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Chapter 3

PSYC 251 Chapter Notes - Chapter 3: Gregor Mendel, Heredity, Phenotype

Course Code
PSYC 251
Stanka A Fitneva

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Biology and Behaviour
Nature vs. nurture
- These two factors – heredity and environment – work in concert to influence both the
ways in which you are like other people and the ways in which you are unique
- Our modern understanding of how characteristics are transmitted from parent to
offspring originated with insights achieved by Gregor Mendel (19th century Austrian
monk) who observed distinct patterns of inheritance in the pea plants he crossbred in
his monastery garden
- Current estimates of the number of human genes, 21,000, much fewer that previously
- To our surprise, most of these genes are possessed by all living things (we share them
with bears, bees, bacteria…)
- Development results from the close and continual interplay of nature and nurture – of
genes and experience – and this interplay is the focus of the following section
Genetic and Environmental Forces
- Three elements
1. Genotype: the genetic material an individual inherits
2. Phenotype: the observable expression of the genotype, including both body
characteristics and behaviour
3. Environment: every aspect of the individual and his or her surroundings
(including prenatal experience) other than the genes themselves
- Five relations that are fundamental in the development of every child:
1. The parents’ genetic contribution to the child’s genotype
2. The contribution of the child’s genotype to his or her own phenotype
3. The contribution of the child’s environment to his or her phenotype
4. The influence of the child’s phenotype on his or her environment
5. The influence of the child’s environment on his or her genotype
- See figure 3.1 on page 89
1. Parent’s Genotype – Child’s Genotype
- The transmission of genetic material – chromosomes and genes – from parent to
- Non-coding DNA (junk DNA) is vital to functioning – play supporting role in
influencing genetic transmission by regulating the activity of protein-coding genes
- Every individual has two copies of each gene, one on each chromosome inherited
from the father and one on the chromosome from the mother
- Your biological children will receive half of your genes, and your grandchildren will
have one-quarter
- Sex chromosomes: it is always the father (with the Y chromosome) that determines
the gender of the child
- Diversity and individuality: mutation (more variability, more likely to survive);
random assortment of chromosomes in the formation of egg and sperm, where 23
pairs of chromosomes are shuffled randomly; “crossing over”, where some of the
chromosomes that parents pass on to their offspring are constituted differently from
their own
2. Child’s Genotype – Child’s Phenotype
- Although every cell in your body contains copies of all the genes you received from
your parents, only some of those genes are expressed
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