Chapter 13 Flashcards
autosomes
any chromosomes that is not a sex chromosome
homologs
contain the same genes in the
same position along the chromosome; contain different versions of genes
locus
position of a gene
diploid
two sets of chromosomes
- one from each parent
what does a ploidy indicate
number of complete chromosomes sets it contains
what does meiosis convert cells to
diploid to haploid
what is the difference between haploid and diploid
diploid cells have 2 pairs of homologous sets of chromosomes and haploid only have 1 set of chromosomes
zygote
has a diploid chromosome number,
one set from each parent
- fertilized egg
what is the importance of meiosis
- genetic variation
- prevents chromosome # from doubling
what are the phases of meiosis 1
Early prophase I
Late prophase I
Metaphase I
Anaphase I
Telophase I
late prophase 1
- homologs begin to separate but remain attached at points called chiasmata
- crossing over occurs between homologous non sister chromatids
chiasmata
where genetic material is exchanged
synapsis
when chromosomes first cross over
metaphase 1
- paired of homologs line up at metaphase plate randomly
anaphase 1
homologs separate and move to opposite ends of cell
telophase 1
homologs finishing moving to poles of cell
what happens at the end of meiosis 1
cytokinesis and results in daughter cells with only one chromosome of each homologous pair
what are the phases of meiosis 2
Prophase II
Metaphase II
Anaphase II
Telophase II
what does not occur in meiosis 2
no chromosomes replication occurs
what does meiosis 2 only work with
sister chromatids
what does meiosis 2 result in
four haploid daughter cells with each type of chromosome
- four haploid cells with un replicated chromosomes
random fertilization
combination of each
unique sperm with each unique egg increases genetic
variability.
when does independent orientation occur
at metaphase 1
independent orientation
- Each pair of chromosomes independently aligns at the
cell equator. - equal probability of the maternal or
paternal chromosome facing a given pole
what could happen if things go wrong in meiosis
- chromosomes may not get pulled apart correctly
- both homologs or sister chromatids could move to same pole
- products will be abnormal
nondisjunction
meiotic error that results in abnormal gametes
- both homologs or sister chromatids could move to same pole
how do mistakes occur
nondisjunction results in gametes that
- Contain an extra chromosome (n + 1)
- Lack one chromosome (n − 1)
what type of gametes lead to trisomy
n+1
- too many chromosomes
what type of gametes lead to monosomy
n-1
aneuploid
Cells with too many or too few of a chromosome
what causes mistakes to occur
- random errors
- maternal age
- egg devolvement
when do primary oocytes enter during embryonic devolvement
meiosis 1
where do oocytes rest until sexual maturation
prophase 1
what can also cause a error in meiosis
longer time period occurs until ovulation, greater the chances of something going wrong
mitosis vs meiosis
- meiosis is followed by two consecutive cell divisions and mitosis is followed by only 1 cell division
- each gametes in meiosis is genetically different from one another
