Genetics and Prenatal Development The Beginning of Life Conception

The Human Cell The human body is comprised of over 200 different kinds of cells which are the smallest self-contained structures Cell membrane: the outside layer of the cell Cytoplasm: is comprised of specialized structures Mitochondria: are the powerhouses that process nutrients and provide the cell’s energy Endoplasmic reticulum, Golgi apparatus, and ribosomes: produce proteins Neucleus: The inner part of the cell

The Nucleus Chromosomes Genes Deoxyribonucleic acid (DNA)

Chromosomes Rod shaped structures found in the center of the nucleus of every cell in the body. Each sperm and each ovum contains 23 chromosomes. The chromosomes contain the DNA and genes. The fertilized egg (zygote) and all the body cells that develop from it (except the sperm cells and the ova) contain 46 chromosomes.

Chromosomes 22 of the pairs are called autosomes and are numbered from largest to smallest. The autosomes are not involved in determining sex. The 23rd pair are the sex chromosomes: XX in females XY in males

Karyotype A photograph of a cell’s chromosomes arranged in pairs according to size

A Portion of a DNA Molecule

DNA Deoxyribonucleic Acid Nucleotides are the building blocks of DNA They contain 4 nitrogen-carbon-hydrogen basis that bond to form specific pairs: adenine can only pair with thymine cytosine can only pair with guanine The combination of base pairs cannot vary

DNA What Can Vary: 1- Which side of the ladder each base comes from 2- The order in which the base pairs occur along the ladder 3- The overall number of base pairs These variations account for differences between species. All organisms use just these 4 bases, but with different numbers and arrangements

DNA There are 3.12 billion base pairs in human DNA The DNA in each normal human being is about 99.9% the same as every other normal human being Only .1% accounts for the biological contribution to all our individual differences in physical and psychological characteristics

DNA Single Nucleotide Polymorphisms (SNPs) A large portion of the .1% individual difference takes the form of single nucleotide polymorphisms. SNPs (snips) are nucleotide variations that occur on average about every 1,250 base pairs

DNA They determine the nature of each cell in the body and how it will function. At each level of the spiral or rungs of the ladder are particular chemical pairs. The arrangement of these pairs along the DNA molecule determines which kind of proteins will be formed in the cell.

Genes The basic unit of genetic information They determine the nature and the function of the cell. The human genes (about 120,000) are referred to as the human genome. A genome is the full set of genes in each cell of an organism.

Proteins Proteins are molecules that perform an array of crucial functions in the human body: Enzymes: break down and altar biochemicals Hemoglobin: binds with oxygen allowing it to be transported to cells throughout the body Collagen: in bones and connective tissues Hormones: regulate physical growth

Genes and Protein Synthesis A nuclear enzyme attaches to a segment of DNA causing nucleotide bonds to separate. Transcription occurs resulting in messenger RNA (mRNA). Transfer RNA (tRNA) initiates translation into amino acid. Ribosomes move along the RNA bonding amino acids into polypeptide chains which make proteins.

1- Transcription: the transfer of information from an DNA molecule into an RNA (ribonucleic acid) molecule. 2- Messenger RNA (mRNA): a type of RNA synthesized from DNA; attaches to ribosomes to specify the sequence of amino acids that form proteins. 3- Translation: the transfer of information from an RNA molecule into a Polypeptide, in which language of the nucleic acids is translated into that of amino acids.

Celera Genomics The Human Genome Project In June 26, 2000, they both made an announcement that the “correct alphabetical order of the 3.12 billion letters” of the human genome had been mapped. It will be many years before the incredibly complex functions of the genome in making and maintaining a living human being are fully understood.

Scientific Breakthroughs Greater insights into disease will be achieved Cures may be found Incurable diseases may be prevented There will be new insights into the evolutionary origins of humans

Controversial Issues Will it be ethical for parents to have their children screened prior to birth and decide not to have a child with a genome that is merely undesirable ? What about employers not hiring people with bad genomes and insurance companies refusing to insure them?

Cell Division and Reproduction When the cell is ready to divide and reproduce: the DNA staircase unwinds and the two long chains separate each chain attracts new biochemical material from the cell to synthesize a new and complementary chain Ultimately a new cell is formed

Terms Gametes: Sex cells (ovum or sperm) Diploid cells: Cells having 2 copies of each chromosome Haploid gametes: Gametes having 1 copy of each chromosome

Meiosis Meiosis takes place in the testicles and ovaries. A diploid cell (having 2 copies of each chromosome) undergoes a special form of cell division to create haploid gametes (having 1 copy of each chromosome). An egg and a sperm fuse together to form a new diploid cell called zygote (a process called fertilization)

Mitosis In the first step of mitosis, all chromosomes are copied, so that instead of 2 copies, the cell briefly has 4 copies of each chromosome. Shortly afterwards, the cell divides in half, resulting in two cells each has a complete copy of the genetic information. These cells grow larger and eventually undergo mitosis.

Mitosis: each cell divides and duplicates itself exactly Meiosis: How reproductive cells (ova and sperm) are produced Results in gametes, cells that contain only 23 chromosomes

In Males Meiosis takes place in the testes and involves 2 rounds of division Results in 4 fertile sperm cells By puberty, males begin producing many thousands of sperm cells on an ongoing basis, and they continue to do so through out their life span In Females Meiosis begins in the ovaries before birth and partly completes all of the roughly 400,000 ova a woman will ever have. It occurs in a two-stage process.. Results in one relatively big ovum and 2 small polar bodies that aren’t capable of being fertilized

Mutation A mutation is an alteration in the DNA that typically occurs during mitosis and meiosis. In most cases mutation is maladaptive and the new cell simply dies or repairs and eliminates the mutation A small number of of mutations are viable – the cell survives

Mutation In mitotic cell division, if a viable mutation occurs early in development, it will then be passed along to all cells replicated. In meiotic cell division, mutation only affects the ensuing gametes and stops there, Unless a mutated gamete happens to be involved in producing offspring – in which case the mutation can be passed along to the next generation and beyond.

Gregor Mendel (1800s)

Genotype The genetic makeup of a given individual Recessive Gene The gene pair that determines a trait in an individual only if the other member of that pair is also recessive Phenotype The traits that are expressed in the individual Dominant Gene One gene of a gene pair that will cause a particular trait to be expressed

Alleles A pair of genes, found on corresponding chromosomes, that affect the same trait The child might inherit an allele for brown eyes (B) from the father and an allele for blue eyes (b) from the mother The child’s genotype for eye color would be Bb. What actual eye color will the child display? The allele for brown eyes is dominant (B). The allele for blue eyes is recessive (b). The dominant trait will be expressed as the phenotype

Homozygous Referring to the arrangement in which the two alleles for a simple dominant- recessive trait are the same. Homozygous Individual (Eye Color) Could be BB or bb Heterozygous Referring to the arrangement in which the two alleles for a simple dominant-recessive trait differ. Heterozygous Individual (Eye Color) Could be Bb, or bB The chance for having blue eyes is 25%

Incomplete Dominance Where people with a single recessive gene for a trait show some of the trait along with other normal manifestations. Example: Sickle-cell anemia

Sickle-Cell Anemia Occurs at its highest rate in individuals of black African ancestry. People with a single recessive gene for the trait have a marked percentage of abnormal “sickle-shaped” red blood cells that interfere with oxygen transport throughout the body. They also have normal (dominant) red blood cells as well.

Sickle-Cell Anemia The sickle cells are resistant to malarial infection, so those individuals with the trail would have survived long enough to have children in areas of the world where mosquito-borne malaria is highly prevalent. Sickle-cell carriers experience pain in the joints, blood clotting, swelling and infections under conditions of oxygen shortage. It occurs when a person inherits both recessive alleles

Codominance Where neither the dominant nor recessive allele is dominant and the resulting phenotype is a blend of the two. Example: If an individual gets an allele for each blood types A and B, the result is type AB blood type

Polygenic Inheritance The overall system of interactions among genes and gene pairs More complex traits do not result from the alleles of a single gene pair, but rather from a combination of many gene pairs In determining height, several gene pairs combine to create people with taller or shorter phenotype.

Inherited Disorders Sex-Linked Disorders Autosomal Disorders Genetic Disorders Chromosomal Disorders Autosomal Disorders

Sex-Linked Disorders Involve the sex chromosome # 23 Occur via dominant-recessive patterns A recessive gene on the X chromosome is more likely to be expressed as the phenotype males because the Y chromosome has no allele that might contract the gene.

Genetic Sex-Linked Disorders 1- Color Blindness Genetic X-linked recessive disorder. Occurs in 1 of 10 males 2- Hemophilia A and B Recessive disorders that affect 1 of 5,000 males. These interfere with normal blood clotting and occur at different loci (the position on a chromosome occupied by a particular gene) on the X chromosome.

Chromosomal Sex-Linked Disorders 1- Fragile X Syndrome Occurs in about 1 of 1,200 males and 1 of 2,500 females. Results from a breakage of the tip of an X chromosome. 2- Klinefelter Syndrome (XXY, XXXY, XXXXY) Occurs in about 1 of 1,000 males. It is caused by an extra X chromosome

Chromosomal Sex-linked Disorders 3- Superfemale Syndrome (XXX, XXXX, XXXXX) Occurs in about 1 of 1,000 females. Women appear normal, but tend to score slightly below average in intelligence. 4- Supermale Syndrome (XYY, XYYY, XYYYY) Occurs in about 1 0f 1,000 males. The men tend to be taller than average, with a greater incidence of acne and minor skeletal abnormalities.

Chromosomal Sex-linked Disorders 5- Turner’s Syndrome (XO) Occurs in about 1 of 10,000 females. One of the X chromosomes is either missing or inactive. These women have immature female appearance, do not develop secondary sex characteristics, and lack internal reproductive organs.

Autosomal Disorders Disorders involving the other 22 pairs of chromosomes. Can result from an extra chromosome or defective genes

Genetic Autosomnal Disorders 1- Angelman’s syndrome Occurs in about 1 of 10,000 to 15,000 people. It is determined by a set of mutated genes on chromosome 15. 2- Cystic Fibrosis A recessive disorder that occurs in about 1 of 2,5000 people of white European ancestry. Related to a mutated gene on chromosome 17. Characterized by excessive secretion of the mucus in the body.

Genetic Autosomal Disorders 3- Huntington Disease A dominant disorder that occurs in about 1 of 10,000 people. A dominant gene on chromosome 4 is responsible. It causes degeneration of neurons producing dementia, and random jerking movements.

Genetic Autosomal Disorders 4- Phenylketonuria (PKU) A recessive disorder that occurs in about 1 of 10,000 people. A defective gene on chromosome 12 is responsible 5- Prader Willi Syndrome A recessive disorder that occurs in 1 of 10,000 to 15,000 people. It is determined by a set of mutated genes on chromosome 15.

Genetic Autosomnal Disorders 6- Sickle-Cell Anemia Occurs in about 1 of 12 U.S. blacks. The defective gene on chromosome 11 is responsible. 7- Tay-sachs Disease A recessive disorder that occurs in about 1 of 5,000 people of European Ashkenazi Jewish ancestry. Defective gene on chromosome 15 is responsible.

Chromosomal Autosomal Disorders Down Syndrome Occurs in about 1 in 1,000 live births. An extra chromosome is attached to the 21st pair. Risk increases with maternal age. Pregnancies of women over age 35 accounts for 20% of Down syndrome birth

Genetics and Environment Sandra Scarr Active genotype-environment effects Passive genotype-environment effects Evocative genotype-environment effects

Stop and Discuss Gametes Zygote Monozygotic twins Dizygotic twins Diploid cells Haploid gametes Dominant/recessive genes Chromosomes Genes DNA Meiosis Mitosis Allele Phenotype/genotype Homozygous/hetrozygous

Genetic Counseling Can help couples obtain valuable information about the parents’ genetic makeup . It can help potential parents to evaluate genetic risk factors in childbearing and enable them to make intelligent decisions. It includes analysis of parental medical records and family histories to construct a family pedigree.

Family History Parental Conditions Neonatal deaths Malformations Mental retardation Congenital anomalies (e.g. club feet) Diseases that run in families Inability to thrive Genetic or chromosomal abnormality Infertility Mother/father’s age Stillbirths Ethnic background Exposure to toxic agents Cancer

Detecting Birth Defects Amniocentesis Chronic Villus Sampling Ultrasound Sonography Maternal Blood Test

Genetic Engineering Alteration of Human Genes 1- Gene Therapy 2- Germ-line Genetic Alterations Germ-line Genetic Intervention 3- Genetic Enhancement

1- Gene Therapy Genetic alteration of somatic cells to treat disease. Researchers inject genes that are targeted to treat a particular disease in to a patient’s blood stream. When the genes arrive at the site of the defective genes, they produce chemicals that can treat the problem.

2-Germ-line Genetic Alteration Can correct problems for unborn individuals and future generations. It targets the genes in the reproductive cells – the egg and the sperm that combine the DNA to conceive a new human. Scientist might detect defective cells soon after conception, removing them from the mother and placing them in a test-tube culture. Gene therapy could be employed to correct the defects in the cells. The result could be cloning. Parents could some day customize their children.

3-Genetic Enhancement Non therapeutic genetic alteration An attempt to enhance an already healthy genetic makeup by inserting a gene for improvement (e.g. height, intelligence, eye color)

What Do You Think?

Cloning Producing genetic replicas of the organism

Stop and Discuss In the light of scriptural truth, how ethical are these issues? 1-Amniocentesis 2-Chronic villus sampling 3-Gene therapy 4-Germ-line genetic alteration 5-Genetic enhancement

Stages of Prenatal Period 1- Germinal Stage (fertilization to 2 weeks) Blastocyst Cell Division Specialized Cells

2- Embryonic Stage (2 weeks to 8 weeks) 1-Ectoderm (outer layer) Skin, teeth, hair, sense organs, brain, spinal cord 2-Endoderm (inner layer) Digestive system, pancreas, respiratory system 3-Mesoderm (in between both) Muscles, bones, blood, circulatory system

3- Fetal Stage (8 weeks to birth) Fetus Increases in size Proportions similar to adults

Environmental Influences 1- Habituation 2- Classical Conditioning 3- Operant Conditioning 4- Social Learning

Sociocultural Influences Paul Blates (87, 88) Normative Age-Graded Influence The biological and social changes (e.g. aging, entering school, marriage) Normative History-Graded Influence Historical events (e.g. wars, depression) Nonnormative Influences Individual environmental factors (e.g. divorce, unemployment)

Prenatal Care Diet The father’s involvement Age of mother Illness of mother Drug use Alcohol Teratogens