Presentation on theme: "Meiosis and Human Reproduction"— Presentation transcript:
1 Meiosis and Human Reproduction SPERMATOGENESISOOGENESIS
2 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.”
4 Review1. 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) !
5 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.
6 Review4. Genes are swapped between homologous chromosomes during prophase I of meiosis when chromosomes are paired as tetrads. This process is called crossing over
7 Sex Determination1. Autosomes (22 pairs): chromosomes that are the same in males and females2. Sex chromosomes (23rd pair): final “pair” of chromosomes that are different in males and femalesa. Females are XXb. Males are XY3. Genes that are found on sex chromosomes are sex-linked.
8 Chromosome mutations: change in the number or structure of chromosomes 1. Inversion: a section of a chromosome is reversed in order2. Translocation: non-homologous chromosomes swap regions3. Deletion: part of a chromosome is removed4. Duplication: region of a chromosome is doubled5. Nondisjunction: chromosome pairs do not separateduring meiosis*Many genetic disorders result from chromosome nondisjunction during meiosis (diagram, page 401)
9 Chromosome mutations: change in the number or structure of chromosomes
10 Chromosome mutations can be observed using a karyotype 1. Karyotype: the arrangement of homologous pairs of chromosomes2. Common chromosomal defectsa. Down Syndrome (Trisomy 21)b. Edwards Syndrome (Trisomy 18)c. Patau Syndrome (Trisomy 13)d. Turner Syndrome (X)e. ______________ Syndrome (XXY)
11 Karyotype for a person with Down Syndrome Extra chromosome at the 21st positionCharacteristics facial features such as widely-spaced eyes, flat noses, and large tonguesMild to severe mental retardation