meiosis - exam 2 Flashcards
number of chromosomes in gametes
1n egg + 1n sperm
number of chromosomes in zygotes
2n
meisosis, fertilization, & mitosis in human life cycle
2n parents –> meiosis –> 1n gametes
fertilization –> 2n zygote
mitosis
homologous chromosomes
2 pairs of sister chromatids
autosomes
non sex chromosomes
allele
alternate versions of the same gene
prophase I unique stuff
synapsis occurs
crossing over occurs
synapsis
pairing of homologous chromosomes
maternal & paternal come together
synaptonemal complex
protein lattice between homologous chromosomes
crossing over
exchange of genetic material between non-sister chromatids
1 maternal & 1 paternal
recombinant chromatids
new combination of alleles
sometimes genes break during crossing over & get fixed in a different way
metaphase I
homologous pairs align on metaphase plate
random alignment = independent assortment
anaphase I
kinetochore MTs shortern at the same time as the synaptonemal complex degrades
homologous chromosomes separate & move to opposite sides of cell
sister chromatids stay attached
telophase I
each half of cell has complete 1n set of replicated chromosomes
each chromosome = 2 sister chromatids
- 2 haploid cells –> both are n=3
interkinesis
no dna replication
both cells enter meiosis II
prophase II
just like mitosis
metaphase II
chromosomes aligned on metaphase plate
anaphase II
sister chromatids separated –> moved to opposite poles of cell
telophase II
chromosomes decondense
nuclei reform
meiosis II results in what
four haploid daughter cells (n=3)
how does meiosis increase genetic variability
mutation
random alignment of chromosomes on metaphase I plate
crossing over
fertilization
nondisjunction
homologous chromosomes or sister chromatids don’t separate from each other
how does nondisjunction lead to abnormalities
homologous chromosomes fail to separate
sister chromatids fail to separate
