Cell Division: Variations, regulation, Cancer Flashcards
how many chromosomes do humans have
46, 23 pairs
how many chromosomes does each parent contribute at fertilization
23 (haploid)
what happens in prophase
the chromosomes condense and become visible
what happens in pro metaphase
the spines attach to the centromere
what happens in metaphase
the chromosomes line up in the middle of the cell
what happens in anaphase
the centromeres split and the chromosomes move to opposite poles
what happens in telophase
nuclear envelope re-forms and chromosomes decondense
how does a contractile ring work
in animals, a contractile ring of actin pinches cell in two
in plants, a new cell wall is synthesized
what is meiotic cell division
reduces the number of chromosomes by Hal to produce haploid gametes or sports that have one copy of each chromosome
describe the two meiotic cell divisions
meiosis consists of two successive cell divisions. First is reductional (chromosomal number is halved), second is equational (chromosomal number stays the same)
describe meiosis 1
homologous chromosomes pair and exchange genetic material. centromeres do not split and sister chromatids do not separate.
describe meiosis 2
similar to mitosis: chromosomes align on the metaphase plate, centromeres split, sister chromatids separate
the similarity between meiosis 2 and mitosis suggests that
meiosis is evolved from mitosis
what does male meiotic cell division result in
four functional sperm cells
what does female meiotic cell division result in
one functional egg, three polar bodies
what are cyclins
proteins that increase and decrease during cell cycle.
they form complexes withcyclin-dependant kinases (CDK), activating the CDKs to phosphorylate to get proteins involved in cell division
what is p13
protein that prevent cell division in the presence of dna damage
what is cancer
uncontrolled cell division that results from mutations in genes that control cell division
what are tumor suppressors
encode proteins that block cell division
how do cancers form
cancers usually result from several mutations in prooncogenes and tutor suppressor genes that have accumulated over time within the same cell
explain segregation of the X and Y chromosomes during meiosis
segregation of the X and Y chromosomes during meiosis results in half the sperm receiving an X chromosome and half receiving a Y
describe the X-linked gene inheritance pattern
X-inked genes show a crossers inheritance pattern, in which affected individuals are almost always male. Affected males have unaffected sons, and a female with an affected father can have affected sons
genes that are close together in the same chromosome are _____ and do not undergo ______
genes that are close together in the same chromosome are linked and do not undergo independent assortment
what are recombinant chromosomes
they result from crossing over between genes on the same chromosome and show non-parental combinations of alleles
what are non-recombinant chromosomes
have the same configuration of alleles as one of the parental chromosomes
describe the fact that most Y-linked genes are passed from father to son
- Y chromosomes contain a gene called SRY that results in male development
- In y-linked inheritance, only males are affected and all sons of an affected males are affected.
- Females are never affected and do not transmit
what are autosomes
chromosomes other than the sec chromosomes
segregation f the sex chromosomes predicts a ___ ratio of females to males
1-1
describe random fertilization
with random fertilization, had are expected to be XX, hals XY.
the sex of each birth appears to be ransom relative to previous births
what is the secondary sex ratio
the secondary sex ratio at birth shows slight excess of males
what is wild type
the most common phenotype in a population
what is criss-cross inhertitance
an X-chromosome present in a male one generation must be transmitted to a female in the next generation, and in the next generation it can be transmitted back to a male
what is nondisjunction
chromosomes that fail to separate in meiosis
describe the nondisjunction of the X chromosome
can result in eggs containing either two X chromosomes or no X chromosomes
describe nondisjunction in autosomes
results in fetuses that have extra copies or missing copies of entire chromosomes
sisters of an infected male have each ____ chance of being a heterozygous carrier
50%
what are linked genes
genes that are sufficiently close together in the same chromosome
describe linked genes
they tend to be transmitted together in inheritance and do not assort independently of each other
when crossing over occurs outside the interval between genes, there is no ____ between the allele of the genes
in this case, there is no recombination between the alleles of the genes
crossing over between two genes
this results in two recombinant and two non recombinant chromosomes
what is the overall frequency of recombinant chromosomes
this is a measure of the genetic distance between the two genes
