Mechanisms of Genetic Transmission Genetic information is combined

Mechanisms of Genetic Transmission § Genetic information is combined and transmitted by gametes, the reproductive cells of a child’s parent § In the father the gametes are produced in the testicles (each is called a sperm cell) § In the mother they are developed in the ovaries (each is called an ovum or egg cell)

Mechanisms of Genetic Transmission (continued) § The sperm and egg cells contain genetic information molecular structure called genes § The genes form threads called chromosomes § Genetic material that the child will inherit from the parent is contained in the chromosomes

Mechanisms of Genetic Transmission (continued) § Each human sperm or egg cell contains 23 chromosomes § All other cells of the body contain 46 chromosomes and about 100, 000 genes § A single chromosome may contain as many as 20, 000 genes

DNA § The genes are made up of DNA (deoxyribonucleic acid) § DNA have a spiral chemical structure that allows them to divide easily and duplicate DNA molecules § DNA contains the genetic information that directs the form and function of each body cell as it develops

DNA (continued) § DNA is shared at conception when a sperm (father) penetrates the egg from the mother § Within a few hours the walls of the sperm cell and the nucleus of the egg cell both begin to disintegrate releasing its chromosomes which join to form a new cell § The new cell formed is called a zygote

Meiosis and Mitosis § All cells of the body develop from this original zygote through a process called cell division § The sperm and ova contains only 23 chromosomes making them unique from other body cells § This ensures that when an egg and sperm join to form a new zygote the zygote will contain the complete set of 46 chromosomes (23 pair)

The human body contains 100 trillion cells. There is a nucleus inside each human cell (except red blood cells). Each nucleus contains 46 chromosomes, arranged in 23 pairs. One chromosome of every pair is from each parent. The chromosomes are filled with tightly coiled strands of DNA. Genes are segments of DNA that contain instructions to make proteins— the building blocks of life.

Meiosis and Mitosis (continued) § The zygote contain the genetic materials from which all of an individual’s cells are formed § The reproductive cells (gametes) divide by a process called meiosis and recombine into a zygote at conception § All other cells will develop from the zygote through a simpler division called mitosis

Meiosis and Mitosis (continued) § Mitosis involves: § 1. 23 pairs of chromosomes of a cell duplicate themselves and divide into two identical sets § 2. The two sets of chromosomes move to opposite sides of the cell § 3. A new wall forms between them, resulting in two new identical cells containing the same set of chromosomes, genes and DNA

Gametes and Zygote Sperm Ovum Gametes (reproductive cells) Fertilization Zygote

The Process of Meiosis for Sperm Cells Cell with 46 chromosomes (only one pair of homologous chromosomes is shown here). Each member of the pair has begun to replicate similar to mitotic cell division. First meiotic cell division begins, but does not proceed as in mitosis. Instead of the replicated chromosome splitting apart, one member of each homologous pair becomes a part of the first-generation daughter cell. The second meiotic division proceeds after the first is completed; now the replicated chromosome acquired in the first-generation daughter cell splits apart. Each of the four gametes produced by the two-step process now has acquired one member of the pair of homologous chromosomes.

The Process of Mitosis Cell nucleus with a pair of chromosomes Chromosomes split and replicate to produce two identical pairs The pairs separate, and the cell divides Each daughter cell now has a pair of chromosomes that is identical to the original pair

GENOTYPE AND PHENOTYPE · GENOTYPE: Set of genetic traits a person inherits; a person’s inborn capacity or potential · PHENOTYPE: Set of traits a person actually displays, resulting from a combination of the person’s genotype (potential) and life experiences that modify that potential

Individual Genetic Expression (continued) § Examples of phenotype may include a certain height, intelligence score, shyness § Phenotype results from all the interactions of the person’s genotype with the environment from conception onward

Genes (dominant and recessive) § Genes are inherited in pairs (one from each parent) § Dominant gene--in a paired set of genes, the gene with the greater influence in determining physical characteristics § Recessive gene--in a paired set of genes, the gene that influences or determining physical characteristics only when no dominant gene is present

Genes (dominant and recessive) continued § A dominant gene will influence a child’s phenotype even if it is paired with a recessive gene § A recessive gene must be paired with another recessive gene to be able to influence the phenotype § If paired with a dominant gene its influence is blocked

Genes (dominant and recessive) continued § Eye color--blue eyes (recessive trait), brown eyes (dominant trait) § a child’s eyes will remain blue only if they have received the appropriate blueproducing gene from both parents § If they received it from only one parent or from neither they will end up with brown eyes (dominant)

Genes (dominant and recessive) continued § Genes may take on two or more alternatives forms called alleles § a person who inherits two identical alleles for a particular trait is homozygous for that trait § if they inherit two different alleles for the trait it is heterozygous

Polygenic § Blood type and eye color have a limited number of distinct ways of transmission § height, weight, skin color, personality, behavioral traits are polygenic (involve many genes) § Environment influence them in important ways (can diet and change weight)

Determination of Sex § One pair of chromosomes among the 23 is largely responsible for determining whether a child is male or female § In women the pair of chromosomes is XX § In men the pair is XY § all eggs cells contain a single X chromosome § a sperm cell may contain either an X or Y

Determination of Sex (continued) § If a Y bearing sperm fertilizes the egg, a male (XY) zygote develops § If a X bearing sperm fertilizes the egg a female (XX) zygote develops

Genetic Abnormalities § Sometime too many or too few chromosomes transfer (or transfer a defective gene) to newly forming zygote § This may affect a child mentally, physically or both § Inheriting too many or too few chromosomes is usually fatal

Genetic Abnormalities (continued) § In a few cases children with a missing or an extra chromosome survive § Down syndrome--caused by extra 21 st chromosome or transfer or part of the 21 st on to another chromosome

Genetic Abnormalities (continued) § § § § Characteristics of Down’s Syndrome almond shaped eyes, round head stubby hands and feet may have abnormal heart and intestinal tract facial deformities vulnerable to diseases such as leukemia as they age fall behind developmentally

Genetic Abnormalities (continued) § Usually levels out at the moderately retarded level § most live until middle adulthood § they are able to do simple routines and hold these type of jobs § more frequent in mothers over the age of 35

FREQUENCY OF DOWN SYNDROME (PER 1000) Relationship Between Maternal Age and the Incidence of Down Syndrome 100 90 80 70 60 50 40 30 20 10 0 15 20 25 30 35 40 MATERNAL AGE (YEARS) 45 50

Pictures of Down’s syndrome individuals

Down Picture #2

An adult Down’s person

Genetic Abnormalities (continued) § Klinefelter Syndrome-§ results from inheriting an extra chromosome (usually an X) resulting in an XXY pattern § affects males (they are sterile, have small testes) § have normal intelligence § affect about 1/800

Klinefelter Syndrome is caused by a chromosome variation involving the sex chromosomes. The person with Klinefelter Syndrome is a male who, because of this chromosome variation, has a hormone imbalance. While Dr. Harry Klinefelter accurately described this condition in 1942, it was not until 1956 that other researchers reported that many boys with this description had 47 chromosomes in each cell of their bodies instead of the usual number of 46. This extra sex (X) chromosome causes the distinctive make-up of these boys. All men have one X chromosome and one Y chromosome, but sometimes a variation will result in a male with an extra X. This is Klinefelter Syndrome and is often written as 47, XXY. There are other, less common variations such as 48, XXYY; 48, XXXY; 49, XXXXY ; and XY/XXY mosaic. All of these are considered Klinefelter Syndrome variants.

Klinefelter Karotype

Klinefelter individual

Genetic Abnormalities (continued) § Turner syndrome-§ results from having only one sex chromosome (X 0) affecting females § will develop learning disabilities § not fully sexually differentiated § are very short as adults (4 and 5 ft. ) § have webbed necks § ears are set lower than usual

Adults with Turner syndrome are short, averaging around four feet, eight inches in height. But girls with Turner syndrome don't start life as very short individuals - they become short over time, growing more slowly than their sisters and friends with each passing year. Studies have shown that a medicine called recombinant human growth hormone, or GH, can improve the height of girls with Turner syndrome. However, these studies have tended to start GH treatment around age 9 or later, after years of deteriorating growth. So, even with treatment, many girls remain shorter than would be expected based on the heights of their parents. The purpose of this new study is to determine if GH started at a young age can prevent the growth failure typical of girls with Turner syndrome. In addition, the study will monitor all participants for development of ear infections and hearing loss, problems that trouble many girls with Turner syndrome.

A Turner’s syndrome infant

A Turner’s syndrome teen

Disorders from Abnormal Genes § § § Three types of genetic disorders: 1. dominant gene disorder 2. recessive gene disorder 3. multifactorial gene disorder Dominant gene disorder require only one abnormal gene from either parent to affect a child

Disorders from Abnormal Genes (continued) § Huntington disease (dominant gene disorder) § gradual deterioration of the central nervous system, causing mental retardation and uncontrollable movements § appear when person is in their 30’s or 40’s § always fatal

Disorders from Abnormal Genes (continued) § Recessive gene disorder-§ can occur when the fetus inherits a pair of recessive genes, one from each parent § Cystic Fibrosis--involves production of thick mucus, clogging the lungs § causes delayed growth and sexual maturation, shortened life and vulnerable to infections

Disorders from Abnormal Genes (continued) § Sickle-Cell Disease--red blood cells take on a sickle shape instead of a round shape § These cells get caught in the blood vessels cutting off circulation, reducing oxygen supply causing pain § have bacterial infections § degeneration of organs (due to lack of oxygen) § few live past 40 years of age

Disorders from Abnormal Genes (continued) § Tay-Sachs Disease--disease of the nervous system (chemical imbalance) § about age 6 months will show poor tolerance for sudden loud noises, seem weak and slow to develop § lead to seizures, deafness and blindness § most die by age 3

Disorders from Abnormal Genes (continued) § Phenylketonuria (PKU)--occurs in 510/1000, inability to utilize an amino acid called phenylalanine (found in milk, meat) and needed for normal growth § increases in levels of phenylalanine in the blood and spinal fluid affects the brain causing deterioration of cognitive functioning and mental retardation

Disorders from Abnormal Genes (continued) § Multifactorial disorders-§ result from a combination of genetic and environmental factors § Neural tube defects--result when the tube enclosing the spinal cord fails to close completely or normally § Sometimes the upper part of the brain is absent or underdeveloped

Disorders from Abnormal Genes (continued) § Causes include heredity and environmental aspects such as pollutants, poor nutrition, diseases (diabetes) § geographical background and racial/ethic background) § British Isles has the highest § U. S. highest is in the Appalachian region

Disorders from Abnormal Genes (continued) § Cleft palate/lip--when the upper lip and/or roof of the mouth fail to grow resulting in a split or “cleft” § If severe may lead to difficulties breathing, speaking, hearing and eating § surgery can usually repair the problem

Disorders from Abnormal Genes (continued) § Congenital heart disease--structural and/or electrical abnormalities in the formation of the heart § medication and surgery can usual correct

Prenatal Diagnostic Techniques § Diagnostic techniques after conception but before birth § Ultrasound--high frequency sound waves are projected through the mother’s womb § Waves bounce off the fetus creating a television image of the size, shape, and position of the fetus

Prenatal Diagnostic Techniques (continued) § § § Ultrasound can be used to: determine age of fetus multiple pregnancies physical defects in internal/external organs determine Down’s Syndrome (extra fold of skin on the neck)

Prenatal Diagnostic Techniques § Amniocentesis--performed at weeks 14 -18 § Using, ultrasound a slender needle is inserted through the mother’s abdomen into the uterus and the amniotic sac and a sample of amniotic fluid is withdrawn § Fluid contain the cells which hold the genetic makeup of the fetus § can be used to determine if they have abnormal chromosomes

Prenatal Diagnostic Techniques (continued) § Amniocentesis § It can also determine disorders such as Down’s Syndrome, neural tube defect and sex of the baby

Prenatal Diagnostic Techniques (continued) § Chorionic Villus Sampling (CVS) § tests for most of the same disorders as amniocentesis does § performed between the 8 th & 10 th week of pregnancy § involves collecting and analyzing tissue by inserting a catheter through the vagina into the uterus between the uterine lining and the chorion (surrounds the embryo, becomes the placenta later)

Prenatal Diagnostic Techniques (continued) § This technique lets parents know very early whether the fetus has inherited any serious defects § primary risk of procedure is miscarriage § Fetoscopy--inserting a fetoscope (telesopic type fiber optic lens through the abdomen into the uterus to observe the amniotic fluid, placenta, and fetus § performed 15 th-18 th week

Prenatal Diagnostic Techniques (continued) § Fetoscopy is used to observe already identified problems or to confirm other prenatal tests § Maternal Serum Alpha Fetoprotein § test measuring the amount of alphafetoprotein (AFP) in the mother’s blood § performed 15 th-18 th week § fetoprotein is produced by the fetus and passes from the amniotic fluid through the placenta into the mother’s bloodstream

Prenatal Diagnostic Techniques (continued) § High level of AFP are associated with various problems as anencephaly (lacking a brain), spina bifida, and Down’s Syndrome § Percutaneous Umbilical Blood Sampling (PUBS) § experimental method of sampling fetal blood by guiding a needle through the mother’s abdomen and uterus and umbilical vein § performed between the 18 th and 36 th week

Prenatal Diagnostic Techniques (continued) § Used to diagnosis numerous conditions, such as Down Syndrome, neural tube defects, cystic fibrosis)

Risk of Selected Genetic Disorders Chromosomal Down Syndrome Klinefelter syndrome (XXY) Fragile X syndrome Turner syndrome (XO) Dominant Gene Polydactyly Achondroplasia Huntington disease Recessive Gene Cystic fibrosis Sickle-cell disease Tay-Sachs disease 1/800 men 1/1, 200 male births 1/2, 000 female births 1/3, 00 women 1/300 - 1/100 1/2, 300 1/15, 000 - 1/5, 000 1/2, 500 white persons (risk of being a carrier is 1/25) 1/625 African Americans (risk of being a carrier is 1/10) 1/3, 600 Eastern European Jews(risk of being a carrier is 1/300) X Linked Hemophilia 1/2, 500 male babies Multifactorial Congenital heart disease Neural tube defect Cleft lip/cleft palate 1/125 1 - 2/1, 000 1/1, 000 - 1/5, 000 Sources: ACOG (1990); Blatt (1988); Diamond (1989(; Hagerman (1996); Selekman (1993); Stratford (1994).

Who Should Seek Prenatal Counseling? 1. Couples who already have a child with some serious defect such as Down syndrome, spina bifida, congenital heart disease, limb malformation, or mental retardation 2. Couples with a family history of a genetic disease or mental retardation 3. Couples who are blood relatives (first or second cousins) 4. African Americans, Ashkenzzi Jews, Italians, Greeks, and other high-risk ethnic groups 5. Women who have had a serious infection early in pregnancy (rubella or toxoplasmosis) or who have been infected with HIV 6. Women who have taken potentially harmful medications early in pregnancy or habitually use drugs or alcohol 7. Women who have had X rays taken early in pregnancy 8. Women who have experienced two or more of the following: stillbirth, death of a newborn baby, miscarriage 9. Any woman thirty-five years or older Source: Adapted from Fienbloom & Forman (1987) p. 129

Behavior Genetics § Behavior genetics--is the study of how genetic inheritance (genotype) and environmental experience jointly influence physical and behavioral development (phenotype)

Behavior Genetics (continued) § Four concepts of behavior genetics § range of reaction-the range of possible phenotypes that an individual with a particular genotype might exhibit in response to the specific sequence of environmental influences they experience § influences as neighborhood, child’s family, school and community etc.

Behavior Genetics (continued) § Canalization--tendency of genes to narrowly restrict the development of certain phenotypic characteristics to a single or relatively limited number of outcomes in spite of environmental pressures toward other outcomes § early perceptual-motor (crawling, sitting up are canalized)

Behavior Genetics (continued) § Others include personality, temperament, intellectual functioning § Gene-Environment Relationship§ patterns of interaction between a newborn infant and his caregiving environment and the extent to which that pattern supports the expression and development of the child’s inborn traits

Behavior Genetics (continued) § § Examples include: shyness athletic ability parents may display their own genetically inherited traits that support the development of similar traits in their children

Behavior Genetics (continued) § A passive gene-environment relationship§ if support for the development of traits come from others (parents and family members) § Evocative gene-environment relationship§ displayed by child of certain traits evokes support from others

Behavior Genetics (continued) § Active gene-environment relationship-§ when a child with a particular trait actively seeks out support from others with similar traits (sports, etc. )