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Chapter 3

PSYA01H3 Chapter Notes - Chapter 3: Genetic Marker, Meiosis, Twin

Course Code
Steve Joordens

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Heredity and Genetics
Genetics: study of genetic make up of organisms and how it influences their physical behavioural characteristics
study of structure 7 functions of genes, how they are transmitted from one generation to another, & how they operate in
Heredity: sum of traits and tendencies inherited from a persons parents and other biological ancestors
Gregor Mendel
experimental crossbreeding with pea plants, uncovered principles of heredity
concluded how height, colour, seed shape, and other traits could be transmitted from one generation to the next
Heredity determined by DNA
genes are small units of DNA that direct the synthesis of proteins & enzymes according to the particular sequences of
nucleotide bases they contain
junk” DNA—not involved in direct synthesis of proteins and known as non-coding DNA. Thus, non coding sequences
of DNA may plya a ritical role to regulate the processes of other genes that synthesize proteins by genes. Non coding DNA
can affect evolution.
Genome: total set of genetic material of an organism
24 diff DNA molecules in women
25 diff DNA molecules in men
30 000- 40 000 genes w/in human genome
human genome is only twice number in a common housefly
Genes influence physical & behaviour development in only one way: protein synthesis
the order if amino acids in proteins are specified by the nucleotide A, T,G, and C linked together on DNA molecule
sequence of 3 nucleotides corresponds to particular amino acid
**There are no genes for behaviour, only for physical structures and physiological processes that are related to behaviour*
Enzymes: govern processes that occur within every cell in body & thus control each cells structure and function

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Chromosomes: threadlike structures in the nuclei of living cells; contain genes.
each set of chromosomes contain a diff DNA molecule and hence, a diff sequence of genes
we inherit 23 individual chromosomes from each of our parents, giving us 23 pairs—46 individual chromosomes—in
most cells of the body
Sperm & ova differ from bodily cells in 2 important ways:
contain only one member of each chromosome pair
some of the genetic info on one member of a pair has been exchanged w/ the info on the other member
Meiosis: form of cell division by which new sperm and ova are formed. The chromosomes w/in the cell are randomly
rearranged so that new sperm and ova contain 23 individual chromosomes
23 pairs of chromosomes break apart into 2 groups, with one member of each pair joining one of the groups
cells split into 2 cells, each of which contains 23 individual chromosomes
assignment of chromosomes to groups= random process; thus, a single individual can produce 223 diff ova or sperm
Sex is determined by the 23rd pair of chromosomes: the sex chromosomes
women (XX)
men (XY)
men contain both X and Y chromosome, half of the sperm they produce contain an X chromosome and half contain a Y
Y-bearing sperm=boy X-bearing sperm= girl
Alleles: alternative forms of same gene
each parent contribute same allele for eye colour to their child=homozygous
if parent contribute diff alleles=heterozygous
Sexual reproduction increases a species ability to adapt to environmental changes
Sokolowski, Pereira, and Hughes (1997)
fruit fly larvae experiment
rover travel long

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sitter travel short
raising many generatrions of fruit flies under crowded conditions incr the frequency of rover
conversely, low densitiy environments selected for sitter
rover phenotypes were better adapted to high density conditions bc their behaviours were more likely to lead to food
patch that was not crowded with other larvae
when environments were not crowded, however, sitter larvae exploted patches more efficiently
hemophilia(sex-linked gene): incr tendency to bleed from minor injuries
recessive trait caused by a gene on X chromosome that fails to produce a protein necessary for normal blood clotting
females have 2 X chromosomes, they can carry an allele for haemophilia but still have normal blood clotting if other
allele is normal
males have only a single X chromosomes, if gene for blood clotting carried on this chromosome is faulty, they develop
Sex influenced genes: sex-related genes that express themselves in both sexes, although the phenotype appears more
frequently in one sex than other
baldness: develops in men if they inherit either or both alleles for baldness, but is not seen in women, even when they
inherit both alleles
expression of pattern baldness is influences by sex hormones, which are diff for men and women
Chromosomal aberration: rearrangement of genes w/in chromosomes or a change in total number of chromosomes
deletion of chromosome 5 causes cri-du-chat syndrome—have G.I and cardiac problems, severe problems in mental
function, and make crying sounds like a cats mewing
directly related to amt of genetic material that is missing
early special education training permits learn self care and communication skills
Down syndrome: chromosomal aberration resulting in an extra 21st chromosome.
impairments in physical, psychomotor, and cognitive development
named after John Langdon Down who provided first medical description of this condition
children have heart and resp complications
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