Genetics + Prenatal

Question 1

Chromosomes

Answer 1

A thread-like structure composed of DNA and proteins found in the nucleus of most living cells. Chromosomes carry genetic information in the form of genes

Question 2

Genes

Answer 2

Segments of DNA that encode functional products, typically proteins. Genes act as the basic units of heredity

Question 3

Zygote

Answer 3

A single-cell organism formed by the fusion of a male sperm cell and a female egg cell during fertilisation. It contains a complete set of chromosomes from both parents and undergoes cell division to develop into an embryo

Question 4

Alleles

Answer 4

Different versions of a gene that arise due to variations in the DNA sequence. They can produce different traits in an organism

Question 5

Homozygous

Answer 5

(i.e. BB or bb): A genetic condition where an individual has two identical alleles for a particular gene

Question 6

Heterozygous

Answer 6

(i.e. Bb): A genetic condition where an individual has two different alleles for a specific gene

Question 7

Genotype

Answer 7

The genetic makeup of an organism, consisting of the specific alleles inherited from both parents. It determines potential traits but does not always directly dictate phenotype

Question 8

Phenotype

Answer 8

The observable characteristics or traits of an organism, which result from the interaction of its genotype with the environment

Question 9

Dominate genes and disorders caused by them

Answer 9

Express phenotype even in heterozygous states

• Huntington disease (rare neurodegenerative disease):
  Affects muscle coordination (Huntington’s chorea)

Question 10

Recessive genes and disorders caused by them

Answer 10

Only express phenotype when in homozygous states

• Phenylketonuria (PKU):
  Inability to metabolise phenylalanine; Cognitive deficits, seizures, shortened lifespan

Question 11

Down syndrome

Answer 11

• Extra copy of chromosome 21
• 1 in 1000 births
  Life expectancy: 60 years

Question 12

Fragile X

Answer 12

• Lengthening of FMR1 gene on X chromosome
• 1 in 3600 boys
• in 4000-6000 girls
• Commonly meeting autism criteria (physical features, developmental delay, behavioural/emotional)

Question 13

Mullerian ducts

Answer 13

Precursors to female organs

Question 14

Wolffian ducts

Answer 14

Precursors to male organs

Question 15

What happens to the sex chromosomes after 7-8 weeks

Answer 15

XY: Gene on the Y chromosome makes testes develop, the Testosterone makes Wolffian system develop into male external and internal genitalia = the Mullerian (female) system is absorbed

XX: In absence of testosterone the Mullerian system develops into female external and internal genitalia and the Wolffian (male) system is absorbed

Question 16

Distributions to sex determination examples (HINT: AIS, CAH)

Answer 16

Example 1
Androgen Insensitivity Syndrome (AIS)
○ XY genetically but body doesn’t detect and respond to male hormones

Example 2
Congenital Adrenal Hyperplasia (CAH)
○ XX genetically, exposed to excessive levels of male hormones

Question 17

Fertilisation

Answer 17

Single cell > Sperm fusses with egg in fallopian tube > zygote formation

Question 18

Germinal period

Answer 18

First 14 days
Zygote travels towards uterus
Divides and forms blastocyst
16 and 64 cells
Blastocyst implants itself in the uterine wall = miss your period

Morning after pill can work by releasing an large does of hormones to make the uterine wall inhabitable for blastocyst

Question 19

Embryonic period

Answer 19

3rd to 8th week (most at risk)
○ Blastocyst implants in the uterine wall
○ Period of organogenesis (organ growth and formation)
Layers of cell differentiate

Question 20

Layers of cells

Answer 20

Ectoderm (outer layer)
- Nervous system, skin, hair

Mesoderm (middle layer)
- Muscles, bones, circulatory system

Endoderm (inner layer)
- Digestive system, lungs, urinary tract and other vital organs

Question 21

What happens at 4 weeks of development

Answer 21

• Beginning of the formation of major organs
  Heart beating after 24 days

Precursors to the brain = Flat surface of cells that curve around each other to close around its tubes (top half of tube = brain, bottom half of tubes = spinal cord)

Question 22

What happens at 6 weeks of development

Answer 22

Head is larger (half the volume of the embryo)

Question 23

What happens at 8 weeks of development

Answer 23

Head is still 1/3 volume of embryo
All internal organs and formed or even functioning

Question 24

Fetal period

Answer 24

The last 7 months

Rapid growth and refinement of organs
Fetus is more responsive
Behaviour becomes increasingly regular and integrated
Fetuses become liable 22 - 28 weeks

Question 25

What happens at 12 weeks of development

Answer 25

2nd trimester Sex differentiation has occurred

Question 26

What happens at 18 weeks of development

Answer 26

Baby moves and rapidly grows

Question 27

What happens at 6 months of development

Answer 27

Fetus is capable of responding to light Able to hear sound (bones formed) - 75db - Mothers voice and heartbeat are heard best

Question 28

Cat in the hat study (1986)

Answer 28

Mums were asked to read the Dr. Sues books twice everyday for the last 6 week of the pregnancy After baby was born were tested using operant condition (attached to a feeding nipple and would listen to their mother reading cat in the hat or a different story and another person reading that) ○ Babys learnt that they could change the person talking by changing their sucking rate

Question 29

What happens at 7 months of development

Answer 29

- 3rd trimester - Fetus puts on wait in the form of fat beneath the skin - Respiratory risk for preterm birth - baby's born between 30 - 33 weeks have worse outcomes due to lungs still producing Surfactant (Keeps air pockets of the lungs open when breathing)

Question 31

Preterm infant factors

Answer 31

- Born at 36 weeks of earlier - Low birth weight (<2500g) - 7% of all births <37 weeks - Certain groups at higher risk ○ Indigenous mothers ○ Young mothers (<20 years old) ○ Older mothers (>40 years old) ○ Multiple births ○ First time mothers

Question 32

Limits of viability (infants)

Answer 32

The gestational age where there infant has 50% chance of surviving their first year ○ 24 weeks threshold Lung development is the limiting factors into baby's survival (give steroids to mum)

Question 33

Factors to consider with viability of infants

Answer 33

- Birth weight (heavier = better) - Gender (girls = estrogen in lung development) - Multiple or singleton (competition for resources with sibling in utero) Steroids

Question 34

Limit of viability at 23 weeks

Answer 34

- Relatively heavy girl, singleton + steroids = 80% chance of survival - Relatively small boy, twin + no steroids = 20% chance of survival

Question 35

Interventions with preterm infants

Answer 35

Containment and lighting (86% US NICU) Kangaroo care (98% US NICU) - Skin-to-skin contact - Accelerates development of regulatory processes Tactile-kinesthetics stimulation (massage) (38% US NICU) - Stimulates growth - Decreases stress behaviours - Earlier discharge