week 23 Flashcards
what was LECA
a single-cell organism which predominantly reproduced by mitosis, not meiosis.
what does fission mean
division into two equally-sized offspring
what does budding mean
unequal divison; smaller offspring
what does fragmentation mean
the parent breaks into many small new individuals
what is phylogeny
study of evolutionary history and relationships between groups of organisms
what are the two sexes in higher plants
pollen and ovules
what is the r number and what does it mean
the reproduction number. R of 1= population stays the same per generation. R of 2= population doubles per generation.
name some costs of sexual reporduction
two individuals needed, costly for R number.
need to locate a mate.
need two different gametes
what are cavendish plants
they are sterile (no seeds)- asexual reproduction. all are clones and are susceptible to Panama disease
what are hermaphrodites
they generate both male and female gametes
what is klinefelter syndrome
Phenotypic males with XXY resulting in infertility
what is turner syndrome
phenotypic females with X0 (one X) resulting in infertility
what is the SRY gene
sex-determining region of Y on males (testis determining factor)
what do Leydig cells do
produce the steroid hormone testosterone
what are the roles of WNT4 and SOX9 proteins in sexual determination
WNT4- active in female embryo
SOX9- active in male embryo
what generates ovaries and testes in the mammalian embryo
the SRY sex determination pathway
when is sex determined in humans
6 weeks after fertilisation, when the SRY gene is first expressed (males) or not expressed (females)
when does gonad development start
Indifferent gonad development starts early, but has no sex-specific features until after sex determination
what are genital ridges
structures in early embryonic development that contain somatic gonadal precursor cells and gove rise to gonads
how to genital ridges differentiate into the indifferent gonad
genital ridges contain somatic gonadal precursor cells. Germline stem cells migrate into the genital ridge. The genital ridge becomes the indifferent gonad
what is gametogenesis
process where gametes (sex cells) are formed from germ cells in the gonads (ovaries in females, testes in males)
what are Sertoli cells
necessary for sperm production in males, promote spermatogenesis
what are spermatogonia
cells in the testes which give rise to mature sperm through a process called spermatogenesis
what are sex-specific differences in gametogenesis in humans
Oogenesis produces a single large ovum vs. the male process (spermatogenesis), which produces four tiny sperm. In females, one oocyte is usually selected to mature per 28-day ovarian cycle. In males, continued mitotic divisions of spermatogonia through most of life.
what is the capacitation and acrosome reaction
acrosome- the organelle surrounded by plasma membrane on the sperm, containing sperm receptor for egg protein and other enzymes.
Capacitation- occurs in female tract as sperm swims. The acrosome membrane fuses with the sperm cell membrane, exposing sperm receptor for egg protein. sperm is now primed, ready to fuse with egg
what is a blastocyte
6 day old human embryo
what is the trophoblast
Outer layer of cells part of the placenta but not the embryo. secretes enzymes
what component of the blastocyst does the embryo almost entirely develop from
The epiblast.
how are aquatic embryo development systems simpler than terrestrial
they are just an embryo, no placenta or extra-embryonic structures
what is a blastula
a ball of cells (blastomeres) with a fluid-filled cavity called a blastocoel. cells of the early blastula are totipotent, cells progressively loose totipotency as they commit to cell fates.
what are amniotes
a large tetrapod (4 limbs) vertebrate animal group (including humans) with an amnion.
what is an amnion
a fluid-filled sac surrounding the embryo of amniote organisms. the fluid has the same salt concentration as the ocean
what is hCG
a hormone produced by pregnancy, secreted in urine and identified by pregnancy tests. secreted from the trophoblast until later in pregnancy where the placenta stops making hCG.
what is the corpus luteum
a temporary endocrine gland forming after ovulation, if fertilisation occurs, the corpus luteum is maintained by the trophoblast and hCG and secretes estradiol and progesterone.
when does the corpus luteum degenerate
after ovulation if fertilisation does not occur. if fertilisation occurs the corpus luteum doesnt degenerate until 2nd/ 3rd trimester later in pregnancy.
how is the immune system altered during pregnancy
the immune system becomes more tolerant of the foetus foreign antigens, preventing rejection
when is the placenta developed and producing estrogen and progesterone
week 5
define cell potency
a cells capacity to generate different kinds of specialised cells
define the term terminally differentiated
a fixed single cell type
what are monoblasts
only one layer blast cells. no true tissues e.g. sponges
what are diploblasts
only two layers blast cells. a digestive cavity, one opening which serves as mouth and anus e.g. jellyfish
what are triploblasts
three layers of embryonic blast cells- each layer restricted to different future potentials. a mouth, anus and gut in between. e.g. humans
define gastrulation
a movement and reorganisation of cells that is linked to creation of three fundamental layers of blast (or stem) cells in the early embryo.
what are the three primary germ layers which form during early embryonic development
ectoderm, mesoderm and endoderm. These have very different restricted pluripotency
what are bilateria
Organisms with bilateral symmetry and are all triploblastic. they have anterior/ posterior, dorsal/ventral
what are homeotic genes
genes which determine the identity of body segments or structures during embryonic development, they encode transcription factors
what is the hox gene cluster
a cluster of related homeotic genes. expression of HOX proteins is a global positioning system, giving regional identity in animals.
what is synpolydactyly
a genetic condition caused by a mutation in the human homeotic gene. many severe suspects die before birth
how does the homeotic gene work to control the identity of body structures
by regulating the expression of other genes to control differentiation.
what is the Cambrian explosion
a period of rapid diversification of animal life
