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Sexual Life Cycles: Meiosis

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Presentation on theme: "Sexual Life Cycles: Meiosis"— Presentation transcript:

1 Sexual Life Cycles: Meiosis
Chapter 13

2 Learning Target 1 I can explain how offspring acquire genes from parents by inheriting chromosomes. I can distinguish between asexual and sexual reproduction.

3 Where do your genes come from?
Ever wonder where you got your traits from? And where they got their traits from?

4 What’s a gene? A segment of DNA which codes for a protein
Can code for an enzyme, a structural protein or a regulatory protein This determines an organism’s traits More next unit…

5 Asexual reproduction No gametes produced One parent
Prokaryotes – binary fission Single-celled eukaryotes Yeast – budding Amoeba – binary fission Simple multicellular eukaryotes Hydra – budding Complex multicellular eukaryotes - regeneration Sea stars Planaria

6 Sexual Reproduction Gametes produced by meiosis Two parents
Direct contact not required Plants: pollination strategies vary Animals: release of gametes into environment (aquatic)

7 I can distinguish between the following pairs of terms:
Learning Target 2 I can distinguish between the following pairs of terms: Somatic cell and gamete Autosome and sex chromosome Diploid and haploid Zygote and fertilization

8 Important Vocabulary Diploid Haploid Somatic cell Gamete Diploid
Body cell Gamete Reproductive cell (sperm or egg) Diploid Contains 2 sets of homologous chromosomes (2n) Haploid Contains 1 set of homologous chromosomes (n) Diploid Haploid

9 Important Vocabulary, CONT.
Zygote Fertilized egg Fertilization Union of sperm and egg cells in sexual reproduction Autosome Chromosome 1-22 (everyone has) Sex chromosome Chromosome (XX = female, XY= male)

10 I can explain how haploid and diploid cells differ from each other.
Learning Target 3 I can explain how haploid and diploid cells differ from each other. I can state which cells in the human body are diploid and which are haploid.

11 Haploid Vs. Diploid Somatic cells are diploid
Only gametes are haploid – why?

12 Learning Target 4 I can explain how meiosis generates haploid daughter cells from diploid parent cells. I can list the phases of meiosis I and meiosis II and describe the events characteristic of each phase. I can describe what homologous chromosomes are. I can explain how the spindle fiber separates either homologous chromosomes of sister chromatids. I can recognize the phases of meiosis from diagrams or micrographs. I can explain how genetic recombination occurs.

13 Meiosis: Production of gametes
Alternating processes, alternating stages Chromosome number must be reduced Diploid  Haploid 2n  n Humans 46  23 Meiosis reduces chromosome number Fertilization restores chromosome number Haploid  Diploid n  2n Necessary for sexually reproducing organisms to produce gametes

14 Steps of Meiosis Meiosis I DNA replication Meiosis II
Interphase Prophase I Metaphase I Anaphase I Telophase I Meiosis II Prophase II Metaphase II Anaphase II Telophase II DNA replication 1st division of meiosis separates homologous pairs 2nd division of meiosis separates sister chromatids *just like mitosis*

15 Homologous chromosomes
Paired chromosomes Both chromosomes carry a pair of genes Control same inherited characters Homologous = same information Chromosome 17


17 Spindle fibers and chromosome movement

18 I can compare and contrast mitosis, meiosis I and meiosis II.
Learning Target 5 I can compare and contrast mitosis, meiosis I and meiosis II.

19 Mitosis Vs. Meiosis I VS. Meiosis II

20 Learning Target 6 I can explain how independent assortment, crossing over and random fertilization contribute to genetic variation in sexually reproducing organisms.

21 Independent assortment
Random orientation of homologues at metaphase plate during metaphase I Independent assortment in humans produces 223 (8,388,608) different combinations

22 Crossing Over During Prophase I
Homologous pairs swap pieces of chromosome Sister chromatids intertwine and cross over each other Breakage and re-fusing of DNA Creates completely new combinations of traits in the next generation

23 Random fertilization Random ovum fertilized by a random sperm
Any 2 parents will produce a zygote with over 70 trillion (223 x 223) diploid combinations

24 Learning Target 7 I can explain why heritable variation is crucial to Darwin’s theory of evolution by natural selection.

25 Sexual reproduction creates variability
Allows us to maintain both genetic similarity and differences Why is this significant to evolution by natural selection?

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