Unit 5: Chapter 13 Flashcards
during meiosis, _____ _____ are paired
homologous chromosomes
one from maternal parent and one from paternal parent
homologous chromatids exchange genetic material during what process
crossing over
heredity
the transmission of traits from one generation to the next
genetics
the scientific study of heredity and variation
genes
segments of DNA
gametes
sperm and egg cells
asexual reproduction
one parent produces genetically identical offspring by mitosis (not meiosis)
a haploid has how many chromosomes
23
a diploid has how many chromosomes
46
each human somatic cell has how many chromosomes arranged in pairs
46
homologues
each set two chromosomes that pair up
one from each parent
each carries genes that control the same characteristics
sister chromatids
two identical parts that make up one chromosome
meiosis ensures that each gamete receives one complete ______
haploid set of chromosomes
a cell with one set of chromosomes is called a
haploid
for humans, 23 chromosomes
gametes are haploid cells
a cell with two set of chromosomes
diploid
humans: 46
somatic cells
female homologous pair of chromosomes
XX
males homologous pair of chromosomes
XY
autosomes
the 22 pairs of chromosomes that don’t determine sex
fertilization
the fusing of gametes
forms diploid
ultimately forms zygote
similarity between meiosis and mitosis
both are preceded by the replication of chromosomes
3 differences between meiosis and mitosis
during meiosis:
2 sets of cell divisions
4 daughter cells instead of 2
each daughter cell is a haploid
four phases of meiosis 1
prophase 1
metaphase 1
anaphase 1
telophase 1
what happens during meiosis 1
homologous chromosomes separate
results in two haploid daughter cells with replicated chromosomes
what happens in meiosis 2
sister chromatids separate
results in four haploid daughter cells with nonreplicated chromosomes
what happens during interphase (before meiosis 1)
chromosomes are replicated to form genetically identical sister chromatids
this new chromosomes replicates, forming two centrosomes
which stage of meiosis is the longest
prophase 1
what happens during prophase 1
chromosomes condense
each pair of chromosomes forms a tetrad, or a group of four chromatids
synapsis and crossing over
synapsis
during prophase 1
homologous chromosomes loosely pair up
align gene by gene
crossing over
prophase 1
nonsister chromatids exchange DNA segments
metaphase 1
tetrads line up at the metaphase plate, with one chromosome facing each pole
microtubules from both poles attach to the kinetochores of both chromosomes of each tetrad
anaphase 1
pairs of homologous chromosome separate
one chromosome moves towards each pole
the sister chromatids remain attached at their centromere during this process
telophase 1 and cytokinesis
animal cells: cleavage furrow forms
plant cells: cell plate forms
NO chromosome replication
prophase 2
spindle apparatus forms
chromosomes move towards metaphase plate
metaphase 2
sister chromatids are arranged on metaphase plate
no longer genetically identical
kinetochores of sister chromatids attach to microtubules from opposite poles of cell
anaphase 2
sister chromatids separate and move towards opposite poles
telophase 2 and cytokinesis
chromosomes arrive at opposite poles
nuclei form and chromosomes de-condense
cytoplasm is separated by cytokinesis
what is the result of meiosis?
4 daughter cells
each has a haploid set of unreplicated chromosomes (because of crossing over)
three mechanisms that contribute to genetic variation
independent assortment of chromosomes
crossing over
random fertilization
independent assortment of chromosomes
homologous pairs of chromosomes are randomly oriented during metaphase 1
so any pair of chromosomes can be sorted into the daughter cells regardless of what happens to other pairs
random fertilization
any sperm can fuse with any unfertilized egg
