week 21 Flashcards
what are the stages of mitosis
Prophase, Prometaphase, Metaphase, Anaphase and Telophase
what are somatic cells
any body cells that do not produce gametes (egg/sperm)
what are germ cells
a diploid reproductive cell that gives rise to a gamete
whats the difference between diploid and haploid
diploid= 2 sets of chromosomes
haploid= 1set of chromosomes
what is the locus
the particular location on a particular chromosome where genes are located
what are histones
proteins, which help with the folding and structural support of chromosomes. DNA is wrapped around histones
how does methylation affect DNA
affects how tightly coiled the DNA is and switches genes off
how many chromosomes do humans have
23
what are autosomes
the 22 pairs of chromosomes that do not determine sex
what is the human karyotype
an ordered display of the pairs of chromosomes in a cell
what is epigenetics
the study of the chemical modification of specific genes or gene-associated proteins of an organism
when does meiosis begin
after S phase in cell cycle
what happens in meiosis I
homologous chromosomes separate. 2 haploid daughter cells are formed- reductional division.
what happens in meiosis II
sister chromatids separate. 4 haploid daughter cells are formed. each with a haploid set of unreplicated chromosomes.
whats the difference between mitosis and meiosis in terms of chromosome sets
mitosis conserves number of chromosome sets while meiosis reduces the number of chromosome sets (from diploid to haploid).
whats unique about meiosis
at the metaphase plate there are paired homologous chromosomes (tetrads) instead of individual replicated chromosomes. homologous chromosomes separate instead of sister chromatids. synapsis and crossing over- homologous chromosomes physically connect and exchange genetic info.
what is the chiasma
the crossover point on homologous chromosomes which join to form an X shape
what is genetics the study of
heredity and variation
are identical twins the same
monozygotic (identical) twins are genetically identical and morphologically similar
what is a mutation
spontaneous changes in genetic information
what are the sources of variation
sexual reproduction and mutations
what is anagenesis
micro evolution, describing gradual change within a single lineage over time
what is cladogenesis
macro evolution, describes the branching of evolutionary lineages where an ancestor can give rise to two or more descent species.
what is a lineage
a sequence of species, each of which is considered to have evolved from its predecessor
what is autopolyploidy
polyploidy within a single species, where multiple copies of the same genome are present
what is allopolyploidy
polyploidy resulting from the combination of chromosomes from different species, often from hybridisation
define polyploidy
a condition where and organism or a cell has more than two complete sets of chromosomes
define allopatry/ allopatric speciation
Species divergence happens due to geographically isolated areas. the same event can affect many lineages at once
define sympatry/ sympatric speciation
Speciation occurs in the same area, genetic isolation without a geographical barrier. caused by sexual selection.
what is genetic isolation
when populations diverge to the point where they can no longer interbreed
define geogra[hic differentiation
different forms of the same species in different geographical areas
what are the types of selection
directional- when one extreme phenotype is favoured
diversifying/ disruptive- two extreme phenotypes are favoured, while the average is less succesful
stabilising- when the average phenotype is favoured
what is the S phase of the cell cycle
the period where the cell replicates its DNA
when does mitosis occur
before cytokinesis, after G2 in the cell cycle
what is the composition of chromosomes in diploid cells
46 chromosomes in total; 23 from each parent
what is meiosis
cell division producing gametes each possessing the haploid number of chromosomes and haploid content of DNA. allows reproduction where offspring have half genetic info from each parent
how many daughter cells are produced by meiosis
4 haploid daughter cells.
what are tetrads
two pairs of homologous chromosomes, resulting in 4 chromatids in meiosis
what is independent assortment of chromosomes
each homologous pair can line up independently during metaphase I, producing genetic variation
how does the chiasmata crossing over point produce variation
sister chromatids break and rejoin
what does natural selection result in
accumulation of genetic variations favoured by the environment
