LESSON 6 Flashcards
in mitosis, Daughter cells are genetically ______ to parent cell – same kind and number of ______
identical ; chromosomes
Mitosis occurs in ____ or body cells
somatic
This is called its _____ number or the total number of chromosomes in a somatic cell.
diploid
Diploid means “_____” and is written as “2N”.
2 sets
the process in which the number of chromosomes in the original cell is reduced by HALF through the separation of homologous chromosomes
meiosis
meiosis is the process in which the number of chromosomes in the original cell is reduced by ____ through the separation of _____ chromosomes
HALF ; homologous
Meiosis occurs in _______ only
sex organs
Males (___) – sex organs are the ___ in humans
Females (___) – sex organs are the ___ in humans
XY - testes
XX - ovaries
Meiosis produces ___ cells – cells with ___ the number of chromosomes as the original cell
sex ; ½
Males – meiosis produces _____
Females – meiosis produces ______
4 sperm ; 1 (viable) egg
Females – meiosis produces 1 (viable) egg
The other 3 cells are called ______ – they give up their _____ to nourish the 1 good egg.
polar bodies ; cytoplasm
Egg and sperm (sex cells) are also called _____
gametes
Gametes have ½ the number of chromosomes as somatic (body) cells. We call this the haploid number. Haploid means “____” and is written as “N”.
1 set
If human diploid number is 46, what is its haploid number? ____
23
*When does meiosis occur in humans?
1.Males beginning at _____
2.Females ______ – all eggs are produced before birth and at puberty eggs mature
puberty ; before birth
Nuclear membrane and nucleolus disappear
prophase 1
Each chromosome is composed of two sister chromatids held together by a centromere and is called _____.
dyad
Crossing over takes place between two non- sister chromatids
prophase 1
Each chromosome is composed of two sister chromatids held together by a centromere and is called dyad.
prophase 1
one from the father and one from the mother); along a point called chiasma (plural, chiasmata)
crossing over
crossing over takes place between two non-sister chromatids, one from the father and one from the mother); along a point called _____ (plural, chiasmata)
chiasma
a pair of homologous chromosomes
tetrad
site of synapsis and crossing over
chiasma
homologous pairs of chromosomes align along the center of the cell
metaphase 1
Spindle fibers increase in number and attach to the kinetochore of each chromatid to facilitate movement.
metaphase 1
separation of daughter chromosomes
anaphase 1
sister chromatids attached to the centromere
anaphase 1
at this stage, there are 46 double stranded chromosomes, which is equivalent to 92 chromatids.
anaphase 1
The two daughter cells are completely divided.
telophase 1
The number of chromosomes in both cells is the same.
telophase 1
This is the short pause between meiosis I and meiosis II.
interkinesis
This is similar to interphase of mitosis, except that, here, there is no replication of chromosomes.
interkinesis
At this stage, there are 23 double stranded chromosomes, which is equivalent to 46 chromatids
prophase 2
Each chromosome is composed of two sister chromatids that are joined by a centromere and are attached to the spindle fiber
metaphase 2
The sister chromatids are now called sister chromosomes as they move toward the opposite poles.
anaphase 2
The cleavage furrow eventually produces a total two daughter cells, each with a haploid set of chromosomes.
telophase 2
Homologous (matching) chromosomes pair up before _____
1st cell division
Homologous chromosomes:
-look alike
-code for same traits
-receive one from each parent
During 1st division, homologous chromosomes exchange genes during process called “_______”
crossing over
These homologous chromosomes separate during _____ of meiosis – so chromosomes in gametes are different from each other due to ________
2nd division; crossing over
Crossing over increases _______ and is the reason why siblings look different
genetic variation
______ – process by which an egg and sperm unite
Fertilization
______ – fertilized egg
Zygote
______ – organism in early stage of development
Embryo
