Ch2 Nature with Nurture Can t ignore nature How much of a person s development and identity is genetically determined Many universals of being human things that make us unique o Ex bipedalism walking talking Canalization all humans inherit o the degree to which an element of development is dictated by the genetic program that o Some things are highly genetically controlled like eye color others are more easily influenced greater variations o The universals of human development are highly canalized o Earlier development is more canalized more universals o Areas of greater inter individual diversity are less canalized What is it that makes us have so much in common o The Genetic Code o Each animal species has its own number of chromosomes o We share some of our genetic makeup with even simple organisms o 98 99 of human DNA is identical to chimps o Genetic variation from one human to the next is small Only a tiny quantity of DNA contributes to human variation in traits and capacities Every person has a slightly different genetic code but the human genome is 99 1 99 9 the same for any 2 people How does one become who they are o The principles of genetic transmission determine characteristics that make us human and contribute to individual differences in appearance and behavior o Inheritance of harmful recessive genes and abnormalities of the chromosomes are major causes of serious developmental problems o Prenatal diagnosis and genetic counseling help people at risk for transmitting hereditary disorders assess their chances of giving birth to a healthy baby Genetic Foundations o The basic unit of heredity gene o Composed of DNA o Genes are carried on rod shaped structures called chromosomes o Chromosomes store and transmit genetic information The chromosomes are found in the nucleus of every cell Contain the complete set of instructions for the development of the human being o Genetic Foundations Chromosomes long strands of DNA DNA contains the instructions to make proteins which leads to production and reproduction of cells The instructions are organized into genes Genes segments of DNA located along the chromosomes the basic unit for transmitting heredity DNA substance of which genes and chromosomes are made Chemical bases are the rungs o Adenine o Thymine o Guanine o Cytosine o DNA found on genes IN the cells nucleus o Humans have 46 chromosomes 23 pairs and about 25 000 100 000 genes The same 46 chromosomes are found in every cell of the body except the gametes sex cells Of the 23 pairs of chromosomes 22 pairs are numbered according to their size Chromosome 1 the largest and chromosome 22 the smallest o Karyotype Map of Chromosomes Cells divide o Most cells are created through the process of mitosis o Gametes sex cells are produced through meiosis o Mitosis Cell nuclei contain chromosomes Chromosomes split and produce identical replicas The replicas separate and the cell divides Each new daughter cell is a replica of the original and of the sister There is a limit in the number of times a cell can divide Hayflick limit the maximum number of times a cell can divide o The Sex Cells The 23rd chromosome pair is the sex chromosome and determines sex In a process called meiosis the sex cells divide to form 2 cells containing 23 chromosomes each 22 of the 23 pairs of chromosomes look identical However the 23rd is different 2 types X chromosome Y chromosome New individuals are created when the sex cells or gametes sperm in males and ova in females combine Each gamete formed through a cell division process called meiosis contains only 23 chromosomes When the gametes combine at conception the resulting cell called a zygote again has 46 chromosomes During meiosis males contribute an X or Y chromosome If X chromosome sperm penetrates the eggs membrane it s a girl The Beginnings of Life Development begins at conception when the sperm penetrates the ovum The organism is first called a zygote and is the fused nuclei of the sperm and egg The genotype of the zygote is the genetic information on the 23 chromosome pairs Genotype specific composition of an individual s genes o Meiosis Gene Pairs Phenotype observable characteristics of an individual o Gene pairs are closely matched on 22 of the 23 chromosomes o On the 23rd pair XX female XY male X is a relatively large chromosome Y is short and carried much less genetic material o The sex of a new organism is determined by whether X or Y bearing sperm fertilizes the ova Homozygous Heterozygous o Two forms of each gene each called an allele occur at the same place on the chromosomes one inherited from the mother and one from the father o If the alleles from both parents are alike the child is homozygous and will display the inherited trait o If the alleles are different the child is heterozygous and the phenotype or visible trait depends on the relationships between the alleles o In the case of additive heredity the child s phenotype is a mixture of the mother s and Additive Heredity father s genes Ex height skin color Dominant Recessive Inheritance o Many heterozygous pairings show a pattern of dominant recessive inheritance in which only one allele called dominant affects the child s characteristics while the other allele called recessive has no effect o Carriers don t exhibit the trait but can pass it on to their children o Examples of Dominant and Recessive Characteristics Dominant Dark hair Curly hair Facial dimples Recessive Blonde hair Straight hair No dimples o Many disabilities and diseases follow the rules of dominant recessive inheritance are Inheritance of harmful recessive genes the product of recessive alleles Dominant and Recessive Diseases anemia Tay sachs disease o Dominant Huntington s Marfan Syndrome Dominant Recessive Inheritance o More are recessive Cooley s anemia cystic fibrosis PKU most common sickle cell o If both parents are heterozygous carriers there is a 25 chance that the child will be normal 50 chance the child will be a carrier and 25 chance the child will be affected by the disease o Males and females have an equal chance to inherit recessive disorders on autosomes 22 23 matching pairs of chromosomes Sex Linked Inheritance o When harmful allele is carried on X chromosome x linked inheritance applies o Recall Y chromosome is about 1 3 as long and lacks many corresponding alleles to override those of the X chromosome o The female with 2 X chromosomes benefits from a greater variety of genes Ex hemophelia color