Ch.10 Key Meiosis - answer key PDF

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AP Biology Ch. 10 Meiosis and Sexual Life Cycles Key concepts 10.1 Offspring acquire genes from parents by inheriting chromosomes. 10.2 Fertilization and meiosis alternate in sexual life cycles. 10.3 Meiosis reduces the number of chromosome sets from diploid to haploid. 10.4 Genetic variation produced in sexual life cycles contributes to evolution. 1.

Heredity is the transmission of traits from one generation to the next.

2.

Variation - exists in populations that reproduce sexually, offspring are not identical to their parents.

3.

Genetics is the scientific study of heredity and hereditary variation.

4.

Each parent passes on 23 chromosomes to their offspring. These chromosomes are made up of many sections of DNA called genes.

5.

All of an individual’s genes are called their genome.

6.

In animals and plants, reproductive cells called gametes are the vehicles that transmit genes from one generation to the next.

7.

Except for small amounts of DNA in the mitochondria and chloroplasts, the DNA of a eukaryotic cell is packaged into chromosomes in the nucleus.

8.

One chromosome has between several hundred to a few thousand genes.

9.

A gene’s specific location along the length of a chromosome is called the gene’s locus (loci).

10.

Asexual reproduction is when a single individual gives rise to offspring.  These offspring are identical to their parent.  This type of reproduction occurs through the process of mitosis  Variation can occur through mutations  Some multi-celled organisms can reproduce this way through cloning (hydra)

11.

Sexual reproduction is when two parents give rise to an offspring.  These offspring show greater varation  Siblings can show a wide variety of genetic combinations

12.

Somatic cell : a body cell that has 46 chromosomes (in humans)

CONCEPT 10. 2: Fertilization and meiosis alternate in sexual life cycles 13.

A life cycle is the generation-to-generation sequence of stages in the reproductive history of an organism, from conception to the production of its own offspring.

14.

In humans, each somatic (body) cell has 46 chromosomes

15.

The diagram below is called a karyotype

16. Homologous Chromosomes (Homologs) are chromosomes that carry genes that control the same trait (these gene are located at the same loci)  You get one of each pair from each parent  Pairs #1-#22 are autosomes  Pair #23 are called sex chromosomes because they determine sex. (A male has XY, a female has XX) 17. Sperm and egg are called gametes or sex cells. In humans they have 23 chromosomes. (This genetic material consists of zero homologous pairs) 18. Somatic cells are considered to be diploid due to the fact that each cell has 2 sets of chromosomes (2n) 19. Sex cells are considered to be haploid due to the fact that each cell has 1 set of chromosomes (1n) 20. When two gametes (1n) come together fertilization has occurred, the resultant cell is called a zygote(2n) 21. Somatic cells are produced through the process of mitosis therefore they are identical. 22. Sex cells are produced in the gonads (ex. testes in males, ovaries in females.) This occurs through the process of meiosis (oogenesis  1 ootid and 3 polar bodies, spermatogenesis  4 sperm)

23. The importance of the process of meiosis is that it reduces the chromosome # so that all generations of humans have 46 chromosomes (no mutations) Sexual Life Cycles Human Life Cycle

24.

Alternation of Generations is a type of life cycle that includes both haploid (n) and diploid (2n) multicellular stages. 

Sporophyte is the multicellular diploid stage. During this stage spores are produced through meiosis.



_Gametophyte_ is the multicellular haploid stage that is produced from the spores which then divides through mitosis.

CONCEPT 10. 2: Meiosis reduces the number of chromosomes from diploid to haploid Meiosis overview

Steps of Meiosis (Campbell)

25. Meiosis is broken down into 2 divisions called meiosis I and meiosis II 26. Meiosis I is called the reduction division because the cell begins as a diploid cell and produces two haploid cells. 27. Meiosis II is similar to mitosis except during the shortened interphase II DNA replication does not occur. 28. These two divisions result in four daughter cells, each with half as many chromosomes as the parent cell.

Meiosis I Phase

Interphase

Picture

(Reduction Division) Events

Replication of DNA during the S phase. Each cell has 46 chromosomes and 92 sister chromatids,

Prophase I

Metaphase I

Chromosomes form and homologs synapse. Crossing over occurs. Spindle formation is complete. Nucleolus & nuclear membrane disappear. Tetrads line up on the metaphase plate. Independent assortment occurs.

Anaphase I

Homologous chromosomes separate and move towards opposite poles.

Telophase I

Chromosomes uncoil into chromatin. Nucleolus and nuclear membrane reappear. Spindle breaks down. Cytokinesis begins

Interkinesis

No DNA Replication occurs. Division of cytoplasm and organelles does occur.

Meiosis II

(Equational Division)

Prophase II

Metaphase II

Chromatin coils to chromosomes. Spindle forms. Nucleolus and nuclear membrane disappear. Chromosomes are located on the metaphase plate. Because of crossing over the chromosomes are not identical.

Anaphase II

Telophase II & Cytokinesis

Sister chromatids separate and move to opposite poles. Chromosomes uncoil. Nucleolus and nuclear membrane reform. Spindle breaks down. Cytokinesis ocurrs resulting in 4 haploid cells.

Three unique events that occur in meiosis I. 29. During Prophase I, replicated homologs pair up and become physically connected in a process called synapsis. This complex of four homologous chromatids is known as a tetrad. This event allows for genetic rearrangement between non-sister chromatids known as crossing over. The X-shaped region where the non-sister chromatids are connected is known as the chiasma. 30. At metaphase I of meiosis, chromosomes are positioned on the metaphase plate as pairs of homologs, rather than independent chromosomes, as in metaphase of mitosis.

31. In anaphase I, homologs separate and move to the poles while in anaphase of mitosis sister chromatids separate and move toward the poles. BioFlix -Meiosis Meiosis Square Dance Differences in mitosis and meiosis (check those that apply) Mitosis 2 new cells are formed from each original

X

4 new cells are formed from each original Replication of chromosomes occurs Doubled chromosomes pair to form tetrads Haploid cells are formed Diploid cells are formed

X

X X X X

X

Results in gametes Results in somatic cells Chromosomes move to the center of the cell

Meiosis

X X X

CONCEPT 10. 4: Sources of variation in meiosis

X Sources of Variation (Campbell)

32. Independent Assortment_ is the random placement of the maternal and paternal chromosomes (with respect to other maternal and paternal chromosomes) during Metaphase I (phase), 33. The # of possible combinations in humans due to this process is 223 or 8.4 million.

34. Crossing over is the exchange of genes by homologous pairs, this occurs during prophase I.

35. The third source of variation that adds to the genetic variation of meiosis is random fertilization which could produce a zygote with about 70 trillion diploid combinations.

36. Nondisjunction is the failure of homologous chromosomes to separate during meiosis I or when sister chromatids do not separate during meiosis II. 37. If a gamete with an abnormal # of chromosomes unites with another normal gamete, the resulting zygote will also have an abnormal number of chromosomes, a condition known as aneuploidy.  Trisomy is when there are three copies of a chromosome Examples: Down Syndrome (Trisomy 21) Klinefelter Syndrome (XXY)  Monosomy is when there is one copy of a chromosome Example: Turner syndrome (XO)

38. Polyploidy is a condition in which some organisms have more than two complete sets of chromosomes 39. Translocation is when part of one chromosome breaks off and attaches to a nonhomologous chromosome. Example: cri du chat

Downs syndrome (Trisomy 21) Trisomy 13 Trisomy 15 Trisomy 18 Klinefelter Syndrome Turner Syndrome Cri-du-chat 15/21 translocation Fragile X...