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Meiosis
• Standard 2a
Meiosis is an early step in sexual reproduction in
which the pairs of chromosomes separate and
segregate randomly during cell division to produce
gametes containing one chromosome of each type.
• Standard 2b
Only sperm and egg (gametes) are made by the
process of meiosis.
• Standard 2d
New combinations of alleles may be generated in a
zygote through the fusion of male and female
gametes (fertilization)
●
Standard 2e
Approximately half of an individual’s DNA
sequence comes from each parent.
- sexual reproduction to
produce sperm and eggs
-replicating(copying)
the DNA/chromosomes
once, and dividing twice
• Interphase I
– DNA replicates
• Prophase I – chromosomes pair up
**Crossing-Over – chromosomes
from the same pair exchange
portions producing new
combinations (variation)
continued
Metaphase I –chromosomes
line up in the middle
Anaphase I –chromosomes
separate
Telophase I & Cytokinesis
– two new HAPLOID cells
are formed
• Prophase II –
chromosomes pair
up
• Metaphase II –
chromosomes line
up
continued
• Anaphase II – sister
chromatids separate
• Telophase II &
Cytokinesis – 4 unique
haploid daughter cells
are made
• In females, 1
becomes an egg
In males, all 4
become sperm
Fertilization – uniting two haploid cells
(egg and sperm) to form a diploid zygote
during sexual reproduction
-50% of the genetic material comes from each
parent.
Sex Chromosomes
- Male sex chromosomes – XY
- Female sex chromosomes – XX
Autosomes – all other chromosomes
• Production of two
genetically identical
diploid cells
•Production of
four genetically
different haploid
cells, gametes
5 Essential Questions - Meiosis
1. What are chromosomes?
2. Which cells undergo meiosis? Describe the
final products of meiosis.
3. What happens to alleles during meiosis?
4. What % of DNA is contributed by a mother?
A father?
5. What is the result of fertilization?