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PSYC 2110
Gillian Wu

CH 3: HEREDITARY INFULENCE ON DEVELOPMENT  Genotype: genes that you inherit; phenotype: expression of genes into a measurable characteristic PRINCIPALS OF HEREDITARY TRANSMISSION  Zygote: a protective nucleus that surrounds a ovum and sperm in order to protect the egg from being fertilized by more than one sperm (1/20 a size of a head of a pin)  Zygote contains the 46 chromosomes – which consist of genes (used to build proteins)  DNA: can replicate itself, but undoing the coil and the remaining half will guide the replication method (how a zygote becomes a human)  Zygote moves from the fallopian tube to the uterus while going through mitosis (all cells contain an exact copy of our 46 chromosomes)  Germ cell = sex cells (used to produce gametes – sperm/ova)  Steps of meiosis: o Germ cells duplicate themselves (46 chromosomes) o Crossing over happens – exchange segments of genetic materials o Cells become 2 new cells (which have 46 chromosomes each) o These cells then divide to make 4 germ cells (with 23 unpaired chromosomes)  Independent assortment: principal that states each chromosomal pair will segregate independently to all other pairs during meiosis (provides uniqueness) – each parent can produce 2^23 combinations from their sperm/ova  Monozygotic twins: happens when a zygote splits into 2 separate, but identical cells  Dizygotic twins: mother releases 2 ova at the same time and these are fertilized by 2 different sperms  Incidence of multiple births (have 3+ kids at the same time) has increased greatly; due to assisted reproductive technologies (read more about this in slides)  Karyotypes: used to show a portrait of a persons 46 chromosomes  Genes promote development by producing a.acids (necessary for the function of new cells) o Cells also guide differentiation to cells o Genes are also used for regulating development (being turned on and off by regulatory genes) i.e. having a growth spurt  Environmental influence can be used to determine if a genotype is going to become a phenotype o Gene-environment interactions: experience-expectant interactions: effects of the external environment that are experienced by all humans; experience-dependent interactions: effects of the external environment experienced by only some people Fragile X syndrome: a defective X gene passed from mother to child and can lead to the child being mild-severely mentally retarded Turners: XO; Klinefelters: XXY or XXXY; supermale: XYY, XYYY, etc HOW ARE GENES EXPRESSED?  Simple dominant-recessive inheritance, codominance, sex-linked inheritance, polygenic inheritance  Alleles: one pair of genes – one from the mother and one from the father  Simple-dominant recessive inheritance: when one allele will dominate another to and be expressed as a phenotype  Homozygous: when both alleles are the same type (either dominant or recessive)  Heterozygous: when a person inherits a dominant and recessive allele  Carrier: inheriting a recessive allele but not displaying it as a phenotype – but they can pass this on to their offspring  Codominance: phenotype produced is a compromise between the two genes i.e. being a blood type of AB means that you equally express those types (no domination) o Another example is when one heterozygous allele is stronger than another but fails to mask the others effects (sickle cell) – there is an incomplete dominance: the sickle cell is a recessive allele, but when one is present in the blood it leads other to taking its shape o Sickle cell anemia: happens when a person has two recessive genes for sickle cell  Sex-linked inheritance: traits that are determined by the sex genes – vast majority of sex-linked attributes of recessive genes are found only on X chromosomes (so there more common in men since men only need one X chromosome from there mothers; so if they carry the recessive X, they will have the disorder) i.e. colour blindness – females need to get 2 recessive genes of colour blindness where men only need 1  Polygenic inheritance: human characteristics that are influenced by many alleles – height, weight, susceptibility to cancers o These characteristics are not either/or possibilities (colour blind or not), instead they are on a continuum – most ppl being in the middle and some being at the extremes (bell curve) – to date we don’t know how MANY genes exactly influences these characteristics, all we know is that it gives many variations to humans HEREDITARY DISORDERS  Congenital defects: problems present at birth, but not detectable when a child is born i.e. the gene for Huntington’s o Include disorders caused by chromosomal abnormalities, genetic abnormalities and environment  Chromosomal abnormalities: happen when there are additional or fewer than normal chromosomes o Sex chromosomes: females having only one X chromosome (XO) or males getting an extra X or Y chromosome (XXY or XYY) o Autosomal Abnormalities: common are trisomy’s: when there are 3 genes of one chromosome (down syndrome)  Genetic abnormalities: most genetic problems are based on recessive traits (so both parent needs to have an provide to their offspring; not true for sex linked since males will always get it if a female gives a recessive gene for a problem) o Dominant gene abnormalities: child will develop the disorder by getting the dominant gene from any parent (the parent would also show the defect, i.e. Huntington’s) o Mutations: changes in the chem structure of a gene that produces a new phenotype (are spontaneous) Predicting Hereditary Disorders  Genetic counseling: parents can assess the likelihood that their children will be free of hereditary defects – for chromosomal and genetic abnormalities o Use a pedigree (complete family history of each parent) to identify any relatives that may have a hereditary disorder; they are the ONLY basis to determine if a child can be affected o DNA analysis can also determine if parents carry genes for disorders Detecting Hereditary Disorders  Amniocentesis: prenatal screening for pregnant women where the amniotic fluid is extracted so the fetal body cells can be tested for abnormalities (normally done on women over 35) – can detect more than 100 disorders o The risk of miscarriage > the risk of birth defects for women under 35 o Problem is the procedure can only be done and11-14 weeks, so parents have little time to decide if they want a 2 trimester abortion  Chorionic villus sampling (CVS): alternate procedure for the 1 , where tissue is collected for the amniotic fluid – can be performed at 8-9 weeks; greater chance of miscarriage or limb deformiti
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