tutorial 1: prenatal development

how many chromosomes are their in the human genome in total?

46 in total

23 pairs

what are genes?

segments of DNA

have a specific place on chromosomes

what is the function of genes?

help cells reproduce themselves and regulate protein synthesis

what is the function of proteins?

building blocks of cells

regulate internal processes of cells

what is one important thing to remember about genes and their influence?

they dont work independent from each other but in collaboration

what is one way genes can be influenced by teh environment?

gene expression is affected by hormones and hormones are affected by the environment (eg.light, behaviour, temperature)

how does stress and radiation affect gene expression?

stress → damage of DNA

radiation → changes rate of DNA synthesis

what is the gene wide association model?

look at the whole genome to find genes linked to disease

→ compare the egentc variation in healthy individuals to the variation in individuals with the disease → variation in the sick people points to location of the possibly disease causing gene

what is linkage analysis?

used to find a disease causing gene

find location of a gene in relation to a marker gene

what is Mitosis?

process in which body cells divide to produce two identical daughter cells.

what is Meiosis?

process when gametes (sperm or egg cells) are beig formed

what happens during Mitosis?

the nucleus in the cell duplicates and then the cell divides into two identical cells with again 46 chromosomes in total

which chromosome determines the gender?

chromosome 23

male: xy

female: xx

what is a zygote?

formed when teh sperm and egg cell combine

half of the genetic material is from dad and half from mom

how does genetic variation come about?

• pieces of the chromosomes in each pair are exchanged

• mutations

what are monozygotic twins?

twins with 100% identical DNA

the egg seperated after fertilization into two identical copies

what are dizygotic twins?

twins that share about 50% of their genes

two different egg cells are being fertilized by two different sperm cells (division before fertilization)

what are four genetic principles?

• dominant and recessive genes,

• sex linked genes,

• genetic imprinting

what are dominant genes?

they override the influence of recessive genes

only one needs to be resent so that trait is expressed

are most mutated genes recessive or dominant?

recessive

who is more likely to have x-linked disease?

males because they dont have a backup x chromosome if one is damaged

what are females with x linked mutations called?

carriers

what is genetic imprinting?

genes have different effect depending on wether they were derived from mom or dad

on of the genes is silenced and the other one expressed

what can happen if there is disturbed genetic imprinting?

diseases like Beckwith-Wiedemann syndrome (growth disorder) or Wilms tumour (cancer)

what does polygenic inheritance mean?

not a single genes determines characteristic but the collaboration of many different ones

what are the two things abnormalities can be caused by?

harmful genes or something going wrongin meiosis

what are the two kinds of abnormalities ?

chromosomal and gene linked abnormalities

whats the cause of downsyndrome?

there is an extra copy of chromosome 21

may be caused by unhealthy gametes

what is the earliest you can do fetal sex determination?

7 weeks into pregnancy

what does the success of in vitro fertilization depend?

age of the mother

what are the three different heredity environment correlations?

passive, evocative and active (niche picking)

what is the passive heredity-environment correlation?

parents provide an environment to child which fits to their genotype (if they are good reader, academically inclined they might provide more books; if they are very social they will create a very social environment around them and their child)

what is the evocative envrionment-heredity correlation?

the genotype of the child causes their environment to respond to them in a specific way

(more social, smiling child might get more attention; a more loud child might receive negative responses from adults and peers)

what is the active environment heredity correlation?

according to their genetic predisposition the child selects and environment

(more atheltic genotype → seek athletic hobbies and friends)

what is the epigentic view?

believes that there is constant interaction between environment and genes

both influence each other

(eg. diet, stress toxins influence which genes are being expressed)

what is the G x E interaction?

specific genes interact with specific aspects of environment

• eg. depression is only expressed when a stressful live is experienced as well

• or attachment isssues only form if there is a certain gene

how many chromosomes do gametes have?

23

how many divisions are there in meiosis?

two divisions that result in fourcells with each 23 chromosomes

what are autosomoes and how many are there?

non sex chromosomes

22

what is independent assortment?

alleles end up in the new cell independent from each other

→ contrinuted to genetic variety

what is crossing over?

the homologous chromosome pairs exchange their information

→ contributes to genetic variation

On what levels can the interaction between environment and genes take place?

• intracellular

• extracellular

• external-environment

what are
“experience-expectant interactions” ?

experiences influencing the genes that are the same for evry human

what are “experience dependant interactions”?

experiences interacting with genes that are different for every person

what does homozygous mean?

someone having the same allele for a trait twice

(eg. AA or aa)

what is heterozygous?

someone having two different alleles for a trait (one dominant and one recessive)

(eg. Aa or aA)

what are the four main patterns of genetic expression?

• dominant-recessive inheritance

• codominance

• sex-linked inheritance

• polygenic (multiple gene) inheritance

what is the chance of a child inheriting the recessive trait if both parents are heterozygous?

1/4

what is codominance?

both alleles are equally expressive, the one is not more dominant than the other => the expressed phenotype will be a compromise/mix

(eg. blood type)

what is incomplete dominance?

one allele is more dominant than the other however not enough to completely muter the other gene so some of the recessive gene will still be expressed

(eg. sickle cell anemia)

what is sex linked inheritance?

traits that are being inherited via genes located on the sex chromosome (mainly the x chromosome)

what is an example of a sex linked trait?

colour blindness

what happens to the number of possible genotypes and phenotypes when the number of collaborating genes increases?

the increase and follow a normal bell curve

what are congenital effects?

abnormalities and problem present at birth, caused by genes, prenatal influences or birth complications

which prenatal diagnostic test can be done the earliest?

chorionic villus sampling (8th to 9th week)

what is germ line therapy?

unhealthy genes are replaced with healthy ones in the embryo which leaves a permanent effect

what is gestation?

time during which the child develops in the uterus

what is the germinal stage and how long does it last?

the time of the zgote, two weeks after fertilization

how long is the embryonal stage?

beginning of third week until the end of the 8th week

what is the amniotic sac?

membrane around the embryo that contains the amniotic fluid and acts like a protective buffer against physical shocks

what is the placenta?

develops during pregnancy and provides the baby with nutrients and oxygen while removing waste products

→ formed by the tendrils connectign the embryo to the uterus

what is the umbilical cord?

connects baby to the abdomen and placenta, carries blood back and forth from baby and placenta

carries oxygen and nutrients to the baby, removes carbon dioxide and waste

why can some substances from the mothers blood reach the infant?

because the placentas membrane is semipermeable

what are the three layer called into which the embryo divides?

1. endoderm

2. mesoderm

3. ectoderm

what does the endoderm layer include?

gastrointestinal tract, bronchi, trachea, eustachian tubes, glands and vital organs (liver, lungs, pancreas)

what does the mesoderm include?

muscles, sceleton, kidneys, circulatory and excretory systems, reproductive system and inner skin layer

what does the ectoderm layer include?

nervous sysem and sensory organs, hair, nails, skin and skin glands

how does teh nervous system form?

when the ectoderm layer folds in on itself after 4th/5th week of gestation to form the neural tube

in what stage do most anomalies occur?

embryoic stage because the rapid development is making it especially vulnerable

what happens when the neural tube doesnt close properly?

child will have spina bifida

what does cephalocaudal developemt mean?

development is advancing from head downwards

what does proximal-distal mean?

development advances from central part od body to the outisde

when is the foetal stage?

lasts from the beginning of third month until birth

what is the age of viability?

22 to 26 weeks → if born at that point the baby would have a chance of surviving

(if born before the baby could not survive without intense intervention)

what are teratogens?

environmental factors leading to congenital abnormalities

what is neonatal abstinence syndrome?

happens to babies born addicted

→ irritable, unable to regulate arousal, trembling, shrill crying, rapid respiration and hyperactivity

what is the less severe version of “foetal alcohol syndrome”?

fetal alcohol effects (FAE), “alcohol related neuropsychological disorder”

what are the three stages of childbirth and how long do they last?

1. stage → contractions in 10-15 minute intervals (8-14h)

2. child comes through vaginal canal (1h)

3. placenta comes out through the vaginal canal

what are the consequences of caesarian delivery for the baby?

• affected by the medications for mother

• increase risk for preterm and low weight for future babies

• not really affects cognition or future hospitalization

what are three perinatal risk factors?

• deprivation of oxygen (foetal anoxia, switching from uterus to outside)

• breech birth → starting labour with feet towards vagina

• preterm, respiratory distress syndrome

how many weeks is the normal gestation period?

38 weeks