Download MEIOSIS and MUTATIONS

MEIOSIS AND MUTATIONS
TERMS AND INFORMATION
1. sexual reproduction- use of gametes to
reproduce; necessary to have 2 different cells
2. gametes - sex cells; sperm and egg; haploid
3. somatic cells- an organism’s body cells; diploid
4. haploid - having one set of chromosomes;
gametes
5. diploid - having 2 sets of chromosomes; somatic
cells
I. Meiosis- 2 stages of cell division that result in
formation of gametes (sex cells/ haploid cells)
A. Meiosis I
1. our cells have 2 sets of chromosomes
(1 set of 23 from mom, 1 set of 23
from dad)
2. each chromosome in male set has a
corresponding chromosome in the
female set
3. homologous chromosome- same type
of chromosome contributed by each
parent
4. Prophase I- replicated chromosomes seek out
their homolog and form a tetrad
crossing over occurs between homologs,
exchange portions of their chromatids
5. Metaphase I- tetrads line up in the middle
of the cell
6. Anaphase I- spindle fibers separate
homologs from each other.
7. Telophase I- nucleus reappears,
cytokinesis, each cell has one of the
homologs or homologous chromosomes
B. Meiosis II- no more replication b/c it was already
done during interphase
1. Prophase II, Metaphase II, Anaphase II,
Telophase II
2. similar to mitosis, as cells go through
another round of division
3. sister chromatids separate or segregate,
but in Meiosis I the homologs split
P-2
M-2
A-2
T-2
4. results in gametes or sex cells with a haploid
number of chromosomes
a. males- 1 cell = 4 sperm produced
b. females- 1 cell = 1 egg or ovule;
unevenly divided so 1 egg gets most
of the cytoplasm. Remaining 3 cells
are called polar bodies and
usually don't participate in
reproduction.
5. Meiosis produces haploid cells so that when a
sperm & egg fuse during fertilization, the zygote will
have the same total number of chromosomes that each
parent had
C. Contributors to Diversity in Organisms
1. Meiosis I- during prophase- crossing over
gives different combinations of genes than
before by mixing homologous chromosomes
2. Meiosis II, segregation of chromosomes into
separate gametes
3. Mutations can change survival or reproduction
rates of species
a. lethal- expression that results in death
b. neutral- no effect on survival or reproduction
c. beneficial- expression that results in survival
and/or reproductive advantages
II. Genes and types of Mutations
A. Genes
1. are a length of DNA located on
chromosomes.
2. there are thousands of genes on
each chromosome that encode
information
3. gene expression is caused by
controlling the sequence of amino acids
in a protein
4. genes are factors that control traits
5. linked genes - genes on the same
chromosome
B. Gene Mutations
1. caused by a change in amino acid sequence of a protein
2. impacts of mutations lethal, neutral, beneficial
3. gene mutation- change to 1 or several bases in nucleotide
sequence of DNA
a. bases added, deleted, replaced (changed)
i. point mutation - single base or base pair change (Sickle Cell)
ii. frameshift mutation - 1 missing/added base, transcribed by
mRNA
b. mutations are rare b/c cells have proofreading and correction
enzymes
c. these chance events (mutations) are caused by mutagens
ex. viruses, UV light, chemicals like mustard gas
Deletion and addition Mutations animation
C. Chromosomal Mutations- change in structure or
number of chromosomes
Detected by KARYOTYPING which matches
homologous chromosomes in a diploid cell by:
1. size of chromosome
2. length of chromatid arms
3. centromere location
Samples are collected by doing either an amniocentesis or
chorionic villus sampling.
Karyotype of a normal
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female
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Karyotype of a normal
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male
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fig 3.
Theoretically Normal Chro mosome Structure
note : ea ch letter or seg men t o n a chro m oso m e rep resen ts a g en e in pro per locu s
A
B
C
D
E
F
and
G
H
I
J
K
Structure (colored letters come from the fig 3. above)
a. deletion - loss of part of a chromosome AC l DEF
b. duplication - segment is repeated ABBC l DEF
c. inversion - orientation is reverse of normal AED l
CBF (twisting)
d. translocation - parts are broken off and added to
another chromosome
ex. ABC l DEF and GH l IJK is changed to ABC l
JK and GH l IDEF
1.
2. Nondisjunction deals with whole chromosomes
or sets of chromosomes "not coming apart"
a. with one chromosome- during meiosis cell
gets both copies of a chromosome and the other cell
is missing one chromosome because sister chromatids
didn’t separate
i. monosomy - is the condition of having only
1 chromosome of a homologous pair,
Turner Syndrome= monosomy of 23rd pair
ii. trisomy -is the condition of having 3
chromosomes of a homologous pair,
Down Syndrome (21st pair), Klinefelter
Synd (23rd pair), XYY syndrome (23rd pair)
b. polyploidy- extra sets of chromosomes in the
same cell
*animals die, but plants get larger
i. haploid (1N)- 1 set of chromosomes,
human gamete has 23 chromosomes
ii. diploid (2N)- 2 sets of chromosomes,
human body cells have 46 chromosomes
iii. triploid (3N)- three sets of
chromosomes
iv. tetraploid (4N)- four sets of
chromosomes
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