Transcript Sexual Preproduction and Meiosis

Asexual Reproduction
Sexual Reproduction
• recombination of genetic material
• More combinations means there is a higher
chance at least some will survive a
catastrophe
• Offspring not identical to parents
Sexual Reproduction
• Union 2 haploid
(1n) gametes
(Such as Sperm
and Egg)to form
a diploid (2n)
Zygote
Diploid vs Haploid
• These terms refer to the number of sets of
chromosomes an organism has.
• Humans are Diploid, we have two sets of
chromosomes 46 total or 23 Pairs of
“Homologous” chromosomes
• Sperm and eggs are haploid they only
have 23 chromosomes each.
• When sperm and egg join the resulting
zygote will have 46 chromosomes
Homologous Chromosomes
• Homologous means “Like” or “Same”
• Homologous chromosomes are
chromosomes that code for the same
genes. Remember that a gene codes for
a protein that may result in a trait.
• The homologous chromosomes may have
different version of the genes called
“Alleles” They code for the same trait but
may have different forms or colors.
Meiosis
• The process of making a haploid cell
• Also known as a reduction division
because the number of chromosomes is
reduced in this process.
• Two stages
– Meiosis I
– Meiosis II
– Results in 4 haploid (1N) Gamates
Meiosis I
– DNA is Replicated
– Homologous chromosomes line up in
metaphase.
– This is when genetic recombination can
occur… so not all offspring from the same pair
will be identical! Very important for variation
within a population and for the rise of new
species.
– Results in 2 haploid cells
Meiosis I
Meiosis II
– DNA in NOT replicated in the two haploid cells
– chromatids separate and divide
– results in 4 haploid (1n) cells.
Meiosis II
Prophase II
Metaphase II
Meiosis II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.