Module 2 - Early Development Process Flashcards
Each one of us originated from
two germ cells – a sperm and an ovum.
Germ cells are produced through
meiosis: the cell division process that results in a germ cell containing 23 chromosomes (not to be confused with mitosis).
Females are born with all of their ___________, whereas males make ___________ ________________
ovum, sperm continuously.
Meiosis involves two cycles of cell division called
meiosis 1 and meiosis 2
Sex cells are also known as __________
gametes
Each cycle of meiosis involves the same four phases as mitosis
PMAT. Just like mitosis the parent cell copies its DNA before cell division begins so each single stranded chromosome becomes double-stranded.
In prophase 1 the chromosomes condense and join together in pairs (one from father and one from mother). Genes are swapped in a pair called crossing over.
Metaphase 1 - pairs of chromosomes line up in the middle of the cell. Fibres attach the chromosomes to two bodies on opposite sides of the cell.
Anaphase 1 - the fibres seperate the pairs
Telophase 1 - two nuclei form and then the cell splits into two cells, each with 23 double-stranded chromosomes
Meiosis 2:
Each cell will divide again to form 4 cells with 23 single-stranded chromosomes
Prophase 2 - chromosomes condense and the nucleus breaks down
Metaphase 2 - the chromosomes line up in the middle of the cell.
Anaphase 2- Fibres pull single-stranded chromosomes apart
Telophase 2 - nuclei form and finally, the cells divide
The 4 cells produced by meiosis are genetically …
different to each other and to the original cell. This genetic variety explains why children can look and behave so differently from one another
During conception, how many sperm are released into the female ?
an average of 500 million (!!!)
sperm must swim for 6-7 hours to reach their destination
only about 200 sperm actually get close to the egg
A fertilized egg is known as
a zygote (at this point prenatal development has begun. )
Prenatal development is broken into 3 main stages:
The germinal period - weeks 0-2
the embryonic period - weeks 3-8
and the fetal period. - weeks 9 - birth
The first two weeks of prenatal development are known as
the germinal period. During this time, the zygote is rapidly dividing.
Day 1 - fertilization
Day 2-4: cell division takes places
Day 4-5: blastocyst reaches uterus
(Approximately 4-5 days after fertilization, the zygote enters the uterus from the fallopian tube. The zygote is now referred to as the blastocyst – it forms as a hollow ball of cells and will implant into the wall of the uterus.)
Day 5-9: Blastocyst implants
The germinal period comes to an end when the blastocyst is fully embedded, which takes about one week.
What prenatal development period lasts from implantation to 8 weeks?
embryonic period.
-cell differentiation begins
-beginnings of all organ systems are forming.
-Embryonic development follows a cephalocaudal pattern of development, meaning that areas near the head tend to develop first.
-By the end of the embryonic period, all bodily systems are functioning.
Three layers of cells differentiate
Ectoderm: The ectoderm will become the nervous system, nails, teeth, inner ear, eye lens, and epidermis.
Mesoderm: The mesoderm will become muscles, bones, circulatory system, and skin.
Endoderm: The endoderm will become the digestive system, lungs, urinary tract and glands.
At what stage of prenatal development does the neural tube form?
Embryonic period.
The neural tube - the precursor to the Central Nervous System.
The neural tube is created when the ectoderm folds in on itself, creating a u-shaped groove.
What is the embryo’s support system?
- the amniotic sac
- the placenta.
What are the functions of the placenta?
allowing nutrients, oxygen, and waste to pass through, while at the same time preventing maternal blood from mixing with the blood of the developing embryo.
When does the zygote enter the uterus from the fallopian tube?
Approx 4-5 days after fertilization (zygote is now referred to as the blastocyst)
What is the amniotic sac?
a liquid-filled sac in which the embryo floats, helping to protect it and maintain a constant temperature.
When does The fetal period begin?
at the end of the 2nd month and lasts until birth.
What happens during the fetal period of development?
development continues to be rapid and cephalocaudal in nature.
11-12 weeks, the fetus starts to become more active (spontaneous movements, reflexes) although movements are not felt by the mother until the fetus becomes larger, usually around 16 weeks.
20 weeks, the fetus starts to have facial expressions and begins putting on weight.
A premature birth at 20-22 weeks old has a chance of survival with significant medical intervention. However, 23 weeks is considered the age of viability, or the point at which the brain and lungs are developed enough for survival without major medical intervention.
What happens when the blastocyst becomes implanted in the uterine wall?
Begins to differentiate.
1st - into an inner cell mass that becomes the embryo
and outer mass that becomes the organism’s support system
Then the inner cell mass differentiates into several layers that will form various systems of the body
Then a fold in the top layer develops into the neural tube
What does the neural tube become?
One end of the tube will become the brain and the other the spinal cord.
The fetal experience includes
movement
sensory experiences
learning
Fetal behaviour - movement helps…
promote muscle development. Interestingly, there are large individual differences in prenatal activity, with these differences continuing into infancy. In other words, an active fetus is likely to become an active newborn.
Fetal behaviour - sensory experiences…
A fetus experiences some degree of sensory input from all five senses, although visual input is minimal.
Since a fetus can move around, it can experience tactile sensations such as kicking the walls of the uterus.
Amniotic fluid contains both odours and flavours (related to what the mother ingests), which a fetus can smell and taste. Researchers suspect that this may be one way in which cultural flavour preferences are transmitted.
A fetus can hear the world around them. This includes both the maternal world (e.g., mom’s heartbeat) and the outside world (e.g., voices of their family members).
Fetal behaviour - Learning…
When discussing fetal learning, we are only considering learning in its most simple form - habituation and dishabituation.
In other words, this essentially allows researchers to examine whether a fetus gets “bored” of a stimulus and if interest peaks when the stimulus is changed.
Research suggests that the nervous system of a fetus is developed enough to engage in this type of basic learning (e.g., they habituate to repeated stimuli). A fetal brain, however, is not yet developed enough to engage in more complex forms of learning.
Meiosis
cell division that produces germ cells
Ectoderm
the outermost layer of cells of an embryo in early development, which includes nerve cells
Mesoderm
the middle layer of cells of an embryo in early development, which includes the bones
Endoderm
the innermost layer of cells of an embryo in early development, which includes the lungs
Amniotic sac
a transparent, fluid-filled membrane that surrounds and protects the fetus
Placenta
a support organ for the fetus that consists of semi-permeable membrane
Germinal Period
- Blastocyst develops
- period ends at implantation
- begins at fertilization
Embryonic Period
- Neural tube develops
-Weeks 3-8 - 3 layers of cells form during this period
Fetal Period
-A premature infant may survive is born during this period.
- The mother will begin noticing movements during this period.
-Main feature of this period is weight gain
What is a teratogen?
is anything that has an adverse impact on development
What are examples of teratogens?
Chemicals
Medications
Recreational Drugs
Alcohol and Nicotine
Some Viruses and Bacteria
Maternal Health
The impact that a given teratogen will have on a developing fetus depends on many factors, including:
Type of Teratogen
Dosage
Duration of Exposure
Timing of Exposure
Genetics of the Mother
Genetics of the Fetus
Most infamous teratogen
Thalidomide, a medication that was approved for pregnant women without proper testing. Thalidomide resulted in serious birth defects for newborns who were exposed in utero.
Teratogen - alcohol
Germinal Period - organ system have not yet started to develop, mild alcohol consumption is unlikely to result in major birth defects
Embryonic period - major organ systems are rapidly developing. Exposure to teratogens during this period can cause major structural abnormalities. Exposure to alcohol can have significant impact on CNS.
Fetal Period- teratogen exposure during this period is more likely to result in physiological defects or minor structural abnormalities.
**The more mothers drink, the more likely it is to have an effect on their child; however, some babies will be unaffected due to their mother’s and/or their own genetic endowments.
Why are Major structural defects less likely to happen in the fetal period?
Because the basic organ systems are already in place.
what is one of the leading causes of preventable birth defects and developmental disabilities.
Alcohol.
But, not all pregnancies with such exposures will result in birth defects. First, there is a dose-response relationship between exposure to teratogens like these and the likelihood of negative outcomes. In other words, the higher the dose, the greater the likelihood of negative outcomes. Second, both maternal and fetal genetic susceptibilities (e.g., variation in the rate a drug will be metabolized) influence the final outcome.
The second most common drug used during pregnancy
Cannabis
maternal cannabis use during pregnancy has adverse impacts on children across development. Longitudinal research indicates that children exposed to cannabis early in development are at a greater risk for attention deficits, increased hyperactivity, and increased likelihood of substance use.
While this is likely to continue to be an active area of research, it is important to note that there is no evidence that there is a safe amount of cannabis exposure for a developing fetus.
Are sushi and chicken pox considered teratogens?
Sushi - no
Chicken pox (Varicella) - yes.
What two things contribute to development
both genes and the environment contribute to development. Nature versus nurture is no longer a debate.
What represents the “nature” factor when it comes to development
genes
What carries all of the “instructions” for making a person, which are packaged in genes.
DNA (deoxyribonucleic acid)
genes code for ____________, NOT for _____________
proteins, specific behaviors
What is the key ingredient that determines a cell’s characteristics and functions.
Proteins
Cells contain different forms of the same gene called
alleles.
This “back up copy” is helpful to ensure proper development.
What is responsible for most human traits?
polygenic inheritance
although every cell contains all genes, only some….
only some genes are expressed, and only some genes result in observable characteristics
Genotype
The set of genes that an organism carries
Phenotype
Expressed characteristics, influenced by genes and environment.
Ex: a baby has brown eyes.
most human traits, including eye colour, are the result of polygenic inheritance.
What controls where and how much protein is made by a gene, effectively turning the gene “on” or “off”?
Epigenetic “markers”
This occurs naturally during prenatal development when cells are differentiated (e.g., one cell becomes a brain cell while another becomes skin)
Identical twins originate from the same…
DNA
Epigenetics
The study of how DNA interacts with a multitude of smaller molecules found within cells, which can activate and deactivate genes
Genes in DNA are expressed when they are…
read and transcribed into RNA, which is translated into proteins by structures called ribosomes.
What mostly determines a cell’s characteristics and function?
Protein
What can boost or interfere with the transcription of a specific gene?
Epigenetic changes.
The most common way interference happens is that DNA or the proteins it is wrapped around gets labelled with small chemical tags.
The set of all the chemical tags that are attached to the genome of a given cell is called the epigenome.
