Lesson Overview - Enfield High Schoolenfieldhigh.sharpschool.com/UserFiles/Servers... · Lesson...
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Lesson OverviewLesson Overview11.4 Meiosis11.4 Meiosis11.4 Meiosis11.4 Meiosis
Lesson OverviewLesson Overview MeiosisMeiosis
Question #1What must occur in order for Mendel’s principles to hold true?
An organism with two parents must inherit a single copy of every gene from each parent
When that organism produces gametes, those two sets of When that organism produces gametes, those two sets of genes must be separated so that each gamete contains just one set of genes
Chromosomes are the carriers of genes, therefore, chromosomes must be separated
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Question #2What is a diploid cell?
Diploid = “Two sets”
Diploid cells of most adult organisms contain two complete sets of inherited chromosomes (homologous sets of inherited chromosomes (homologous chromosomes) and two complete sets of genes
Homologous chromosomes are the two sets of chromosomes (one from the male parent and one from the female parent)
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Question #2What is a diploid cell?
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Question #3What is a haploid cell?
Haploid = “One set”
Haploid cells contain only a single set of chromosomes, and therefore a single set of genestherefore a single set of genes
The gametes of sexually reproducing organisms are haploid
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Question #4What is meiosis?
Process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell
One diploid cell goes through two separate divisions, producing four haploid cells
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Question #5Human Cell 2N = 46
Sperm cells (N) have 23 chromosomes
Egg cells (N) have 23 chromosomes
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Question #6What happens prior to meiosis I?
The cell undergoes a round of chromosome replication during interphase
Each replicated chromosome consists of two identical chromatids, joined at the centromere
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Question #7PROPHASE I
Spindle forms in the cell
Each replicated chromosome pairs with its corresponding homologous chromosome
This pairing forms a structure called a tetrad
Crossing over occurs during prophase I
In crossing-over, sections of non-sister chromatids are exchanged (this produces new combinations of alleles in the cell)
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Question #7PROPHASE I – CROSSING OVER
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Question #7PROPHASE I
Tetrad (homologous chromosomes) consisting of 2 sets of sister chromatids
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Question #7METAPHASE I
Paired homologous chromosomes line up across the center of the cell
The spindle fibers attach to each tetrad
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Question #7ANAPHASE I
Spindle fibers pull each homologous chromosome pair toward opposite ends of the cellof the cell
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Question #7TELOPHASE I and CYTOKINESIS
A nuclear membrane forms around each cluster of chromosomes
Cytokinesis follows telophase I, forming two new cells
Each cell has ½ the genetic material of the original parent cell
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Question #7PROPHASE II
The spindle reforms in both of the cells that were created during meiosis I
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Question #7METAPHASE II
Chromosomes (paired sister chromatids) line up in the center of the cell
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Question #7ANAPHASE II
The paired chromatids separate
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Question #7TELOPHASE II and CYTOKINESIS
The nucleus begins to reform around the chromosomes in each cell
Cytokinesis of meiosis II results in four haploid daughter cells
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Question #8Gamete to Zygote
MEIOSIS
Sperm (N) Egg (N)
Zygote (2N)
MITOSISMITOSIS
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Question #9Mitosis and Meiosis – Similarities
Both are preceded by a complete copying, or replication, of the genetic material
Both have spindlesBoth have spindles
Both have the movement of chromosomes
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Question #9Mitosis and Meiosis – Differences
Mitosis has one cell division (meiosis has two cell divisions)
Mitosis produces two cells (meiosis produces four cells)
Mitosis only has sister chromatids line up and separate (meiosis has Mitosis only has sister chromatids line up and separate (meiosis has homologous chromosomes line up and then sister chromatidsline up)
Mitosis maintains the chromosome number (meiosis cuts the chromosome number in half
Mitosis ends with two diploid cells (meiosis ends with four haploid cells)
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Question #10Thomas Hunt Morgan’s Conclusions
Each chromosome is actually a group of linked genes
Chromosomes assort independently (not the individual genes)
Alleles for different genes tend to be inherited together from one generation to the next when those genes are located on the same chromosome
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Question #11Alfred Sturtevant’s Conclusion
The farther apart two genes were on a chromosome, the more likely it would be that crossing-over would occur between them
� If two genes are close together, then crossovers between them should � If two genes are close together, then crossovers between them should be rare
� If two genes are far apart, then crossovers between them should be more common
He used the frequency of crossing-over between genes to determine their distances from each other (and he also created gene maps from that data)
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Question #12Curved and dumpy OR Curved and vestigial (small)
Curved wing and dumpy wing are more likely to cross over
The farther apart, the more likely crossing-over will occur
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Question #13Least likely to cross over
Purple eye and Light eye are the least likely to cross over
The closer together the genes are, the less likely they are to cross overcross over
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Question #14Gene Map
In which gene map is the probability of crossing-over between A and D greatest?
Number 3Number 3
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Question #15Gene Map
In which gene map is the probability of crossing-over between A and D the least?
Number 4Number 4
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Question #16Gene Map
In which map are genes C and D most closely linked?
Number 2
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Question #17Gene Map
In map 4, which genes are least likely to cross over?
C and B
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