Sexual reproduction & Genetic inheritance PHA: Biology 9 Moretti and Dickson

Asexual vs. Sexual Reproduction Asexual Reproduction One parent Parent and offspring are genetically identical (clones) Reproduce using MITOSIS Sexual Reproduction Two parents Offspring are genetically different from parents Reproduce using MEIOSIS (makes eggs and sperm) and FERTILIZATION (egg and sperm join) Objectives for Class: Describe the difference between asexual and sexual reproduction

Sexual reproduction cycle:

Human body cells contain… Over 20,000 genes stored on 46 chromosomes 23 pairs of homologous chromosomes Everyone has pairs 1-22 23rd pair = sex-determining chromosomes Females = X X Males = X Y Objectives for Class: Explain how karyotypes are made and be able to identify homologous chromosomes in a human karyotype. Differentiate between a male and female karyotype.

Karyotyping Activity – Part I Complete up through page 4. Individual A Individual A Circle 3 pairs of homologous chromosomes Answer the questions about each karyotype on the packet. Objectives for Class: Explain how karyotypes are made and be able to identify homologous chromosomes in a human karyotype. Differentiate between a male and female karyotype.

Major Genetics Terms Gene: Alleles: Chromosome: A section of DNA that holds instructions for making one protein Ex: gene for hemoglobin protein Alleles: Different versions of a gene Ex: normal hemoglobin allele vs. mutated hemoglobin allele Chromosome: A long strand of DNA, coiled and wrapped up, that contains many genes Homologous Chromosomes:  A pair of chromosomes that contain the same genes but not necessarily the same alleles

Major Genetics Terms (continued) Diploid: A cell that contains TWO COPIES of every chromosome (in homologous pairs) All human body cells except gametes are diploid. Haploid: A cell that contains ONE COPY of every chromosome Gametes are haploid.  Gametes: Egg or sperm cells, used in sexual reproduction. Contain HALF the number of chromosomes as all other body cells (they are haploid!) Meiosis: The process of making gametes. 1 Diploid cell  4 Haploid cells Separates homologous chromosomes into different cells

Sexual reproduction cycle:

Start: Diploid Cell Start: Diploid Cell End: 4 Haploid Cells (46 Chromosomes in Humans) Start: Diploid Cell (46 Chromosomes in Humans) Meiosis I: chromosomes line up with homologous pairs, which then separate (sister chromatids stay together) Mitosis: chromosomes line up single file and sister chromatids split Meiosis II: sister chromatids split (like mitosis) End: 4 Haploid Cells (23 Chromosomes in Humans) Cells different from starting cell (half the # of chromosomes) End: 2 Diploid Cells (46 Chromosomes in Humans) Cells same as starting cell

Summary of Meiosis: DNA is replicated once Draw this diagram! DNA is replicated once Chromosomes and cells are divided twice: Meiosis I: Homologous chromosomes pair up and separate Forms 2 haploid cells Chromosomes still have sister chromatids Meiosis II: Sister chromatids separate Final result: 4 haploid gametes with HALF the number of chromosomes as the original cell Gametes Objectives for Class: Explain how meiosis produces 4 haploid sex cells (gametes) – eggs and sperm

Now think about this… Why do siblings with the same parents look different from each other? In other words: How can the same mom and dad produce many different kids, with different genes? Meiosis creates genetic diversity between gametes – no two eggs are alike! No two sperms are alike! You will investigate this in the Modeling Meiosis activity right now.

Two Ways Meiosis generates genetic diversity between gametes: Independent alignment of homologous pairs during Metaphase I. A cell with 2 homologous pairs yields 4 possible gametes. How many are possible with 23 homologous pairs?

Two Ways Meiosis generates genetic diversity between gametes: 2. Crossing over during Prophase I. One sister chromatid trades a section of DNA with its homologous partner. Creates new combinations of alleles on chromosomes. Can happen at multiple places along the chromosome, allowing for a nearly infinite number of different gametes.