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Meiosis a Dr. Production

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1 Meiosis a Dr. Production

2 Watch the 3 minute video segment "Asexual Reproducers" at http://www
Also view the 4 minute video segment "The Red Queen" at While viewing the videos answer the following questions: What are 2 advantages and 2 disadvantages of sexual reproduction? What are 2 advantages and 2 disadvantages of asexual reproduction?

3 Importance of Meiosis 1. Allows conservation of Allows genetic variation chromosome number in sexually reproducing species

4 Does a 5 year old boy have mitotic divisions occurring?
Does a 5 year old boy have meiotic divisions occurring? Does a 5 year old girl have mitotic divisions occurring? Does a 5 year old girl have meiotic divisions occurring?

5 Essential knowledge 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization. a. The cell cycle is a complex set of stages that is highly regulated with checkpoints, which determine the ultimate fate of the cell. 1. Interphase consists of three phases: growth, synthesis of DNA, preparation for mitosis. 2. The cell cycle is directed by internal controls or checkpoints. Internal and external signals provide stop-and-go signs at the checkpoints. Mitosis-promoting factor (MPF) Action of platelet-derived growth factor (PDGF) Cancer results from disruptions in cell cycle control 3. Cyclins and cyclin-dependent kinases control the cell cycle. 4. Mitosis alternates with interphase in the cell cycle. 5. When a cell specializes, it often enters into a stage where it no longer divides, but it can reenter the cell cycle when given appropriate cues. Nondividing cells may exit the cell cycle; or hold at a particular stage in the cell cycle.

6 Essential knowledge 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization. c. Meiosis, a reduction division, followed by fertilization ensures genetic diversity in sexually reproducing organisms. 1. Meiosis ensures that each gamete receives one complete haploid (1n) set of chromosomes. 2. During meiosis, homologous chromosomes are paired, with one homologue originating from the maternal parent and the other from the paternal parent. Orientation of the chromosome pairs is random with respect to the cell poles. 3. Separation of the homologous chromosomes ensures that each gamete receives a haploid (1n) set of chromosomes composed of both maternal and paternal chromosomes. 4. During meiosis, homologous chromatids exchange genetic material via a process called “crossing over,” which increases genetic variation in the resultant gametes. 5. Fertilization involves the fusion of two gametes, increases genetic variation in populations by providing for new combinations of genetic information in the zygote, and restores the diploid number of chromosomes.

7 Essential knowledge 3.A.2: In eukaryotes, heritable information is passed to the next generation via processes that include the cell cycle and mitosis or meiosis plus fertilization. LO 3.7 The student can make predictions about natural phenomena occurring during the cell cycle. LO 3.8 The student can describe the events that occur in the cell cycle. LO 3.9 The student is able to construct an explanation, using visual representations or narratives, as to how DNA in chromosomes is transmitted to the next generation via mitosis, or meiosis followed by fertilization. LO 3.10 The student is able to represent the connection between meiosis and increased genetic diversity necessary for evolution. LO 3.11 The student is able to evaluate evidence provided by data sets to support the claim that heritable information is passed from one generation to another generation through mitosis, or meiosis followed by fertilization.

8 Essential knowledge 3.A.3: The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. a. Rules of probability can be applied to analyze passage of single gene traits from parent to offspring. b. Segregation and independent assortment of chromosomes result in genetic variation. 1. Segregation and independent assortment can be applied to genes that are on different chromosomes. 2. Genes that are adjacent and close to each other on the same chromosome tend to move as a unit; the probability that they will segregate as a unit is a function of the distance between them. 3. The pattern of inheritance (monohybrid, dihybrid, sex-linked, and genes linked on the same homologous chromosome) can often be predicted from data that gives the parent genotype/phenotype and/or the offspring phenotypes/genotypes.

9 Essential knowledge 3.A.3: The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring. c. Certain human genetic disorders can be attributed to the inheritance of single gene traits or specific chromosomal changes, such as nondisjunction. • Sickle cell anemia • Tay-Sachs disease • Huntington’s disease • X-linked color blindness • Trisomy 21/Down syndrome • Klinefelter’s syndrome d. Many ethical, social and medical issues surround human genetic disorders. • Reproduction issues • Civic issues such as ownership of genetic information, privacy, historical contexts, etc. LO 3.12 The student is able to construct a representation that connects the process of meiosis to the passage of traits from parent to offspring. LO 3.13 The student is able to pose questions about ethical, social or medical issues surrounding human genetic disorders. LO 3.14 The student is able to apply mathematical routines to determine Mendelian patterns of inheritance provided by data sets.

10 Meiosis is also called gametogenesis and sporogenesis

11 Meiosis I Is a reduction division

12 X

13 Prophase I leptotene "thin-thread“, appearance of chromosomes zygotene "yolk-thread“, homologues pr side by side & gene by gene = synapsis, forming bivalent pairs or tetrads pachytene "thick-thread“, shortening & thickening of bivalents, crossing over/recombination at synaptonemal complex diplotene "double-thread“, separation of homologues chiasmata: physical evidence diakinesis shortening chromosomes, disintegration of envelope

14 Crossing Over When homologous chromosomes, swap genetic information
Natural Mutation that allows for genetic variety


16 Metaphase Ibivalents migrate to equator
Anaphase Ihomologous chromosomes migrate to poles not sister chromatids Telophase I (interkinesis)

17 Meiosis II Is an equational division

18 Metaphase IIcentromeres attached to spindle fibers
Anaphase IImigration of daughter chromosomes (formerly chromatids)

19 Metaphase sister chromatids separate
Metaphase II sister chromatids separate Metaphase I homologous chromosomes separate


21 Meiosis Animation

22 Gametogenesis

23 Mitosis Meiosis 1 division2 cells 2 divisions 4 cells Daughter cells genetically identical to parent cell & to each other Daughter cells are genetically distinct from parent & each other Division is equational 2n2n 1st division reduction 2n n 2nd division equational n n Sister chromatids migrate Homologous chromosomes & sister chromatids migrate Occurs in somatic/body cells to reproduce body cells Occurs in sex cells produces gametes Diploid diploid cells Diploid haploid No genetic variation Crossing over in tetrads

24 Mitosis/Meiosis Comparison
46 46 23 46 23 24

25 karyotype

26 Nondisjunction Junction place where things are connected, homologous chromosomes in meiosis I and sister chromatids in meiosis II Disjunction separation of junction during anaphase I and anaphase II Non-disjunction failure of chromosomes to properly separate during anaphase I and anaphase II Nondisjunction results in aneuploidy, or abnormal number of copies of chromosomes

27 Nondisjunction/Aneuploidy
Polyploidy 3 or more sets of chromosomes, (more often in plants) can detect before birth w/ amniocentesis or chorionic villi sampling most children w/chromo abnormalities aborted b/4 mother realizes she's pregnant incidents of aneuploidy inc 50x w/ mothers >45 yrs

28 Down’s Syndrome Statistics
The estimated incidence of Down syndrome is between 1 in 1,000 live births. In 1866, Down described clinical characteristics of the syndrome that now bears his name. In 1959, Lejeune and Jacobs et al independently determined that Down syndrome is caused by trisomy 21. Down syndrome is by far the most common and best known chromosome disorder in humans. Mental retardation, dysmorphic facial features, and other distinctive phenotypic traits characterize the syndrome.

29 Down’s Syndrome Karyotype trisomy 21

30 Down’s Syndrome Symptoms
eyes often slant upwards and outwards, and the back of the head may be unusually flat. as high as 40% of Down's babies will have some sort of congenital heart defect will have some level of learning disorder immune system which makes them prone to infections, particularly chest and sinus infections. can have problems regulating their temperature, and can have very dry skin.

31 1. 60 to 80% of people with Down syndrome will have hearing deficits. 
% of children with Down syndrome will have congenital heart disease. 3. Intestinal abnormalities also occur at a higher frequency and may need to be surgically corrected at birth. 4. People with Down syndrome may have more eye problems.  5. Obesity is often noted during adolescence and early adulthood.  % of  people with Down syndrome will have thyroid problems.  7. Skeletal problems like kneecap subluxation, hip dislocation, and atlantoaxial instability  (the first two neck bones are not well aligned because of the presence of loose ligaments) are more common. 8. Other important medical problems should be addressed as well including: leukemia, Alzheimer's disease, immune system concerns, seizure disorders, sleep apnea, and skin disorders.

32 Patau’s Syndrome Statistics
Incidence of Patau syndrome is approximately 1 per 8,000-12,000 live births. Patau syndrome is the least common and the most severe of the viable autosomal trisomies. Median survival is fewer than 3 days. First identified as a cytogenetic syndrome in 1960, Patau syndrome is caused by an extra copy of chromosome 13,

33 Patau’s karyotype trisomy 13

34 Cleft palate

35 Polydactyly

36 cyclopia (single eye) with a proboscis (the projecting tissue just above the eye).

37 Edward’s Syndrome Statistics
Prevalence is approximately 1 in live births. Trisomy 18 was independently described by Edwards et al and Smith et al in Among liveborn children, trisomy 18 is the second most common autosomal trisomy after trisomy 21.

38 Edward’s Syndrome Trisomy 18

39 Edward’s Syndrome Symptoms
Approximately 95% of conceptions with trisomy 18 die in embryonic or fetal life; 5-10% of affected children survive beyond the first year. The high mortality rate is usually due to the presence of cardiac and renal malformations, feeding difficulties, sepsis, and apnea caused by CNS defects. Severe psychomotor and growth retardation are invariably present for those who survive beyond infancy.

40 overlapping digits with the second and fifth fingers overriding the third and fourth fingers respectively

41 Microglassia, microcephaly and other head abnormalities

42 Turner’s Syndrome Statistics
In 1938, Henry Turner first described Turner syndrome, which is one of the most common chromosomal abnormalities. More than 95% of adult women with Turner syndrome exhibit short stature and infertility. Frequency is approximately 1 in 2,000 live-born female infants. As many as 15% of spontaneous abortions have a 45 X karyotype.

43 Turner’s Syndrome Karyotype monosomy 23

44 Turner’s Syndrome Symptoms
Webbed neck Exhibit female phenotype; sterile Short stature, high arched palate

45 Klinefelter’s Syndrome Statistics
Approximately 1 in 500-1,000 males is born with an extra sex chromosome; over 3,000 affected males are born yearly. The prevalence is 5-20 times higher in the mentally retarded than in the general newborn population. In 1942, Klinefelter et al published a report on 9 men who had enlarged breasts, sparse facial and body hair, small testes, and inability to produce sperm. In 1959, these men with Klinefelter syndrome were discovered to have an extra sex chromosome (genotype XXY) instead of the usual male sex complement (genotype XY).

46 Klinefelter’s Syndrome Karyotype Trisomy 23

47 Klinefelter’s Syndrome Symptoms
fetal development is that of a normal male. However, as the child grows and approaches puberty, he experiences excessive gynecomastia, with low serum testosterone levels. Infertility is common, and general appearance is tall and thin. A higher than normally expected percentage of these individuals have been reported to have emotional disorders

48 Extra Y Statistics Most males have the 46-XY karyotype, but about 1 guy in 1000 has two Y chromosomes, and is an XYY ("diplo-Y", "diplo Y", "YY", "polysomy Y"). XYY's average substantially taller, tend to be wiry-built, and tend to have severe acne. Minor birth defects -- like pectus, crooked eye, and minor outturning of the elbows, are supposed to be common in XYY's. Now, XYY boys usually do have serious behavioral and cognitive problems. The extra "Y" in an XYY is obviously not silent (as is the extra "X" in a XXX woman). It seems likely that the second "Y" adds a bit more aggressiveness to a man's overall personality.

49 Extra Y Karyotype trisomy/quadrasomy 23

50 Meta Female Statistics
With 3 X chromosomes (XXX), these females usually have no apparent physical abnormalities except tallness and menstrual irregularities As adults, these individuals are usually an inch or so taller than average with unusually long legs and slender torsos.  They have normal development of sexual characteristics and are fertile.  They may have slight learning difficulties and are usually in the low range of normal intelligence.  They tend to be emotionally immature for their size during childhood.  None of these traits prevent them from being socially accepted as ordinary women.  This type of chromosomal abnormality is apparently rare and little is known about it.  However, the frequency is approximately 1 in 1,000 female infants and it may be more common when the mother is older.  Metafemales are also called "triple-X females."

51 Meta Female karyotype Trisomy 23

52 Cri-du-Chat Statistics
The estimated incidence is about 1 in 50,000 livebirths In 1963, Lejeune et al described a syndrome of multiple congenital anomalies, mental retardation, microcephaly, abnormal face, and a mewing cry in infants Cri-du-chat syndrome is an autosomal deletion syndrome caused by a partial deletion of chromosome 5p. It is characterized by distinctive, high-pitched, catlike cry in infancy with growth failure, microcephaly, facial abnormalities, and mental retardation throughout life.

53 Cri-du-Chat Karyotype

54 Cri-du-chat Symptoms Approximately 75% of the patients with cri-du-chat syndrome die within the first few months of life and about 90% before they are aged 1 year. These figures are from an older study (1978), and decreased morbidity and mortality are most likely with contemporary interventions. Survival to adulthood is possible. Pneumonia, aspiration pneumonia, congenital heart defects, and respiratory distress syndrome are the most common causes of death.

55 Polyploidy in plants common in plants, especially in30%-70% angiosperms, are thought to be polyploid. i.e. Species of coffee plant with 22, 44, 66, and 88 chromosomes suggesting ancestral condition (n) = 11 and a (2n) = 22, from which evolved the different polyploid descendants. Polyploid plants are larger, leading to created varieties of watermelons, marigolds, and snapdragons Plant Probable ancestral haploid number Chromo # Ploidy level domestic oat 7 42 6n peanut 10 40 4n sugar cane 80 8n banana 11 22, 33 2n, 3n white potato 12 48 tobacco cotton 13 52 apple 17 34, 51

56 Origin of Polyploidy Accident Doubling Plants, (vs animals), form germ cells from somatic tissues. If the chromosome content of a precursor somatic cell has accidentally doubled (e.g., as a result of passing through S phase of the cell cycle without following up with mitosis and cytokinesis), then gametes containing 2n chromosomes are formed. Naturally occuring As the endosperm (3n) develops in corn (maize) kernels (Zea mays), its cells undergo successive rounds (as many as 5) of endoreplication producing nuclei that range as high as 96n. When rhizobia infect the roots of their legume host, they induce the infected cells to undergo endoreplication producing cells that can become 128n (from 6 rounds of endoreplication).

57 Polyploidy and Speciation
When a newly-arisen tetraploid (4n) plant tries to breed with its ancestral species (a backcross), triploid offspring are formed. These are sterile because they cannot form gametes with a balanced assortment of chromosomes. However, the tetraploid plants can breed with each other. So in one generation, a new species has been formed.

58 Alternation of Generations

59 Fungi Life Cycle

60 References Nondisjunction Animation: Patau’s Syndrome: Turner’s Syndrome: Klinefeleter’s Syndrome: Cri-du-chat Syndrome: Edward’s Syndrome: XYY: Metafemales:

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