Chapter 9 SAC Flashcards
homologous pairs
chromosomes that are derived from each parent
homologous pairs of chromosomes are organized according to
- size of autosome
- position of the centromere
- the sex chromoosme
Autosomes
chromosomes other than sex chromosomes (44 in humans,22 pairs)
Somatic cells
diploid body cells where sex chromosomes are found
Mitosis
nuclear Division of cells in eukaryotes for growth + repair
Prophase
- chromosomes are already duplicated
- centrioles move to opposite pole of cell
- chromosomes become more visible
- nuclear membrane disintegreates
Metaphase
- spindle fibres attach to chromosomes
- chromosome lines up along the equator
Anaphase
chromatids are pulled apart by spindle fibres, forming 2 sets of chromosomes
Telophase
nuclear membrane forms around the new sets of chromosomes
cytokinesis
division of cytoplasm that follows mitosis
Inputs of Mitosis
1 diploid cell - 2 sets of chromosomes
Output of mitosis
2 diploid daughter cells - genetically identical to parent
Process overview of mitosis
- DNA replicates + chromatids separate = nuclear division
- Cytokineses = cytoplasmsic division
- Only 1 nuclear division
Why is the root tip often used in mitosis?
as it is still growing, therefore still cell division
Advantages of Asexual reproduction
- if the conditions are suitable + stable in a not changing environment,, the organism can produce many genetically identical offspring
- doesn’t need a mate
- well suited to environment
Disadvantages of Sexual reproduction
if the environmental condition changes, then the whole species will be come extinct, as all genetically identical
3 main parts of the Cell Cycle
- Interphase = G1,2,G2
- Mitosis = nuclear division
- Cytokinesis = cytoplsmic division
Gap 1?
- cell growth
- cell is functioning
- producing proteins which some will be enzymes of DNA replication
Synthesis
DNA replication occurs here in readiness for mitosis
Gap 2
- continued cell growth
- producing proteins necessary for mitosis
What happens when there is a problem after DNA replication?
the check point G2 would detect the problem, then the DNA maybe repaired or undergo apoptosis of the cell
What happens when check points don’t function properly?
the faulty cell may continue to divide which leads to cancers
Apoptosis
programmed cell death for the benefit of the whole organism, as it saves energy and resources
Meiosis
call reproduction (division) for the production of gametes needed for sexual reproduction - can also be called reduction division, as the no. of chromosomes in the daughter cells is half of the chromosomes in the original parent diploid cell
Sexual reproduction
requires cell division celled meiosis and it only occurs in specialized diploid cells found in gonads (testes and ovaries)
Why is it important or the gametes to be haploid in meiosis
so that the diploid chromosome number can be restored at fertilization
eg. 23 chromosomes in each gamete, therefore, 46 chromosomes in zygote resulting human
Meiosis 1
lining up of homologous pairs and crossing over occurs in prophase 1
Crossing over
In prophase 1, homologous pairs can exchange genetic material resulting in a genetical variety in gamete
Synapsis
pairing of homologous chromosomes
Chiasma
point of exchange of genetic material between homologous pairs
Independent assortment of chromosomes
homologous pairs separate, 2 cells produce
- the separation of one homologous has no influence on the separation of another homologous pair, resulting in the mixing of m +p chromosomes
ie. more genetic variety in gamete
Independent assortment of homologous pairs of chromosomes
occurs in meiosis 1
Independent assortment of homologous pairs of chromatids
occurs in meiosis 2 when the chromatids are separating
Meiosis 2
chromatids separate, 2 cells produced from each cell from meiosis 1, total of 4 haploid daughter cells that are genetically different from each other and parent cells.
Purpose of Mitosis
to make daughter cells identical to the parent cells for growth and repair
Purpose of Meiosis
to produce sex cell (gametes)
Where does mitosis take place?
in all cells apart from gametes
Where does meiosis take place?
in the ovaries and testes
How many cells does mitosis produce?
2 daughter cells
how many cells does meiosis produce?
4 gametes
What happens to the number of chromosomes in mitosis?
same number as parent cell
What happens to the number of chromosomes in meiosis ?
half as many as in parent cell
How do parent and daughter cells differ genetically in mitosis?
not at all, identical to parent
How do parent and daughter cells differ genetically in meiosis?
contain a mixture of chromosomes from 2 parent gametes
Is there a variation between daughter cells in mitosis?
no, they’re clones
Is there a variation between daughter cells in meiosis
yes, genetically different from each other because chromosomes get shuffled up during division
Aneupoidy
results in one chromosome too many or few
- caused by non-disjunction of chromatids or chromosomes during meiosis
Nondisjunction
when a pair of chromosomes fail to dis-join so that 2 copies of a chromosome are present in the gamete , instead of usually one
Trisomy
union of a gamete with 2 copies of one chromosome, with a normal gamete leads to 3 copies of the chromosome
- down syndrome, 47 XX, XY 21
Monosomy
union of gamete without one chromosome with a normal gamete leads to only 1 copy of the chromosome. Zygote usually dies unless missing chromosome is sex chromosome
ie. 45 XO
Mitosis daughter cell
identical as they’re diploid and somatic
meiosis daughter cell
genetically different as genetic recombination of chromosomes occur
Why are the daughter cells different?
as in meiosis
- Crossing over
- Where there is exchange of genetic material (alleles) between non-sister chromatids of homologous pairs, therefore, different alleles (PROPHASE I) - Independent assortment of chromosomes
- Where the separation of one homologous pair has no influence over another, therefore, mixing maternal and paternal chromosomes (ANAPHASE I)
Chromosome
threadlike structure made up of DNA and protein, only visible during cell division
Haploid
cells with one set of chromosomes (n)
eg. eggs sperm and gametes.
- these cells are produced by gametes
- in humans the haploid number is 23
Diploid
cells with two sets of chromosomes (2n)
- one set derived from each parent
- includes all somatic cell- skin, muscle, wbc
- in humans diploid number is 46
Gametes
eggs, sperm
haploid cells which fuse during fertilization
Genome
all of the genes in a cell which every cell has the same of
Chromatid
copy of a duplicated chromosome, joined to the other copy by the centromere. Required for both cell division and is produced in the S phase of the cell cycle
Somatic cells
Diploid body cells
aka all bosy cells except gametes
Alleles
different variations of genes
Chromatin
chromosomes when not in mitosis or meiosis
ie when NOT dividing
- made up of protein and DNA
homologous pairs of chromosomes
2 chromosomes with the same genes but different alleles
sex chromosomes
chromosome in the genome that is involved in the determination of sex
genes
the basic unit of heredity
centromere
where chromatids are held and the point of attachment for spindle fibers
autosomes
non-sex chromosomes
