HEREDITY WHAT MAKES YOU YOU OVERVIEW VARIATIONS ON

HEREDITY! WHAT MAKES YOU, YOU!

OVERVIEW: VARIATIONS ON A THEME Living organisms are distinguished by their ability to reproduce their own kind © 2011 Pearson Education, Inc.

VOCAB REVIEW… Genetics - study of heredity and variation Heredity - transmission of traits from one generation to the next Variation is the differences

FIGURE 13. 1

HOW DOES HEREDITY HAPPEN? Genes: parents offspring through chromosomes Children inherit genes, not traits Genes - the units of heredity § made up of segments of DNA © 2011 Pearson Education, Inc.

INHERITANCE OF GENES – THE BASICS Genes - passed on via gametes § (sperm and eggs) Each gene has a specific location on a certain chromosome called a locus Most DNA is packaged into chromosomes © 2011 Pearson Education, Inc.

ASEXUAL VS. SEXUAL REPRODUCTION Asexual - a single individual §NO fusion of gametes Clone - genetically identical individuals from the same parent Sexual reproduction – 2 parents, offspring have unique combinations of genes http: //www. youtube. com/watch? v=-B 7 ANli 2 xf. Y © 2011 Pearson Education, Inc.

FIGURE 13. 2 0. 5 mm Parent Bud (a) Hydra (b) Redwoods

WHAT ABOUT US? Humans have 23 pairs of chromosomes in somatic cells (any cell other than a gamete) Somatic cells are 2 n (diploid = 2 sets) because there is one set of chromosomes from ma and one from pa Karyotype © 2011 Pearson Education, Inc.

The two chromosomes in each pair are called homologous chromosomes, or homologs Homologous pairs are: - same length - Same shape - carry genes for the same inherited characters

For humans, the diploid number is 46 Somatic cell = (2 n = 46) Gamete (n=23) © 2011 Pearson Education, Inc.

SEX CHROMOSOMES X and Y Human females have (XX) Human males (XY) Autosomes - The remaining 22 pairs of chromosomes (non-sex chromosomes) © 2011 Pearson Education, Inc.

FIGURE 13. 3 APPLICATION TECHNIQUE Pair of homologous duplicated chromosomes Centromere Sister chromatids Metaphase chromosome 5 m

FIGURE 13. 3 B Pair of homologous duplicated chromosomes Centromere Sister chromatids Metaphase chromosome 5 m

FIGURE 13. 4 Key 2 n 6 Maternal set of chromosomes (n 3) Paternal set of chromosomes (n 3) Sister chromatids of one duplicated chromosome Two nonsister chromatids in a homologous pair Centromere Pair of homologous chromosomes (one from each set)

Fertilization and meiosis alternate in sexual life cycles © 2011 Pearson Education, Inc.

Fertilization (the union of gametes) zygote mitosis (growth/development) adult meiosis gametes …and the cycle repeats… © 2011 Pearson Education, Inc.

Or in terms of chromosomes sets… n + n 2 n (fertilization) 2 n n (gamete production/meiosis) Fertilization and meiosis alternate in sexual life cycles to maintain chromosome number **1 n = haploid © 2011 Pearson Education, Inc.

FIGURE 13. 5 Haploid gametes (n 23) Key Haploid (n) Diploid (2 n) Egg (n) Sperm (n) MEIOSIS Ovary FERTILIZATION Testis Diploid zygote (2 n 46) Mitosis and development Multicellular diploid adults (2 n 46)

THE VARIETY OF SEXUAL LIFE CYCLES - Three main types of sexual life cycles - Differ in the timing of meiosis and fertilization © 2011 Pearson Education, Inc.

FIGURE 13. 6 Key Haploid (n) Diploid (2 n) n Gametes n Mitosis n MEIOSIS n FERTILIZATION n Diploid multicellular organism (a) Animals Zygote 2 n Mitosis n 2 n Diploid multicellular organism (sporophyte) Mitosis n Spores Gametes MEIOSIS 2 n Haploid unicellular or multicellular organism Haploid multicellular organism (gametophyte) n n Gametes FERTILIZATION (b) Plants and some algae n FERTILIZATION MEIOSIS 2 n Zygote Mitosis 2 n Zygote (c) Most fungi and some protists

FIGURE 13. 6 A Key Haploid (n) Diploid (2 n) n We are familiar with this one… Gametes n n MEIOSIS FERTILIZATION 2 n Zygote 2 n Diploid multicellular organism Mitosis (a) Animals

Animals… • Gametes are the only haploid cells in animals § are produced by meiosis § undergo no further cell division before fertilization • Gametes fuse to form a 2 n zygote that divides by mitosis to develop into a multicellular organism © 2011 Pearson Education, Inc.

SOME PLANTS AND ALGAE DO THINGS DIFFERENTLY And we call it an alternation of generations - life cycle includes both a 2 n and 1 n multicellular stage - The 2 n organism (sporophyte) makes haploid (1 n) spores by meiosis © 2011 Pearson Education, Inc.

- spore grows (mitosis) haploid organism called a gametophyte - gametophyte makes haploid gametes by mitosis - Fertilization of gametes results in a diploid sporophyte © 2011 Pearson Education, Inc.

FIGURE 13. 6 B Key Haploid (n) Diploid (2 n) Haploid multicellular organism (gametophyte) Mitosis n n Spores Gametes MEIOSIS 2 n Diploid multicellular organism (sporophyte) n FERTILIZATION 2 n Zygote Mitosis (b) Plants and some algae

And then we have fungi and some protists… - 2 n zygote (meiosis) haploid cells make 1 n multicellular organism - haploid adult produces gametes by mitosis © 2011 Pearson Education, Inc.

FIGURE 13. 6 C Key Haploid (n) Diploid (2 n) Haploid unicellular or multicellular organism Mitosis n n n Mitosis n Gametes MEIOSIS n FERTILIZATION 2 n Zygote (c) Most fungi and some protists

A NOTE ON HAP & DIP • either 1 n or 2 n cells can divide by mitosis • only diploid cells can undergo meiosis In all three life cycles, the halving and doubling of chromosomes contributes to… genetic variation in offspring © 2011 Pearson Education, Inc.

ONE MORE LITTLE DIFFERENCE BETWEEN MITOSIS AND MEIOSIS… Sister chromatids are held together during division by protein complexes called cohesins Mitosis: cohesins are cleaved at the end of metaphase Meiosis: cohesins are cleaved along the chromosome arms in anaphase I (separation of homologs) and at the centromeres in anaphase II (separation of sister chromatids) © 2011 Pearson Education, Inc.