meiosis Flashcards
describe haploid and diploid
diploid having both homologous pair of chromosomes
haploid having one set of each homologous chromosome (n)
what is meiosis
reductive cell division prior to fertilisation in sexual reproduction
why is meiosis needed prior to fertilisation in sexual reproduction
sexual reproduction involves the fusion of the two gambetes during fertilisation in which the nucleus of the male gamete fuses with the nucleus of the female gamete to form the zygotes. Meiosis ensures that a normal number of chromosomes is restored in the zygote
why is meiosis important
when the nucleus of the male gamete fuses with the nucleus of the female gamete, diploid number of chromosomes are restored in this zygote, maintaining normal diploid number of chromosomes in this species
describe prophase one
chromatin thread condenses, coils and shorten to form chromosome which then forms two sister chromatids attached at the centromere
asters form around the centriols which move to opposite poles of the cell
spindle fibre forms and nucluear envelope and nucleulos disappears
Homologous chromosomes with their sister chromatids pair along their entire length during synapsis. Their chromatids may twist and cross at the chiasma, and the strength of their coils can cause them to break and exchange parts, a process called crossing over. This results in new combinations of alleles, leading to genetic variation in the gametes produced.
in telaphase, nuclear envelope reforms around the chromosomes at each opposite pole of the cell
meiosis and fertilisation lead to genetic variations
crossing over between homologous chromosomes during prophase one resulting in new combinations of alleles in non-sister chromatids of homologous chromosomes
random alignment of chromosomes during metaphase one I and reductive division, resulting in genetically different haploid cells)
how does independent assortment of chromosomes lead to variations of gametes produced
one chromosome of each pair can combine independently with either chromosomes of from other pairs. this results in four different gametes being produced from two chromosomes
how do variations work
increases the survival during changes in environment, nature will select favourable characteristics while others die
survived organisms will pass on favourable genes to offspring
difference between mitosis and meiosis
daughter cells have half the number of chromosomes as parent cell
pairing of homologous chromosomes occur during prophase one
crossing over occurs
daughter cells are not genetically identical do parent call
four daughter cells are produced from one parent cell
involves two nuclear division
occurs in the gonads during formation of gambetes while occurs in the normal body cells during growth and repair of body parts
define sister chromatid, non sister and homologous chromosome
sister chromatids are identical copies of a single chromosome after dna replication help together by a centromere
Non-sister chromatids are the chromatids from different chromosomes of a homologous pair
A homologous chromosome refers to a pair of chromosomes that are similar in size, shape, and genetic content, but one is inherited from the mother and the other from the father.
