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Lecture 2

Lecture 2 - Development 2.docx

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Joe Kim

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Development: Part 2 • At conception, a new cell is formed: zygote  contains 23 chromosomes from mum, 23 from Dad (total 46) • Chromosome: threadlike, made of deoxyribonucleic acid (DNA) • Genes: provide chemical code for development, segments of DNAcomprise genes • Results from Human Genome Project: our chromosomes contain about 30-40 thousand genes • Zygote quickly multiplies 2 cells 4 cells 16 … billions of cells @ birth • Each parent can produce more than 8 million genetic combinations • Monozygotic twins: genetically identical- come from same sperm and ovum, which formed one zygote and split into 2 separate zygotes • Dizygotic twins: (no more alike than any 2 siblings) not identical, come from 2 different sperm & ovum… start off as 2 different zygotes • Male determines gender of the child • We all have 23 chromosomes: 22/23 are autosomes and are similar in males and females.  23 pair of chromosomes determines a persons gender!* • Female carries 2 X chromosomes; male carries one X, one Y chromosome  if a father passes on an X, the baby will be a girl (XX), if the father passes on a Y, the baby will be a boy (XY) • Genotype: individual’s inherited genes • Phenotype: expression of individuals genotype in terms of observable characteristics • Four Patterns of Genetic Expression: 1) Simple Dominant Recessive Inheritance: expression of a trait determined by a single pair of genes called alleles  determines the phenotype expression of a particular trait • Heterozygous condition: 2 alleles are diff. and have different affects on the phenotype • Homozygous condition: 2 alleles are the same and have the same effect on expression • Dominant allele is expressed in the phenotype • Recessive allele is not expressed, but still herritable/recessie 2) Polygenetic Inheritence: (more common) expression of multiple pairs of genes to make up a more complex trait 3) Codominance: 2 dominant alleles are equally & fully expressed to produce a phenotype that is a compromise of the 2 genes 4) Sex-Linked Inheritence: genes expressed on X chromosome  XX females inherits an X from mum & dad; XY male inherits X from mum & Y from Dad… o *Because females have 2 X chromosomes, the phenotypic expression of the recessive allele occurs less frequently in females than males, who only have 1 X chromosome  o Females rarely express sex-linked disorders in their phenotype, although they are often genetic carriers Nature vs. Nurture: • Watson believes strongly in nurture- with proper training and environmental control, anyone can become a doctor, musician, athelete or even criminal • Canalization Principle: genotype restricts the phenotype to a small number of possible developmental outcomes… (some developmental processes are buffered against environmental variability) o Ex) infant babbling: despite the diff. language cultures infants can be born into, they all babble in the same way ▯ universal phoneme sensitivity is independent of environment •Range of Reaction Principle: genotype establishes a range of possible responses to different kinds of life experiences ie) height is influenced by many factors: nutrition, sleep, exercise, etc.; however, there is a range of portential for this & other genetic traits and the input from the environment influences how your genotype is expressed as a phenotype (my genetics will only allow me to grow so tall, but environment could alter the final outcome) Gene-Environment Interactions: 1. Passive Genotype Environment Correlations: genes influence environment: environment parents chose to raise their children in, often influenced by the parents own genes ie) parents who are highly athletic will be focused on a big playroom with many active toys (this environment will likely mesh with genetic inheritance of the indi
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