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Jim's Meiosis Notes
Reproduction Review
Asexual (Vegetative) Reproduction
 A form of duplication using only mitosis.
 Example, a new plant grows out of the root or a shoot from an existing
plant.
 Produces only genetically identical offspring since all divisions are by
mitosis.
1. offspring called clones meaning that each is an exact copy of the
original organism
2. this method of reproduction is rapid and effective allowing the
spread of an organism
3. Since the offspring are identical, there is no mechanism for
introducing diversity
Sexual reproduction
 Formation of new individual by a combination of two haploid sex cells
(gametes).
 Fertilization- combination of genetic information from two separate cells
that have one half the original genetic information
 Gametes for fertilization usually come from separate parents
1. Female- produces an egg
2. Male produces sperm
 Both gametes are haploid, with a single set of chromosomes
 The new individual is called a zygote, with two sets of chromosomes
(diploid).
 Meiosis is a process to convert a diploid cell to a haploid gamete, and
cause a change in the genetic information to increase diversity in the
offspring.
Chromosomes in a Diploid Cell
Summary of chromosome characteristics
 Diploid set for humans; 2n = 46
 Autosomes; homologous chromosomes, one from each parent (humans =
22 sets of 2)
 Sex chromosomes (humans have 1 set)
1.Female-sex chromosomes are homologous (XX)
2.Male-sex chromosomes are non-homologous (XY)
Karyotyping
Karyotype - A pictorial display of metaphase chromosomes from a mitotic
cell
Homologous chromosomes- pairs
Spectral Karyotyping- a new method
Ploidy: Number of sets of chromosomes in a cell
Haploid (n)-- one set chromosomes
Diploid (2n)-- two sets chromosomes
Most plant and animal adults are diploid (2n)
Eggs and sperm are haploid (n)
A review of Meiosis
Comparing Meiosis and Mitosis
Chromosome behavior
1. Mitosis: Homologous chromosomes independent
2. Meiosis: Homologous chromosomes pair forming bivalents until
anaphase I
Chromosome number- reduction in meiosis
1.mitosis- identical daughter cells
2.meiosis- daughter cells haploid
Genetic identity of progeny:
1. Mitosis: identical daughter cells
2. Meiosis: daughter cells have new assortment of parental
chromosomes
3. Meiosis: chromatids not identical, crossing over
Meiotic errors
Nondisjunction- homologues don't separate in meiosis1
1.results in aneuploidy
2.usually embryo lethal
3.Trisomy 21, exception leading to Downs syndrome
4.Sex chromosomes
1.Turner syndrome: monosomy X
2.Klinefelter syndroms: XXY
 Translocation and deletion: transfer of a piece of one chromosome to
another or loss of fragment of a chromosome.
Mitosis, Meiosis, and Ploidy
 Mitosis can proceed independent of ploidy of cell, homologous
chromosomes
 behave independently
 Meiosis can only proceed if the nucleus contains an even number of
chromosomes (diploid, tetraploid).
 Trisomy 21 does not prevent meiosis