7121 Lecture Notes - Lecture 2: Quantitative Trait Locus, Sibling Rivalry, Zygosity
21 Jun 2018
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DP LECTURE 2
Heredity’s Blueprint
- Each sperm and ovum contain 23 chromosomes, the genetic material passed form generation to
generation
- At conception, the chromosomes form matching pairs to creat a single celled zygote
- Chromosomes are made up of a chemical substance called DNA
oLong double stranded helix
oPairs = bases
oSequence of bases that provide genetic instructions
oAT, CG
- Genes code the relevant inherited information
- A gene is a segment of DNA along the length of the chromosome
- Can duplicate itslf with mitosis
Genetic foundations
- Genotype – each persons unique collection of 46 chromosomes
- Phenotype – observable expressions of characteristics
Mendeliam inheritance and chromosomes
- Dominance-recessivity of gene pair: one gene in the pair dominates, therefore the phenotype
reflects only the dominant gene
- Homozygosity: two recessive genes (blond or red hair)
- Heterozygosity: one dominate and one recessive gene (brown hair resulting from one brown
haired gene and one blond or red haired gene)
Polygenic inheritance
- Most human traits are influenced by many gene pairs (polygenic), not by one gene pair
(mendelian)
Epigenetics
- Chemical changes in gene expression that do not affect the genetic codde
oNutrition of mother
- Genes can be turned on or off, or enhance or dampen down the magnitude of their influence on
the phenotype
- Helps explain differences in identical twins
- Environmentally induced biochemical gene changes illustrate nature-nurture interplay and offer
promise of future insights into lifespan development
- Behavior genetics – explores joint contribution of nature and nurture in the development of
psychological characteristics
- Some epigenetic changes can be modified
Twinning
- Monozygotic; identical
oOccur in approx. 1/250 pregnancies
oProduced from a single zygote
oSame genotype
oAlways same gender
- Dizygotic; fraternal
find more resources at oneclass.com
find more resources at oneclass.com
o1/70 pregnancies
oGenetic similarities
oDon’t have identical genotypes
oCan be different genders
Twin studies
- Monozygotic twin differences are attributed to nurture, dizygotic twins differ by nature AND
nurture
- Twin pairs, bot MZ and DZ assumed to have same shared environment
- Scientific validity of twin comparisons rests on this assumption
- Physical similarity of MZ may produce more similar environments (parents expectations)
- Genuinely similar twins were treated more similarly than non similar twins, even when parents
were misinformed about zygosity
- Family environments with atleast one twin pair have unique features (hay and O’brien, 1983)
oMultiple birth households encounter more stress
oLags in mental growth of twins in first four years
oSibling rivalry is greatest among same sex DZ
oParadoxes in twins’ performance on specific tasks
Score lower on some tasks
Shared and non shared environment
- Non shared
oDistinctive situations and experiences not shared by other siblings, even twins
- MZ may be motivated to emphasise differences (sibling contrast effect; farber, 1981)
- Lifespan approach allows new findings from twin research (parents from twin pairs are as
closely related to nieces and nephews [born to their co twin] as to their own children – children
of twins design)
Nature and nurture
- Children actively seek out particular environments that best suit their genetic predispositions;
gene-environment correlation
- Even very young infants are capable of shaping and modifying their social and physical
environments
- Non shared experiences probably influence development more than shared influences (plomin,
2008)
- Environments can be heritable as the reflect genetic dispositions – either/both child and parents
- Genetic dispositions set upper and lower limits on possible range influences
Prenatal Development
- Conception to birth – approx. 40wks
- 3 phases
oZygote
Short phase in the pregnancy (about 3 weeks)
Multiples and forms a blastocyst (hollow, fluid filled ball)
Blastocyte burrows into the uterine lining
Other nurturing structures begin to form (yolk sac, placenta, umbilical
cord)
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Each sperm and ovum contain 23 chromosomes, the genetic material passed form generation to generation. At conception, the chromosomes form matching pairs to creat a single celled zygote. Chromosomes are made up of a chemical substance called dna: long double stranded helix, pairs = bases, sequence of bases that provide genetic instructions, at, cg. A gene is a segment of dna along the length of the chromosome. Genotype each persons unique collection of 46 chromosomes. Dominance-recessivity of gene pair: one gene in the pair dominates, therefore the phenotype reflects only the dominant gene. Homozygosity: two recessive genes (blond or red hair) Heterozygosity: one dominate and one recessive gene (brown hair resulting from one brown haired gene and one blond or red haired gene) Most human traits are influenced by many gene pairs (polygenic), not by one gene pair (mendelian) Chemical changes in gene expression that do not affect the genetic codde: nutrition of mother.
