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What happens to the DNA as it continuously keeps getting replicated?
- it shortens
- *that is why they have an "age" limit to how many times they can be replicated
(telomere replication) first step
-when RNA primer is removed from the 5 end of the laggin strand, a strand of aprent DNA remains unreplicated
(telomere replication) 2nd step (2(
-telomerase binds to the overhanging section of single stranded DNA
-telomerase adds deoxyribonucloetides to the end of the parent DNA to extend it
(telomere replication) 3rd step
-telomerase moves down the DNA strand and adds additional repeats
(telomere replication) 4th step
- primase, DNA polymerase, and ligase then synthesize the laggin strand in the 5 to 3 direction
- *this restores the original length of the chromosome
Does telomerase enzyme put an RNA primer or does it have one in its structure?
it has one in it
Stress AND size of telomere
The more stress a person has the smaller the telomere will be
The shorter the telomeres length is...the
less likely of a risk to get aging related diseases
Definition of meiosis
nuclear division that results in cells having half as many chromosomes as the parent cell
In animals when does meiosis occur?
- prior to the formation of eggs and sperm
- *when these two combine the chromosome levels are restored
What is leading hypothesis for meiosis?
genetically variable offspring are more likely to thrive in changing environments
What are homologous chromosomes?
- chromosomes of the same type
- *maternal and paternal that code for G in karyotype
What is an allele?
- different versions of the same gene
- *the stretch in DNA that codes for same function
- **they do not necessairly have to code for same thing
- **one can code for blue eyes and the other brown eyes
What is a karyotype?
- number and type of chromosomes present
- *not everyone has 23 type and 46 chromosomes
What are considered haploid cells?
- sperm and egg
- *they only have one version of chromosome
WHat is haploid?
it is number of distinct types of chromosomes
What does a chromosome do berfore undergoing meiosis?
IN meiosis what happens? (2)
- -parent cells that contains a pair of homologs are seperated into daughter cells.
- *one homolog goes into one daughter cell
- -the sister chromatids in daughter cells seperate creating 4 daughter cells
what does meiosis mean?
During meiosis I, how many different ways can tetrads line up before they separate?
What is gametogenesis?
the haploid cells that were produced in meiosis go on to produce either sperm or eggs
When does a haploid become a diploid?
How does a zygote become a diploid adult?
(steps to meiosis) first step: (3)
-chromosomes replicate in parent cell
-they are in a uncondensed state
(steps to meiosis) step 2 (5)
early prophase I
-nuclear envelope breaks up
-spindle apparatus forms
-synapsis of homologs
(steps to meiosis) Late prophase I
-crossing over of non-sister chromatids
Closer look at synapsis. what happens during synapsis?
- homologs are held together by proteins in the synaptonemal complex
- *during prophase I
closer look at crossing over. What ahppens during crossing over? (2)
-complex of proteins forms where crossing over will occur
-chromosome segments are swapped between non-sister chromatids
When dpes synapsis and crossing over occur?
(steps to meiosis) step 4
-tetrads migrate to metaphase plate
(steps to meiosis) step 5
-homologs separate and begin moving to the opposite sides of cell
(steps to meiosis) step 6
telophase I and cytokinesis
-chromosomes move to the opposite sides of cell then the cell divides
(steps to meiosis) 7th step
meiosis II, Prophase II
spindle apparatus forms
(steps to meiosis) 8th step
meiosis II, Metaphase II
- -chromosomes line up at middle of cell
- *metaphase plate
Small summary of Meiosis II
sister chromatids separate
Small summary of Meiosis I
Homologous chromosomes separate
Small summary of prior to meiosis
-chromosomes replicate which forms sister chromatids
What is Aneuploidy?
condition in which cells have too many or too few chromosomes
(aneuploidy) Turner syndrome (2)
"XO" sex chromosomes
- she is a female with many physical and mental complications
(aneuploidy) Kinefeiter syndrome (2)
-it is a male with female characteristics
What is trisomy?
- having 3 chromosomes per number
- *3 13s
(trisomy)Chromosome number 21 (2)
-has the most cases
Down syndrome AND age of mother
the older the mother is the higher risk the child will have down syndrome
Why is chromosome 21 the most prevalent and not the other chromomes for trisomy?
the other ones typically are rarely born. they die