BIOL SCI 215 Lecture Notes - Lecture 3: Chromatid, Sister Chromatids, Centrosome

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ceriserhinoceros589

28 Jun 2018

School

Northwestern University

Department

Biological Sciences

Course

BIOL SCI 215

Professor

aaronpeterson

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4/6 Meiosis, Mitosis and Aneuploidy

Each adult will have 2 alleles in a gene

Equal segregation of alleles in the gene

Humans have 23 pairs of chromosomes, 2n=46

oColors used to distinguish the different chromosomes

oMost human cells are diploid, but the gametes are haploid

oBody made up of somatic cells [diploid so they would have 23 copies of the

chromosomes] n=23

Mitosis creates this

Sperm and egg create a zygote which grow bigger and bigger and

become an adult. Part of the zygote has been put aside for

reproduction and this creates sperm/egg

Zygote = Diploid cell resulting from fusion of two haploid

gametes, a fertilized ovary

Trillions of somatic cells in adults and almost all have the same DNA

content

Mitosis takes 2n cells and makes 2n cells

How does mitosis ensure all daughter cells are genetically

identical?

Cells have to replicate DNA (S phase) prior to cell division (M

phase)

Stages of the cell cycle: M=mitosis, S=DNA synthesis, G=gap

Interphase (S and G1 and G2) (Chromosome all spread out)

Mitosis

Prophase

Early: Chromosome condensation compacts

DNA into a small volume

Centromere: Connecting sister chromatids,

which are identical, to form a chromosome

Chromatid: 1 DNA double helix

2 homologous chromosomes: Similar not

identical in DNA sequence so they contain two

different alleles

Metaphase: Attachment of spindle to centromeres,

there are two centrosomes on each chromosome

Centrosome: Spot where microtubules are

extended and the place where microtubules

connect between sister chromatids are

centromere

Anaphase: Chromosomes move apart to opposite

poles of the spindle: separation of sister chromatids

ensures each new cell will receive one copy of each

homolog

Centromere splits apart

Telophase: Reassemble nucleo envelope and form two

nuclei

Cytokinesis is division of the cytoplasm after the

nucleus divides

oGametes [Germ line, haploid (n), half the genetic content in the somatic cells]

Human: sperm and egg, Plants: pollen and

Meiosis creates this

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Document Summary

Each adult will have 2 alleles in a gene. Equal segregation of alleles in the gene. Sperm and egg create a zygote which grow bigger and bigger and become an adult. Part of the zygote has been put aside for reproduction and this creates sperm/egg. Zygote = diploid cell resulting from fusion of two haploid gametes, a fertilized ovary. Trillions of somatic cells in adults and almost all have the same dna content. Mitosis takes 2n cells and makes 2n cells. Cells have to replicate dna (s phase) prior to cell division (m phase) Stages of the cell cycle: m=mitosis, s=dna synthesis, g=gap. Interphase (s and g1 and g2) (chromosome all spread out) Centromere: connecting sister chromatids, which are identical, to form a chromosome. 2 homologous chromosomes: similar not identical in dna sequence so they contain two different alleles. Metaphase: attachment of spindle to centromeres, there are two centrosomes on each chromosome.

Related Questions

Match the terms to the definitions provided.

Question 1 options:

	gamete
	somatic cells
	zygote
	sexual reproduction

1.	Reproductive life cycle that involves an alternation between haploid and diploid cells
2.	A single cell with a diploid number of chromosomes resulting from the fusion of an egg and a sperm.
3.	Cells (egg or sperm) resulting from a meiotic division of germ-line cells
4.	The non-reproductive cells found in embryos and mature individuals

Question 2 (5 points)

Match the terms to the definitions provided.

Question 2 options:

	syngamy
	haploid
	meiosis
	diploid
	germ-line cells

1.	The cells that will eventually undergo meiosis to produce gametes.
2.	The number of chromosomes found in gametes (eggs or sperm).
3.	The process by which two haploid gametes fuse to form a new diploid cell.
4.	A specialized reduction division that produces cells with half the normal number of chromosomes.
5.	Two sets of chromosomes present in the somatic cells of adult individuals.

Ploidy refers to the number of complete sets of chromosomes (genes) present in a cell. The number of chromosomes in a complete set is a fixed characteristic of a species. Humans are diploid with two sets of 23 chromosomes. Fruit flies are diploid with two sets of 4 chromosomes. Sexually reproducing organisms are diploid, each somatic cell of an organism has two complete sets ("di" is a prefix indicating 2.). To complete a life cycle and reproduce new members of a species, mating is required. Mating brings a donation from a male and a donation from a female together. However, if the male and female cells remain diploid, the fertilization will result in a tetraploid zygote. In general, these are not viable. A mechanism is needed to form special haploid cells, gametes. The diploid set is split precisely into two complete haploid sets. That mechanism is meiosis.

The complete set of chromosomes of a species is also the complete set of genes of a species, the genome. (Yes, there is a minor contribution from mitochondria and chloroplasts. Inheritance of this information is "cytoplasmic".)

Please answer the following questions:

1. How many chromosomes in a brain cell of a fruit fly? How many chromosomes are in a liver cell of a human? Explain both answers.

2. How many chromosomes are in a fruit fly unfertilized egg? How many chromosomes are in a human egg? Explain both answers.

3. Why is meiosis necessary for sexually reproducing organisms? How many chromosomes are in a human zygote? Relate the two answers.

4. What is a gene allele? Suppose there is a gene called "bingo" and it is present once in a complete haploid set. How many alleles of "bingo" does a diploid individual have? How many copies or versions of the gene "bingo" are present in a diploid individual?

5. Modern DNA sequencing clearly identifies alleles by showing the different DNA sequence of each allele. These alleles may be termed structural alleles (I coined the term for this problem.). Classical genetics only dealt with phenotypes or visible traits. As a result, alleles of genes were identified by functionality, usually normal or non-functional. Using your knowledge of gene structure and gene expression, postulate a relationship between structural alleles and functional alleles. (include relative amounts; more, less, or equal).

What is a genome? What is a genome made of? Describe the bacterial genome. How do bacteria reproduce? What is binary fission? Distinguish between a chromosome and chromatin. Where are chromosomes located in eukaryotic cells? What is the chromosome made of? What is a centromere? What is the centromere's role? What are sister chromatids and how do they arise? Distinguish between somatic cells and germ (gametes) cells. Describe the cell cycle. What are the different phases? What occurs during S phase? What is interphase? How is the cell cycle controlled?

Describe mitosis. What are the phases of mitosis? What occurs in each of the phases of mitosis? What is cytokinesis? How does this differ between plant and animal cells? What is a kinetochore? Where does it form? What is its role? What is the role of microtubules in mitosis? What is a centriole and what is it composed of? What is a centrosome and what is its role in mitosis? What is the metaphase plate and why is this important? What is the mitotic spindle, its role and its makeup? What defines a diploid cell? How many copies of each chromosome is in a diploid cell? What about a haploid cell? Why do the daughter cells of mitosis always have the same complement of chromosomes?

Describe meiosis. What are the phases of meiosis? What occurs in each of the phases of meiosis? Distinguish between meiosis I and meiosis II and describe how each of these processes compare to mitosis. Why do animal cells undergo meiosis? What is a gamete? What is a zygote? What are recombination, crossing-over, and chiasma? When and why does this occur? What is meant by 'homologous pair of chromosomes'? Why don't the daughter cells of meiosis have the same genetic makeup? What controls the segregation of chromosomes into the gametes?

What are genetic characters? What are genetic traits? What is an allele? What is a locus? How many alleles at each locus would a human cell have and why? Distinguish between genotype and phenotype. What is meant by a dominant gene? What is meant by a recessive gene? How do these differ? What is the genotype of a homozygous dominant organism? What is its phenotype? What is the genotype of a homozygous recessive organism? What is its phenotype? What is the genotype of a heterozygous organism? What is its phenotype? What is a genetic cross? Distinguish between the P, F1, and F2 generations. What is a true-breeding line? What is the genotype and phenotype of a cross between homozygous dominant and homozygous recessive parents? If the F1 progeny are crossed, what would be the genotype and phenotype of the F2 generation? What would be the phenotypic ratio? What would be the genotypic ratio? Be ready to generate Punnet square tests or probability analyses of crosses involving more than one genetic locus. Describe a dihybrid cross where two alleles are homozygous dominant in one parent and homozygous recessive in the other. What would be the phenotypic ratio of the F2 generation from this dihybrid cross? What is meant by independent assortment? Be prepared to calculate probabilities resulting from different crosses.

Distinguish between complete and incomplete dominance. How would incomplete dominance alter the results of a hybrid cross? What would the resulting F2 generation phenotype and genotype ratios be? What is codominance? How does this affect the results of crosses? Be prepared to determine likely blood types of parents based on the blood types of their offspring. What is a polygenic trait? What is a carrier state for a genetic disease? What is meant by linked genes? How does this affect expected outcomes of genetic crosses? How is gene linkage used for chromosomal mapping? Distinguish between autosomes and sex chromosomes. What sex chromosomes are found in women? What sex chromosomes are found in men? What are sex-linked traits? Be prepared to give the results of crosses that involve sex-linked recessive traits. What is the process of nondisjunction? What are the likely results? Why is this important? What is a Barr body? Recognize the genetic abnormality of Downs Syndrome, Turner's Syndrome, and Klinefelter's Syndrome.

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BIOL SCI 215 Lecture Notes - Lecture 3: Chromatid, Sister Chromatids, Centrosome

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