4PAHPDEV Psychology and Development Week 2
BSc Psychology Year 1 The Biology of Development
THE BIOLOGY OF DEVELOPMENT
RECOGNISE THAT DEVELOPMENT IS INFLUENCED BY GENES, THE
ENVIRONMENT, AND THEIR INTERPLAY OVER TIME
GENETICS
Chromosomes
• Located inside the nucleus, chromosomes are structures that contain out genetic
information and determines our inherited traits
• There are typically 46 chromosomes (with approximately 20,000 genes) in most cells with the
exceptions being egg and sperm cells which contain 23 chromosomes
DNA
• Chromosomes contain one long, thin molecule of deoxyribonucleic acid (DNA)
• DNA is made up of nucleotides that are held together by two twisted parallel strands, each
containing one of four nitrogen bases: adenine, cytosine, guanine, or thymine
o Only bases that are compatible will bond together: adenine and thymine, and
cytosine and guanine
Genes and Proteins
• Genes are distinct segments of DNA found on chromosomes that encode for specific
proteins depending on the sequence of the nitrogen bases
o Each protein performs a different function, like determining physical traits, triggering
chemical reactions, regulating gene expression, and carrying chemical messages
• Genes trigger the production of proteins only when a particular change in the environment
signals them to activate
o The gene splits, causing the base pairs to separate, allowing free nucleotides to bind
to exposed bases and create a copy of the gene called messenger RNA (mRNA)
o The mRNA leaves the nucleus and acts as a template in the cell for building proteins
1
,4PAHPDEV Psychology and Development Week 2
BSc Psychology Year 1 The Biology of Development
CELL DIVISION AND REPRODUCTION
Sexual Reproduction
• Sexual reproduction involves the fusion of haploid gametes (the sperm and egg, with only
one set of chromosomes), combining their genetic material to form diploid cells with two
sets of chromosomes
o Chromosomes from the sperm and egg are homologous (similar in shape and
function), allowing them to pair during fertilisation
Meiosis
• Meiosis occurs in reproductive organs to produce gametes
a) All the 46 chromosomes from a parent’s cell are duplicated
b) Crossing over between chromosomes facilitates diversity
of genetic inheritance between reproductive cells
o Crossing over leads to genetic variation as
homologous chromosomes exchange equivalent
sections, altering which gene variants are inherited
c) The chromosome pairs separate to form two cells
o Segregation also causes variation since this separation into two cells means that the
offspring only receives one of each pair of chromosomes
d) The chromosomes separate again to form reproductive cells
with 23 chromosomes
o Independent assortment creates genetic variability
through the random assignment of chromosomes
from the parent’s father and mother to form the
gametes
e) When the sperm cell fertilises an ovum, a zygote is formed with 23 pairs of chromosomes (46
chromosomes in total)
Mitosis
• The process in which a cell duplicates its chromosomes and then divides into daughter cells
that have the same number of chromosomes as the parent cell
o The cells grow exponentially since each cell divides to produce new ones with a full
46 chromosomes
• This occurs following the fusion of the egg and sperm in sexual reproduction
2
,4PAHPDEV Psychology and Development Week 2
BSc Psychology Year 1 The Biology of Development
a) A zygote occurs with 46 chromosomes
b) Each chromosome splits in half (lengthwise) to produce a duplicate of itself
c) The duplicates move away from each other as the cell begins to divide
d) The cell has divided in two with the same set of chromosomes as the other and as the original
parent cell
INHERITANCE
The Transmission of Traits
• On a pair of homologous chromosomes, each chromosome carries an allele at the same
gene position
o These are alternate forms of the same gene, with one inherited from the mother and
the other from the father
• If they are the same from both parents, they are homozygous for that particular gene or trait
associated with it
• If they are different for that particular trait, they ae heterozygous
o This combination can either produce an outcome that is an intermediate between the
two traits (e.g. mixed race) or the more powerful, dominant allele may be expressed
over the weaker, recessive allele (e.g. brown eyes)
Sex Chromosomes
• 22 pairs of the chromosomes are autosomes, while the 23rd pair are sex chromosomes
o The 23rd pair determines the individual’s sex – a female has XX chromosomes, and a
male has one X from his mother and a smaller Y from his father
• The larger X chromosome has no counterparts on the Y chromosome, allowing recessive
genes linked to the X chromosome (X-linked genes) to be expressed without being masked
o This makes many developmental disorders more prevalent in males than females
such as autism spectrum disorder (ASD)
Genetic Complexity of traits
• Polygenicity describes the involvement of many genes with one trait which is common with
many characteristics such as intelligence, creativity and sociability (Plomin & Deary, 2015)
• The candidate gene approach attempts to identify links between specific alleles and traits
to provide insights into their heritability
o However, this is challenging due to the vast combinations of genes and
environmental factors involved in gene expression
o This can explain why some traits influenced by genes do not run in families as some
traits rely on a certain configuration of many genes
• Genes are also often pleiotropic where they code for many traits rather than just one
3
, 4PAHPDEV Psychology and Development Week 2
BSc Psychology Year 1 The Biology of Development
GENETIC DISORDERS
• People can inherit harmful alleles of certain genes, which can interfere with normal physical
and psychological development
Treatment and
Disorder Nature Incidence Cause Diagnosis
Prevention
Physically and Heredity; Amniocentesis, Special physical
mentally retarded extra full or alphafetoprotein training;special
development; partial assay, chorionic education, speech
Down
sometimes, 1/999 chromosome villi sampling, therapy; surgical
Syndrome
cardiovascular and 21 chromosome correction of
respiratory analysis problems with the
abnormalities heart and hearing
Underdeveloped Chromosomal Blood tests Hormone therapy to
secondary sex abnormality; promote secondary
characteristics; only 1 X sex characteristics;
infertility; short 1/1200- chromosome counselling; special
Turner
stature; social 1400 instead of two education to lessen
Syndrome
immaturity; webbed females deficits
neck; cardiovascular
and renal
abnormalities
Social and Heredity; Behavioural Special education
1/2000-
communicative polygenic tests and behavioural
4000 males
Autism impairments; interventions
1/5000
restricted behavioural
females
repertoires
EPIGENETICS
• Epigenetics is the study of how genes come to be expressed (Armstrong, 2013)
• Genotype is the specific genetic makeup of an individual and phenotype is an individual’s
observable characteristics
o Genotype is present from conception, but its expression into phenotype can be
affected by other parts of genetic inheritance and the environment, such as where
the given cell is in the body and what other genes and DNA are present
phenotype = genotype + environment
• An environmental or genetic trigger can lead to a cascade of subsequent genetic and
environmental changes
4
BSc Psychology Year 1 The Biology of Development
THE BIOLOGY OF DEVELOPMENT
RECOGNISE THAT DEVELOPMENT IS INFLUENCED BY GENES, THE
ENVIRONMENT, AND THEIR INTERPLAY OVER TIME
GENETICS
Chromosomes
• Located inside the nucleus, chromosomes are structures that contain out genetic
information and determines our inherited traits
• There are typically 46 chromosomes (with approximately 20,000 genes) in most cells with the
exceptions being egg and sperm cells which contain 23 chromosomes
DNA
• Chromosomes contain one long, thin molecule of deoxyribonucleic acid (DNA)
• DNA is made up of nucleotides that are held together by two twisted parallel strands, each
containing one of four nitrogen bases: adenine, cytosine, guanine, or thymine
o Only bases that are compatible will bond together: adenine and thymine, and
cytosine and guanine
Genes and Proteins
• Genes are distinct segments of DNA found on chromosomes that encode for specific
proteins depending on the sequence of the nitrogen bases
o Each protein performs a different function, like determining physical traits, triggering
chemical reactions, regulating gene expression, and carrying chemical messages
• Genes trigger the production of proteins only when a particular change in the environment
signals them to activate
o The gene splits, causing the base pairs to separate, allowing free nucleotides to bind
to exposed bases and create a copy of the gene called messenger RNA (mRNA)
o The mRNA leaves the nucleus and acts as a template in the cell for building proteins
1
,4PAHPDEV Psychology and Development Week 2
BSc Psychology Year 1 The Biology of Development
CELL DIVISION AND REPRODUCTION
Sexual Reproduction
• Sexual reproduction involves the fusion of haploid gametes (the sperm and egg, with only
one set of chromosomes), combining their genetic material to form diploid cells with two
sets of chromosomes
o Chromosomes from the sperm and egg are homologous (similar in shape and
function), allowing them to pair during fertilisation
Meiosis
• Meiosis occurs in reproductive organs to produce gametes
a) All the 46 chromosomes from a parent’s cell are duplicated
b) Crossing over between chromosomes facilitates diversity
of genetic inheritance between reproductive cells
o Crossing over leads to genetic variation as
homologous chromosomes exchange equivalent
sections, altering which gene variants are inherited
c) The chromosome pairs separate to form two cells
o Segregation also causes variation since this separation into two cells means that the
offspring only receives one of each pair of chromosomes
d) The chromosomes separate again to form reproductive cells
with 23 chromosomes
o Independent assortment creates genetic variability
through the random assignment of chromosomes
from the parent’s father and mother to form the
gametes
e) When the sperm cell fertilises an ovum, a zygote is formed with 23 pairs of chromosomes (46
chromosomes in total)
Mitosis
• The process in which a cell duplicates its chromosomes and then divides into daughter cells
that have the same number of chromosomes as the parent cell
o The cells grow exponentially since each cell divides to produce new ones with a full
46 chromosomes
• This occurs following the fusion of the egg and sperm in sexual reproduction
2
,4PAHPDEV Psychology and Development Week 2
BSc Psychology Year 1 The Biology of Development
a) A zygote occurs with 46 chromosomes
b) Each chromosome splits in half (lengthwise) to produce a duplicate of itself
c) The duplicates move away from each other as the cell begins to divide
d) The cell has divided in two with the same set of chromosomes as the other and as the original
parent cell
INHERITANCE
The Transmission of Traits
• On a pair of homologous chromosomes, each chromosome carries an allele at the same
gene position
o These are alternate forms of the same gene, with one inherited from the mother and
the other from the father
• If they are the same from both parents, they are homozygous for that particular gene or trait
associated with it
• If they are different for that particular trait, they ae heterozygous
o This combination can either produce an outcome that is an intermediate between the
two traits (e.g. mixed race) or the more powerful, dominant allele may be expressed
over the weaker, recessive allele (e.g. brown eyes)
Sex Chromosomes
• 22 pairs of the chromosomes are autosomes, while the 23rd pair are sex chromosomes
o The 23rd pair determines the individual’s sex – a female has XX chromosomes, and a
male has one X from his mother and a smaller Y from his father
• The larger X chromosome has no counterparts on the Y chromosome, allowing recessive
genes linked to the X chromosome (X-linked genes) to be expressed without being masked
o This makes many developmental disorders more prevalent in males than females
such as autism spectrum disorder (ASD)
Genetic Complexity of traits
• Polygenicity describes the involvement of many genes with one trait which is common with
many characteristics such as intelligence, creativity and sociability (Plomin & Deary, 2015)
• The candidate gene approach attempts to identify links between specific alleles and traits
to provide insights into their heritability
o However, this is challenging due to the vast combinations of genes and
environmental factors involved in gene expression
o This can explain why some traits influenced by genes do not run in families as some
traits rely on a certain configuration of many genes
• Genes are also often pleiotropic where they code for many traits rather than just one
3
, 4PAHPDEV Psychology and Development Week 2
BSc Psychology Year 1 The Biology of Development
GENETIC DISORDERS
• People can inherit harmful alleles of certain genes, which can interfere with normal physical
and psychological development
Treatment and
Disorder Nature Incidence Cause Diagnosis
Prevention
Physically and Heredity; Amniocentesis, Special physical
mentally retarded extra full or alphafetoprotein training;special
development; partial assay, chorionic education, speech
Down
sometimes, 1/999 chromosome villi sampling, therapy; surgical
Syndrome
cardiovascular and 21 chromosome correction of
respiratory analysis problems with the
abnormalities heart and hearing
Underdeveloped Chromosomal Blood tests Hormone therapy to
secondary sex abnormality; promote secondary
characteristics; only 1 X sex characteristics;
infertility; short 1/1200- chromosome counselling; special
Turner
stature; social 1400 instead of two education to lessen
Syndrome
immaturity; webbed females deficits
neck; cardiovascular
and renal
abnormalities
Social and Heredity; Behavioural Special education
1/2000-
communicative polygenic tests and behavioural
4000 males
Autism impairments; interventions
1/5000
restricted behavioural
females
repertoires
EPIGENETICS
• Epigenetics is the study of how genes come to be expressed (Armstrong, 2013)
• Genotype is the specific genetic makeup of an individual and phenotype is an individual’s
observable characteristics
o Genotype is present from conception, but its expression into phenotype can be
affected by other parts of genetic inheritance and the environment, such as where
the given cell is in the body and what other genes and DNA are present
phenotype = genotype + environment
• An environmental or genetic trigger can lead to a cascade of subsequent genetic and
environmental changes
4
