Exam 3 Meiosis And Recombination

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Meiosis:

from Greek, meaning “reduction” or “make smaller”

cell division responsible for the generation of ... (i.e. sperm and oocytes)

specialized program of two coupled cell divisions used by eukaryotes to maintain the proper ... number for the species during sexual reproduction

reduces chromosomal number in half, such that fusion of male and female gametes during fertilization restores proper chromosome number

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gametes
chromosome

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During meiosis, cells are going from a ... state (2n, or # chromosomes) to a ... state (n, or 23 chromosomes).

Reducing our chromosome number by half requires # consecutive divisions, termed meiosis I and meiosis II (with no DNA synthesis or S phase between the two divisions).

one parent cell (2n) produces # daughter cells (n)

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diploid
46
haploid
2
4

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Homologous chromosomes:

pair of “matching” chromosomes consisting of one chromosome donated by the mother and one chromosome donated by the father

each member of the pair (“homolog”) ... segregates into one of the two daughter cells during meiosis I

# pairs of homologous chromosomes, so each gamete has more than 8 million (223) possible chromosomal combinations

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randomly
23

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Homologous pairs encode for the same genes, but they have different versions of these genes, or different ...

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alleles

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Homologous chromosomes pair during ...

to allow for crossing-over and genetic exchange between pairs --> ...

to ensure proper ... during anaphase I

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prophase 1

recombination

segregation

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Prophase I → pairing and recombination of homologous chromosomes

consists of 5 morphological stages, which are:

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leptotene
zygotene
pachytene
diplotene
diakinesis

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during prophase 1:

paired homologous chromosomes form a bivalent structure, or .. in a process called ...

homologous chromosomes become “zipped” together forming ...

... holds the homologues together

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tetrad
synapsis

synaptonemal complex

cohesin

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highlights of prophase 1:

nonsister chromatids of homologous chromosomes randomly exchange segments (...)

regions that have crossed-over remain tightly bound, forming ...

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recombination

chiasmata

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Meiosis continues with the ... chromosomes being pulled apart during metaphase I, anaphase I, and telophase I (in similar fashion to what occurs during mitosis.)

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homologous

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... behavior differs in meiosis and mitosis.

... rotate 90° in meiosis I so that they face the same direction and move together

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Kinetochore
kinetochores

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Meiosis II:

Prophase II
Metaphase II
Anaphase II
Telophase II

main function: separation of ...

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sister chromatids

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Genetic diversity: random assortment of homologous chromosomes

For each pair of homologs, the choice of spindle orientation in meiosis I is random, that is each homolog has two equivalent options for the direction to migrate.

does not create ... versions of genes, but it guarantees the production of offspring with novel ... of chromosomes

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new
combinations

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... is the failure of the chromosomes to properly segregate during meiotic or mitotic anaphase, resulting in daughter cells with abnormal numbers of chromosomes.

...= One or a few chromosomes above or below the normal chromosome number. For example, three number 21 chromosomes or trisomy 21 (characteristic of Down Syndrome) is a form of this. In most conditions, there is an extra copy (or missing copy) of a single chromosome.

...= Having more than 2 sets of chromosomes. For example, instead of 46 chromosomes, the organism would have 92 or 138.

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Nondisjunction
Aneuploidy
Polyploidy

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trisomy of chromosome 21 = ...

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Down's Syndrome

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trisomy of chromosome 13 = ...

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Patau's Syndrome

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trisomy of chromosome 18 = ...

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Edward's Syndrome

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extra X chromosomes in males - ie XXY, XXXY, XXXXY = ...

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Klinefelter Syndrome

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... = segregation of homologous chromosomes

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disjunction

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trisomy of the X chromosome in females- ie XXX = ...

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Triple X Syndrome

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absence of X chromosome in females - ie XO = ...

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Turner Syndrome

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an extra Y chromosome in males = ...

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XYY Syndrome

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Oogonia

Forming oocytes stop at the diplotene stage of ... prior to birth and lay dormant within the ovaries protected by the follicle.

Menstruated oocytes (released from the follicle) continue meiosis I and arrest at ... until fertilization.

all possible oocytes are present in the female ovaries at birth and age as the female ages --> more prone to ... during segregation (nondisjunction)

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prophase I
meiosis II
errors

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Spermatogonia

... divide without arrest in the seminiferous tubules, and sperm are produced at a steady pace throughout the male lifetime

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continuously

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Incidence of Down Syndrome ... with increasing maternal age

Eggs have been bombarded with enviromnental insults

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increases

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what process is this?

non-sister chromatids of homologous chromosomes randomly exchange segments of genetic information over regions of homology

leads to offspring having different combinations of genes from their parents and can produce new chimeric alleles

chromosomes are expected to cross over at many points along their length

can occur with small probability at any location along chromosome

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recombination

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mechanism of recombination:

one of the chromatids is partially ...

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degraded

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-Meiosis involves ... cell divisions.
-The products of meiosis are ...
-The products of meiosis are ...
-Prophase I is (shorter/longer) in meiosis.
-... is increased in meiosis.
-Kinetochore ... differs in meiosis.
-Chromatid cohesion differs in meiosis (...).

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two
haploid
genetically different
longer
Recombination
behavior
synaptomenal complex