human development - mccc

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 cell-

to-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

Couples learn more about their genes

and can make informed decisions

about childbearing

Decreases risk of unexpected,

spontaneous abortion

Prevents complications and determines

risk

Genetic Counseling