本期的內(nèi)容是（遺傳）信息的傳遞。本文集的這一部分是遺傳、進(jìn)化與生態(tài)學(xué) Genetics, Evolution, and Ecology. 這門課理論上建議在閱讀完文集的第一部分的內(nèi)容之后再開始學(xué)習(xí)，但基礎(chǔ)不足的朋友也可以嘗試閱讀喔~

這一部分的主要內(nèi)容均來自 Prof. Angela J. Roles 的課程，因此本文集的這一部分均不會標(biāo)記為原創(chuàng)。但由于文本來源不清晰，UP主還是一個(gè)字一個(gè)字碼出來的文章，本文禁止非授權(quán)的轉(zhuǎn)載，謝謝！

Lesson 6: Information TransMission

[1] Overview

Information transMission from parent to offspring

????Division of genetic material:

?????Bacteria: binary fission

?????Eukaryotes: mitosis and meiosis

?????Archaea: variable—sometimes similar to bacteria or eukarya, sometimes unique

Schematic of Caulobacter bacterial cell cycle with asymmetric division:

The Life Cycle of a Cell:

?Important Events

?Create a copy of the genomic DNA (the info).

?Segregate (separate) the information into daughter cells.

?Divide the cytoplasMic contents between daughter cells.

?

[2] Mitosis and cytokinesis

Slime mold, Dictyostelium discoideum

Plant cell cytokinesis

A cell plate grows from inside the cell out to the edges, separating the daughter cells.

?

[3] Binary Fission

- Binary fission in a bacterial life cycle: Bacillus licheniformis

- This bacterium lives in barbules of bird feathers and reproduces via binary fission. Under stress, it produces dormant spores.

?What are the basic features of the life cycle?

????- Reproduction, ploidy

????- Habitat(s)

????- Trophic level

????- Adaptations

?

[4] Life Cycles

Consider life cycles: Culex, a mosquito

?This eukaryote undergoes mitosis during growth and produces haploid gametes via meiosis;

?Meiosis and mating with a mosquito of the opposite sex may increase genetic variation;

?Survives stressful conditions by entering diapause from the egg, larval, or adult stages.

[5] Meiosis

Diploid nuclear division resulting in 4 haploid cells

?????Showing a genome with 1 chromosome (n=1 and 2n=2);

?????The B gene is present on this chromsome with two possible alleles: allele B and allele b;

?????Blue = chromosome copy inherited from parent 1;

?????Orange = chromosome copy inherited from Parent 2.

Meiosis in detail (Picture below)

?

[6] Crossing-Over

Synapsis -?Physical pairing of homologous chromosomes.

? Recall: this is a 3-D structure;

?Synapsis of homologous chromosomes (forming tetrads) happens because of similarity of DNA sequences;

?Tetrads line up on the metaphase plate, leading to reduction from diploid to haploid nuclei.

Crossing-over occurs during synapsis; the physical connection enables the exchange between chromatids.

? Letters mark a particular place on the chromosome, like the address of a gene.

?Centromeres are marked by the oval on the left of each chromatid;

?Multiple crossing-over events may happen for each homologous pair.

?

[7] Meiosis I

Meiosis I (when all the good stuff happens)

?

[8] Mendel’s Laws

Mendel’s Laws on display

?The Principle of Independent?Assortment

????- All chromosomes inherited from one?parent will not necessarily end up in?the same daughter cell.

????- Non-homologous chromosomes sort?independently of each other.

?? Principle of Segregation

????- The 2 copies of 1 chromosome (1?set of genes) do not end up in the?same daughter cell;

????- Each daughter cell contains 1 copy?of each different chromosome, in?the form of a replicated?chromosome.

[9] Meiosis II

What’s happening in Meiosis II?

Questions to Think:

?Why do you think biologists differentiate ploidy from chromosome copy?number?

?Compare binary fission to mitosis:

????- How are they different? Similar?

????- What are the relative advantages of each?

?Compare mitosis to meiosis

????- How are they different? Similar?

????- What are the relative advantages of each?

?When does each process occur in the life cycle of an organisM?

????- Does this suggest anything about the function or possible adaptive value of?the process?

?What might happen if there is an error during the process or some event?fails to occur at all?

????- Are any of the resulting daughter cells likely to be viable?