BIOL 142 Chapter Notes - Chapter 13: Homologous Chromosome, Allosome, Y Chromosome

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13 Mar 2018

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Fertilization: the fusion of the nuclei of two gametes to form a zygote with a nucleus. Gamete: a haploid reproductive cell that can fuse with another haploid reproductive cell of the opposite sex to form a diploid zygote; most multicellular eukaryotes have two distinct forms of this: egg cells (ova) and sperm cells. Exceptions to the haploid and diploid rule are seen in polyploid species. Egg (ova): a mature female gamete and any associated external layers. The number of chromosomes is constant from cell to cell within a multicellular organism. Meiosis: in sexually reproducing organisms, a special two-stage type of cell division in which one diploid (2n) parent cell produces haploid (n) cells (gametes); results in halving of the chromosome number. Drosophila cells have 8 chromosomes, but just five distinct types, distinguished by their size and shape. Three of these chromosomes always occurred in pairs. In males, the x and y chromosomes were unpaired.

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.

Which statement describes a similarity between the diploid and haploid phases of plant life?

both are multicellular

both are immediately followed by meiosis

both end in fertilization

both contain spores

both contain sporophytes

A zygote is formed ____.â

by the fusion of male and female somatic cells

directly by meiosis in fungi

by the mitotic divisions of spores in plants

by the fusion of egg and sperm nuclei

after a fertilized egg undergoes mitotic divisions to mature

Human skin color is an example of ____, while sickle-cell anemia is an example of ____.â

incomplete dominance; pleiotropy

pleiotropy; polygenic inheritance

incomplete dominance; multiple alleles

polygenic inheritance; pleiotropy

multiple alleles; epistasis

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).

BIOL 142 Chapter Notes - Chapter 13: Homologous Chromosome, Allosome, Y Chromosome

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