Meiosis 22-23

​Meiosis

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Question: What are Homologous Chromosomes?​

​Diploid- a cell that contains two sets of chromosomes

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Human cells have 46 Chromosomes​ that are homologous pairs (23 pairs)

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Fruit Flies have 8 chromosomes (4 pairs)

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​Cells

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Multiple Choice

All human have _________ chromosomes

• 23

• 46

• Diploid

• Haploid

​Homologous- a pair of chromosomes with similar DNA sequences that come from separate parents

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How many chromosomes do you think reproductive cells have?

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​Parental DNA

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​Gametes: are haploid reproductive cells in sexually reproducing organisms

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Haploid: Cells have only a single set of chromosomes​

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These cells fuse together forming a zygote cell with combining each half set to form a diploid cell​

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​Sexual Reproduction

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Multiple Choice

A human has 46 chromosomes in their body cells.  What is the haploid number?

• 46

• 92

• 23

• 12

​Sexual reproduction occurs when two organisms of the same species share DNA in order to create

new and genetically unique offspring.

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A warrior princess donates 23 chromosomes and a comedian donates 23 chromosomes

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What are some benefits that could result in their offspring?

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Meiosis ​

​Meiosis - a type of cell division in sexually reproducing organisms that reduces the number of chromosomes to form gamete cells​

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The shuffling and separation of homologous chromosomes ​

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​Meiosis

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Multiple Choice

Sex cells divide using a process called meiosis

• True

• False

​There are 2 phases of Meiosis

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​Phase I

Prophase I, Metaphase I, Anaphase I, and Telophase I​

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Phase II

Prophase II, Metaphase II, Anaphase II, and Telophase II​

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​Details: Meiosis

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​Details

Somatic cells vs. Gamete cells​

Somatic cells are body cells that undergo mitosis​

Gamete cells are reproductive cells that undergo meiosis​

​Interphase

​Cell growth phase and DNA replication (same as mitotic cells)

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DNA is replicated in S phase​

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​Prophase I

​Crossing over

• Exchange of genetic material between two homologous (same) chromosomes

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Details:

Crossin​g over Increases genetic variation​

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Meiosis ​

Multiple Choice

In which phase does crossing-over happen?

• Prophase I

• Prophase II

• Metaphase I

• Anaphase II

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Prophase I (1) - Crossing over ​(genes cross over)

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Meiosis ​

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​Prophase I

Chromosome form and Crossing over​ occurs

Metaphase I

align in the middle​​

Anaphase​ I

Independent Assortment​ "apart"

​Telophase I

2 genetically unique cells​ due to crossing over

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Meiosis ​

Multiple Choice

What phase is  shown in the picture?

• anaphase 1
• anaphase 2
• metaphase 1
• telophase 1

​Without DNA replication the cell undergoes cellular division again (reducing chromosomes)

​Prophase II

Metaphase II​​

Anaphase​ II​

​Telophase II

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Resulting in

4 genetically Unique (haploid)

daughter cells

with 23 Chromosomes​

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Meiosis ​

​Parents contribute half the number of chromosomes for each child

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Haploid gametes by males are called sperm in some plants it is referred as pollen

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Haploid gametes by females is called an egg​ (because only one out of the four gets cytoplasm)

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​Genetic Variation

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​Chromosomes assort (mix) independently not individual genes

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​Gene Linkage

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​Summarize Meiosis