Genetics - 3.2 Chromosomes Flashcards
Understandings:
- Prokaryotes have one chromosome consisting of a circular DNA molecule
- Some prokaryotes also have plasmids but eukaryotes do not
- Eukaryote chromosomes are linear DNA molecules associated with histone proteins
- In a eukaryote species there are different chromosomes that carry different genes
- Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes
- Diploid nuclei have pairs of homologous chromosomes
- Haploid nuclei have one chromosome of each pair
- The number of chromosomes is a characteristic feature of members of a species
- A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length
- Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex
Prokaryotic genetics
- no nucleus = genetic material in cytoplasm in nucleoid (consists of a single chromosome consisting of a circular DNA molecule (genophore) (DNA = ‘naked’ = not associated with proteins for additional packaging))
- plasmids = small, circular DNA molecules containing only a few genes and can self-replicate = ideal vectors for gene manipulation in labs (present in some pro. cells, NOT in eukaryotic cells (naturally)
–> bacteria cells = exchange plasmids via sex pili = bacterial conjugation -> this exchange of genetic material = allows bacteria to evolve new features within a generation
Eukaryote genetics:
- genetic material in these cells = multiple linear molecules of DNA associated with histone proteins -> packaging of this = greatly compacted structure/efficient storage
- more into on organisation on bioninja!
Identifying genes
Eukaryotic chromosomes (= carry specific gene (position of such on chromosome = locus)) = linear molecules of DNA are compacted during cell divisions - has a constriction point = centromere (breaks chromosome into 2 parts (long = Q arm, short = P arm))
Eukaryotic = species = have lots of chromosomes (all different in size and position of centromere)
Autosome vs Heterosome
Female = XX
Male = XY
sex chromosomes = homologous in women but not in men
male sperm with X = embryo growing = girl
male sperm with Y = embryo growing = boy
-> remaining chromosomes in organism = AUTOSOMES (do not determine sex)
chromosome size
(all info to be found on bioninja)
Autoradiography = John Cairns
Chromosome number
(refer to pg 6 of booklet)
- characteristic feature of members of a particular specific = likely to be incapable to interbreeding - offspring of interbreeding = infertile
Genome size
genome = haploid set of chromosomes in a gamete/microorganism/in each cell of a multicellular organism / the whole of the genetic info of an organism
- varies greatly between organisms and is not a valid indicator of genetic complexity
General rules:
1. viruses and bacteria tend to have very small genomes
2. prokaryotes typically have smaller genomes than eukaryotes
3 sizes of plant genomes can differ due to the capacity for plant species to self-fertilise and become polyploid
Homologous chromosomes (chromatids, centromere)
= maternal/parental chromosome paries
- some structural features
- same genes at the loci positions (alleles may differ)
- must separate in gametes (via meiosis) prior to reproduction = to prevent chromosome # continually doubling each generation
“chromosomes usually appear as single strands but just before cell division DNA replicates - the double strand appearance consisting of two sister CHROMATIDS connected at the CENTROEMRE”
Sexually reproducing organisms = inherit genetic sequences from both patients = ie organisms - 2x copies of each chromosomes
Diploid and Haploid
Diploid = total number of homologous chromosomes (ie 2 sets of chromosomes (in humans = 46)
= given the symbol 2n
Haploid = number of chromosomes in a single set (sex cells (gametes) = with 1/2 # of chromosomes = hapoild (ie, in humans = 23))
= symbol = n
= WHEN HAPLOID GAMES FUSE = DIPLOID CELL (ZYGOTE) = NEW ORGANISM
Compare and contrast:
Diploid:
1. 2 gene copies (alleles) for each trait
2. all somatic (body) cells in organism = diploid (new diploid via mitosis)
3. = mainly in animals (+ most plants)
Haploid:
1. single gene copy (alleles) for each trait
2. all SEX cells (gametes) = haploid = derived from diploid cells via meiosis
3. = also found in bacteria and fungi (expect when fungi is reproducing)
Karyotype (and karyogram)
Karyotype = full complement of chromosomes in an organism (# and types of chromosomes in a eukaryotic cell)
Determined via:
1) harvesting cells
2) chemically inducing cell division then arresting mitosis whole chromosomes are condensed
3) stage during mitosis is halted will determine whether chromosomes appear w/ sister chromatids or not
Karyogram = photograph of karyotype (karyotype is isolated and stained homologous pairs are arranged according to their size and structure)
Uses for karyotyping:
- prenatal diagnosis of chromosome (eg downs syndrome)
- determine the gender of an unborn child
Steps in PREPARING A KARYOTYPE:
- sample of cells is taken
- white blood cells are removed
- cells undergo mitosis and stop at metaphase (induced)
- the chromosomes (now visible) are stained and spread out on a slide and photographed
- the photograph is cut up and the chromosomes are arranged in homologous pairs according to size, shape, banding pattern and position of centromere
