relative to other alleles of the same gene
Define: Gene pool
All the genes and alleles present in a sexually reproducing POPULATION that can be passed onto the next generation
Define: Mutation
A sudden change in the DNA of an organism, only source of new alleles
What do mutations do and how does it effect the gene pool?
- It create new alleles that are able to be inherited and then enter the population and to be passed on
- creates more genetic variation within a population and increases the size of the gene pool
What do mutations do and what is the effect on organisms?
- Mutations cause new proteins to be created as new alleles are created by the change in the base sequence
- mutations can be beneficial (eg. longer hair in cold climate), neutral (eye colour) or detrimental (sickle’s cell anemia)
How can mutations become hereditary?
Mutations can only become hereditaryif the mutation is on the gamete and only if it is fertilised
How do mutations enter the gene pool?
- Mutations enter the gene pool if they mutate the DNA on the reproductive cells (male=sperm, females=eggs)
- immigration of new alleles from new organisms
How do mutations happen?
They can occur in two ways, either spontaneously (happens for no reason) or induced (caused by mutagens such as radiation, chemicals or sudden temp changes)
What are Karyotypes/Karyograms?
A picture of the chromosomes lined up from pair 1 (the biggest) to pair 22 (the smallest) plus the sex chromosomes
What is the purpose of meiosis?
To produce gametes for sexual reproduction and create variation
How does meiosis work?
It involves 10 steps: Early Prophase 1 Mid Prophase 1 Late Prophase 1 Metaphase 1 Anaphase 1 Telophase 1 Prophase 2 Metaphase 2 Anaphase 2 Telophase 2
What is Early Prophase 1?
chromosomes unscramble themselves, shortened and thickened and duplicate themselves, they then join at the centromere to form sister chromatids creating 92 sister chromosomes
What is Mid prophase 1?
homologous chromosomes (chromosomes that are the same type, ie same length, alleles on the same locus etc.) pair up forming tetrads (A set of 2 homologous chromosomes
What is Late prophase 1?
Spindle fibers and heads begin to form and the homologous pair of chromosomes create a chiasma where genetic material is swapped between non-sister chromatids - this is where crossing over occurs which causes a huge increases in genetic variation as this creates parental combinations and recombinations, this creates genetic variation as it creates recombinants which are unique chromatids
What is Metaphase 1?
the homologous chromosomes line up along the equator randomally and independently orient themselves, independent assortment occurs here which is a huge source of genetic variation as there are a huge number of combinations that can be created once the spindle fibers pull the homologus chromosomes apart.
What is Anaphase 1?
The spindle fibers pull apart the tetrads taking to each side of the nuclei 46 chromosomes (23 homologous pairs)
What is Telophase 1?
A new nuclei forms around each of the 23 homologous pairs of chromosomes forming 2 new unique nuclei with 23 unique homologous pairs in each
What is Prophase 2?
Spindle fibers and heads form, there is no duplication in meiosis 2
What is Metaphase 2?
The 23 homologous pairs of chromosomes independently line up along the equator again randomly, again this is independent assortment so massive genetic variation as there is a massive number of different combinations, spindle fibers attach themselves to chromatids
What is anaphase 2?
Spindle fibers pull apart the chromosomes to form chromatids
What is Telophase 2?
New Nuclei forms around the four sets of 23 chromatids creating a haploid cell, these are now gametes
Define: Segregation
The separation of pairs of of alleles during the formation of reproductive cells so that the gametes contain only one allele instead of the normal two. Segregation is the result of the separating homologous chromosomes during anaphase 2
Define: Independent assortment
When the homologous chromosomes line up along the equator RANDOMALLY and INDEPENDANTLYA of each other ceating new combinations of chromosomes
Define: Crossover/Recombination
Exchange of genetic material between inner chromatids of tetrads, swap over genetic material to form new combinations of the same chromosome l~l x ^l~l^ => ^l~l* ^l~l* ~=centromere
Define: Chiasma
The point where the inner chromatids of a tetrad break off and rejoin thereby exchanging genetic material during Crossover/Recombination
Define: Homologous chromosomes
A pair of chromosomes (one from each parent) that have the same genes at the same locus but may have have different versions of the genes (different alleles)
Define: Chromatid
A single strand of a homologous chromosome not joined to another chromatid by a centromere that only has one out of the pair of alleles
Define: Centromere
the point where 2 chromosomes are joined together to form a homologous pair of chromosomes
Define: Allele
An alternate form of a gene ie eye colour blue, green etc.
Define: Locus
The position of an gene on a chromosome
Define: Haploid
Half the number of chromosomes in a cell (23 chromatids ie gametes) also known as n=23
Define: Tetrad
A pair of homologous chromosomes that have paired up and are lining up along the equator ie Metaphase 1 —> ^l~l^ : l~l l=chromosome ^=allele A *=allele a :=equator ~=centromere
Define: Autosome/Autosomal
non sex chromosomes, humans have 44 autosomal chromosomes (22 pairs)
Define: Sex Chromosomes
The X and Y chromosomes that determine gender, for humans XX = female, XY= male
Define: Somatic cell
Body cells other than the sex cells, are diploid
Define: Incomplete Dominance
When two recessive alleles are expressed together to create a blend of the 2 genotypes
Define: Complete Dominance
When one allele is expressed over another, eg in Aa, A will be expressed fully over a
Define: Co-Dominance
When two dominant alleles are expressed in equal quantity, ie roan cows, when a pure bred white cow mates with a pure bred red cow, genotype WR, the phenotype is a cow that is 50% red and 50% white
Define: Lethal Alleles
Genes that have a a lethal effect when they exist as one of the homozygous genotypes
Define: Dihybrid Inheritance
Crossing over of 2 non linked genes at the same time ie AaBb
Define: Multiple alleles
Genes with 3 or more possible alleles
Define: Geneome
All of the genes of an indivisual person
Define: Genotype
A description of a persons alleles, ie AaBb etc.
Define: Phenotype
The physical expression of the genotype
Define: Homozygous
When the allele at a give locus are the same, ie ‘AA’ (can be recessive or dominant)
Define: Hetrozygous
When the alleles at a give locus are not the same ie ‘Aa’
Define: F1/F2 generation
The first and second generation of offsprings, ie Parents –> F1 generations –> F2 generation –> etc.
Define: Punnet square
A box used to do genetic cross, ie ‘Aa’ x ‘Aa’
Define: Dominant allele
The allele that is always expressed in the genotype (only 1 copy needed)
Define: Recessive allele
The allele that is only expressed if homozygous, dominant allele must be absent
Define: Test/back cross
Testing an unknown genotype showing dominant phenotypes by crossing organism with known homozygous recessive organism, from this we can determine the unknown genotype by looking at the ratios of offsprings and making a logical guess
Define: Evolution
Changes in the allele frequency in a POPULATION over many generations
Define: Natural selection
the process where organisms with more benefical alleles are more likely to survive in a given envrionment and are therefore more likley to pass on these successful alleles ontop their offspring
Define: Migration
Movement of indivisuals in or out of a population
Define: Genetic Drift
RANDOM changes in the allele frequency DUE TO CHANCE, such as extreme natural events,
Define: Founders effect
- Change in allele frequencies when a new population arises from a few colonising individuals whose allele frequencies are NOT representative of original population
- New population is geographically isolated from original population so there is no gene flow
- different environmental factors which cause natural selection to favour organisms with different phenotypes which can lead to speciation
Define: Bottleneck effect
- Recovery of a population after a catastrophic event where only a few organisms survive
- These organisms build up population again, however alleles may have been lost (few remaining individuals are highly unlikely to have representative allele frequency of old population), recovered population will have reduced GENETIC DIVERSITY
Define: Non random mating/Artifical selection
When every oraganism doesn’t have an equal chance of mating (fruit flies won’t mate with white eye flies) or they are artifically bred (dogs, cats etc.)
Define: Disruptive selection
-When individuals with variationson either side of the mean are selected for while individuals with variationsclosest to the mean are selected against -This causes a population to develop 2 mean peaks going in different directions, over time this leads to speciation
Define: Directional Selection
When a variation of a population on either side of the mean is more selected for while the other extreme side is selected against causing the mean of the population to move, ie peppered moths, during industrial revolution the moths that survived were darker so the darker the moth, the more likely it was to survive
Define: Stabilising selection
When variation of a population on either side of the mean is selected against, this causes a very narrow and high mean with very little variation, ie Coelacanth fish have remained unchanged for millions of years as they have a very stabilising selecting
Define: Autosome
Non sex-linked, not inherited
What is meiosis?
Type of cell division producing 4 daughter cells each genetically different and with the haploid number of chromosomes
Define: pedigree
An organism that is homozygous for all alleles
Define: Linked genes
Genes that are located on the same chromosome
Define: Dihybrid cross
When 2 different characteristics controlled by 2 NON LINKED genes are being crossed at the same time
Define: Monohybrid cross
When 1 characteristic controlled by a gene or linked genes are being crossed over at the same time
Describe a dihybrid cross
Phenotype ratio=9:3:3:1
How do you cross linked genes?
You do a monohybrid cross but instead of just 1 genotype, you cross both
How does the distance between genes on a chromosome affect it’s chance of recombination?
The further apart the genes are the more likely they will be split apart due to recombination as there is a higher chance that the chiasma will form between them
What is the phenotype ratio of a cross between an AaBb x aabb if the genes are on the same chromosome?
1:1 (AaBb and aabb), this is because these genes are linked, however this ratio may not be exact and heterozygous genotypes may be produced (Aabb or aaBb) in very small numbers due to random formation of chiasma during recombination causing the alleles to form recombinants
What are the types of inheritance?
Co-dominance Complete dominance Incomplete dominance Lethal allele Multiple alleles
What is complete dominance?
It is when a dominant allele is expressed over a recessive allele, dominant allele is expressed as either homozygous dominant or heterozygous, a recessive allele can only be expressed as homozygous recessive ie eye colour where if a brown eyed person (BB) is crossed with a blue eyed person (bb) their offspring will be heterozygous and all offspring will have brown eyes (Bb)
What is codominance?
It is when 2 dominant alleles are crossed and they are equally expressed in the organism
What is incomplete dominance?
It is when 2 recessive alleles are in a genotype and neither is expressed fully, instead they find a mid way point, ie snap dragons, white flower crossed with red flower produces pink flower as red and white alleles are recessive and pink is midway point
What process of meiosis produces the most genetic variation? Why?
Independent assortment, this is because there are 2^23 different combinations that the homologous chromosomes can make when lining up on the equator, this process occurs twice. Also, unlike recombination, it affects both chromatids in the homologous chromosomes which means that more genetic material is being shuffled creating MORE VARIATION, recombination only swaps genetic material between the inside chromatids and only occurs once
What is sexual reproduction?
It is the process of an egg and sperm cell fusing, each containing genetic material from either the mother or father. The fusion of these gametes produces a genetically different offspring from the mother and father
Define Centromere
The point where 2 chromatids join to make a homologous pair
Define Chromosome
A structure in the nucleus made up of DNA which holds the genetic information of an organism
Define Diploid
Full or complete number of chromosomes (somatic cells)
Define Gamete
A sex cell (egg or sperm), it contains the haploid number of chromosomes
Define Gene
A section of DNA on a chromosome that codes for a protein/characteristic
Define geneome
all of an organisms genes
Define adaptation
A feature of an organism that helps it survive in its environment, can be structural, physiological or behaivoural
Define gene flow
The introduction of genes/alleles from one population to the gene pool of another population (immigration and emmigration)
Define Environmental factors
Factors which select for or aganist particular phenotypes in the process of natural selection
Define sexual selection
Selection based on choice of mating partners, leads to evolutionary change if choices are based on differences in INHERITED characteristics
Define Sex linked genes
Genes found on the sex chromosomes
What are the types of inheritance?
Complete dominance, Incomplete dominance, Co-dominance, Lethal alleles, Multiple alleles
