Class Notes (808,232)
Canada (493,093)
Psychology (3,899)
PSY2105 (185)

Chapter 3 - Genetics.docx

14 Pages
Unlock Document

University of Ottawa
David Collins

PSY 2105 F Chapter 3 Genetics September 17 2012 Heredity and Genes  Genetics o study of the structure and function of genes  genes - small unit of chromosomes that direct the synthesis or proteins  chromosomes - long strands of DNA  heredity o sum of inherited traits and tendencies The structure and composition of DNA Genes serve as “recipes” for the synthesis of proteins and enzymes. Mechanisms of Inheritance: Cell Division  Cells are comprised of three divisions: o Nucleus contains the chromosomes  Chromosomes: strands of the genetic material DNA  Each human cell contains 23 chromosome pairs (yielding 46 total chromosomes per cell)  Autosomes comprise 22 of the 23 pairs  Sex chromosomes comprise the 23rd pair o Males are XY, females are XX 1 PSY 2105 F Chapter 3  Cytoplasm fills the cell interior  Cell membrane encases the cell  Cells form two groups based on function: o Body cells: form the structures of the body  Reproduce by mitosis: Forming two identical cells, each equipped with 23 pairs of chromosomes o Germ cells: form the reproductive cells  Reproduce by meiosis: forming four cells with each cell containing only 23 chromosomes  These cells are the gametes: ova or sperm  During conception, a sperm merges with an ovum to form a new cell containing 23 pairs of chromosomes  Mitosis o refers to a process by which 2 identical cells are produced  Meiosis o refers to a process in 4 cells are produced, with each containing only 23 chromosomes Figure 3.1 Mitosis and meiosis. Mitosis results in two cells identical with the parent and with each other. Meiosis results in four cells different from the parent cell and from each other. 2 PSY 2105 F Chapter 3  Crossing over o During meiosis, the x-shaped chromosomes line up and intermix, yielding a novel genetic product Figure 3.2 Crossing over results in the exchange of genetic material. After the cross-over, all four strands are different Inside the Chromosome  DNA - the basic genetic material, formed from pairs of base nucleotides o The bases form pairs such as adenosine-thymine or guanine-cytosine o The DNA strand is in the form of a double helix made up of a series of base pairs Figure 3.3 Structure and Replication of DNA Heredity and Genetics 3 PSY 2105 F Chapter 3 Human Chromosomes  We have 46 chromosomes, or 23 pairs.  44 of them are called autosomes and are numbered 1 through 22. Chromosome 1 is the longest, 22 is the shortest.  The other 2 chromosomes are the sex chromosomes: the X chromosome and the Y chromosome. 4 PSY 2105 F Chapter 3 Side Bar: Genetics and Sex  Variation – genetic diversity  Sources o Sexual reproduction o Random variation  Mutations  Chromosomal aberrations Genetic Variation – Sex  Sexual reproduction o recombination of genes o spread/creation of advantageous traits  Is this why sex evolved? Why Did Sex Evolve?  Red Queen Hypothesis o spread/creation of advantageous traits "Well, in our country," said Alice, still panting a little, "you'd generally get to somewhere else — if you run very fast for a long time, as we've been doing.“ "A slow sort of country!" said the Queen. "Now, here, you see, it takes all the running you can do, to keep in the same place. If you want to get somewhere else, you must run at least twice as fast as that!"  DNA repair hypothesis o maintain healthy genes What is Sex? Meiosis (break and reconstruct parental DNA | Germ Cell – Unique DNA (example: sperm) | Fertilization / Syngamy (haploid fusion)  Sex is recombination + outcrossing  sex is a process of genetic mixing o need not involve reproduction  Why is genetic mixing a good idea? 5 PSY 2105 F Chapter 3 Two Processes of Sex o Recombination:  physical breaking and rejoining of DNA molecules (crossing over) o Outcrossing:  DNA involved in recombination come from two different individuals Costs of Sex  Compared to asexual reproduction: o genetic costs o energy costs o costs of producing males o sex undoes what it creates (variation)  Why take a chance and break DNA? o not even guaranteed an advantageous trait  But, what if chromosome defective?  Need a system to repair it - sex!! Data consistent with sex as DNA repair:  Sex in simple organisms (e.g., bacteria) o if bacteria cannot “have sex”, they are extremely sensitive to DNA damaging agents o increased recombination rate when exposed to such agents o yeast  outcrossing increases in response to DNA damage Sex – Final Thought  Reason for sex - proper upkeep of genes? o cope with DNA damage and mutations  Maintenance of sex may be different from original purpose o DNA repair system came first, then other functions 6 PSY 2105 F Chapter 3 Mendel’s Studies Principles of Heredity  Mendel argued that certain traits are transmitted from parents to child o Each trait is governed by two elements with one from each parent o Phenotype: the expressed trait o Genotype: the underlying genes that govern the trait Genetics  Alleles o alternate forms of gene pairs o homozygous - same two o heterozygous - different genes make up pair  phenotype controlled by dominant allele (not recessive)  Example o brown eye colour is dominant Heredity and Genetics Mendel’s Studies: Common Genetic Traits 7 PSY 2105 F Chapter 3 Principles of Genetic Transmission  Principle of dominance: Some genes are always expressed (dominant gene), others are recessive (recessive gene)  Polygenic inheritance occurs when traits are determined by a number of genes  Incomplete dominance occurs when the dominant gene does not completely suppress the recessive gene  Codominance occurs when both genes are dominant and thus both are expressed  Genomic Imprinting occurs when an allele from one parent is biochemically silenced and only the other allele affects the phenotype Genetic Disorders: Hereditary Disorders  Mutations (genetic variations) can be adaptive or maladaptive  Dominant disorder o Huntington’s chorea:  a fatal syndrome in which the nervous system degenerates in adulthood (age 30-40)  dominant lethal gene  degeneration of brain areas  dementia, physical impairments (choreic movements)  onset past sexual maturity  Recessive disorder o Diseases with errors of metabolism  Tay-Sachs disease:  a fetal disease in which the nervous system disintegrates because the body cannot break down fats in brain cells  Phenylketonuria (PKU):  an inherited disease in which the body cannot process the amino acid phenylalanine  amino acid in high-protein foods  homozygous gene for synthesizing a faulty enzyme  causes severe brain damage  routinely screened for at birth  treatment involves restrictive diet: Eat a diet low in this amino acid during critical periods of brain development o Diseases without errors of metabolism  Sickle-cell anemia (SCA) Figure 3.5 Scanning electron micrographs of red blood cells from normal individuals (left) and individuals with sickle-cell anemia (right). 8 PSY 2105 F Chapter 3 Structural Defects in the Chromosome  Autosomal disorders o Down syndrome st  21 pair of chromosomes has a third member  Results in mental retardation, poor muscle tone, and distinctive facial features  Greatest risk occurs in mothers between the ages of 45-49 years  From NADS  It occurs in approximately one in every 700-800 live births  It is the most frequently occurring chromosomal disorder  Down syndrome is not related to race, nationality, religion or socioeconomic status  There are 3 chromosomal patterns that result in Down syndrome 1. Trisomy 21 o Caused by having faulty cell division that results in the baby having three’s #21 chromosomes in either the egg or the sperm fails to separate properly o The extra chromosome is replicated in every cell of the body.95% of all people with Down Syndrome have trisomy 21 2. Translocation accounts for only 3% to 4% of all cases o In translocation a part of chromosome #21 breaks off during cell division and attaches to another chro
More Less

Related notes for PSY2105

Log In


Don't have an account?

Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.