Transcript Homologous chromosome

MEIOSIS
SOURCE
BIOLOGY: CONCEPTS AND CONNECTIONS
BY CAMPBELL, REECE, MITCHELL, TAYLOR
4.1 Chromosomes, genes, alleles
and mutation
Define:
A. Chromosome: is made of long thread of DNA
packaged with proteins. It is replicated before
division and visible in a stained cell.
B. Chromatin: eukaryotic genetic material made of
DNA and protein.
C. Chromatid: one of the two copies of
chromosome after it has replicated.
D. Gene: a heritable character that controls a
specific character.
More definitions
E. Genome: the genetic complement of an
organism.
F. Mutation: change in the nucleotide
sequence of a DNA of a chromosome
H: Homologous chromosome: chromosomes
in the diploid cell which contains the same
sequence of genes from different parents. .
Distinguish eukaryotic DNA and prokaryotic
DNA
Gene mutation
Gene mutation: mutation happens on only one
gene.
Chromosomal mutation: mutation affects more
than one genes.
Figure 10.16A
Normal hemoglobin DNA
C T
Mutant hemoglobin DNA
C A T
T
mRNA
mRNA
G A A
G U A
Normal hemoglobin
Sickle-cell hemoglobin
Val
Glu
Figure 10.16B
Normal
gene
mRNA
Protein
Nucleotide
substitution
A
U G A A G U
Met
A U G A
Met
Lys
U
U G G C G
C
Phe
Gly
Ala
U A G C
A G U U
Lys
Phe
Ser
G C
A
A
Ala
U Deleted
Nucleotide
deletion
A U G A A G
Met
U
U G G C G
Ala
Leu
Lys
C A
U
His
Inserted
Nucleotide
insertion
A U G A A G
Met
Lys
U
U G
Leu
U G G
C G C
Ala
His
MEIOSIS OVERVIEW
* Diploid cell produces 4 haploid daughter cells
* Daughter cells are NOT genetically identical to the
parent or to each other (there is genetic variation)
* Sex cells (gametes: egg and sperm) are produced by
meiosis
* Meiosis is the basis of sexual reproduction (two
parents produce sex cells that fertilize to form the
zygote)
PREPARED BY CANAN ÇERMEN
SOURCE: BIOLOGY: CONCEPTS AND CONNECTIONS BY CAMPBELL, REECE, MITCHELL, TAYLOR
PREPARED BY CANAN ÇERMEN
SOURCE: BIOLOGY: CONCEPTS AND CONNECTIONS BY CAMPBELL, REECE, MITCHELL, TAYLOR
MEIOSIS consists of 2 consecutive cell
divisions: Meiosis I and Meiosis II
INTERPHASE
These events are same as mitosis:
* DNA and centriole replication
* Protein synthesis increases
* ATP synthesis increases
PROPHASE I
These events are same as mitosis:
* Chromatin condenses into visible chromosomes
* Nucleolus disappears
* Nuclear membrane disappears
* Duplicated centrioles start moving to opposite
poles
* Spindle fibers begin to form
PROPHASE I
continued
These events are different than mitosis:
* Homologous chromosomes pair up forming
tetrads
* Crossing-over occurs between non-sister
chromatids of homologous chromosomes
(Crossing-over: exchange of genetic material)
PREPARED BY CANAN ÇERMEN
SOURCE: BIOLOGY: CONCEPTS AND CONNECTIONS BY CAMPBELL, REECE, MITCHELL, TAYLOR
HOMOLOGOUS CHROMOSOMES
* carry same genes for the same characteristics
* they are of same length, same shape
* one is inherited from the organism’s father, the
other from the mother
METAPHASE I
These events are different than mitosis:
* Tetrads line up at the equator of the cell
These events are same as mitosis:
* Spindle fibers are attached to the chromosomes at
the centromeres
ANAPHASE I
These events are different than mitosis:
* Homologous chromosomes are pulled to
opposite poles by the spindle fibers
TELOPHASE I
These events are same as mitosis:
* Chromosomes decondense into chromatin
* Nucleolus reforms
* Nuclear membrane reforms
* Spindle fibers disappear
* Cytokinesis starts
MEIOSIS I is a reduction division.
* The chromosome number is halved:
2 haploid cells are produced.
* These haploid cells are different than normal
haploid cells: their chromosomes have 2 sister
chromatids.
MEIOSIS II is the same as mitosis.
The difference is that it starts with haploid cells.
The aim of meiosis II is to create real haploid cells
where chromosomes have only single
chromatids.
PREPARED BY CANAN ÇERMEN
SOURCE: BIOLOGY: CONCEPTS AND CONNECTIONS BY CAMPBELL, REECE, MITCHELL, TAYLOR
PROPHASE II
METAPHASE II
ANAPHASE II
TELOPHASE II
CYTOKINESIS
These events are same as mitosis.
FACTORS LEADING TO GENETIC VARIATION IN
SEXUAL REPRODUCTION
* Crossing-over
* Random orientation of chromosomes
* Separation of homologous chromosomes
* Fertilization
Karyotype of human female
PREPARED BY CANAN ÇERMEN
SOURCE: BIOLOGY: CONCEPTS AND CONNECTIONS BY CAMPBELL, REECE, MITCHELL, TAYLOR
Karyotype of human male
NONDISJUNCTION
* An error in meiosis, in which either homologous
chromosomes or sister chromatids do not
separate.
* It can happen with autosomal chromosomes or
gonosomal chromosomes.
PREPARED BY CANAN ÇERMEN
SOURCE: BIOLOGY: CONCEPTS AND CONNECTIONS BY CAMPBELL, REECE, MITCHELL, TAYLOR
Trisomy
Down syndrome
If a normal gamete fertilizes a gamete with
nondisjunction,
the fertilized egg will have
either one more or one less copy of an
autosomal or gonosomal chromosome.
HL 10.1
Outline the formation of chiasmata in the process of
crossing over.
- Two homologous chromosomes come
together by synapsis.
- Two homologous chromosomes overlap each
other (attach each other at different points).
- The connection parts are called chiasmata.
- They exchange genetic materials.
- They separate from each other.
10.1.3. Explain genetic variation
Depending on how homologous pairs line up
during metaphase 1, the genetic combination
of daughter cells will change.
C
E
c
e
Crossing over
1
Breakage of homologous chromatids
C
E
c
e
2
Tetrad
(pair of homologous
chromosomes in synapsis)
Joining of homologous chromatids
E
C
Chiasma
c
e
3
Separation of homologous
chromosomes at anaphase I
C
E
C
c
e
E
c
e
4
Separation of chromatids at
anaphase II and
completion of meiosis
C
E
C
e
c
E
c
e
Parental type of chromosome
Recombinant chromosome
Recombinant chromosome
Parental type of chromosome
Gametes of four genetic types