I.
Meiosis
A. Cell division that results in gametes w/ half the number of chromosomes
as the parent cell
B. 2 phase process: after interphase, cell enters Meiosis I (PMAT and
cytokinesis) and then goes through Meiosis II (PMAT and cytokinesis
1 cell (2n) ---meiosis I---> 2 cells (2n) ---meiosis II---> 4 cells (n)/gametes
C. In sexual reproduction, total chromosome number in the fertilized egg cell
(zygote) is doubled (2n, diploid); the chromosome number is cut in half in
meiosis (n, haploid); these two processes keep the number of chromosomes
balanced throughout continuing generations
D.
II.
Chromosomes
A. DNA in long strands, combined with proteins and enzymes, make up
chromatin ("colored string")
B. In interphase and leading into prophase, chromatin shortens and
condenses to form chromosomes ("colored bodies")
C. One set of chromosomes is received from each parent
1. these chromosomes pair up according to size and location of the
centromere to form homologous pairs of chromosomes
2. homologous chromosomes contain matching bands of genes in the
same locations
3. the last pair of chromosomes determine gender: XX is female, XY is
male
4. too many or too few chromosomes results from nondisjunction
III.
Nondisjunction and karyotypes
A.
Nondisjunction - failure of homologous chromosomes to separate
properly
1.
In meiosis 1, one chromosome from each homologous
chromosome pair moves to each pole of the cell
2.
In nondisjunction, both chromosomes of a homologous pair
move to the same pole
3.
2 kinds of gametes result: one gamete has an extra
chromosome, one gamete is missing a chromosome
a.
after fertilization, the zygote will have an extra
chromosome if the gamete with the extra chromosome
fuses with a normal gamete; called "trisomy".
b.
organisms with an extra chromosome often survive;
organisms lacking one or more chromosomes usually
do not; called "monosomy".
B.
C.
Karyotypes
1.
metaphase chromosomes, usually from a fetus, are
photographed, enlarged, and arranged in pairs according to
length and location of the centromere
2.
results in a chart of human chromosome pairs used to identify
an abnormal chromosome number in cells
a.
can identify trisomies: 21(Down's syndrome), 18
(Edward's syn.), 13 (Patau's syn.)
b.
monosomies: sex chromosomes (XO - Turner's syn.) and
autosome #5 (Cri du chat)
**autosome - the chromosomes that do not determine
gender
Mutations
1.
change in the sequence in DNA
2.
from error in replication, transcription, cell division, or by external
agents (i.e. uv rays)
3.
Can take place in:
a. reproductive cells - (egg or sperm) - passed on to offspring
b. body cells - not passed on to offspring
c. genes controlling cell division - results in uncontrolled cell division
(cancer)
4.
Types of mutations DNA sequence:
TAC
AAA
TCG
ACC
ACT
mRNA codons:
AUG
UUU
AGC
UGG
UGA
amino acids:
methionine phenylalanine serine tryptophan STOP
a. point mutation - change in a single nucleotide in DNA or base pair in
mRNA
mRNA codons:
AUG
UUa
AGC
UGG
UGA
amino acids:
methionine LEUCINE serine tryptophan stop
b. frame shift mutation - a single DNA nucleotide is lost or added;
mRNA codons are shifted by one base and every codon after that is
different
DNA sequence:
TAC
AAT
CGA CCA
CT...
mRNA codons:
AUG
UUA
amino acids:
methionine leucine
GCU
GGU
GA...
alanine glycine
c. deletion - part of a chromosome is left out
ABCDE - FGH
BCDE - FGH
d. insertion - part of a chromatid breaks off and is added to the SISTER
chromatid
ABCDE - FGH / ABCDE - FGH
ABABCDE - FGH / CDE - FGH
e. inversion - part of a chromosome breaks off and reattaches
backwards
ABCDE - FGH
ABCDE - HGF
f. translocation - part of a chromatid breaks off and attaches to a NONSISTER chromatid
ABCDE - FGH
RSTUV - XYZ
--->
RSTABCDE - FGH
UV - XYZ