Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Genomic imprinting wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Gene expression programming wikipedia , lookup
Designer baby wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Y chromosome wikipedia , lookup
X-inactivation wikipedia , lookup
Microevolution wikipedia , lookup
Chapter 12 Meiosis and Sexual Reproduction Albia Dugger • Miami Dade College 12.1 Why Sex? • In sexual reproduction, offspring arise from two parents and inherit genes from both • Asexual reproduction produces genetically identical copies of a parent (clones) Advantages of Sexual Reproduction Sexual Reproduction in Animals and Plants Introducing Alleles • Genes are regions in DNA that traits (ice cream) • Alleles are different forms of the same gene (vanilla, chocolate) • Offspring of sexual reproducers inherit new combinations of alleles, the basis of traits Life cycle of humans 46 46 X mitosis 23 23 46 46 92 Some day I am going to be a sperm, or 4 even! Dad’s cell But, you have to get the correct 23 – what do I want to donate for my baby? In order to do this, our cells use the machinery set up for mitosis, that is, the chromosomes are copied first and compacted, then they can get moved around So, let’s talk about replicated chromosomes. There are 23 pairs of homologues. Double set/ Diploid # 2N = 46 Single set/ Haploid # N = 23 One pair Where is meiosis occurring? 2N 2N 2N 2N 2N 2N 2N N 2N Spermatogenesis In females: 2N 2N N 2N 2N 2N 2N 2N 2N Oogenesis Occurs 3 months in utero Homologous chromosomes Gene for hair color brown black Gene for lip size G C A T T A thin fat T A G C C G Alleles Gene for hair color A B brown a black b T A G C C G C D C Gene for lip size d E G C A T T A thin fat E Replication of homologues One chromatid centromere Summary of Steps in Meiosis Meiosis Meiosis I One diploid nucleus to two haploid nuclei 1 Prophase I. Homologous chromosomes condense, pair up, and swap segments. Spindle micro- tubules attach to them as the nuclear envelope breaks up. plasma membrane nuclear envelope breaking up 2 Metaphase I. The homologous chromosome pairs are aligned midway between spindle poles. 3 Anaphase I. The homologous chromosomes separate and begin heading toward the spindle poles. 4 Telophase I. Two clusters of chromosomes reach the spindle poles. A new nuclear envelope forms around each cluster, so two haploid (n) nuclei form. spindle centrosome one pair of homologous chromosomes Stepped Art Meiosis Meiosis II Two haploid nuclei to four haploid nuclei 5 Prophase II. The chromosomes condense. Spindle microtubules attach to each sister chromatid as the nuclear envelope breaks up. 6 Metaphase II. The (still duplicated) chromosomes are aligned midway between poles of the spindle. 7 Anaphase II. All sister chromatids separate. The now unduplicated chromo somes head to the spindle poles. 8 Telophase II. A cluster of chromosomes reaches each spindle pole. A new nuclear envelope encloses each cluster, so four haploid (n) nuclei form. No DNA replication Stepped Art Meiosis I – Prophase I Synapsis is actually occurring here, with crossing over Synapsis, crossing over pairing of homologues Sperm Formation in Animals 2 3 4 1 male germ cell sperm Stepped Art Egg Formation in Animals 5 6 7 egg female germ cell Stepped Art Fertilization • Chance combinations of maternal and paternal chromosomes through fertilization produce a unique combination of genetic information • Fertilization • The fusion of two haploid gametes (sperm and egg) resulting in a diploid zygote Fertilization Comparing Mitosis and Meiosis Meiosis I One diploid nucleus to two haploid nuclei Prophase I Anaphase I • Chromosomes condense. Telophase I • Homologous • Homologous chromosomes pair. Metaphase I • Chromosome clusters arrive chromosomes • Crossovers occur (not shown). • Chromosomes align midway separate and move opposite spindle poles. • Spindle forms and attaches between spindle toward at spindle • New nuclear envelopes form. chromosomes to spindle poles. poles. • Chromosomes decondense. poles. • Nuclear envelope breaks up. Stepped Art Comparing Mitosis and Meiosis Mitosis One diploid nucleus to two diploid nuclei Prophase • Chromosomes condense. • Spindle forms and attaches chromosomes to spindle poles. • Nuclear envelope breaks up. Metaphase • Chromosomes align midway between spindle poles. Anaphase Telophase • Sister chromatids • Chromosome clusters arrive separate and move opposite spindle poles. toward at spindle • New nuclear envelopes form. poles. • Chromosomes decondense Stepped Art Comparing Mitosis and Meiosis Meiosis II Two haploid nuclei to four haploid nuclei Prophase II Metaphase II Anaphase II Telophase II • Chromosomes condense. • Chromosomes • Sister chromatids • Chromosome clusters arrive • Spindle forms and attaches align midway separate and move at spindle poles. chromosomes to spindle poles. between spindle toward opposite • New nuclear envelopes form. • Nuclear envelope breaks up. poles. spindle poles. • Chromosomes decondense. Stepped Art Mouse Cell Nuclei During Meiosis Practice