Download Human Development

Human Development
Genetics
and
Heredity
Early Development
Human life is the
continuation of two
living cells
Sperm and ovum:
GAMETES
each contains genetic
material
Early Development
Zygote: fertilized ovum
2 sets of genetic material fuse =
“blueprint of developmental guidelines”
within hours the zygote duplicates and
divides
differentiation of cells also occurs:
“specialization” process
Early Development
Fetal life = approx 9 months
Critical stages of organogenesis
1st trimester
Extensive cell division, migration, and cellto-cell interaction
Developing organs very susceptible to harm
from external influences
– Brain does not completely develop intrauterine
and continues development postpartum
The Genetic Code
Sequence of
chemical bases in
DNA
Chromosome: DNA
molecule that
carries the genes
transmitted from
parents to child
The Genetic Code
Gene: specific
segments of a
chromosome
the basic unit of
heredity
The Genetic Code
Normally, humans have 23 pairs of
chromosomes which carry approximately
100,000 distinct genes
1 chromosome in each pair is from the
mother, 1 from the father
matching of the pairs occurs at conception
22 pairs- autosomes
The Genetic Code
23rd pair = sex
chromosomes
XX = female
XY = male
Sperm determines
sex (carries X or Y
chromosome)
The Genetic Code
Genotype: each person’s different
genetic arrangement
person’s genetic potential for a trait
includes those characteristics carried by
the recessive genes
The Genetic Code
Phenotype: actual expression of the
trait
Dominant/Recessive: the phenotype
reflects the dominant gene while the
recessive gene is masked
allows for differences within the family
examples:
eye color
ear lobes
Developmental Malformations
Teratogens: agents that cause fetal
abnormalities
Identifiable causes of malformations
genetics (20%)
exogenous teratogens (5%)
drugs, alcohol, X-rays
most causes are unknown
Exogenous Teratogens
Physical
X-rays
alpha, beta, gamma rays
increased incidence of malformations in
children born to mothers exposed during
pregnancy to the A-bomb
Exogenous Teratogens
Chemical: agents used in industry or
ingested as drugs
FAS: fetal alcohol syndrome
growth retardation
decreased mental processes and low IQ
flat face with wide spread eyes
**mother drinks when she’s unaware of
pregnancy**”
Exogenous Teratogens
Chemical
Thalidomide: “sleeping pill” introduced in
the late 50’s to decrease nausea and
insomnia
malformed, shortened limbs: phocomelia
(seal limb)
over the course of 5 years, greater than
3,000 children were born to women on
thalidomide during pregnancy
Exogenous Teratogens
Chemical
marijuana, cocaine, heroine, tobacco
irritable
decreased self-control
learning difficulties
caused by decreased oxygen in the
placenta; creates limited brain growth
Exogenous Teratogens
Microbial: various infections could
directly or indirectly affect the fetus
Rubella = German measles
heart defects
microencephaly (small brain)
micropthalmia/blindness
**contracted only if unimmunized mother is
infected with rubella virus during the first
trimester**
complete prevention if immunized
Chromosomal Abnormalities
Structural
Deletion
Translocation
Inversion
Ring formation
Numerical
Monosomy
Trisomy
Chromosomal Abnormalities
Trisomy 21 (Down’s Syndrome)
Most common numerical abnormality
Occurs 1 in 700 births
Incidence rises with maternal age
Symptoms include:
Typical facial features: wide face, low
bridged nose, closely set slanted eyes,
tongue protrusion
Cognitive delay
Chromosomal Abnormalities
Symptoms of Down’s Syndrome:
Muscle hypotonia
Laxity
Recurrent patellar dislocation
Atlantoaxial instability
Scoliosis
Dysplasia of hips
Alzheimer’s disease
Occurring at an earlier age
Congenital cardiac abnormalities
Single Gene Disorders
• Basic genetics:
•
Genes can be dominant or recessive
• Dominant overshadow the recessive
• 1 dominant + 1 recessive = dominant
trait expressed
• 1 recessive + 1 recessive = recessive
trait expressed
Single Gene Disorders
Autosomal dominant inheritance
Only 1 copy of gene need be present to
express trait
Osteogenesis Imperfecta
Disorder of collagen synthesis affecting
bones and connective tissue
Osteogenesis Imperfecta
Symptoms: vary according to type,
but may include
Fractures
Brittle teeth
Weak muscles
Hearing problems
Scoliosis
Thin skin
Decreased height
Single Gene Disorders
Autosomal recessive inheritance
2 copies of gene need to be present to
express trait
Cystic fibrosis
Most common autosomal recessive disease
Cystic Fibrosis
Etiology:
Reduced pancreatic enzymes that cause malfunction of
mucous membranes and mucous producing glands
Leads to intestinal malabsorption problems and
excessive production of thick mucous in bronchi
Symptoms:
Malnutrition
Chronic, recurrent pulmonary infections
Productive cough
Dyspnea
wheezing
Prognosis: median lift expectancy 37 yrs old
X-linked Recessive Disorders
Expressed on X chromosome
Primarily occurs in males
Muscular dystrophy
Duchenne’s and Becker’s
Lack of dystrophin in skeletal muscles
Progressive wasting of muscles
Genetic Counseling
Couples learn more about their genes
and can make informed decisions
about childbearing
Decreases risk of unexpected,
spontaneous abortion
Prevents complications and determines
risk