Chapter 11-PowerPoint Flashcards
Where does meiosis occur?
germ-line cells
What ploidy are germ-line cells?
diploid
What are the germ-line cells called in meiosis?
gonads
What are the gonads in males?
testes
What are the gonads in females called?
overaries
What is produced in meiosis?
sperm and ova
What is the production of sperm and ova called?
gametogenesis
What is the ploidy of gametes?
haploid
What does fertilization produce?
zygote
What is the ploidy of a zygote?
diploid
What is variability?
mixing gentic information
Where does variability occur (asexual or sexual reproduction)?
sexual reproduction
What are the steps in meiosis 1?
G1, S, G2, M, I
What are the steps in meiosis 2?
G1, G2, M, I
What are the differences in the steps of meiosis 1 vs meiosis 2?
Meiosis 2 doesn’t have an S phase and the G1 and G2 phases are shorter
When does crossing over happen?
prophase 1 of meiosis 1
What happens in crossing over?
homologous chromosomes pair and non sister chromatids exchange chromosomes segments
Which is reduction division?
meiosis 1
What is separated in meiosis 1?
homologous chromosome
What is separated in meiosis 2?
sister chromatids
Where else does separation of sister chromatids?
anaphase of mitosis
What is a synapsis?
homologues pair along their length
What is Homologous recombination?
Genetic exchange (crossing over) occurs between homologous chromosomes.
What is Reduction division?
Meiosis involves two successive divisions, with no replication of genetic material between them.
meiosis 1
—no S phase
What is the synaptonemal complex?
protein that helps connect homologues
In homologous chromosomes have the same? what is different?
genes are the same, but different sequence
What alleles?
different version of each gene in a homologous pair
ex. A vs a
What does crossing over lead to?
diversity
What is a chiasmata?
site where crossing over has occurred, thickened spots
After crossing over will the sister chromatids be identical?
no
What is equational division?
meiosis 2
Does the second meiotic division further reduce the number of chromosomes?
no, n -> n (just separating sister chromatids)
Does the first meiotic division further reduce the number of chromosomes?
yes, 2n -> n
What happens in prometaphase 1?
- nuclear envelope breaks down completely
- spindle enters the former nuclear area
- The two chromosomes of each pair attach to kinetochore microtubules leading to opposite spindle poles
- Sister chromatids remain attached to each other
When does the nuclear envelope start to break down?
prophase 1
What happens in metaphase 1?
- Terminal chiasmata holds homologous pair together.
- Joined pairs of homologues line up on metaphase plate.
Is the orientation of each pair in metaphase 1 random?
yes
What stage does independent assortment occur?
metaphase 1
How many combinations does the variation of orientation in metaphase 1 lead to?
2^n
In humans how many combinations are possible from independent assortment?
2^23
What happens in anaphase 1?
- Spindle fibers begin to shorten and pull whole centromeres toward poles.
- The two chromosomes of each homologous pair separate and move to opposite spindle poles as the spindle microtubules contract
- Each chromosome still has two sister chromatids
- Random orientation results in independent assortment
What happens in telophase 1?
- Chromosomes are segregated into two clusters; one at each pole.
- Nuclear membrane re-forms around each daughter cell.
- nucleolus starts to appear
- Sister chromatids are no longer identical due to crossing over.
What is interkinesis?
the single spindle of the first meiotic division
disassembles and microtubules reassemble into two
new spindles for the second division
What happens in Prophase II?
Chromosomes condense and a spindle forms
What happens in Prometaphase II?
- Nuclear envelope breaks down
- spindle enters the former nuclear area
- spindle microtubules attach to the two kinetochores of each chromosome
What happens in Metaphase II?
Spindle microtubules align chromosomes on the metaphase plate
What happens in anaphase II?
Spindles separate the two chromatids of each chromosome and pull them to
opposite spindle poles
What happens in telophase II?
- Chromatids decondense to extended interphase state
- Spindles disassemble and new nuclear envelopes form around the chromatin
- creates 4 haploid cells
When does nondisjunction occur?
When homologous chromosomes or sister chromatids do not separate correctly in meiosis 1 or 2
What does nondisjunction result in?
zygote will have a extra number of chromosomes
What is the male sex chromosome?
XY
What is the female sex chromsomes?
XX
In females are the XX chromosomes fully homologous?
yes
In males are the XY chromosomes fully homologous?
No, they are partly homologous
What does meiosis in plants, fungi, and algae produce?
spores
What are 3 sources of genetic variability?
crossing over, independent assortment, unique sets of male and female gametes
How many times can crossing over occur on the same chromosome pair?
one or more time
In the random/unique joining of male and female gametes what are the chances that two children of the same parents receive the same combination of chromosomes?
1 out of (2^23)^2
or
1 out around 70 trillion
Is the haploid or diploid dominate in animals?
diploid
Is the haploid or diploid dominate in all plants, and some algae and fungi?
they alternate (about 1/2 and 1/2)
Is the haploid or diploid dominate in some algae and fungi?
haploid
