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) + Egg (23)

=A new human (46) !

Review3. 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 removed4. Duplication: region of a chromosome is doubled5. 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 defectsa. 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_Prenatal

DiagnosticImage5.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/turnersynd

romexnoy.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/edwards.jpg

• http://www.specialchild.com/archives/poster-child075.jpg• http://www.wehs.warren.k12.ky.us/WEHS/Departments/

Science%20Department/AP%20Web%20Sites/kruti/patau.jpg• http://medicalimages.allrefer.com/large/syndactyly.jpg• http://www.somi.org/newspubs/profiles/photos/jenna_cole.jpg

• www6.district125.k12.il.us • https://www.youtube.com/watch?v=6EG6u-

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