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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