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1st cleavage of zygote results in the formation of how many blastomeres

Key Terms. cleavage: In embryology, this is the division of cells in the early embryo.; trophoblast: The membrane of cells that forms the wall of a blastocyst during early pregnancy and provides nutrients to the embryo, and later develops into part of the placenta.; zygote: A fertilized egg cell.; morula: A spherical mass of blastomeres that forms following the splitting of a zygote; it. The development of multi-cellular organisms begins from a single-celled zygote, which undergoes rapid cell division to form the blastula. The rapid, multiple rounds of cell division are termed cleavage. Cleavage is illustrated in (Figure 1a). After the cleavage has produced over 100 cells, the embryo is called a blastula class 12 Reproductive System cleavage in Zygote neet. Cleavage in Human Zygote. Formation of Morula: Formation of a solid ball of the cell, looks like Mulberry. · 32 cell stage, reach uterus on 4th day (after 72 hours). · Ist cleavage is Holoblastic (complete) & unequal Spiral cleavage can vary between species, but generally the first two cell divisions result in four macromeres, also called blastomeres, (A, B, C, D) each representing one quadrant of the embryo. These first two cleavages are not oriented in planes that occur at right angles parallel to the animal-vegetal axis of the zygote Human embryo undergoes holoblastic cleavage or complete cleavage. This cleavage results in the formation of blastomeres of unequal sizes. Among the blastomeres, there are many small sized micromeres and few largely sized macromeres. This is known as unequal holoblastic cleavage

27.2B: Cleavage of the Zygote - Medicine LibreText

Cleavage and Blastula Stage Biology for Majors I

During cleavage, there is no growth in the blastomeres. The total size and volume of the embryo remain the same. The cleavages result in a compact mass of blastomeres called morula. It gets transformed into a blastula While the zygote is passing through the fallopian tube, it undergoes cleavage, a process of rapid mitotic divisions that result in the formation of progressively smaller cells. These smaller cells, called blastomeres, are totipotent (capable of forming a complete embryo). The first mitotic division of the zygote occurs about 30 hours after. The first few cleavages occur simultaneously in all of the blastomeres (cells), but, as the number of cells increases, simultaneity is lost, and the blastomeres divide independently. Little growth occurs between divisions. Even after several divisions, the group of blastomeres is about the same size as the original zygote

Since cleavage is impeded by the vegetal pole, there is a very uneven distribution and size of cells. Cells are more numerous and smaller at the animal pole of the zygote than at the vegetal pole. In holoblastic eggs, the first cleavage always occurs along the vegetal-animal axis of the egg, and the second cleavage is perpendicular to the first The third cleavage is equatorial, perpendicular to the first two cleavage planes, and separates the animal and vegetal hemispheres from one another (Figures 8.8 and 8.9). The fourth cleavage, however, is very different from the first three. The four cells of the animal tier divide meridionally into eight blastomeres, each with the same volume

class 12 Reproductive System cleavage in Zygote neet

  1. utes after fertilization, the zygote divides into two cells. The two-cell blastomere state, present after the zygote first divides, is considered the earliest mitotic product of the fertilized oocyte. These mitotic divisions continue and result in a grouping of cells called blastomeres
  2. Cleavage Patterns And Morphogenesis. A fertilized zygote undergoes series of mitotic divisions known as cleavage, which results in the formation of multicellular embryo. In organisms that produce eggs with little yolk, the zygote divides by holoblastic cleavage. In such cleavages, the entire cell is divided equally. Click to see full answer
  3. utes for over 2 hours and in just 12 hours forms some 50,000 cells. This dramatic increase in cell number can be appreciated by comparing cleavage with other stages of development
  4. Cardinal changes in the structure of the nucleus and chromosomes occur during the formation of the zygote, during the cleavage of blastomeres, the compaction of the morula, and its differentiation into TE and ICM cells, during the formation of a blastocyst, and implantation of the embryo (Baranov et al., 2012; Baranov and Kuznetzova, 2007.

divisions produce separate cells called blastomeres. The first few cleavages occur simultaneously in all of the blastomeres (cells), but, as the number of cells increases, simultaneity is lost, and the blastomeres divide independently. Little growth occurs between divisions Cleavage. 1. Dr. Shoeb Ahmad, Assistant Professor, Department of Zoology, AKI's Poona College of Arts, Science & Commerce, Camp, Pune -01 e-mail: shoeb.zoology@gmail.com Mobile no 9919509673 Page 1 Cleavage Fertilization results into the formation of zygote. The process of segmentation (cleavage) immediately follows fertiliza-tion or any.

Cleavage (embryo) - Wikipedi

Cleavage (embryo) Last updated June 16, 2021. In developmental biology, cleavage is the division of cells in the early embryo.The process follows fertilization, with the transfer being triggered by the activation of a cyclin-dependent kinase complex. [1] The zygotes of many species undergo rapid cell cycles with no significant overall growth, producing a cluster of cells the same size as the. — cleavage begins with a zygote, progresses through compaction to a morula stage and terminates at the start of the blastocyst (blastula) stage — the first eight blastomeres are undifferentiated and have identical potential in mammals; thereafter, blastomeres differentiate into inner & outer cells with different mission 1st cleavage of zygote results in the formation of how many - 41807471 polidoctor216 polidoctor216 3 weeks ago Biology Secondary School answered 1st cleavage of zygote results in the formation of how many blastomeres? 1.four 2.two 3.three 4.six 1 See answer polidoctor216 is waiting for your help. Add your answer and earn points The First Cell Division . The final steps in zygote formation include replication of the male and female DNA and the alignment of chromosomes in preparation for the first cell division through mitosis (mi-to'sis).10 The chromosomes assume a formation called a cleavage spindle, which is a phase of mitosis.. As the 2 sets of chromosomes migrate to opposite ends of the zygote, a crease begins.

Cleavage in human is Zoology Question

25.4: Cleavage and Blastulation. After a large-single-celled zygote is produced via fertilization, the process of cleavage occurs while zygotes travel through the uterine tube. Cleavage is a mitotic cell division that does not result in growth. With each round of successive cell division, daughter cells get increasingly smaller tion. Note the absence of intercellular clefts between some of the blastomeres. The zona pellucida was mechanically removed from both embryos. Fig. 2-1. Cleavage and transport down the oviduct. Fertilization occurs in the ampulla of th oviduct. During the first five days, the zygote undergoes cleavage as it travels down the oviduct and enters. In humans, zygote stage of development occurs during the first day in week one following fertilization (GA week 3) and is described as Carnegie stage 1. This stage is followed by mitosis to form 2 blastomeres and then a solid cell mass called the morula • As the zygote, passes through the uterine tube, it undergoes mitotic cell divisions known as cleavage. 6. • This phase of development begins with the first mitotic division of the zygote and ends with formation of blastocyst. • It extends for 6 to 7 days or a week. 7. • The 1st division of zygote gives rise to two daughter cells Introduction. Early embryos in many species polarize along their radial axis when blastomeres—the cells that result from the initial cleavage divisions of the egg—develop molecularly distinct contacted and contact-free surfaces (Fig. 1 A).Conserved polarity regulators, including the PAR (Partitioning defective) proteins, localize asymmetrically and help to distinguish contacted.

A sea urchin zygote undergoes its first cell division. the formation of the primitive streak is guided by the structure known as the. hypoblast. If an amphibian zygote is manipulated so that the first cleavage plane fails to divide the gray crescent, then Cleavage: Mitotic divisions of the zygote leading to the formation of blastomeres. Morula: A cluster of cells with a mulberry-like surface formed by the cleavage of the zygote. Blastocyst: Emerges from the morula. Outward, the blastocyst is bordered by the trophoblast, inward, the cells of the embryoblast surround the centrally located cavity

cleavage In embryology, cleavage is the division of cells in the early embryo. The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage are called blastomeres and form a compact mass called the morula. Cleavage. Cleavage: Cleavage, a sequence of consecutive cell divisions, accomplishes the mission of the growth of the several cells that must be generated from the single-celled zygote. Blastomeres are cells manufactured during cleavage. Each chromosome in the nucleus divides into two daughter chromosomes so that the two daughter blastomeres maintain the diploid number of chromosomes Following fertilization in mammals, it is generally accepted that totipotent cells are exclusive to the zygote and to each of the two blastomeres originating from the first mitotic division. This.

Embryology - Ch.3 - Stages of Embryonic Development ..

B) In the second cleavage division, one of the two blastomeres usually divides a little sooner than the second. done clear. C) With more cleavage divisions, the resultant blastomeres become larger and larger. done clear. D) Cleavage division results in a hollow ball of cells called morula. done clear As a result, either both or just one could be totipotent, fortuitously, depending for instance on how the randomly oriented axis of the first zygotic cleavage (Louvet-Vallee et al. 2005, Zernicka-Goetz 2005) apportions some spatially restricted developmental information laid in the ooplasm. This does not exclude cases where both blastomeres are. The zygotes of many species undergo rapid cell cycles with no significant overall growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage are called blastomeres and form a compact mass called the morula. Cleavage ends with the formation of the blastula Cleavage. After fertilization, the development of a multicellular organism proceeds by a process called cleavage, a series of mitotic divisions whereby the enormous volume of egg cytoplasm is divided into numerous smaller, nucleated cells.These cleavage-stage cells are called blastomeres.In most species (mammals being the chief exception), the rate of cell division and the placement of the. The fifth cleavage was characterized by the formation of 32 cells. The fifth cleavage plane meridionally divided the 12 marginal blastomeres into 24, and horizontally the four central blastomeres into eight, forming one outer and one inner layer, each with four cells in the central region (Fig. 1H)

23 • Early cleavage patterns vary widely between different groups of animals, based largely on the orientation of the division planes. The simplest pattern is radial cleavage, in which successful division planes are at 90 degree angles relative to each other. This results in the blastomeres aligned directly over or to the side of one anothe The fourth cleavage is very different from the first three. From this point on the orientation of the cleavage planes becomes more and more asymmetrical, leading to the formation of small and larger blastomeres. On account of the cell size, one can distinguish micro-, macro- and mesomeres

DEVELOPMENTAL BIOLOGY 3230: Cleavage refers to the stereotyped pattern of early mitotic divisions that divides up the large volume egg cytoplasm. The early zygote is unique in being so large. Most cells undergo a period of growth between cycles of mitosis, but this is not true for early cleavage stage blastomeres The journey from the zygote to the blastocyst, both in humans and mice, starts with the first cleavage into two daughter cells called blastomeres. During the first 3-4 days embryonic cells divide roughly every 12-18 h. As embryo development progresses, the individual blastomeres are gradually subject to a restriction of their totipotency Describe cleavage, compaction and blastocyst formation. Describe the developmental potential of the blastomere, morula, inner cell mass, and trophoblast. Mitotic divisions of the zygote, results in rapid increase in the number of cells of progressively smaller size. First few blastomeres are totipotent, ability to develop into a.

In embryology, cleavage is the division of cells in the early embryo. The process follows fertilization, with the transfer being triggered by the activation of a cyclin-dependent kinase complex. The zygotes of many species undergo rapid cell cycles with no significant overall growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage. Stages of cleavage. a. Morula stage: About 30 hours after fertilization, the zygote divides into 2 cells (blastomeres), then into 4 blastomeres at 40 hours.; Twelve cell stage is reached after 3 days of fertilization, while the 16 cell stage is reached at the 4 th day (96 hours).; The developing embryo of 12-16 blastomeres is called morula (like a mulberry tree) that enters the uterus nearly 3. The formation of outer and inner cells during the fourth cleavage is the result of differential division into polar/outer cells and apolar/inner cells (inside-outside hypothesis) (Tarkowski and Wroblewska, 1967). The first morphological sign of polarity appears in the blastocyst when at least two cell types can be distinguished: the inner.

Cleavage Biology MCQs for NEET 2020 - VEDANT

Morula usually consists of 16 - 32 cells. The first cleavage in human zygote occurs in the fallopian tube, about 30 hours after fertilization. Second and third cleavage take place about 60 hours and 72 hours after fertilization respectively. Cleavage increases the number of cells, but not result in growth Pages 21 ; This preview shows page 7 - 10 out of 21 pages.preview shows page 7 - 10 out of 21 pages

It comprises a solid ball of cells, which is a result of the rapid cell divisions of a zygote by mitosis. The small, spherical cells in the morula are referred to as blastomeres. Usually, the first cell cleavage by mitosis occurs 24 hours after fertilization. Morula is formed in eggs with a little yolk, which undergoes complete cleavage The fourth cleavage occurs along two planes, parallel to and on either side of the second one, resulting in 16 blastomeres arranged in 4 rows of 4 cells (Fig. 1E). 32-cell stage (13/ 4 hr). The fifth cleavage is a vertical division and is parallel to the first cleavage plane. The resulting 32 blastomeres are arranged in 4 rows of 8 cells (Fig. 1F) Sperm DNA damage causes mirrored mosaicism in two-cell-stage embryos. Early bovine and human embryo development is a near deterministic process regulated by maternally deposited factors until the embryonic genome becomes activated at the four- to eight-cell stage (1, 27).To examine the consequences of sperm DNA damage on the developmental competence of embryos, bovine IVF was performed with. Zygote then undergoes cleavage division. The cleavage results in the increase in the number of cells but the size remains the same as that of the fertilized egg. Morula with 16 cell divide mitotically and produces 32 cells. 32 celled stage is called as blastula and all the cells in blastula are same size as zygote

cleavage stage embryo Human Reproduction Oxford Academi

The larger cell divides first and thus forms the three blastomeres. Then the smaller blastomere divides and thus four blastomeres are formed. It is a 4-celled stage. 2nd cleavage is at a right angle to the 1st cleavage. One member of the large blastomeres of 4-cell stage divides forming 5-cell condition followed by 6-7 stage ultimately 8-celled Formation of the Zygote. 1) Both ovum and sperm each contribute half of the nuclear material of the future zygote; the ovum alone contributes additional genetic factors. [p. 38] 2) It is probable that the zygote before cleavage is already polarized (i.e. has an up and down, left or right). [p hillis2e_ch38. Printed Page 790 (cont.) Menu. Hide page numbers. Cleavage is the initial process that creates cellular building blocks to form the new organism by producing many smaller cells from one. Ultimately, as a result of cleavage, these smaller cells will differ in their cytoplasmic determinants Many eggs undergo reorganizations that localize determinants specifying the developmental axes and the differentiation of various cell types. In ascidians, fertilization triggers spectacular reorganizations that result in the formation and localization of distinct cytoplasmic domains that are inherited by early blastomeres that develop autonomously

The zygote is the first diploid cell that forms following fertilization by fusion of the haploid oocyte (egg) and spermatozoa (sperm) resulting in the combination of their separate genomes. The zygote will therefore form the conceptus, the embryonic (embryo, fetus) and extra-embryonic (fetal membranes, fetal component of the placenta) cellular products of fertilisation Key Terms. blastula: a 6-32-celled hollow structure that is formed after a zygote undergoes cell division; blastomere: any cell that results from division of a fertilized egg; meroblastic: undergoing only partial cleavage; holoblastic: cleaving, and separating into separate blastomeres; inner cell mass: a mass of cells within a primordial embryo that will eventually develop into the distinct. From here the spatial arrangement of blastomeres can follow various patterns, due to different planes of cleavage, in various organisms. Bilateral; The first cleavage results in bisection of the zygote into left and right halves. The following cleavage planes are centered on this axis and result in the two halves being mirror images of one another Mitotic Cleavage of the Blastomeres: After fertilization, the resulting one-celled zygote will rapidly undergo multiple mitotic cleaves as it travels four days toward the uterus. One should recall that the zygote is much larger compared to many cells of the body. Thus the process of cleavage or segmentation results in the production of.

If a sperm penetrates the egg, fertilization results. Tiny hairlike cilia lining the fallopian tube propel the fertilized egg (zygote) through the tube toward the uterus. The cells of the zygote divide repeatedly as the zygote moves down the fallopian tube to the uterus. The zygote enters the uterus in 3 to 5 days A zygote, also known as a fertilized ovum or fertilized egg, is the union of a sperm cell and an egg cell. The zygote begins as a single cell but divides rapidly in the days following fertilization. The zygote's single cell contains all of the 46 necessary chromosomes, getting 23 from the sperm and 23 from the egg

Human Development - Week 1 Questions and Study Guide

(a) pattern of cleavage (b) formation of zygote (c) number of blastomeres (d) fertilization. Answer and Explanation: 18. (a): Based on the amount and pattern of distribution of yolk in the zygote, cleavage is of two types: holoblastic and meroblastic. Holoblastic cleavage divides the zygote and blastomeres completely into daughter cells In contrast to the results of previous studies which stated that the time of first cleavage could be used for selection of embryos at transfer (Shoukir et al., 1997; Sakkas et al., 1998a), no selection for the early-cleaving embryos was performed at embryo transfer in the current study. Instead, the embryos judged to be morphologically best at. The Zygote starts as a single cell and divides asexually by mitosis following the days of fertilisation. The division of the cells takes two weeks, and The Zygote becomes an embryo and then a foetus. The first discoveries of The Zygote formation were made by German Zoologists Oscar and Richard Hertwig in the late 19th century In embryology, cleavage is the division of cells in the early embryo.The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote. The different cells derived from cleavage are called blastomeres and form a compact mass called the morula.Cleavage ends with the formation of the blastula

Cleavage partitions the zygote into many smaller cells. A succession of rapid cell divisions called cleavage follows fertilization. During this period, cells go through the S (DNA synthesis) and M (mitosis) phases of the cell cycle but may skip the G1 and G2 phases. As a result, little or no protein synthesis occurs Mitotic division occurs approximately 35-36 hours after fertilization and results in the formation of two diploid blastomeres. Figure 10.2 Zygote. During the first hours of development after fertilization, the differentiated germ cells, i.e., the oocyte and the sperm cell, must be reprogrammed into a totipotent state

Cleavage in mammals : Zoology Question

- First cleavage may occur along an axis that produces two identical blastomeres - equal devtl potential - 1st 2 blastomeres are similar - totipotent - fate of embryonic cells can also be affected by zygote's characteristic pattern of cleavage. in many species - only zygote is totipotent - 1st cleavage divides cytoplasmic. Although it occurred rarely, displacement of juxtaposed PN to the cortex was strongly associated (P < 0.0001) with direct cleavage into three blastomeres at the first cell division. The times of PN breakdown and first cleavage showed a very consistent trend, occurring earlier or progressively later depending on whether initial male PN. • The result of cleavage is the formation of two identical blastomeres establishing the bilateral symmetry of the adult animal. • The Second cleavage is also oriented from animal to vegetal pole but at right angle to the first and divides the first two blastomeres into 4 equal sized cells 6 The cleavage patterns leading to the formation of TET versus nTET or nTETp embryos were once again significantly different (P < .001). Among the 716 embryos analyzed, a meridonal first division (cleavage pattern 1-4) was observed in 94% of embryos with ∼63%-65% expanded blastocyst formation during the first cleavage. For other vertebrates, however, the axes are not predictable before the onset of Cleavage planes ' Cytoplasm Zygote (0 hrs) 2-Cell(0.7 hrs) a-Cell (1.2 hrs) AN VE sensitive, and results in the formation of the Nieuwkoop center in dorsal vegetal blastomeres. The Nieuwkoo

In embryology, cleavage is the division of cells in the early embryo. The zygotes of many species undergo rapid cell cycles with no significant growth, producing a cluster of cells the same size as the original zygote. The different cells derive During cleavage of the mammalian zygote, the resultant blastomeres become smaller and smaller. Comment on this statement. Answer: The repeated division of fertilised egg into a group of smaller cells is called cleavage. The first cleavage is vertical and produces two unequal cells. The second cleavage is at right angles and produces 4 cells 29-4 The First Trimester. Cleavage and blastocyst formation. Blastomeres. Identical cells produced by cleavage. Morula. Stage after 3 days of cleavage. Pre-embryo is a solid ball of cells resembling mulberry. Reaches uterus on day 4 or 5. cleavage and blastocyst formation. Blastocyst. Forms from morula. Hollow bal Pronucleus of sperm reaches the pronucleus of egg and fused which results the formation of the zygote nucleus. Two centrioels of the sperm more further apart by this time and from a division spindle for first cleavage. The division of blastomeres and gets filled with a fluid 51) If an amphibian zygote is manipulated so that the first cleavage plane fails to divide the gray crescent, then _____. A) the daughter cell with the entire gray crescent will die B) both daughter cells will develop normally, because amphibians are totipotent at this stag

Zygote - an overview ScienceDirect Topic

The zygote is defined as the cell that results from the fusion between two gametes, one female and the other male. According to the genetic load, the zygote is diploid, which means that it contains the complete genetic load of the species in question Zygote 24. In this species, the body plan is specified by a stable positional system set up by a cytoplasmic rotation in the zygote that occurs before first cleavage. (In contrast, the mitochondrial genetic information of the zygote comes entirely from the mother via the ovum.(wikipedia.org)Fertilization of the ovum to form a new human organism, the human zygote Note: This has nothing to do with bosoms. If you were hoping to learn about the female body, you will be disappointed. In embryology, cleavage is the first thing that happens to a fertilized cell, also known as a zygote. It is the repeated divisio.. Zhan et al. defined as the abrupt cleavage of one blastomere into three daughter blastomeres or an interval of cell cycles less than 5 h. Therefore, they describe direct unequal cleavage at first cleavage as DUC‐1, at second cleavage as DUC‐2, at third cleavage as DUC‐3 and embryos exhibiting multiple DUCs as DUC‐Plus Zygote First polar body Ovulation Ovary Blastocyst Cleavage Zona pellucida Blastomeres Implanted blastocyst (6 days) Morula (72 hours) 2-celled stage (30 hours) Corpus luteum Maturing follicle Secondary oocyte Second polar body Egg pronucleus Sperm pronucleus Fertilization (0 hours) Sperm cell 29-20 Migration of the Conceptus Figure 29.

The development of multi-cellular organisms begins from a single-celled zygote, which undergoes rapid cell division to form the blastula. The rapid, multiple rounds of cell division are termed cleavage. After the cleavage has produced over 100 cells, the embryo is called a blastula pole of the zygote (see Figure 1 legend), indicating that polar body extrusion often occurs on the side opposite to the point of sperm entry. At the first cleavage, the bead is localized in most embryos to the cleavage plane between the two ½ blastomeres, whereas at the second cleavage, the bead usually marks the ½ blastomere that divided first

Cleavage does more than merely subdivide the substance of the egg quantitatively into smaller units, the blastomeres, which are then of such a size that they can readily undergo the subsequent events of blastulation, gastrulation, and interaction that are involved in formation of tissues and organs Embryonic development also embryogenesis is the process by which the embryo forms and develops. In mammals, the term refers chiefly to early stages of prenatal development, whereas the terms fetus and fetal development describe later stages. Embryonic development starts with the fertilization of the egg cell (ovum) by a sperm cell, (spermatozoon). Once fertilized, the ovum is referred to as a. Embryologies similar to or like. Zygote. Eukaryotic cell formed by a fertilization event between two gametes. Wikipedia. Blastomere. Type of cell produced by cleavage of the zygote after fertilization and is an essential part of blastula formation. In humans, blastomere formation begins immediately following fertilization and continues through. The process of formation of the multicellular zygote from the single-celled zygote is called embryogenesis. Question 2. What kind of cell divisions take place during cleavage? Answer: Mitosis division but it is without growth phase. Question 3. What are blastomeres? Answer: The cells formed as a result of cleavage are called blastomeres.

zygote and in both blastomeres (AB and CD) at time points immediately after first cleavage (265-280 min after zygote deposition (AZD) (Fig. 1B). Beginning 15 min after cytoki-nesis, however, the in situ signal starts to fluctuate in a repro-ducible manner, being stronger first in CD (in 78%; n 14 o none of your bis 47. 1. 1) Even in the absence of sperm, metabolic activity in an egg can be artificially activated by ________. A) abnormally high levels of carbonic acid in the cytosol. 2. 2) The formation of the fertilization envelope requires an increase in the cytosolic concentration of ________ Overall, ~37.7% (N=20/53) of early cleavage-stage embryos exhibited micro-/multi-nuclei formation in one or more blastomeres. This suggests that unlike mice, which rarely exhibit micronucleation during initial mitotic divisions ( Vazquez-Diez et al. 2019 ), encapsulation of mis-segregated chromosomes into micronuclei prior to EGA is conserved. cleavage. [ ′klēv·ij] (crystallography) Splitting, or the tendency to split, along planes determined by crystal structure and always parallel to a possible face. (embryology) The subdivision of activated eggs into blastomeres. (geology) Splitting, or the tendency to split, along parallel, closely positioned planes in rock