Intro to medical genetics Flashcards
Genome, DNA
an organisms total DNA content. DNA=contains the genetic information needed to specify all aspects of embryogenesis, development, growth, metabolism, and reproduction-what makes us functional
diploid
organism that carries two genome copies. 2n=46
haploid
any cell that has 1n=23. Germ cells or gametes carry a single copy of the genome
human genome contained w/in nucleus:
22 autosomes and 2 sex chromosomes, x and y. additionally, DNA is also contained in the mitochondria.
Genes
sequences of base pairs that encode info for proteins, found on chromosomes. Range from <100 to several million bps.
exon
coding sequence
intron
non-coding sequence b/w two exons . . . regulatory element
Regulatory elements
HRE-hormone responsive elements
Promoters-always at 5’ end of gene, followed by introns and exons.
Enhancers
General features of a chromosome: Centromere
Centromere:repetetive sequences. Primary constriction on a chromosome-sister chromatids are held together here and kinetochore is formed. Attaches to mitotic spindle so chromosomes properly aligned during mitosis and meiosis and required for proper segregation of chromosomes.
General features of a chromosome: Telomere
the end of each chromosome arm. human telomeres end with tandem copies of TTAGGG, which is required for the proper replication of chromosome ends. Specialized Repetetive seqs of DNA-ensure integrity of chromosome during cell division.
General features of a chromosome: p and q arm
p=”petite” or short arm, q= long arm
Locus
location in the genome of a gene or genetic marker
alleles
alternative forms of a gene or a genetic marker
heterozygous
2 diff alleles at a locus (a,b)
homozygous
2 identical alleles at a locus (a,a)
haplotype
series of alleles on a single chromosome-likelihood to inherit one or the other haplotype from a parent is 50%. All alleles present on a single chromosome are referred to as haplotype
germline
cells that develop into gametes
somatic cells
all cells that contribute to one’s body
autosomes
22 pairs of chromosomes that are alike in males and females.
sex chromosomes
2 X in females; X,Y in males
homologous chromosomes/homologues
members of a pair of chromosomes; carry matching genetic information-they have the same genes in the same sequence; but may have different alleles
alleles
identical or slightly different forms of the same gene. alternate forms of genes, multiple varieties coding for similar proteins
Phenotype
Gene expression:observable characteristics:
physical
biochemical
disease status
Cell cycle: how many chromosomes does a cell have entering mitosis?
4n=92
Cell cycle
G1: Growth phase, immediately after mitosis; each cell has 1 diploid copy of genome.
G0: Arrested, non-dividing phase, neurons, rbc’s; liver cells-but not permanent
S: Synthesis, DNA content has doubled; each cell now contains 2 copies of the diploid genome. 4n=92
G2: Growth, ribonucleic acids, proteins are produced and cell enlarges->dbl mass before mitosis.
Interphase
G1, S, G2 phases together constitute interphase
Mitosis
occurs during cell division of somatic cells.
Diploid cell generates identical diploid cell.
No recombination (normally)
Stages of Mitosis: Prophase
initiates mitosis, condensation of chromosomes and formation of mitotic spindle. Centrosomes,microtubule organizing centers, form foci from which microtubules radiate.
Stages of Mitosis: Prometaphase
nuclear memb breaks up; chromosomes disperse and attach via kinetochores to microtubules of mitotic spindle. Congression: chromes move towards mid-point b/w spindle poles.
Stages of Mitosis: Metaphase
chromosomes reach max condensation; alligned at equatorial plane of cell.
Stages of Mitosis: Anaphase
Chromes separate at centromere->sister chromatids become independent daughter chromosomes, moving to opposite poles of the cell.
Stages of Mitosis: Telophase
Chromes decondense, nuclear membrane reforms around each daughter nuclei and gradually resumes it’s interphase appearance.
Stages of Mitosis: Cytokinesis
Cytoplasm cleaves, completing the process of cell division-> 2 complete daughter cells containing all genetic info of original cell.
Meiosis
Occurs during gamete formation; a diploid progenitor cell generates four haploid gametes; 1 round of DNA synthesis followed by 2 rounds of chromosome segregation and cell division. Recombination frequent; has 2 phases: meiosis I, II are two successive meiotic divisions.
Recombination
Exchange of genetic material b/w homologous chromosomes. must be b/w paired chromosomes, any other exchange can lead to mutation
Meiosis I
aka “reduction division”-chromosome # is halved (2n->n) through pairing of the homologues in prophase followed by segregation to diff cells at anaphase. Recombination/crossing over occurs here
Meiosis II
1 chromatid from each chromosome passes to daughter cell.
Prophase I
chromes begin to condense; homologues pair and crossing over occurs->recombinant chromes. Chromes continually condense and become shorter and thicker during all 5 phases of prophase I
Prophase I: Leptotene
chromes (already replicated during preceding S phase) condense; closely aligned-> indistinguishable. Form pairs of chromosomes(bivalents) consisting of 4 chromatids(tetrads)
Prophase I: Pachytene
crossing over b/w pairs of homologous chromes to form chiasmata-point holding together 2 bivalents/tetrads which is the location of crossovers.
Chiasmata
actual location of crossovers. 2 homologues of each bivalent are held together at this point.
Prophase I: Diplotene
homologous chromes start to separate but remain attached by chiasmata. After recombination; synaptonemal complex begins to break down.
Prophase I: Diakinesis
homologous chromosomes continue to separate, the chiasmata move to the ends of the chromes. Chromes meet max condensation.—> by telophase I the 2 haploid sets of chromosomes have normally grouped at opposite poles and the cell divides into 2 haploid daughter cells and enters meiotic interphase and meiosis II soon follows. *No S phase b/w the 1st and 2nd meiotic divisions.
Meiosis II
n=23 chromosomes from reduction division. The 2 daughter cells from meiosis I divide to form 4 haploid cells, each containing 23 chromosomes. Similar to mitosis
Meiosis II: Prophase II
chromosomes begin to condense and nuclear membrane dissolves, spindle fibers form.
Meiosis II: Metaphase II
spindle fibers attach to chromosomes and they line up in center of cell.
Meiosis II: Anaphase II
Centromeres divide and sister chromatids move to opposite ends of cell as spindle fibers shorten
Meiosis II: Telophase II
Chromosomes reach opposite ends, nuclear membrane forms–>cytokinesis
Spermatogenesis
Takes place after puberty in testes. Spermatozoa are formed in the seminiferous tubules after sexual maturity.
Oogenesis
Begins during prenatal development.
-Diplotene arrest-oogenesis is arrested, incomplete–> will be completed in puberty under hormonal stimulation; primary oocyte–> secondary oocyte.
Metaphase arrest-2nd arrest during puberty at metaphase; will only be completed if there is fertilization. *chromosome abns more common in aging mothers b/c cells are arrested longer in diplotene.
