Genetics Exam 3 Study Guide
46. In the Calvin Bridges model for sex determination in Drosophila melanogaster, how many autosomes are represented by the letter A? Understand how to represent male and female genotypes using this method with the 8 total chromosomes in the fruit fly.
"A" = a set of 3 autosomes >normal fertile female having 8 total chromosomes is designated as 2A2X >normal fertile male having 8 total chromosomes is designated as 2AXY. 2A3X- meta female (AAXXX) 3A3X or 2A2X-female (AAAXXX or AAXX) 4A3X or 3A2X- intersex (AAAAXXX or AAAXX) 2AX or 2AXY- male (AAX or AAXY) 3AXY- metamale (AAAX or AAAXY)
28. What are the two main theories of sex determination?
1. Sex is dependent upon genes on the chromosomes. >autosomes >gonosomes (sex chromosomes) 2. Sex is dependent upon the environment (more primitive species) >External Stimuli - Ex. light, moisture, temperature, chemical. >Internal Stimuli - Ex. hormonal
17. What three changes occur when a spermatid differentiates into a mature sperm?
1. loss of cytoplasm 2. addition of flagellum 3. addition of acrosome (all of these aid sperm, lots of traveling to do!)
23. Why does a pollen grain have two haploid nuclei? What is the purpose of each nuclei?
1n fuses with the polar nuceli to produce the endosperm (3n) 1n fuses with the egg to produce the zygote (2n)
24. One of the two nuclei in the pollen grain divides again to produce two male gametes. What nuclei do each of these two male gametes unite with in the female embryo sac?
>Once a pollen grain lands on the stigma, it will start to germinate (grow) down the style until it reaches the ovary. >When the tube nucleus enters the ovule it will degenerate the synergid nuclei. The antipodal nuclei will break down as well. >One of the nuclei in the pollen grain will go through mitosis again (duplicate). This results in 2 sperm nuclei. >One sperm fertilizes the egg cell--> form a diploid zygote >the other sperm combines with the two polar nuclei of the large central cell of the megagametophyte --> forms a triploid nucleus >The large cell of the gametophyte will then develop into the endosperm, a nutrient-rich tissue which provides nourishment to the developing embryo.
69. How can you distinguish a male fruit fly from a female fruit fly?
>males have sex combs >dark abdomen >usually relatively smaller
64. What is a Free Martin in cattle?
A freemartin or free-martin (sometimes martin heifer) is an infertile female mammal with masculinized behavior and non-functioning ovaries. >Genetically the animal is chimeric: Karyotyping of a sample of cells shows XX/XY chromosomes. The animal originates as a female (XX), but acquires the male (XY) component in utero by exchange of some cellular material from a male twin >Externally, the animal appears female, but various aspects of female reproductive development are altered due to acquisition of anti-Müllerian hormone from the male twin
49. Define Aneuploid, Euploid, and Polyploid.
Aneuploid: Having an abnormal number of chromosomes -usually the addition or loss of one or two chromosomes -Not having a number that is a multiple of the haploid. >Autosomal ex. Trisomy 21 (Down's Syndrome) >Sex Chromosomal ex. Turner's and Klinefelter's Syndromes. Euploid: Having a chromosome number that is an exact multiple of the haploid number Polyploid: Having more that two homologous sets of chromosomes (more that 2N; ex. 3N, 4N, etc.)
29. What are the two types of chromosomes?
Autosomes - all chromosomes other than sex chromosomes (same in diploid males and females). Sex chromosomes - Chromosomes particularly concerned with the determination of sex (X and Y and Z & W)
56. What are Barr bodies? Do Barr bodies occur in somatic and/or reproductive cells?
Barr Body: a small, densely staining structure in the cell nuclei of female mammals >consisting of a condensed, inactive X chromosome >It is regarded as diagnostic of genetic femaleness. >found in female somatic cells ONLY
45. What sex are parthenogens in birds? What sex are mammalian parthenogens?
Bird Parthenogens: Male (homogametic sex) Mammalian Parthenogens: Female (homogametic sex)
7. Describe what is meant by the saying "slipping off the ends."
Chiasmata: The X-shaped, microscopically visible region representing homologous chromatids that have exchanged genetic material through crossing over during meiosis. 1 = chiasma #>1 = chiasmata "slipping off the ends": terminalization of chiasmata -The slipping of chiasmata towards the ends of bivalents is called as terminalisation. They separate along with the cell -When tetrads, which are composed of two pairs of sister chromatids, begin to split the only points of contact are at the chiasmata.
62. Define Chimera.
Chimera: An individual formed from two different cell lines or the fusion of two non-identical fertilized eggs (embryos), but which is composed of cells that all have the genotype of one sex (male or female).
5. What are cross-over events? Why are they important? Do cross-over events occur between sister chromatids or between non-sister chromatids?
Cross-Over Event: Process in which homologous chromosomes exchange portions of their chromatids during meiosis (Prophase 1- Pachytene) Importance: resulting in a mixture of parental characteristics in offspring; accounts for genetic variation, because due to the swapping of genetic material during crossing over, the chromatids held together by the centromere are no longer identical. Occurs between: NON-sister chromatids
55. What is the Mary Lyon Hypothesis?
Dosage Compensation: Inactivation of all but one X chromosome >This allows the dosage relationship between # X and # autosomes to be the same in males and females. >Females (XX) do not express a sex-linked trait more markedly than hemizygous males X Y). >Only one X chromosome required for cell to function - other X chromosomes (1 in normal individuals) are inactivated (more dense and stain darker). >Because X chromosome inactivation does not normally occur in the very early developmental stages of germ cells, each ovum still receives an X chromosome from the female parent. >Because approximately 15 % of X chromosome genes may escape inactivation, sex chromosome aneuploid individuals (ex. XXY and XXX ) can be affected by the over-expression of X chromosome genes.
38. List examples of external stimuli that can determine sex in Environmental Sex Determination. List the example of internal stimuli that can determine sex.
External: -light -moisture -temperature -chemical Internal: -hormonal
68. Is fruit fly red and white eye color a sex-linked trait? Is fruit fly normal and vestigial wing type a sex-linked trait?
Eye Color: sex-linked >If the genes are on x chromosomes (sex-linked), reciprocal crosses in the P generation will not give similar results (F1 and F2 ). >ex: drosophila eye color Wing Type: NOT sex-linked >If the genes are on autosomes, reciprocal crosses in the P generation will give similar results (F1 and F2 ). >ex: drosophila wing shape
44. There are several types of parthenogenesis. Please describe facultative and automictic parthenogenesis.
Facultative Parthenogenesis: when a female can produce offspring either sexually or via asexual reproduction >female produces haploid zygote >female produces diploid zygote Automictic Parthenogenesis: a postmeiotic process in which a haploid cell may either duplicate its chromosomes or join with another haploid cell. In both cases, diploid zygotes develop and grow into diploid adults. >The specific form of avian parthenogenesis in which the egg nucleus recombines with the second polar body >female develops haploid egg that fuses with other oocyte
34. What is the genotype for a person with Turner's syndrome? Is this individual male or female? Are they sterile or fertile?
Female with a missing X chromosome X Sterile
40. Horsetail plant gametophytes sex is also determined by the Environment. Which sex predominates during good growth conditions? The other sex predominates in poor growth conditions.
Female: good growth conditions in environment Male: bad growth conditions in environment
39. Bonellia veridis the Green Spoonworm has Environmental Sex Determination. Describe what would cause a larva to differentiate into a male. What allows larvae to become female?
Green spoon worms begin life colourless and adrift in a sexually undifferentiated larval state: whether they end up male or female depends on where they settle if bonellia virdis is isolated: female -female will then secrete toxin called bonellin if bonellia virdis larvae is near an adult female (exposed to bonellin): larva will go into the female and develop into a male environmental influence, chemical
61. Define Gynandromorph. What is a bilateral gynandromorph?
Gynandromorph: An individual that developed from a single fertilized egg (embryo) and which is composed of both male and female genotype cells (sexual mosaic). Bilateral Gynandromorph: A gynandromorph can have bilateral asymmetry—one side female and one side male. >Bilateral gynandromorphy arises very early in development, typically when the organism has between 8 and 64 cells. >Later stages produce a more random pattern. >Alternatively, the distribution of male and female tissue can be more haphazard ( non-bilateral)
58. Define Hemizygous.
Hemizygous: Having only one allele of a given gene. Ex: X^AY or X^a Y Homozygous Ex: X^AX^A or X^aX^a Heterozygous: Ex: X^AX^a
63. What is a Hermaphrodite?
Hermaphrodite: An individual that possesses both male and female gonads, with the social environment usually controlling whether the individual takes on a male or female reproductive role.
71. What is a holandric gene? Give an example of a holandric trait.
Holandric Gene: carried on the Y chromosome -only passed by males onto their sons ex: hairy ear rims (pinna)
33. In mammals, a normal male is the heterogametic sex and a normal female is the homogametic sex. Define heterogametic and homogametic. Which sex is heterogametic in birds (such as chickens)?
Homogametic Sex: produces one kind of gamete in reference to the sex chromosomes. >human females (XX) >bird males (ZZ) Heterogametic Sex: produces two kinds of gametes in reference to the sex chromosomes. >human males (XY) >bird females (ZW)
31. How many autosomes and how many sex chromosomes do humans have? Chickens? Drosophila melanogaster?
Humans: 22 pairs of autosomes 1 pair of sex (23 pairs- 46) Chickens: 38 pairs of autosomes 1 pair of sex (39 pairs- 78) Drosophila melanogaster: 3 pairs of autosomes 1 pair of sex (4 pairs- 8)
66. What is a reciprocal cross? What is the purpose of doing a reciprocal cross? How do you know if a trait is sex-linked or not?
In genetics, a reciprocal cross is a breeding experiment designed to test the role of parental sex on a given inheritance pattern >All parent organisms must be true breeding to properly carry out such an experiment >AA (fem) X aa (male) AND aa (fem) X AA (male) Purpose: to determine if a trait is sex-linked normal phenotypic ratio: autosomal abnormal phenotypic ratio: sex-linked Identifiers of Sex Linked Traits: 1. Occurs more often in males than females. 2. Gene is transmitted from an affected male through his daughters to 1/2 of his grandsons. 3. Never transmitted from father to son. 4. An affected female had to have an affected father and an affected or carrier mother.
35. What is the genotype for a person with Klinefelter's Syndrome? Is this individual male or female? Are they sterile or fertile?
Male with an extra X chromosome XXY Sterile
20. Which parts of a flower are the male structures? Which parts are the female structures?
Male: Stamen anther filament Female: Pistil stigma style pollen tube ovary ovule
25. Of the four haploid megaspores that are formed from the diploid megaspore mother cell, how many survive? What happens to the surviving megaspore(s)?
Megaspore: A spore from a heterosporous plant species that develops into a female gametophyte. Egg mother megaspore (2n cell) --> meiosis --> 4 1n cells -- (3 of the 4 die)-> single surviving megaspore --> 3 rounds of mitosis --> a single 8 n cell 3 antipodals 2 polar nuclei 2 synergids 1 egg nucleus 2 n goes to endosperm 1 n goes to zygote 5 n degrade >of the 4 haploid megaspores that are fromed from the diploid megaspore mother cell, only ONE survives >surviving megaspore undergoes mitosis to become egg
8. Are Meiosis I and II reductional division and/or equational division?
Meiosis I - Reductional division (Because the ploidy is reduced from diploid to haploid) Meiosis I 1 X (2N, 4C; G2) ------> 2 X (1N, 2C; no S) Meiosis II - Equational division (analogous to mitosis, in which the sister chromatids are segregated, creating four haploid daughter cells (1n, 1c)) Meiosis II 1 X (1N, 2C) ----------> 2 X (1N, 1C) Final Product 4 X (1N, 1C)
22. Does a diploid microspore mother cell undergo meiotic divisions to become a pollen grain or an egg during sporogenesis?
Microspore: A spore from a heterosporous plant species that develops into a male gametophyte Pollen Grain mother microspore (2n cells) --> 2 meiosis --> 4 1n cells --> 1 mitosis --> 2 1n cells 1n goes to endosperm 1n goes to zygote
1. Understand the differences between Mitosis and Meiosis.
Mitosis >a type of cell division that results in two daughter cells each having the same number and kind of chromosomes as the parent nucleus >typical of ordinary tissue growth. Meiosis >a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell (reductive division), as in the production of gametes. >(genetics) cell division that produces reproductive cells in sexually reproducing organisms (germ-line cells)
11. N = the number of complete sets of chromosomes or the gene (allele) complement number and C = Amount (mass) of DNA in the nucleus. Describe how the values of N and C change during Mitosis and during Meiosis I and Meiosis II.
Mitosis: 1 X (2N, 4C) --> 2 X (2N, 2C) equational Meiosis I: 1 X (2N, 4C) --> 2 X (1N, 2C) reduction Meiosis II: 1 X (1N, 2C) --> 2 X (1N, 1C) equational
57. How do you calculate the number of Barr bodies in an organism?
N-1
48. Define nondisjunction. What is the implication of a nondisjunction event during Anaphase I?
Nondisjunction: the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division >usually resulting in an abnormal distribution of chromosomes in the daughter nuclei Nondisjunction in Anaphase 1: >Nondisjunction in meiosis I occurs when the tetrads fail to separate during anaphase I. >At the end of meiosis I, there will be 2 haploid daughter cells, one with n+1 and the other with n-1. Both of these daughter cells will then go on to divide once more in meiosis II, producing 4 daughter cells, 2 with n+1 and 2 with n-1.
6. During which stage of Prophase I do cross-over events occur? During which stage of Prophase I are the cross-over events visualized as chiasmata?
Pachytene: cross-over event occurs Diplotene: cross-over visualized as chiasmata
43. Honey bees that hatch from a fertile egg are females and bees that hatch from an unfertilized egg are males. What term describes when unfertilized eggs become activated and develop into viable individuals as part of the normal life cycle? What other animals have been found to exhibit this phenomenon?
Parthenogenesis: When unfertilized eggs may become activated and develop into viable individuals as part of the normal life cycle. • Parthenogenesis may occur in a number of invertebrate groups (i.e. insects) as well as in scattered vertebrate species (some fishes, a few lizards, and even turkeys). Males (drones): haploid 1N Females (workers and queen): diploid 2N
4. Describe the events that occur during the specific stages of Prophase I: a. Leptotene b. Zygotene c. Pachytene d. Diplotene e. Diakinesis
Prophase I: a. Leptotene: the initial condensation and coiling of chromosomes, which appear as very long threadlike structures b. Zygotene: homologous chromosomes have begun to pair and synapse laterally into bivalents or tetrads; beginning of crossing over c. Pachytene: synapsis is complete, bivalents have become shorter and thicker. homologous chromosomes are held tightly into position by synaptonemal complex; crossing over occurs d. Diplotene: the chromosomes of each bivalent begin to undergo repulsion or separate from each other. chiasmata become visible (multiple chiasmata); crossing over is now complete e. Diakinesis: nuclear envelope fragments and nucleoli disperses; chromosomes complete condensing, tetrads ready for metaphase; only one chiasma, maybe less; "slipping off the ends"
47. The Calvin Brides model shows how sex is determined based on the ratio of X chromosomes to the number prior to A. Write the values to get a metafemale, a fertile female, an intersex fly, a fertile male (don't forget the Y chromosome), and a metamale.
Ratio of X Chromosomes : Autosome Sets 2A3X- meta female 1.5 3A3X or 2A2X-female 1.0 4A3X - intersex 0.75 3A2X - intersex 0.67 2AX or 2AXY- male 0.5 3AXY- metamale 0.33
50. A human embryo begins with a bipotential gonad (able to differentiate into either the male or the female reproductive tract). Describe the role of the genes SRY and DAX1 in directing the bipotential gonad to differentiate into the male or female reproductive tract.
SRY: gene region >This has been positively identified as the gene encoding the testis determining factor (TDF). >When injected into normal (XX) female mice, it caused them to develop as males. >The gene acts via two established mechanisms: 1. inhibiting p450 2. enhancing mullerian-inhibiting substance DAX1 (gene NR0B1) >an orphan nuclear receptor that regulates adrenal and gonadal development >SRY and DAX-1, interact in early periods of development of the gonadal ridges, expressing both in testicular and ovarian tissue >lack of male sex hormone leads to production of mullerian duct(ovaries)
37. How is chicken sex determined? What is a rooster's genotype? What is a hen's genotype?
Sex is dependent upon genes on the chromosomes Rooster: XX aka ZZ Hen: XY aka ZW
67. Define sex-linkage.
Sex linkage: is the phenotypic expression of an allele that is dependent on the gender of the individual and is directly tied to the sex chromosomes. >In such cases there is a homogametic sex and a heterogametic sex.
65. Describe the difference between sex-influenced and sex-limited gene expression.
Sex-Influenced Gene Expression: a trait that is caused by a gene whose dominant expression differs in male and females; (e.g., male patterned baldness) Sex-Limited Gene Expression: autosomal genes expressed only in one sex (e.g., hen feathered vs cock feathered)
42. Many reptile species, including Alligator mississippiensis, exhibit a type of Environmental Sex Determination known as Temperature Dependent Sex Determination. Describe Temperature Dependent Sex Determination.
Temperature-dependent sex determination: a type of environmental sex determination in which the temperatures experienced during embryonic/larval development determine the sex of the offspring. 33 degrees- male #<33 and #>33 -female
2. Contrast the terms tetrad and bivalent when discussing chromosomes.
Tetrad- the association of a pair of homologous chromosomes (4 sister chromatids) physically held together by at least one DNA crossover. -the group of four sister chromatids found within the homologous pair -|||| Bivalent- one pair of chromosomes (sister chromatids) in a tetrad -the pair of two homologous chromosomes found during prophase 1 of meiosis 1 -XX
3. What is a tetrad, a dyad, and a monad when discussing chromosomes in Meiosis?
Tetrad-the association of a pair of homologous chromosomes physically held together by at least one DNA crossover -This physical attachment allows for alignment and segregation of the homologous chromosomes in the first meiotic division. Dyad- consists of 2 identical chromatids (sister chromatids) attached together at the centromere. -Chromosomes are in the dyad form before mitosis, and in the monad form after mitosis. Monad- a single piece of DNA -the monad chromosome
53. What is the function of the p450 aromatase gene?
The SRY protein (TDF) binds the p450 aromatase gene and inhibits its activity. >The p450 aromatase gene has a protein product that converts the male hormone testosterone to the female hormone estradiol.
52. What hormone/substance causes regression of the Mullerian duct?
The SRY protein (TDF) enhances the activity of the gene for: Mullerian Inhibitory Substance (MIS) >induces testicular development and the digression of female reproductive ducts. How? -inhibition of aromatase -decreased estrogens -regression of mullerian duct --> absent female sex structures
51. The embryonic Mullerian Duct becomes the male or female reproductive tract (circle one). The embryonic Wolffian Duct becomes the male or female reproductive tract (circle one).
The embryonic Mullerian Duct becomes the female reproductive tract. >leads to ovaries The embryonic Wolffian Duct becomes the male reproductive tract. >leads to testes
12. Contrast the two models explaining chromosome separation: Traction Fiber vs. Pac-man.
Two models to explain chromosome separation by spindle fibers: 1. Traction-fiber: >Separation force is produced along the fibers (sliding model). >Best explains separation in metaphase and in meiosis. 2. Pac-man: >Separation forces by disassembly of microtubules at kinetochore (centromere) region. >Best explains separation in mitosis. • One or both models are probably responsible for separation in both mitosis and meiosis.
27. Explain why the endosperm is 3n after fertilization. What is the purpose of the endosperm?
Why 3n? union of a sperm cell with two polar nuclei during double fertilization Function? provides nourishment to the developing embryo in angiosperm seeds.
32. Is the X or the Y chromosome larger?
X chromosome is larger
59. Why are normal calico cats always female?
X inactivation (lyon hypothesis/lyonization) >a female cat that is heterozygous for the orange and black coat-color alleles and shows the classic "calico" pattern of orange, black, and white fur X^BX^O >allele for black is expressed in some sections of fur >allele for orange is expressed in some sections of fur >NO BLENDING
36. How is protenor sex determined? What is the sex of a protenor with 1X? With 2X?
XX/X0-> 1:1 ratio of sex in offspring. depends on the random distribution of x chromosome in male gametes. XX = female X__ = male
60. To get a male calico cat, what would his genotype have to be? What aneuploid condition is this in humans?
XXY : male cat -infertile -testicular hypoplasia X^BX^OY Klinefelters syndrome in humans
30. What is the genotype of a normal human male? What is the genotype of a normal human female?
XY -Male has unlike sex chromosomes (heterogametic) (i.e., mammals) XX -Female has like sex chromosomes (homogametic)
19. What is the importance of the zona reaction and the vitelline block during fertilization?
Zona Reaction: a modification of the zona pellucida in response to fertilization, which alters the solubility and binding properties of the zona pellucida -Cortical reaction creates barrierat ZP level. -ZP changes to block polyspermy -Polyspermy is the fertilization of oocyte by more than one sperm, resulting in embryo death Vitelline Block- Cortical reaction can alter oocyte membrane, resulting in a vitelline block to prevent additional sperm fusion all together: Female defenses select for ever more aggressive male sperm, however, leading to an evolutionary arms race. On the one hand, polyspermy creates inviable zygotes and lowers female fitness.
70. What cross in chickens will produce offspring that can be distinguished by sex at hatch just by looking at the down (feather) color in the chicks?
a non-barred male (bb) crossed with a true-breeding barred hen (B-) >males have lighter heads, sometimes with a white or yellow spot >females have darker down color often with a black or brown spot or stripes on their heads or with darker stripes on their backs.
21. What is the micropyle in the female part of a flower?
a small opening in the surface of an ovule, through which the pollen tube penetrates, often visible as a small pore in the ripe seed (in seed it is where water enters). simple terms: where the pollen grain grows down into the ovarythe opening
15. Place the following terms in order of progression of spermatogenesis: a. Spermatid, Secondary Spermatocyte, Sperm, Spermatogonium, Primary Spermatocyte b. When does the first meiotic division occur? When does the second meiotic division occur? Ex: Which division occurs between the Primary and Secondary Spermatocyte?
a. In Order of Progression: 1. spermatogonium 2. primary spermatocyte 3. secondary spermatocyte(2) 4. spermatids(4) 5. sperm(4) b. I) Spermatocytogenesis: spermatogonium(2N)→mitosis → primary spermatocyte(2N) →first meiotic division → secondary spermatocyte(1N)→second meiotic division→ spermatid(1N) 1x (2N, 4C) → 4x(1N, 1C) "Genetic" II) Spermiogenesis: Spermatid → Spermatozoan (1N, 1C) → (1N, 1C) "Metamorphic" - loss of cytoplasm - addition of flagellum - addition of acrosome (all of these aid sperm, lots of traveling to do!)
16. Place the following terms in order of progression of oogenesis: a. Primary Oocyte, Oogonium, First Polar Body, Second Polar Body, Ovum (Egg), Secondary Oocyte, Ootid b. When does the first meiotic division occur? When does the second meiotic division occur? c. When are the first and second polar bodies formed? In mammals, what triggers the formations of the first and second polar bodies?
a. Order of Progression: 1. oogonium 2. primary oocyte 3. secondary oocyte and first polar body 4. second polar body and ootid 5. ovum(egg) b. FETUS 1. Oogonium (lx) (2n) undergoes cell growth and mitotic division to produce oogonia (nx) (2n). 2. Start of Meiosis I (Prophase I).Transformation of oogonium (1x) (2n) to 1º (primary) oocyte (1x) (2n) by passage through Prophase I up to zygotene/pachytene and cell growth. BIRTH 3. 1º oocyte (2n) arrested in Prophase I (zygotene/pachytene). 4. Growth of follicle, 1º oocyte (2n), and zona pellucida. PUBERTY 5. Pre-ovulatory surge of luteinizing hormone (LH). 6. Resumption of Meiosis I. 7. 1º oocyte (lx) (2n) transformed to 2º oocyte (1x) (1n) and first polar body (1x) (1n) after completion of Meiosis I. 8. 2º oocyte arrested in Meiosis II (Metaphase II) FERTILIZATON 9. Sperm (ln) penetration. 10. Meiosis II resumes. 11. Formation of zygote (2n). 12. Formation of second polar body (1n). 13. First polar body (1n) completes mitotic division to produce two more polar bodies (1n) c. Formation of Polar Bodies: triggered by luteinizing hormone (LH) Puberty: 7. 1º oocyte (lx) (2n) transformed to 2º oocyte (1x) (1n) and first polar body (1x) (1n) after completion of Meiosis I. Fertilization: 12. Formation of second polar body (1n). 13. First polar body (1n) completes mitotic division to produce two more polar bodies (1n)
26. Describe the fates of the following nuclei in the embryo sac of the female part of a flower: antipodals, polar nuclei, synergids, egg.
antipodals (3): degenerates polar nuclei (2): 1 sperm unites with the two polar nuceli to form endosperm synergids (2): help the pollen nucleus reach the egg cell for fertilization then degenerate egg (1): 1 sperm unites with egg to form zygote/embryo
41. Cucumber and muskmelon will produce female flowers with exposure to what chemical? Hint: This chemical is also a gas given off by rotting or ripening fruit.
ethylene
9. Does pairing of homologous chromosomes occur during Meiosis I, Meiosis II, and/or during Mitosis?
homologous chromosomes ONLY pair during meiosis I -enables crossing over and reduction division
14. Where does oogenesis occur?
in the outermost layers of the ovaries until the mature ovum moves to the fallopian tube
18. What is the acrosome reaction? Why is it important for sperm?
it helps the sperm penetrate the egg and prevents other sperm from invading the egg
54. What could happen in a male organism if the male sex hormones controlling secondary sex characteristics (testosterone, dihydrotestoterone) are not produced and secreted?
may cause genotypic and phenotypic sex contrast: >Lack of male sex hormone and presence of female sex hormone from ovary: -stimulates development of 2º sexual organs and characteristics (fem). >Presence of male sex hormone from testis: -stimulates development of 2º sexual organs and characteristics (male).
10. DNA has been packaged into the loop packaging stage during interphase and progresses to a rosette packaging by the Leptotene stage of Prophase I. What extent is the DNA packaged by the Pachytene stage of Prophase I?
review of DNA packaging: 1. naked DNA 2. Nucelosome 3. Solenoid 4. Loop 5. Rosette 6. Coil 7. Chromatid/chromosome What extent is the DNA packaged by the Pachytene stage of Prophase I? 7. chromatid/chromosome
13. Where in the testes does spermatogenesis primarily occur?
seminiferous tubules of the testes
