Transcript Meiosis Chapeter 11 section #4

Meiosis & Genetics
Sexual Cell Reproduction
Ch. 10.2
Genetics
The Study of Inherited
Characteristics
Chromosome
DNA
Code
for
traits
Genes on chromosomes:
• Segments of
DNA on a
chromosome
• Code for a
trait
Hair
Color
Eye
Color
Gene
Segment
For
Hair color
Trait
• Characteristic
• Feature
• Variations in
a population
Chromosome Number
•Homologous
Different # for different
species
Chromosomes
• Full set = 2N=Diploid
are
the
sets
of
• N=
pair
•each
# pairs
• 1 pair from mother
• 1 pair from father
• Humans= 23 pairs or
• 46 total
Autosomes & Sex Chromosomes
Autosomes = # 122 for all traits
except sex
Sex chromosomes=
Pair # 23 XX(female) or
XY(male)
Why do cells divide by Meiosis?
Sperm
• To reduce
chromosome number
• In sex cells
• Or in single celled
organisms:
• Under changing
conditions for
• Chromosome Variety
N egg
N
2N baby
Gonads make gametes!
Testes
make
sperm
Gonads make gametes!
Ovaries
make
eggs
Gamete develoment
2N
1N
• Imature egg or
sperm cell = full set
of chromosome (2N)
• Undergoes meiosis
with 2 cell divisions
• Develops into a
mature egg or sperm
(1N)
Meiosis in the Gonads
Sperm
Meiotic cell
division
Egg
Stages in Meiosis:
• Interphase
•
•
•
•
•
•
•
•
Prophase I
Metaphase I
Anaphase I
Telophase I
Prophase II
Metaphase II
Anaphase II
Final Telophase
• Full set of
chromosomes (2N)
• DNA has doubled
(4N)
• 1st cell division (2N)
• DNA does not
double
• 2nd division
• Sperm & Egg (1N)
Meiotic Cells……..
2N
• Divide twice to
• 1/2
Chromosome
number
• “Haploid”
• Sperm or eggs
Immature
Egg or
sperm
4N
2N
1N
1N
2N
1N
1N
Genetic Recombination
• Variety in
chromosomes from
• Crossing over =
• Exchange of parts
• Of Homologous
chromosomes
A B
B
A
Nondysjunction = chromosomes
fail to “dis-join” or separate:
• Trisomy=gamete
with 3 of one type
• Monosomy=gamete
with 1 of one type
• Tripoidy= zygote
with three of one
type
2N
egg
2N
2N
Eggs forming
2nd division
2N
empty
+
1N
sperm
1N
1N
= 3N
Down Syndrome= 3 of #21
Klinefelter’s = XXY
Turner’s Syndrome
• XO sex chromosome
• Instead of XX female
• Or XY for male:
X
+
Empty
sperm
=
XO