Week 3 Flashcards
Humans are… (chromosomes)
diploid - each cell has 2 copies of each chromosome
How many chromosomes in the complete human genome?
complete genome has 23 pairs of chromosomes (46) - 23 from mom and 23 from dad
Why arent all children with same parents identical?
Meiosis - The process by which sex cells—eggs and sperm—are produced - that are unique - crossing over creates uniqueness
Which chromosome goes into which cell is random
Functions of meiosis
Shuffling of genetic content
Reducing genetic content
Mother produces 1 egg and father produces 4 sperm during meiosis
What happens in meiosis 1? What is the unique process
- 2 homologus pairs separate and migrate to two different cells
- Cell division when the original cell punches closed and splits in the middle - separating the cells
RESULT: two haploid daughter cells
Crossover - pair of homologous chromosomes pair up and exchange sections of DNA
Get a unique chromosome that has never existed before
Break at some random (but exactly the same point) and switch
What happens during meiosis II?
- Four daughter cells created from the two intermediate daughter cells
- Each cell splits in half resulting in a chromatid (one half of the symmetric chromosome) - Each of the four daughter cells has one chromatid which is ready to pair with the homologous chromatid that is introduced as a result of mating
RESULT: sex cell- egg or sperm with 23 chromosomes
Donor insemination
Donor semen is introduced into the female reproductive system
Intrauterine inesemination - semen injected into the uterus - does not have to travel through the mucus plug in the cervix
Use ultrasound imaging to place sperm in the best location to increase odds
IVF
Both sperm and eggs removed and introduced in the laboratory
Conception happens in the lab and the conceptus is placed in the uterus after a few days
8 mil babies born through IVF
Parents of children conceived via fertility methods were warmer, more responsive to their children and more emotionally involved, spent more time interacting - at 6 years
No difference at 12 years
zygote
Fertilized egg
beginning of prenatal period which typically lasts 38 weeks and is divided into 3 stages
Germinal Period
- Period of rapid cell division
1. Cells double every 12 hours - zygote travels from fallopian tube to the uterus
2. Zygote stage lasts for about 4 days until it develops into a hollow sphere of 100 cells - blastocyst - specialization begins (already has some structure and specialization - 3 layers - outer- hair skin, middle- skeleton, inner, internal organs) - Estimated that 40% of blastocysts do not proceed to the next stage
3. Germinal period ends when the blastocyst implants in the uterine wall - a week to 12 days after conception - Burys in uterine wall and opens up the mother’s blood vessels - access to blood supply - use nutrients in bloodstream and introduce hormones - end menstrual cycling
Pregnancy tests taken before implantation will read negative
End - blastocyst is less than a millimeter
blastocyst - specialization
3 layers -
outer- hair skin,
middle- skeleton,
inner, internal organs
The Embryonic Period - 2mm to 3cm
Begins once the blastocyst has completely implanted in the uterine wall - embryo - finds a blood vessel and opens the blood vessel - access to nutrients and o2 in bloodstream
3-8th week after conception -differentiation, specialization and growth
Embryo consists of 3 concentric layers
Ectoderm - will become hair, skin, sensory organs, eyes and ears, nervous system
Mesoderm - becomes muscles bones and circulatory system
Endoderm - digestive system and lungs
When does CNS start developing (embryonic period)
develops early from the end of the second week after conception - early in the 6th week
At what point in the embryonic period does the embryo have a basic body plan?
4 weeks after conception - embryo has a basic body plan - arm and leg buds - body is curved tightly like a shrimp
Face has 4 folds of tissue that will become facial features - primitive heart that beats and circulates blood
cephalocaudal - and when?
After 4th week - prenatal development is cephalocaudal - features near the head develop sooner than the rest of the body
When does facial development occur in the embryonic period
Facial development - 5 & 8th weeks
By the end of the 8th week -human like face with eyes, ears, mouth and nose
What is developed by the 8th week?
What is the status of movement
arms legs and fingers, toes developed, heart and circulatory system circulate the nutrients via the placenta and umbilical cord, digestive system developed, lungs and respiratory formed , kidneys-
baby is moving but movements are uncoordinated and jerky - not felt by mother
What does the amniotic sac do
Embryo rests in an environment designed to provide it with nutrients, remove waste and protect it from injury - lives inside the amniotic sac which is filled with amniotic fluid - protect from impact and temperature changes
What is the purpose of the umbilical cord
umbilical cord brings in fresh blood with oxygen and nutrients and removes blood high in co2 and waste.
Placenta
a highly vascularized spongy organ through which oxygen and nutrients are delivered to the fetus and carbon dioxide and waste are removed
Placenta - mother or baby?
Classic view - structure that the mother and fetus build together - original site of maternal nurturance
Reality - placenta develops with the embryo - embryo’s DNA
Structure designed to be parasitic - invades the uterine wall, bores into blood vessels and reconfigures them so they cannot constrict - mother cannot resist sharing nutrients with the fetus without reducing her own nutrients
Fetus raises mother’s blood pressure and blood sugar
Parental Investment based on relationship
Mother would like to invest in developing fetus - opportunity for genetic representation but only to an extent. Also wants to recover from the pregnancy with enough health and resources to support future pregnancies
Father - if long term partner - interests aligned but if pregnancy is short-term - all investment into child none into mother
- Blood pressure and blood glucose is higher - baby takes as much as they can get - may not be related to siblings
- Epigenome may be different from father - creating a placenta thats more invested in - status of relationship has a physiological impact on the sperm can epigenetically modify their DNA
The fetal period
Weeks nine - end (38) - growth and development
Fetus starts weighing an ounce
9 Weeks milestones
IOS DEGN
All internal organs are present but still developing
Sexual differentiation has started
External genitalia - weeks 7-12
Fingers toes and nails by the 4th month
12 WEEKS -
FT ESM
Fetus can form a fist, wiggle toes, suck thumb
Will respond to external stimulation - touch and noise
Fourth month - still enough room to swim, kick and turnabout
- Movement increases in the second half of pregnancy
16 WEEKS
S 2 M
Fetus will swallow amniotic fluid - kidneys working and the kidneys begin to produce urine - excreted into the amniotic sac
fetus may weigh 200g
mother can feel movement- Fluttering
20 WEEKS
I 8 MH
Inhales amniotic fluid as practice breathing - lungs start working - can smell it
From week 20 on fetus will gain 8 pounds
Maturation of the nervous, respiratory and digestive systems take place at this point
20-28 - hair eyebrows and eyelashes develop and skin thickens
28 WEEKs
EAST
Fetus may be well-developed enough to survive on its own - potentially viable
- Critical factors to survival - lungs ability to exchange co2 for oxygen, stomach digest food, brain’s ability to control
breathing,swallowing, body temp
Born this early - need to be protected against temp changes - lack layer of fat that develops in the 8th month
Eyes open and auditory system functions - brain development is similar to a newborn
Antibodies
Mother contributes disease fighting antibodies - tailored to diseases that mother has encountered - protect new born until they can produce their own antibodies at 6m
Last Month
Quiet sleep periods or rem slee
Monozygotic twins
What makes twinning more likely?
When does zygote divide?
How often?
Is it heritable?
one zygote - identical genomes - identical twins
Single zygote divides within the first few days of conception identical genomes
research with animals has found factors in embryonic development that make such twinning more likely (e.g., temperature, oxygen levels, and the age of the ovum when fertilized).
1 in 285 births.
Not heritable, does not vary across ethinic groups, no known variables that predict
Sharing placenta (chorion) and sacs
If the membrane that forms the placenta (the chorion) has already developed when they split- share a placenta
If not separate
Earlier split after conception means different sacs, few days later is shared
Placenta and similarities
This can affect development: Monozygotic twins who shared a placenta are more similar than those who did not share a placenta on measures such as IQ, on 20 different personality measures, on birth weight, and congenital anomalies