chapter 2 Flashcards
what is a chromosome?
structure within living cells that contain genetic material
what is chromatin?
DNA + proteins
what are diploid species?
two sets of chromosomes forming a homologous pair
do homologous pairs have the same allele?
no, they have the same gene loci but different allele
what chromosome isnt a homologous pair?
sex chromosomes
what is asexual reproduction?
pre existing cell divides to produce new cells
what is an example of asexual reproduction?
wound healing and cell replacement in adult organisms
what is binary fission?
bacteria replicated chromosomes then divides into two daughter cells- genetically identical
what is interphase?
G1, S and G2
what is G0?
non dividing state- cell can enter this stage when it is aging and theres DNA damage, temporary lack of nutrition, or its normal differentiation program
what is senescence?
cell aging and DNA damage- permanent
what is quiescence?
temporary lack of nutrition and/or growth factors-reversible
what happens during G1 phase?
cell prepares to divide, accumulates proteins and reaches a restriction point where the cell MUST complete the cycle
what happpens during S phase?
chromosomes are replicated
what are sister chromatids?
two copies of a chromosome joined together at the centromere to form an X shape
what happens during G2?
cell accumulates the materials that are necessary for nuclear and cell division- checks if there are any mutations or errors with DNA copying
how many chromosomes and chromatids are present during G2?
46 chromosomes but 92 chromatids
what are astral microtubules?
project towards plasma membrane
what are polar microtubules?
project into region between two spindle fibers
what are the stages of mitosis?
PPMAT- prophase, prometaphase, metaphase, anaphase, telophase
what happens during prophase?
nuclear membranse dissociate and two centrosomes move apart- mitotic spindle begins to form
what happens during prometaphase?
centrosomes reach opposite poles, spindle fibers interact with sister chromatids
what happens during metaphase?
pairs of sister chromatids align along a plane called the metaphase plate
what happens during anaphase?
cohesin bond that holds the sister chromatids together is broken and chromatids are pulled to opposite sides
how many chromosomes are present DURING anaphase?
92 chromosomes are now on opposite sides of the cell
what happens to the kinetochore and the polar microtubules as anaphase proceeds?
kinetochore microtubules shorten and the polar microtubules lengthen
what happens during telophase?
nuclear membrane reforms to form two separate nuclei by the formation of a cleavage furrow
What is the outcome of mitotic cell division?
Produce two identical daughter cells with the same number of chromosomes as daughter cells- genetically identical
What is meiosis?
The process of two diploid parents making gametes with half the amount of genetic material (haploid)- one chromosome from each homologous pair
How many divisions are in meiosis?
Two successive divisions to reduce the number of chromosomes from diploid (parent) to haploid (gamete)
What happens during prophase I of meiosis?
Chromosomes are replicated and undergo synapsis and form the synaptonemal complex and undergo crossing over
What is synapsis?
Recognition process where homologous chromosomes find each other and align (homologous chromosome 1 with homologous chromosomes 1)
What is crossing over?
Physical exchange of chromosomes- critical for proper segregation and genetic variation- produce chiasma connection
what happens during prometaphase I?
Spindle apparatus is complete and chromatids are attached to the kinetochore microtubules
What happens during metaphase I?
Chromosomes are aligned along metaphase plate- opposite homologous pairs are linked and will be pulled apart
What happens during anaphase I?
Homologous chromosomes separate from one another but connection holding sister chromatids together does not break
What happens during telophase I?
Homologous pairs reach poles and nuclear membrane reforms
What is the outcome of meiosis I?
Produce two non-identical cells, each with half the number of chromosomes but chromosomes are Still in pairs
What happens in meiosis II?
Meiosis two is now similar to mitosis but without the extra replication, sister chromatids are already replicated and are now just separated to form 4 haploid cells
What two factors affect genetic variation of chromosomes?
Crossing over during prophase I and random separation of homologous chromosomes depending on how they line up along the metaphase plate during metaphase I
What are the possible combinations in humans?
2^23= 8,388,608 possible combinations based on the 23 pairs of chromosomes
How do eukaryotic organisms produce offspring?
Through sexual reproduction
What is gametogenesis?
Formation of gametes (haploid) from parents (diploid) which will then fuse through fertilization to form a new diploid organisms
What are isogamous species?
Produce gametes that are morphologically similar like fungi and algae
What are heterogamous species?
Produce gametes that are morphologically different- such as sperm, which are small and mobile and eggs, which are very large and in mobile
What is spermatogenesis?
Production of sperm occurring in the testes, diploid spermatogonial cell divides to produce two cells- one spermatogonial cell and one primary spermatocyte. Primary spermatocyte will go through meiosis I and II to produce four haploid spermatids- mature into sperm cells
What is the structure of sperm?
Long flagellum and a head with a haploid nucleus- head is capped by an acrosome, which contains digestive enzymes that enable sperm to penetrate through the egg
What is oogenesis?
Production of egg cells which occurs in the ovaries- diploid oogonia cells produce diploid primary oocytes before birth- primary oocytes initiate meiosis I in utero but stop at prophase 1 until ovulation where they reach metaphase II and will only complete meiosis if fertilized
How does primary oocyte activation occur?
Monthly; produce two haploid cells through asymmetric division, a large secondary oocyte which will enter meiosis II and a small polar body containing the other half of the chromosomes will undergo apoptosis.
What type of oocyte enters meiosis?
The large secondary oocyte enters meiosis monthly
What are the two life cycles of plants?
Haploid gametophyte generation and the diploid sporophyte generation
What’s the cycle of plants?
Cells in sporophyte undergo meiosis to produce haploid cells called spores, spores will then divide with mitosis to produce the gametophyte, which produces gametes which upon fertilization grow into a plant
How does gamete formation occur in flowering plants?
In anthers, diploid microsporocyte undergo meiosis to produce four haploid micro spore- undergo mitosis to form a pollen grain which will form two sperm cells.
In ovaries, diploid megasporocytes undergo meiosis to produce four haploid megaspores- undergo mitosis and develop into the embryo sac which will produce an egg cell
How does fertilization occur in flowering plants?
Begins when pollen lands on stigma, tube cell develops into a pollen tube that makes contact with an ovule- undergo mitosis to produce two haploid sperm; double fertilization occurs when sperm fertilizes egg to create zygote, second sperm units with the central cell to produce am endosperm (3 sets of haploid chromosomes)
What is heterogametic sex and homogametic sex?
Heterogametic will produce two different types of gametes, two different sex chromosomes and homogametic produce only one type (females having two x)
How is sex determined in mammals?
Males will produce half the sperm cells with X chromosomes and half with Y, depending on the cell that fertilizes the egg will determine the sex of the zygote.
How is sex determined In insects?
Some males are X0 and some are XY, Y does not determine maleness. It is the ratio between the X chromosomes and the number of sets of autosomes- if the ratio is 0.5- it will be male and if the ratio is 1 it will be female q
What happens if the ratio between x and autosomes isn’t 1 or 0.5?
If you have a ratio of 0.67 which is in between both sexes you will have an intersex offspring. Will have both female and male parts
what is a homogametic specie?
males contain two
Z chromosomes
what are heterogametic species?
females have one Z and one W chromosome
how does sex determination work in bees?
maples are produced from unfertilized haploid eggs and females are diploid produced from fertilized eggs
what is environmental sex determination for reptiles?
sex is controlled by temperatures rather than sex chromosomes
what is environmental sex determination in nemo fish?
large female fish exhibits dominance which inhibits hormone production and makes males, if female dies, male eggs become females and cycle starts again
