Meiosis

1
Meiosis Genetics

• Sexual Cell Reproduction
• Ch. 10.2

2
Genetics

• The Study of Inherited Characteristics

3
Chromosome

DNA Code for traits
X
4
Genes on chromosomes
Hair Color

• Segments of DNA on a chromosome
• Code for a trait

X
Eye Color
5
Gene Segment For Hair color

6
Trait

• Characteristic
• Feature
• Variations in a population

7
Chromosome Number
Homologous Chromosomes are the sets of each pair

• Different for different species
• Full set 2NDiploid
• N
• pairs
• 1 pair from mother
• 1 pair from father
• Humans 23 pairs or
• 46 total

8
Autosomes Sex Chromosomes
Autosomes 1-22 for all traits except sex
Sex chromosomes Pair 23 XX(female)
or XY(male)
9
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
10
Gonads make gametes!
Testes make sperm
11
Gonads make gametes!
Ovaries make eggs
12
Gamete develoment

• Imature egg or sperm cell full set of
  chromosome (2N)
• Undergoes meiosis with 2 cell divisions
• Develops into a mature egg or sperm (1N)

2N
1N
13
Meiosis in the Gonads
Sperm
Meiotic cell division
Egg
14
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)
• 2nd division (1N)

15
Meiotic Cells..
Immature Egg or sperm
2N

• Divide twice to
• 1/2 Chromosome number
• Haploid
• Sperm or eggs

4N
2N
2N
1N
1N
1N
1N
16
Genetic Recombination

• Variety in chromosomes from
• Crossing over
• Exchange of parts
• Of Homologous chromosomes

B
A

• X

X
B
A
17
Nondysjunction chromosomes fail to dis-join
or separate

• Trisomygamete with 3 of one type
• Monosomygamete with 1 of one type
• Tripoidy zygote with three of one type

2N

• 2N

Eggs forming
2nd division
2N
empty
1N
1N

2N egg
3N

1N sperm
18
Down Syndrome 3 of 21
19
Klinefelters XXY
20
Turners Syndrome

• XO sex chromosome
• Instead of XX female
• Or XY for male

XO
X

Empty sperm