Chapter 11-4: Meiosis and Sexual Reproduction

Chapter 11-4: Meiosis Key concepts from this section: Summarize the process of meiosis. Describe the role of gametes in sexual reproduction. Organize human chromosomes into homologous pairs. California content standards: Genetics 2 a, b, e

Ca Standards: Genetics 2a: Sexual reproduction requires gametes to be produced via meiosis. Chromosomes segregate randomly during this process. Genetics 2b: Meiosis only happens in certain cells. Half of an individual’s DNA comes from each parent.

Review: Asexual reproduction, 1 parent, offspring identical to parent. (Mitosis) Chromosome number stays the same. Mitosis is responsible for growth, repair, reproduction.

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Organisms can reproduce asexually (DNA contributed by 1 parent) Review Organisms can reproduce asexually (DNA contributed by 1 parent) OR sexually (DNA contributed by 2 parents). 11-4

The main idea for this section: Chromosome number is reduced in meiosis. This homologous pair gets separated. 11-4

In sexual reproduction, the genetic info of one parent is combined with that of another parent to produce a genetically distinct offspring (offspring with traits of both parents). 11-4

Meiosis is an early step in sexual reproduction. Mitosis (simple cell division): chromosome # remains the same. Meiosis: chromosome # is reduced. Meiosis is an early step in sexual reproduction. 11-4

Animals: sperm and eggs Plants: pollen and eggs Terms to know Gametes: special sex cells which join together to form a new organism. (contain ½ the number of chromosomes of parents – haploid.) Animals: sperm and eggs Zygote is formed. Plants: pollen and eggs Seed/fruit is formed. 11-4

Single cell formed in this fusion is called a zygote. Terms to know Fertilization: fusion of nuclei of male and female gametes. (original chromosome number is restored) Single cell formed in this fusion is called a zygote. 11-4

Body cells of every species have a certain number of chromosomes. 168 26 62 8 86 11-4

Chromosome extremes The record minimum number of chromosomes belongs to a species of ant. The males only have 1 chromosome. The record for maximum is in a species of fern which has approximately 1260 chromosomes. 11-4

Any cell that has 2 complete sets of chromosomes is called diploid. All of your body cells are diploid (23 pairs = 46 chromosomes) A cell with only 1 complete set of chromosomes is called haploid. 11-4

Diploid organisms have chromosomes arranged in pairs Diploid organisms have chromosomes arranged in pairs. These pairs are called homologous pairs Humans have 23 pairs (46 chromosomes) in each body cell. 11-4

Homologous pairs in human genome Centromere 11-4

Exact copies (sister chromatids) Anatomy of a chromosome One from mom, one from dad (homologous pair) Gene for brown eyes } } Gene for blue eyes Exact copies (sister chromatids) 11-4

Meiosis occurs only in certain cells within an organism. A cell-division process where the number of chromosomes per cell is cut in half. Meiosis occurs only in certain cells within an organism. The job of these cells is to produce sex cells ( ). gametes 11-4

Meiosis Examples Plants animals Anthers: produce pollen Ovaries: produce “eggs” which, when pollinated, develop into seeds and fruit. Testes: produce sperm Ovaries: produce eggs 11-4

Stages of Meiosis 11-4

Difference between Mitosis and Meiosis? Well, in my opinion, the big difference is in the alignment.

Note that this sep-aration is random Tetrad Note that this sep-aration is random Prophase I Metaphase I Anaphase I 11-4

During prophase I: Synapsis: homologous chromosomes line up next to each other and form a “tetrad”. Crossing over (chiasma): genetic material is exchanged between homologous chromosomes. 11-4

Another source of genetic variation! 11-4

Are these daughter cells diploid or haploid? Question: Are these daughter cells diploid or haploid? Telophase I Interphase II Note: Interphase II is not in your book. 11-4

Look Familiar? Prophase II Metaphase II 11-4

Centromere splits, chromatids separate. Anaphase II Telophase II Cytokinesis End product: 4 haploid cells. 11-4