its all about sex Flashcards
outline the process of prophase I
chromosomes condense and homologous chromosomes line up and pair with each other in a process called synapsis
crossing over occurs allowing the exchange of DNA segments between homologous chromosomes
outline the process of prometaphase and metaphase I
- the nuclear envelope breaks down and meiotic spindles attach to kinetochores
- meiotic spindle is complete and bivalents move to the centre with two centromeres on opposite sides
- orientation of bivalents is random
outline the process of anaphase and telophase I
- two homologous chromosomes seperate and pulled to opposite poles
- centromeres do not split during this stage
- in telophase I chromosomes uncoil slightly and envelope can briefly reappear
what is reductional division
the reduction in the number of chromosomes by a half with each ones at opposite poles
what occurs in meiosis II
results in haploid , gentically different daughter cells
outline cytoplasmic division in female cells after meiosis
cytoplasm is divided unequally in both meiotic divisions with most cytoplasm retained in one miotic product called the oocyte with the other products only having a small amount of cytoplasm which are disgarded = the polar bodies
outline cytoplasmic division in male cells after meiosis
cytoplasm is divided fairly equally resulting in products that all form functional sperm
what is meant by nondisjunction
this results in missing or extra chromosomes
for autosomes it usually results in death of the fetus but occasionally not e.g. down syndrome
how come in sex chromosomes an extra chromosome usually goes unnoticed
XXX- all but one version of the X chromosome are almost deactivatd so an additional one causes little issues
XYY- Y chromosomes are small with few genes so additional copies dont cause an additional effect
what are the key features of sexual reproduction
- recombination creates genetic variety
- meiosis creates gentcially unqiue gametes
what are the disadvantages of reproducing sexually
- destroys adaptive combination alleles
- requires two individuals which leads to cost of seeking, choosing and competing for mates
- production of males which cant bear offspring which reduces reproductive success
what is meant by the term intra-genomic conflict
when gene variations selfishly manipulate the production of gametes to increase their own rate of transmission which affects the rest of the genome and the individual that carries them
what are the advantages of sexual reproduction
- facilitates adaptation to new environments by combining beneficial mutations
- can seperate beneficial from harmful mutations
how do prokaryotes reproduce sexually
conjunction
transformation
transduction
what is conjugation
donor plasmid allows the plasmid to be copied to another bacteria which is then integrated into the genome
