Chapter 3 Humans have 23 pairs of chromosomes 46 in total all organized into genes located at a specific spot on a particular chromosome A Adenine T Thiamine C Cytosine and G Guanine Variation on the genes are called allele and most alleles cause minor differences others drastic Methylation is a material that enhances transcribes connects empowers and alters genes The entire packet of instructions to make a living organism is called the genome A reproductive cell is called a gamete 23 chromosomes and when two gametes combine they create a zygote with 46 chromosomes Genotype is the genes on the chromosomes constitute the organism s genetic inheritance If the code of all the base pairs of the gene from one parent is exactly like the code on the same gene from the other parent the gene pair is homozygous If a gene s code differs from that of its counterpart the two genes still pair up but the zygote is heterozygous 23rd chromosomes are the sex chromosomes In females it is two XX and in males it is XY The zygote duplicates divides and differentiates The first cells of a zygote are called stem cells able to produce any other cell and thus to become a complete person Monozygotic MZ twins from one mono zygote also called identical twins They have identical genetic instructions for appearance psychological traits and disease vulnerability Dizygotic DZ twins also called fraternal twins created from two separate zygotes Assisted reproductive technology ART used by couples who can t conceive a women can take drugs to cause ovulation or the ova can be surgically removed from an ovary and then inserted into the uterus in vitro fertilization IZF Phenotype is the person s appearance behavior and brain and body functions Polygenic is when most traits are affected by many genes and multifactorial is when traits are influenced by many factors including biological and psychological ones Epigenetic refers to environmental factors that surround the genes affecting genetic expression Total number of genes in a person is between 18 000 and 23 000 Dominant recessive pattern in which one allele the dominant gene is more influential than the Some alleles are additive because their effects add up to influence the phenotype other the recessive gene When someone inherits a recessive gene that is not apparent in the phenotype that person is said to be a carrier of that gene because the recessive gene is carried on the genotype X linked gene is when a dominant recessive pattern is located on the X chromosome Copy number variations which are genes with various repeats or deletions of base pairs and they correlate with almost every disease and condition Two syndromes caused by the deletion of the same small part of chromosome 15 but if inherited from the father the child will have Prader Willi syndrome and be obese slow moving and stubborn If inherited from the mother the child will have Angelman syndrome and be thin hyperactive and happy Genes affect every aspect of behavior including social interactions intellectual abilities even political values and reactions Most environmental influences on children raised in the same home are not shared Genes elicit responses that shape development Thus personality may be partly the cause of a person s experiences not merely the result Lifelong people choose friends and environments that encourage their genetic predispositions thus genetic effects increase with age Each person s biochemistry reacts to alcohol causing sleep nausea aggression joy relaxation Biological sex and gender also affect the risk of alcoholism Body size fat composition and forgetfulness sex urges or tears metabolism also affect Heritability is a statistic that indicates only how much of a variation in a particular trait within a particular population in a particular context and era can be traced to genes Down Syndrome also called trisomy 21 is when the person has three copies of chromosome 21 No two people with this are identical but there are similar facial characteristics and hearing problems They are slower to develop intellectually and reach their potential at age 15 Huntington disease is a fatal central nervous system disorder cause by a genetic miscode Fragile X syndrome is caused by more than 200 repetitions of one triplet on one gene too many repetitions are not normal causes cognitive deficits and inherited mental retardation Genetic counseling relieves some worries by providing facts and helping prospective parents discuss sensitive issues Information that genetic counselors are allowed to share if and only if the person wants to hear it the risk is severe and verified and treatment is available Counseling must be individualized because each adult s perceptions are affected by his or her partner present and future children work religion and community