Lesson Overview - Enfield High Schoolenfieldhigh.sharpschool.com/UserFiles/Servers... · Lesson Overview Meiosis Question #11 Alfred Sturtevant’s Conclusion The farther apart two

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


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)


Question #2What is a diploid cell?


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


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


Question #5Human Cell 2N = 46

Sperm cells (N) have 23 chromosomes

Egg cells (N) have 23 chromosomes


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


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)


Question #7PROPHASE I – CROSSING OVER


Question #7PROPHASE I

Tetrad (homologous chromosomes) consisting of 2 sets of sister chromatids


Question #7METAPHASE I

Paired homologous chromosomes line up across the center of the cell

The spindle fibers attach to each tetrad


Question #7ANAPHASE I

Spindle fibers pull each homologous chromosome pair toward opposite ends of the cellof the cell


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


Question #7PROPHASE II

The spindle reforms in both of the cells that were created during meiosis I


Question #7METAPHASE II

Chromosomes (paired sister chromatids) line up in the center of the cell


Question #7ANAPHASE II

The paired chromatids separate


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


Question #8Gamete to Zygote

MEIOSIS

Sperm (N) Egg (N)

Zygote (2N)

MITOSISMITOSIS


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


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)


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


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)


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


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


Question #14Gene Map

In which gene map is the probability of crossing-over between A and D greatest?

Number 3Number 3

1

2

3

4



In which gene map is the probability of crossing-over between A and D the least?

Number 4Number 4

1

2

3

4



In which map are genes C and D most closely linked?

Number 2

1

2

3

4



In map 4, which genes are least likely to cross over?

C and B

1

2

3

4

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Lesson Overview - Enfield High Schoolenfieldhigh.sharpschool.com/UserFiles/Servers... · Lesson Overview Meiosis Question #11 Alfred Sturtevant’s Conclusion The farther apart two