Sexual Reproduction and Meiosis

Sexual Reproduction and Meiosis Ultrasound: Chad Ehlers/Glow Images Copyright McGraw-Hill Education. All rights reserved. No reproduction or distribution without the prior written consent of McGraw-Hill Education.

Why Sex? Reproduction occurs in two main forms: asexual and sexual. Human family: Corbis RF; Amoeba reproducing by binary fission: Carolina Biological Supply Section 9.1 Company/Phototake; Mother cat and kittens: Jane Burton/Dorling Kindersley/Getty Images Figure 9.1

Why Sex? In asexual reproduction, an organism replicates its DNA and splits the contents of one cell into two. This amoeba is reproducing asexually. Human family: Corbis RF; Amoeba reproducing by binary fission: Carolina Biological Supply Section 9.1 Company/Phototake; Mother cat and kittens: Jane Burton/Dorling Kindersley/Getty Images Figure 9.1

Why Sex? Asexual reproduction generates nearly identical offspring. Human family: Corbis RF; Amoeba reproducing by binary fission: Carolina Biological Supply Section 9.1 Company/Phototake; Mother cat and kittens: Jane Burton/Dorling Kindersley/Getty Images Figure 9.1

Why Sex? In sexual reproduction, the DNA of the offspring comes from two parents. Humans, cats, and many other familiar organisms reproduce sexually. Human family: Corbis RF; Amoeba reproducing by binary fission: Carolina Biological Supply Section 9.1 Company/Phototake; Mother cat and kittens: Jane Burton/Dorling Kindersley/Getty Images Figure 9.1

Why Sex? A female parent contributes an egg, and a male parent produces sperm. These cells fuse, yielding the first cell of the next generation. Human family: Corbis RF; Amoeba reproducing by binary fission: Carolina Biological Supply Section 9.1 Company/Phototake; Mother cat and kittens: Jane Burton/Dorling Kindersley/Getty Images Figure 9.1

Why Sex? But attracting a mate and producing sex cells are costly. Why is sexual reproduction so common? Human family: Corbis RF; Amoeba reproducing by binary fission: Carolina Biological Supply Section 9.1 Company/Phototake; Mother cat and kittens: Jane Burton/Dorling Kindersley/Getty Images Figure 9.1

Why Sex? Sexual reproduction produces genetic diversity among offspring, which increases the chance that some offspring survive in changing environments. Section 9.1 Figure 9.2

Clicker Question #1 Which two organisms are genetically the most similar? Pair A Pair B Flower: Doug Sherman/Geofile/RF; Amoeba: Carolina Biological Supply Company/Phototake; Mother cat and kittens: Jane Burton/Dorling Kindersley/Getty Images

9.1 Mastering Concepts How do asexual and sexual reproduction differ? Ultrasound: Chad Ehlers/Glow Images

Meiosis Overview The form of cell division by which GAMETES, with HALF the number of CHROMOSOMES, are produced. DIPLOID (2n) HAPLOID (n) Meiosis is SEXUAL reproduction. TWO divisions (MEIOSIS I and MEIOSIS II). 12

Meiosis Overview Sex cells divide to produce GAMETES (sperm or egg). Gametes have HALF the # of chromosomes. Occurs only in GONADS (testes or ovaries). Male: SPERMATOGENESIS -sperm Female: OOGENESIS - egg or ova 13

Diploid Cells Contain Two Homologous Sets of Chromosomes Most cells in a sexually reproducing organism have two sets of chromosomes: one from the father and one from the mother. Section 9.2 All karyotype photos: CNRI/Science Source Figure 9.3

Diploid Cells Contain Two Homologous Sets of Chromosomes Cells with two sets of chromosomes are called diploid cells. The image to the right shows all of the chromosomes from a diploid human cell. Section 9.2 All karyotype photos: CNRI/Science Source Figure 9.3

Diploid Cells Contain Two Homologous Sets of Chromosomes The numbered chromosomes are called autosomes. These chromosomes are the same for both sexes. Section 9.2 All karyotype photos: CNRI/Science Source Figure 9.3

Diploid Cells Contain Two Homologous Sets of Chromosomes The chromosomes denoted by a letter are the sex chromosomes. In humans, an individual with two X chromosomes is female, and an individual with one X and one Y chromosome is male. Section 9.2 All karyotype photos: CNRI/Science Source Figure 9.3

Diploid Cells Contain Two Homologous Sets of Chromosomes Notice that each chromosome is paired with an equally-sized chromosome (except for when the X chromosome pairs with the smaller Y chromosome). Section 9.2 All karyotype photos: CNRI/Science Source Figure 9.3

Is this individual Male or Female? 23 Sex Chromosomes.the 23 rd set This person has 2 X chromosomes and is a female.

Diploid Cells Contain Two Homologous Sets of Chromosomes The chromosomes of a homologous pair look alike and carry the same sequence of genes for the same traits. Section 9.2 Figure 9.4

Diploid Cells Contain Two Homologous Sets of Chromosomes However, the members of a homologous pair may carry different alleles, which are alternative versions of the same gene. Section 9.2 Figure 9.4

Clicker Question #2 The photo below shows two chromosomes from one cell. Which statement is true? A. Both came from the person s mother. B. The 1-2 pair is identical to the 3-4 pair. C. 1 is identical to 2. D. The chromosomes have not been replicated yet. 1 2 3 4 Flower: Doug Sherman/Geofile/RF

Mastering Concepts What are some differences between autosomes and sex chromosomes? Ultrasound: Chad Ehlers/Glow Images

Target Goals for Meiosis I can describe how meiosis is involved in the production of egg and sperm cells I can describe how the process of meiosis controls the number of chromosomes in a gamete I can describe how meiosis and sexual reproduction contribute to genetic variation

Check Your Understanding What is the difference between a sister chromatid and a chromosome? How are they alike?

Mastering Concepts Give me the big picture idea in the differences between Mitosis and Meiosis? Ultrasound: Chad Ehlers/Glow Images

Mitosis vs. Meiosis

Mitosis

Meiosis

Meiosis Is Essential in Sexual Reproduction Gametes, like the sperm and egg cells in this image, are haploid sex cells. A haploid cell has only one set of chromosomes. Section 9.3 Sperm contacting egg: Francis Leroy, Biocosmos/Science Source Figure 9.15

Meiosis Is Essential in Sexual Reproduction When two haploid cells fuse at fertilization, one diploid zygote is formed. A zygote is the first cell of a new organism. Section 9.3 Sperm contacting egg: Francis Leroy, Biocosmos/Science Source Figure 9.15

Meiosis Is Essential in Sexual Reproduction The organism grows by mitotic cell division. Section 9.3 Mating frogs: Nature Picture Library/Britain On View/Getty Images Figure 9.5

Meiosis Is Essential in Sexual Reproduction In adults, specialized diploid cells called germ cells divide to form haploid gametes. Section 9.3 Mating frogs: Nature Picture Library/Britain On View/Getty Images Figure 9.5

Meiosis Overview Meiosis halves the chromosome number and scrambles alleles. n=2 n=2 2n=4 Section 9.3 Human female karyotype: James Cavallini/Science Source Figure 9.6

9.3 Mastering Concepts How do haploid and diploid nuclei differ? Ultrasound: Chad Ehlers/Glow Images

In Meiosis, DNA Replicates Once, but the Nucleus Divides Twice This summary figure shows the nucleus dividing twice. Section 9.4 Figure 9.11

In Meiosis, DNA Replicates Once, but the Nucleus Divides Twice The cell on the left has two pairs of homologous chromosomes, whereas the cells on the right have two unpaired, unreplicated chromosomes. Section 9.4 Figure 9.11

In Meiosis, DNA Replicates Once, but the Nucleus Divides Twice 2n=4 Section 9.4 All photos Ed Reschke Figure 9.7

In Meiosis, DNA Replicates Once, but the Nucleus Divides Twice n=2 Section 9.4 All photos Ed Reschke Figure 9.7

Clicker Question #3 A zygote of a ferret contains 40 chromosomes. How many chromosomes are in a ferret s sperm cell? A. 10 B. 20 C. 40 D. 80 Flower: Doug Sherman/Geofile/RF

9.4 Mastering Concepts How do the events of meiosis I and meiosis II produce four haploid cells from one diploid cell? Ultrasound: Chad Ehlers/Glow Images

Meiosis Generates Variability The gametes produced in meiosis are different from one another because of: crossing over (prophase I) independent assortment (metaphase I) Section 9.5 Mother cat and kittens: Jane Burton/Dorling Kindersley/Getty Images

Meiosis Generates Variability During crossing over, two homologous chromosomes exchange genetic material during prophase I. Section 9.5 Figure 9.8

Meiosis Generates Variability In independent assortment, chromosome pairs align randomly during metaphase I. Section 9.5 Figure 9.9

Meiosis Generates Variability A germ cell with three pairs of chromosomes has four possible arrangements during metaphase I, yielding eight possible gametes (2 3 = 8). Section 9.5 Figure 9.9

Meiosis Generates Variability If meiosis generates such great variability among gametes, how can siblings be identical? Section 9.5 Identical twins: Barbara Penoyar/Getty Images RF Figure 9.10

Meiosis Generates Variability Sometimes, early in development, an embryo splits in two. Each embryo then develops independently. Section 9.5 Identical twins: Barbara Penoyar/Getty Images RF Figure 9.10

Meiosis Generates Variability Fraternal twins are a testament to the variation among gametes; two sperm cells fertilize two separate egg cells, and the offspring might look very different. Section 9.5 Fraternal twins: Image Source Black/ Getty Images RF Figure 9.10

Clicker Question #4 Many sets of triplets consist of a pair and a spare; that is, two identical babies and one non-identical baby. Producing this arrangement requires sperm and eggs. A. 2 2 B. 1 3 C. 3 1 D. 2 3 Flower: Doug Sherman/Geofile/RF

9.5 Mastering Concepts Explain how different chromosome alignments during metaphase I can result in over 8 million genetically different gametes in a human. Ultrasound: Chad Ehlers/Glow Images

Mitosis and Meiosis Compared Meiosis occurs in germ cells; mitosis occurs in body cells. 2n=4 2n=4 2n=4 n=2 Section 9.6 Figure 9.11

Mitosis and Meiosis Compared Cytokinesis occurs once in mitosis, but twice in meiosis. 2n=4 2n=4 2n=4 n=2 Section 9.6 Figure 9.11

2n=4 Mitosis and Meiosis Compared 2n=4 In mitosis, daughter cells have the same chromosome number as the parent cell. In meiosis, chromosome number is halved. 2n=4 n=2 Section 9.6 Figure 9.11

Mitosis and Meiosis Compared 2n=4 2n=4 In meiosis, homologous chromosome pairing allows for crossing over. This process does not occur in mitosis. 2n=4 n=2 Section 9.6 Figure 9.11

9.6 Mastering Concepts In what ways are mitosis and meiosis different? Ultrasound: Chad Ehlers/Glow Images

Errors Sometimes Occur in Meiosis If chromosomes fail to separate during anaphase I or anaphase II, then abnormal gametes form. Section 9.7 Figure 9.12

Errors Sometimes Occur in Meiosis This image shows how nondisjunction in meiosis I produces gametes with either an extra or a missing chromosome. Section 9.7 Figure 9.12

Errors Sometimes Occur in Meiosis This image shows how nondisjunction in meiosis II produces two gametes with either an extra or a missing chromosome, and two normal gametes. Section 9.7 Figure 9.12

Errors Sometimes Occur in Meiosis Abnormal gametes lead to zygotes with an improper chromosome number. Section 9.7 Figure 9.12

Errors Sometimes Occur in Meiosis Individuals with missing chromosomes often cease developing before birth. An extra chromosome often causes fewer problems than a missing chromosome. Section 9.7 Figure 9.12

Errors Sometimes Occur in Meiosis An extra copy of a chromosome a trisomy causes genetic disorders such as Down syndrome. Section 9.7 Karyotype: CNRI/Science Source; Child with Down syndrome George Doyle/Stockbyte/Getty Images RF Figure 9.13

Errors Sometimes Occur in Meiosis Extra or missing sex chromosomes cause sex disorders. Section 9.7 Table 9.1

Errors Also Occur Within Chromosomes Mutations in chromosome structure can have major effects on an organism. Section 9.7 Chromosomes: Addenbrookes Hospital/Science Source Figure 9.14

Clicker Question #5 In Turner syndrome, a female is born with only one X chromosome. This disorder could arise as a result of nondisjunction in. A. sperm formation B. egg formation C. either sperm or egg formation Flower: Doug Sherman/Geofile/RF

9.7 Mastering Concepts How can nondisjunction during meiosis lead to gametes with extra or missing chromosomes? Ultrasound: Chad Ehlers/Glow Images

Meiosis Produces Human Gametes Sperm cells form in the testes. Egg cells form in the ovaries. Section 9.8 Sperm contacting egg: Francis Leroy, Biocosmos/Science Source Figure 9.15

Meiosis Produces Human Gametes Section 9.8 Figure 9.16

Meiosis Produces Human Gametes Section 9.8 Figure 9.17

Meiosis Produces Spores in Plants Section 9.8 Figure 9.18

9.8 Mastering Concepts What are the stages of sperm and egg development in humans? Ultrasound: Chad Ehlers/Glow Images

Investigating Life: Hermaphrodites and Parasites Meet the Red Queen Why do animals spend so much energy sexually reproducing? Studying a worm that can reproduce either sexually or asexually might help answer this question. Section 9.9 Petri dish: James King-Holmes/Science Source; C. elegans worms: Sinclair stammers/science Source Figure 9.19

Investigating Life: Hermaphrodites and Parasites Meet the Red Queen Natural selection favors sexual reproduction when parasites evolve with their hosts (red bars on graph to right). Section 9.9 Figure 9.20

Investigating Life: Hermaphrodites and Parasites Meet the Red Queen In fact, a population of identical worms that could only reproduce asexually went extinct when exposed to an evolving parasite. Section 9.9 Figure 9.21

Investigating Life: Hermaphrodites and Parasites Meet the Red Queen Sexual reproduction, and therefore meiosis, increases an organism s fitness when faced with a rapidly evolving parasite population. Section 9.9 Figure 9.21