Bio 141 chapter 13
Compare and contrast meiosis and mitosis.
Number of times DNA is replicated 1
Number of cell divisions 1 mitosis, 2 meiosis
Number of daughter cells produced 2 mitosis, 4 meiosis
“Ploidy” of daughter cells stays the same in mitosis, cut in half in meiosis
Type of cells in which the process occurs somatic cells mitosis, germ cells meiosis
Number and genetic make-up of chromosomes in parent cell compared to daughter cells
What is the difference between diploid and haploid? What cells in the body are diploid and which are haploid? What kind of diploid cells can become haploid cells?
Diploid organisms have two alleles of the same gene, each allele carried on a homologous chromosome while haploid organisms only have one allele
Gametes are haploid while almost all other body cells are diploid
Germ cells are diploid and go on to form haploid gametes
If a particular species of plant is made up of cells that each have 30 separate chromosomes, 15 of which appear to be paired in terms of size and shape, what is the “ploidy” of this plant? What is the term for these similar chromosomes? What is the ploidy of a different plant species in which the cells also have 30 separate chromosomes, but there seem to be 10 triplets of similar size and shape? How many different alleles can the same gene of a tetraploid plant have?
The cell is 2n and n is 15 therefore ploidy is 30
These similar chromosomes are homologous chromosomes
The cell is 10n and n is 30 therefore ploidy is 300
It can have 3 different alleles
Draw cells in metaphase of mitosis, metaphase I of meiosis, and metaphase II of meiosis. What is different between the chromosomes in your three drawing?
During metaphase of mitosis, individual chromosomes line up at metaphase plate
During metaphase I of meiosis, homologous pair of chromosomes line up
During metaphase II of meiosis, individual chromosomes line up
Metaphase I of meiosis consists of homologous chromosomes that are paired together while metaphase of mitosis and metaphase II consist of individual chromosomes
Explain what takes place immediately after metaphase in mitosis, meiosis I, and meiosis II. (Don’t just name the phases; describe specifically what happens.) What happens if the steps you just described do not occur correctly during meiosis? State the term for this sort of meiotic error and the term that describes the resulting daughter cells.
During anaphase, either sister chromatids or homologous chromosomes begin to separate and in telophase, they finish moving to opposite poles and the nuclear envelope reforms
If both homologs during meiosis I or both sister chromatids during meiosis II move to the same pole of the parent cell, nondisjunction will occur because the homologs or sister chromatids failed to separate.
What happens during crossing over? Why is “recombination” an alternative term for what happens during the process of crossing over? Does it occur during mitosis? If so, when? If not, explain why not. Does crossing over occur during meiosis? If so, when? If not, explain why not. How does crossing over influence the genetic diversity of gametes?
During crossing over, the non-sister chromatids from each homolog have been broken at the chiasmata and reciprocal changes occur between different homologs. As a result, non-sister chromatids that have both maternal and paternal segments are formed.
Recombination is an alternative term because new combinations of alleles can result within a chromosome
It does not occur during mitosis because mitosis is used to produce daughter cells that are identical to the parent.
Crossing over occurs during late prophase I and it increases genetic diversity by varying the combinations of alleles in each chromosome
What is independent assortment? Explain which step(s) in meiosis lead to independent assortment. Sketch the genetically distinct daughter cells that could result from independent assortment if a diploid parent cell (2n=6) undergoes meiosis.
Independent assortment occurs when chromosomes line up during meiosis I and the homologs separate and each daughter cell gets a random assortment of maternal and paternal chromosomes
During prophase I, chromosomes condense and crossing over occurs after homologous chromosomes come together. Then during metaphase I, homologs are lined up at the metaphase plate and this is when independent assortment occurs
Is self-fertilization likely to result in offspring that are genetically identical to the parent? to each other? Explain why or why not.
No because although both gametes are from the same individual, crossing over during prophase I and independent assortment during metaphase I will create genetic diversity between the offsprings and the parent as well as between the offsprings themselves.