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Meiosis and Human Reproduction
SPERMATOGENESIS
OOGENESIS
Learning Targets
“I Can . . .”
-State the number of chromosomes in a typical
human being.
-Name the two sex chromosomes in a human
female.
-Name the two sex chromosomes in a human
male.
-Define “nondisjunction.”
Chromosomes
Review
1. Human cells are diploid, meaning there are 23
pairs of chromosomes for a total of 46.
2. Human sex cells are haploid. Each sex cell
(gamete) has 23 chromosomes and only one copy
of every gene.
Sperm (23)
+
=
A new human (46) !
Egg (23)
Review
3. Genes are located on chromosomes. The location
where they are found on that chromosome is called a
locus (pl. loci)
*Chromosome theory of heredity: Genes are located
on the chromosomes and each gene occupies a
specific place on a chromosome. A gene may
exist in several forms called alleles, and each
chromosome contains one allele for each gene.
Review
4. Genes are swapped between
homologous chromosomes during
prophase I of meiosis when chromosomes
are paired as tetrads. This process is
called crossing over
Sex Determination
1. Autosomes (22 pairs): chromosomes
that are the same in males and females
2. Sex chromosomes (23rd pair): final “pair”
of chromosomes that are different in males
and females
a. Females are XX
b. Males are XY
3. Genes that are found on sex
chromosomes are sex-linked.
Chromosome mutations: change in the
number or structure of chromosomes
1. Inversion: a section of a chromosome is reversed in
order
2. Translocation: non-homologous chromosomes swap
regions
3. Deletion: part of a chromosome is removed
4. Duplication: region of a chromosome is doubled
5. Nondisjunction: chromosome pairs do not separate
during meiosis
*Many genetic disorders result from chromosome
nondisjunction during meiosis (diagram, page 401)
Chromosome mutations: change in the
number or structure of chromosomes
Chromosome mutations can be
observed using a karyotype
1. Karyotype: the arrangement of
homologous pairs of chromosomes
2. Common chromosomal defects
a. Down Syndrome (Trisomy 21)
b. Edwards Syndrome (Trisomy 18)
c. Patau Syndrome (Trisomy 13)
d. Turner Syndrome (X)
e. ______________ Syndrome (XXY)
Karyotype for a person with Down
Syndrome
Extra chromosome at
the 21st position
Characteristics facial
features such as
widely-spaced eyes,
flat noses, and large
tongues
Mild to severe mental
retardation
Down Syndrome
Edwards Syndrome
Edwards Syndrome
Patau Syndrome
Patau Syndrome
Sex Chromosome Disorders
Turner Syndrome
Klinefelter Syndrome
References
• http://staff.jccc.net/PDECELL/celldivision/chromosome1.gif
• http://www.dhss.mo.gov/Genetics/TalkCornerArchives/07_PrenatalD
iagnosticImage5.gif
• https://images2.clinicaltools.com/images/gene/karyotypes/trisomy13.
jpg
• http://images2.clinicaltools.com/images/gene/trisomyxxy.jpg
• http://images2.clinicaltools.com/images/gene/karyotypes/turnersyndr
omexnoy.jpg
• http://www.bbc.co.uk/scotland/education/bitesize/higher/img/biology/
genetics_adaptation/mutations/07chromosome_mutation.gif
• http://www.biologycorner.com/bio1/meiosis.html
References
• http://www.ispub.com/xml/journals/ijtwm/vol4n2/edwards
-fig1.jpg
• http://www.wehs.warren.k12.ky.us/WEHS/Departments/
Science%20Department/AP%20Web%20Sites/kruti/edw
ards.jpg
• http://www.specialchild.com/archives/poster-child075.jpg
• http://www.wehs.warren.k12.ky.us/WEHS/Departments/
Science%20Department/AP%20Web%20Sites/kruti/pata
u.jpg
• http://medicalimages.allrefer.com/large/syndactyly.jpg
• http://www.somi.org/newspubs/profiles/photos/jenna_col
e.jpg
• www6.district125.k12.il.us
• https://www.youtube.com/watch?v=6EG6u
-am-h0