 | Term | Definition |
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genotype |
genetic makeup of an individual |
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phenotype |
body characteristics, behavioral tendencies, mental functions, etc. |
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GENOTYPE + ENVIRONMENT = |
PHENOTYPE |
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conception |
occurs when 2 gametes (sperm & egg) combine, each gamete contains 23 chromosomes |
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meiosis |
making new gametes; chromosomes each duplicate and pair with each other; crossing over between inner pair members; chromosome pairs split to form 2 cells, chance determines which chromosomes from a pair end up together; each cell splits to form gametes, each w/ 23 single chromosomes. |
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3 sources of variability in genetic material |
crossing over, random sorting, mutations |
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crossing over |
creates new genes sequences in gametes |
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random sorting |
random sorting of each member of chromosome pair into separate gametes |
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mutations |
mutations during gene copying (e.g. insertions, deletions): almost always deleterious, sometimes fatal; very rarely produce advantageous ability. |
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Making new zygotes |
23 single chromosomes in egg combine with 23 in sperm; resulting zygote has 46 total chromosomes, arranged in pairs; first 22 chromosomes are the autosomes, the last two are the sex chromosomes. |
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karyotype |
picture of the 23 chromosome pairs (autosomes and sex chromosomes); example in book of human male |
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genes |
each chromosome contain thousands of genes |
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alleles |
many genes have multiple forms of alleles |
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homozygous |
alleles from both parents alike = homozygous, will display trait. If mom and dad are both BB, then all 4 are homozygous for brown hair (all 4 kids are BB). If mom and dad are both Bb, then 75% of the kids have brown hair (2 are heterozygous for brown hair, 2 of them are homozygous for brown hair with one being BB and one being bb so he is blonde). |
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Dominant |
curly hair, dimples, non-red hair, normal skin pigmentation, farsightedness |
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Recessive |
straight hair, no dimples, red hair, albinism, normal vision |
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dominant-recessive abnormalities (autosomal) |
PKU (Phenylketonuria) (pp individuals) (only way to get PKU is to have both parents being carriers and to end up with both recessive alleles), Tay-Sachs disease (tt individuals) |
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X-linked abnormalities |
red-green color blindness, hemophilia, duchenne muscular dystrophy; Harmful allele on X-chromosome (not on any of the autosomes, instead on the sex chromosome), much less likely to be suppressed because Y-chromosome is so short. Much more frequently observed in males than in females. |
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Chromosomal abnormalities |
Major malformation of entire chromosome (e.g. breakage, duplication, failure to separate properly). Ex: Down Syndrome caused by extra 21st chromosome (Trisomy 21). |
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Down Syndrone |
Phenotype + Environment play a big role in Down Syndrome. Difficulties in parenting Downs kids sometimes heightened by: trouble breastfeeding due to shape of face and palette (messes with child/mother bond), poor eye contact, less readily engaging with objects & environments. BUT, intervention programs and informed parenting shows benefits! |
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Sex chromosome abnormalities |
XYY (Jacob's) Syndrome, XXX (Triple X) Syndrome, XXY (Kleinfelter xyndrome), XO (Turner's) Syndrome |
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XYY (Jacob's) Syndrome |
(1/1000 males): Unusually tall & thin, large teeth, sometimes experience severe acne, slightly lower IQ (10-15 points) (a mild form of retardation) |
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XXX (Triple X) Syndrome |
(1/700 females): Sometimes has no observable signs. Can involve small stature, small head, impaired verbal abilities, delayed puberty, infertility. (wouldn't call it severe retardation). Particularly noticed around age 12-13 because they don't seem to hit puberty at all and they are infertile. |
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XXY (Kleinfelter syndrome) |
(1/700 males): Impaired verbal IQ, tall, female-like bodies, incomplete sex characteristics, often sterile. Treated with hormone therapy. |
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XO (Turner's) Syndrome |
(1/3000 females): short stature, webbed neck, impaired spatial abilities, lack of sexual development at puberty, ovaries not fully developed. Treated with hormone therapy |
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Ultrasound |
High frequency sound waves beamed at uterus; reflection translates into picture that shows size, shape, position of fetus. Can detect: approx. gestational age, multiple pregnancies, gross physical defects (like clubbed foot) |
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Amniocentesis |
: Hollow needle through abdominal wall, obtains sample of amniotic fluid. Cells examined for genetic defects. Small risk of miscarriage (needle could puncture baby and cause death, or . Performed in 2nd trimester. Can detect: Chromosomal abnormalities. |
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Chorionic Villus Sampling |
Extraction of small bit of tissue from chorionic villi on membrane surrounding fetus. Cells examined. Can be used as early as 6-8 weeks, quick results. Some risk. Can detect: Chromosomal abnormalities |
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Preimplantation genetic diagnosis |
Very earlier detection. After in vitro fertilization, remove and examine 1 cell from 8-cell zygote (very very early on). Can detect: Chromosomal abnormalities. |
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Polygenic Traits |
caused by many genes (e.g. intelligence, temperament) |
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Multifactorial Traits |
influenced by by environmental & genetic factors (e.g., schizophrenia) |
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Behavioral Genetics |
Study of how much variation results from the combination of genes and environment. EX: Twin studies & Adoption studies (naturally occurring experiments) |
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Twin studies |
compare concordance of traits across monozygotic and dizygotic twins. Monozygotic: have exactly the same genetic blueprint, but could have different environmental experiences. |
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Adoption studies |
compare concordance of traits across individuals and their adopted vs. biological parents. EX: Danish schizophrenia study: studied 47 adopted SZ patients |
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heritability |
estimate of how much variance in a given trait within a population is attributable to genetic differences between individual s in that population; twin and adoption studies can give us estimates of heritability. |
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Warnings about heritability measurements |
apply to populations, not to individuals; specific to unique circumstances of that populations; high heritability does not imply immutability; do not extend to differences between groups (differences between whites and blacks is hugely environmental, our genes are so similar). |
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