Chapter 5 Heredity. Define heredity. The passing of traits from parent to offspring.
Chapter 13 Meiosis - MCCCnatalep/documents/Chapter13Meiosispost.pdf · Chapter 13 Meiosis • Terms...
Transcript of Chapter 13 Meiosis - MCCCnatalep/documents/Chapter13Meiosispost.pdf · Chapter 13 Meiosis • Terms...
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Chapter 13 Meiosis
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Chapter 13 Meiosis
• Terms – Heredity
• Transmission of traits to offspring – Variation
• Genetic variation in population – Genetics
• Study of heredity – Genes
• DNA coded information for protein – Gametes
• Sperm and egg (and spores)
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sexual reproduction
• 2 parents give rise to genetically unique offspring
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Sexual Life Cycles
• Life cycle – from conception to production of offspring
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• Some organisms can also reproduce asexually
Sea sponge fragmentation Paramecium binary fission
Sea star regeneration ginger rhizome yeast budding
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• Other animals and plants reproduce sexually
Male sea star releasing sperm into water, some sea stars are hermaphrodites and release both sperm and egg
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Germ line cells (gametes) 1n (haploid) Fertilization 1n + 1n = 2n (diploid)
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Sperm + egg--- zygote fertilization
Haploid diploid haploid diploid etc………….
A dog fertilized egg has 78 chromosomes
# in a dog sperm # in a puppy’s brain cell # in a dog embryo cell
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Human chromosomes
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Homologous pairs Autosomes = pairs 1 – 22 Sex chromosomes = pair 23 XX = female XY = male
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• Germ line cells (gametes)– ovary/testes – 1n (haploid) = 23
Fertilization 1n + 1n = 2n Ex. Fruit fly egg has 4 chromosomes (1n). How
many chromosomes in a sperm? A fly larval cell? An adult somatic cell?
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Humans: 2n = n = what makes chromosomes homologous?
Homologous chromosomes
Same length Same genes at same locations
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When meiosis is complete: 4 new haploid cells genetically unique
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Interphase • Same as in mitosis!
Sister chromatids identical
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Stages of Meiosis Prophase I Same as mitosis except………………>
2n = ? The number of pairs of homologous chromosomes is?
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Prophase I
Synapsis replicated homologous chromosomes form a tetrad
What is happening here?
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2n = sister chromatid pairs = total sister chromatids = tetrads =
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Which is prophase of mitosis? Prophase I of meiosis?
No synapsis between homologous chromosomes Synapsis
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Crossing over • Non -sister chromatids
exchange • Creates diversity!
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Prophase I • Crossing over – note chiasma
How many sister chromatids participate in each tetrad?
What is this structure?
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• Metaphase I – Tetrads line up along
metaphase plate
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Which is metaphase of mitosis? Metaphase I of meiosis?
Test your knowledge. How many tetrads in a human ovarian cell in metaphase I of meiosis?
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• Anaphase I Homologs separate and move
towards opposite poles Note: sister chromatids still
connected
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• Which is anaphase of mitosis?
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• Telophase I – Nuclear membranes form cytokinesis
2 haploid daughter cells
Why are these haploid?
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Overview of Meiosis 1
• Bioflix meiosis animation • Bioflix on youtube • Meiosis I is =reduction division Each cell has 1 set of
chromosomes (replicated and recombined)
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Meiosis II
• Prophase II
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• Metaphase II
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• Anaphase II
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Telophase II
4 genetically unique haploid cells
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Meiosis and genetic variation 1. crossing over (prophase I) 2. independent assortment
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3. random fertilization
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Compare mitosis and meiosis
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Overview of Meiosis
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