larry m. frolich, ph.d. biology department, yavapai college meiosis and reproduction meiosis meiosis...

Larry M. Frolich, Ph.D.Biology Department, Yavapai College

Meiosis and Reproduction

• MeiosisMeiosis

• FertilizationFertilization

• DevelopmentDevelopment

• Natural SelectionNatural Selection

• Genetics ReviewGenetics Review


How are genetic traits combined and passed on from parent to offspring

• Meiosis produces gametes or sex cells (eggs and sperm) with just one member of each chromosome pair

• Fertilization results in union of female gamete (egg) with male gamete (sperm)

• Subsequent embryonic, fetal and embryonic development by mitosis and differentiation of cell types produces new individual


Overview of meiosis

• Two nuclear divisions occur to make 4 haploid cells (cells with just one member of each chromosome pair)

• Meiosis results in gametes (egg and sperm)

• Has 8 phases (4 in each meiosis I & II)

18.3 Meiosis


Table 18.2


Alleles• A particular gene, or protein-coding region of

DNA along a chromosome might have a few different variations, called alleles

• The combination of alleles, at a particular gene, or chromosome region, that you get from your mother and father determine your hereditary traits

• Please do the Dragon Genetics lab to understand this


• After meiosis, male and female gametes (sperm and egg) unite to form a new cell—a zygote—that has the full set of 23 pairs of chromosomes (in humans).

Fertilization


Embryonic development—mitosis produces tissues/structures of adult


Some adult features are coded for genetically in alleles or gene varieties of sperm and egg

Be sure to see sickle cell anemia example in this section of the course


Inheritance and Natural Selection• Some combinations of alleles, produced during meiosis

and fertilization might be more advantageous• This is what leads to natural selection. Individuals with

more advantageous traits will survive to reproduce and pass on those traits.

• Darwin realized that slow changes in inherited traits, due to natural selection produced the great evolutinoary history of life.

• Before his synthesis of all the evidence, no one could make sense of living systems. Now, “Nothing in Biology Makes Sense Except in the Light of Evolution”

• --Theodosius DobzhanskyPlease do the Coyote Lab to see how meiosis, fertilization, inheritance and natural selection all work together to produce the gradual change in biological organisms that we call evolution.


GENETICS (review)

• Cells divide and pass on instructions coded in DNA of chromosomes

• Each chromosome is a huge DNA molecule with coded information– DNA replicates to pass on information– DNA is transcribed to make proteins

that run cell metabolism

• Cancer—example of what happens when genetic control goes awry

• Normal inheritance and meiosis


DNA and chromosomes• Long DNA molecules (millions

of base pairs long) in nucleus are called chromosomes

• Each chromosome is organized and packaged or wrapped up with proteins giving it a certain shape

• In humans, 23 pairs of chromosomes– 1 of each pair from mother– 1 of each pair from father

• Total view of all 23 pairs is called karyotype


Mitosis—what happens (overview)• DNA/chrosomes replicate

(make exact copies• Copies line up at center

of cell• Copies pulled to opposite

ends of cells by centromeres/spindles

• Cell membrane pinches off and splits cell into two


Mitosis—constant, fast, keeps body functioning

• Remember, mitosis produces two identical daughter cells

• Mitosis is constantly happening in your body to allow for growth, replacement and repair

• While you read this slide, millions of new cells were produced by mitosis in the tissues of your body!

• Don’t forget cellular scale and intelligence—it’s a whole planet happening at the sub-microscopic level


DNA is structured to replicate

• DNA is “double helix”—two complementary strands wound in a spiral

• Strands separate and DNA replicates by filling in other half of each separated strand

• Famous Watson-Crick model (Nobel prize)


DNA is transcribed to make proteins that run cell metabolism

• DNA is transcribed to mRNA

• mRNA is translated to amino acid sequence

• Amino acid sequence folds up into protein

• Proteins catalyze reactions of cell metabolism

• This process is called “gene expression”—the information in one region of the DNA—a “gene”—is being expressed so that the cell’s metabolism can function


Overview of transcription and translation

Details in web link video animations

REMEMBER: A particular region of DNA that has the code to make a particular protein is called a “gene.”


Regulation of gene expression• Gene expression is regulated—not all genes are

constantly active and having their protein produced• The regulation or feedback on gene expression is how the

cell’s metabolism is controlled. • This regulation can happen in different ways:

1. Transcriptional control (in nucleus):• e.g. chromatin density and transcription factors

2. Posttranscriptional control (nucleus)• e.g. mRNA processing

3. Translational control (cytoplasm)• e.g. Differential ability of mRNA to bind ribosomes

4. Posttranslational control (cytoplasm)• e.g. changes to the protein to make it functional

• When regulation of gene expression goes wrong—cancer!


How are genetic traits combined and passed on from parent to offspring

• Meiosis produces gametes or sex cells (eggs and sperm) with just one member of each chromosome pair

• Fertilization results in union of female gamete (egg) with male gamete (sperm)

• Subsequent embryonic, fetal and embryonic development by mitosis and differentiation of cell types produces new individual


• After meiosis, male and female gametes (sperm and egg) unite to form a new cell—a zygote—that has the full set of 23 pairs of chromosomes.

Fertilization


Inheritance and Natural Selection• Some combinations of alleles, produced during meiosis

and fertilization might be more advantageous• This is what leads to natural selection. Individuals with

more advantageous traits will survive to reproduce and pass on those traits.

• Darwin realized that slow changes in inherited traits, due to natural selection produced the great evolutinoary history of life.

• Before his synthesis of all the evidence, no one could make sense of living systems. Now, “Nothing in Biology Makes Sense Except in the Light of Evolution”

• --Theodosius DobzhanskyPlease do the Coyote Lab to see how meiosis, fertilization, inheritance and natural selection all work together to produce the gradual change in biological organisms that we call evolution. You can download this lab from the Online Lab links for this section of the course.

larry m. frolich, ph.d. biology department, yavapai college meiosis and reproduction meiosis meiosis...

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