Meiosis I Flashcards
what is a trait?
a trait is a variation of a character. for example: black hair, brown hair, blue eyes. character is: eye color, hair color.
how do we get the traits we do from our parents?
we get the coded information for these traits on hereditary units called genes.
what is a gene?
a gene is a segment of a chromosome that directs the synthesis of a functional product.
what is a locus?
the position of a gene along a chromosome is called a locus
genes are transmitted to offspring in plants and animals by?
sexual reproduction
the offspring is a __ of?
mixture of the genes inherited from mother and father.
what is asexual reproduction
offspring is produced by a single parent. all of the genetic information is transmitted.
what organisms reproduce asexually?
- prokaryotes
- single celled eukaryotes: amoeba
- some multicellular organisms: hydra
how many chromosomes do somatic cells have?
46 chromosomes, 2 sets of 23 each
human somatic cells are?
diploid: two copies of each chromosome. homologous chromosomes. (the two copies of chromosome 1 in a cell would be homologous chromosome)
of the 46 chromosomes in a human somatic cell?
22 pairs of non sex chromosomes and the remaining two chromosomes are sex chromosomes.
what are non sex chromosomes called?
autosomes
what are the two sex chromosomes and what is the difference for male and female?
two sex chromosomes are x and y
- male: xy
- female: xx
if you are female you have?
44 autosomes and 2 x chromosomes
- one set from mother: 22 autosomes and x
- one set from father: 22 autosomes and x
if you are a male you have?
44 autosomes and xy chromosomes.
- one set from mother: 22 autosomes and x
- one set from father: 22 autosomes and y
normal karyotype for male/female?
female: 46 in total with 2 x
male: 46 in total with xy
somatic cells undergo?
the cell cycle which includes mitosis and cytokinesis
cells replicate their chromosomes during the?
cell cycle
after replication, the chromosomes?
remain joined together at the centromere.
at this point, they are referred to as?
sister chromatids
human somatic cells contain 46 chromosomes, how many do sex cells contain?
sex cells/gametes/sperm or egg cells: contain 23 chromosomes only
a cell that has one copy of each chromosome is?
haploid.
the human life cycle begins when?
ovum and sperm fuse together to form a zygote.
the zygote is haploid or diploid?
the zygote is diploid because there is a maternal set and a paternal set: 2 sets
all somatic cells in the human are derived by?
mitotic division of the zygote.
the gametes: sperm and ovum are derived by?
meiosis
where does meiosis occur?
meiosis occurs in the gonads
what are the gonads?
ovaries in females and testes in males
meiosis acts to?
half the number of chromosomes
the gametes will have how many chromosomes?
23 chromosomes
meiosis consists of?
2 cell divisions: meiosis i and meiosis ii.
before undergoing meiosis cells…?
replicate their chromosomes in the s phase of the cell cycle.
prior to meiosis, all ?
46 chromosomes have replicated
what are the stages in meiosis i and ii
pmat i and ii
what happens in prophase i?
-nuclear envelope disintegrates
- spindle apparatus forms
- centrosomes move away from eachother
- homologous chromosomes come together : synapsis: leading to the formation of tetrads.
- the homologous chromosomes cross over and exchange dna
- this leads to recombinant chromosome formation
- each chromosome then has a mixture of genes derived from two parents
what is the chiasmata?
regions where crossing over has occurred.
what happens in metaphase i?
the tetrads move to the metaphase plate by the spindle fibers from centrosomes. this movement is random: independent assortment
what happens in anaphase i?
- homologous chromosomes separate and move to opposite ends of the cell.
what happens in telophase i/cytokinesis?
the homologous chromosomes are at opposite ends. the cell then divides by cytokinesis
at the end of meiosis i, how many cells are formed?
2 cells are formed
are the cells formed diploid or haploid?
the cells formed are haploid, they each have one copy of each chromosome, the sister chromatids are still together.
