Lec 6 + 7

Transcription factors

bind promoters and can act as activators or repressors of transcription, activity is controlled (directly or indirectly) by receptors

Activator

Positive regulator (needed for transcription)

Repressor

Negative regulator (prevents transcription)

Signal transduction systems

complex and involve multiple interacting proteins and diverse signaling molecules

enhancer/silencer sites

transcription factors(activators and repressors) that bind distant

identity” of organs or parts of the body

determined by Patterns of transcription factor expression

histon proteins

wrapped in groups of 8 by DNA into nucleosomes, organizes DNA compacts into chromatin

transcriptionally silenced

Genes in tightly packed chromatin, inaccessible to RNA polymerase

symmetry breaking

differentiate by sending signals back and forth

mitosis (or prokaryotic cell division)

daughter cells get the same genes: they are clones

Clonal inheritance

all individuals have the same vulnerabilities, beneficial mutations can’t be separated from deleterious mutations

Transformation

bacteria recombine gene variants that arose in different clonal lineages (like with the mice)

sexual life cycles

ensure recombination is regular and efficient

Meiosis

halves the number of chromosomes from each parent(n=23) and allow for genetic mixing via fertilization, yields four daughter cells, each with one chromosome from each homologous pair.

Chromosomes

Exist in homologous pairs, both present in diploid cells and only one in haploid cells

chromatids

After S-phase each chromosome contains two identical DNA copies, exact copies (have the same alleles of every gene)

Haploid

Sister chromatids separate so that each daughter cell gets one copy of each chromosome(1 chromosome, 2 chromatids)

Diploids

Both homologous chromosome have two chromatids (2 chromosomes, 4 chromatid)

homologous pairs

not identical (can have different alleles)

Diploid Zygote

Haploid(egg) + Haploid(sperm), may have different genotypes than both parents(chromosomes from parents randomly distributed)

Chiasma

Point where non sister chromotids crossover when recombining

Bivalent (meiosis I)

when Chiasma randomly from form, 2 homologous chromosomes(2 pair) are connected and non sister chromotids(4) combine