Cell division and inheritance Flashcards
What are the stages of the cell cycle?
• G1: cellular contents excluding chromosomes replicated
• G0: cell cycle arrest- resting phase or apoptosis
• S: dna replication, each of 46 chromosomes duplicated
• G2: cell double checks duplicated chromosomes for error and changes if needed
• Mitosis
• Cytokinesis
What are the stages of mitosis?
• prophase
• prometaphase
• metaphase
• anaphase
• telophase
• cytokinesis (controversial)
What happens in prophase?
• Duplicated chromosomes condense and sister chromatids join at centromere
• DNA binding proteins including cohesin and condensin
• cohesin forms rings that hold sister chromatids together
• condensin forms rings that coil the chromosomes into highly compact forms
• the mitotic spindle begins to develop and centrosomes move towards opposite poles, microtubules assemble
What happens in prometaphase?
• Nuclear membrane breaks down, forms multiple vesicles
• Spindle microtubules can now directly access genetic material
• Spindle microtubules attach to chromatids (kinetochore of each chromosome)
What happens in metaphase?
• Microtubules shuffle chromosomes to form metaphase plate- to line them up
• Once tension becomes balanced chromosomes stop moving (spindle completed)
What are the three groups of spindle microtubules and their role?
• Kinetochore microtubule: attach the chromosomes to the spindle pole
• Interpolar microtubule: extend from the spindle pole across the equator, almost to opposite spindle pole
• Astral microtubule: extend from spindle pole to cell membrane
What happens during anaphase?
• enzymatic breakdown of cohesin separates chromatids, changes in microtubule length exert pull on chromosomes
1) anaphase A: the kinetochore microtubules shorter and pull chromosomes toward spindle poles
2) anaphase B: astral microtubule anchored to cell membrane pull poles further apart, interpolar microtubules slide past each other and increases pull on chromosomes more
What happens during telophase?
• Chromosomes arrive at the cell poles
- vesicles containing fragments of original nuclear membrane form around two new nuclei
• the spindle microtubules depolymerise
How does meiosis differ from mitosis?
• two divisions
- meiosis 1- reduction division
- meiosis 2- equatorial division
• similar stages to mitosis however:
- dna replication occurs twice
- nuclear division occurs twice
• results in 4 haploid (n) daughter cells- each contain half the nunver of chromosomes of the diploid (2n) parent cell
• occurs in germline cells only
What happens in prophase 1 in meiosis
• Homologous chromosomes pair up
• Synapsis occurs (crossing over), genetic material swaps at chiasmata increasing variation
What happens in metaphase 1 and anaphase 1 in meiosis?
(same as mitosis but with following differences:)
• homologous pairs line up on the metaphase plate
• the homologous pairs split, homologous chromosomes are separated to the poles at anaphase, not individual chomatids
What happens during telophase 1 in meiosis?
similar to mitosis however cells may not fully separate (species dependent)
• DNA does not decondense prior to entering meiosis 2
• no DNA replication
What happens during prophase 2 in meiosis?
• chromosomes condense
• new set of spindle fibres form at right angles to og chromosomes begin moving toward equator of cell
• nuclear envelop disintegrates
What happens during metaphase 2, anaphase 2 and telophase 2 in meiosis?
progress as before but result in 4 genetically non identical haploid daughter cells
what happens during cytokinesis?
cytoplasm divides
Define unit heritance
Hereditary characters are determined by indivisible units of information (alleles of genes)
define dominance
alleles occur in pairs in each individual but the effects of one allele may be masked by those of a dominant partner allele
define segregation
during formation of gametes, the members of each pair of alleles separate so that each gamete carries only one allele of each pair. alleles pairs are restored at fertilisation
define independent assortment
different genes control phenotypic characters and the alleles of different genes re assort independently from
one another
What is the ratio monohybrid cross? (BB x bb)
1- all offspring have Bb so same characteristic
What is the ratio monohybrid cross?
(Bb x Bb)
3:1
what is the ratio in dihybrid cross?
(TtBb x TtBb)
9:3:3:1
What happens in x linked dominant inheritance? X^A
• If only mother carries: Half of all children affected regardless of gender
• If only father carries: all daughters affected, all sons unaffected
• If both carries: all daughters affected, 50% sons unaffected
What happens in x linked recessive inheritance ? X^a
• only mother: 50% females carrier, 50% females unaffected, 50% males affected
• only father: all females carriers, all males unaffected
• both: 50% females carriers, 50% males affected
Who is affected by mitochondrial inheritance?
Only passed down through mothers.
Affected fathers do not pass to offspring
What is complete dominance between alleles
Allele completely masks recessive allele in heterozygote
what is incomplete/partial dominance in alleles?
Heterozygote phenotype is intermediate between that of two homozygous (eg sickle cell)
what is co dominance between alleles?
neither allele is recessive and phenotypes of both alleles are expressed eg blood groups
What is penetrance?
the proportion of individuals in a population who carry a specific gene and express the related trait
the relationship between a genotype and phenotype
what is expressivity?
the degree to which train expression differs among individuals, unlike penetrance, expressivity describes individual variability, not statistical variability among a population of genotypes
