Heredity and the Environment
Genotype: The particular sets of genes that a person inherit from her parents. (No one
has same ones except identical twins)
Phenotype: Environment + Genotype, observable and measureable expression of an
individual’s physical and behavioral characteristics. Psychologist study them.
The process of Genetic Transmission
• In a moist environment of a women’s oviduct, the ovum (female germ cell) and
the sperm (male germ cell) unite to create a zygote.
• Ovum is the largest human cell (90 thousand times heavier than sperm), where
sperm is the smallest of all human cell.
Chromosome and Genes
• Chromosomes: Thread like structure, located in nucleus of a cell that carry
genetic information to help direct development.
• We have 23 pairs or 46 chromosomes. Chromosomes from dad are able to
pair up with mom’s because they are homologous (similar to shape in
• Every cell in your body will have the copies of the original 23 chromosome
pair, expect for one: reproductive cells, because they go through meiosis.
• Meiosis: The process by which a germ cell divides to produce a new germ
cells with only half the normal complement of chromosome; So when male
and female germ cell unite they’ll create a zygote with 46 chromosome. See
Fig 2-1 (p 45)
• Variation is provided: When during meiosis when male/female set of
chromosome is halved to produce germ cell and it goes on to mix with the
other germ cell. The mixing process is random and the random assortment of
homologous chromosome makes possible for 8 million different chromosome
combinations. Also Crossing over: (The process by which equivalent
sections of homologous chromosome switch places randomly, shuffling the
genetic information it carries).
1 • Mitosis: The process in which a body cell divides in two, first it duplicates its
own chromosomes and divides in 2 so the two (daughter) cells both have 46
• Autosomes: Humans have 23 pair of chromosome, only 1 pair is the sex
chromosome (determines gender) and the rest of 22 pairs are autosomes.
Genes, DNA & Proteins
• DNA: Deoxyribonucleic Acid, ladder like molecules that stores genetic
information in cells and transmits it during reproduction.
• Nucleotide: A compound with 1 Nitrogen base (A,TC,G) + 1 simple sugar
+ 1 Phosphate group. The nitrogen containing bases (“risers”) with bond
with compatible base of the opposite side.
• Genes are located at particular site of chromosome and they code for
proteins (made of amino acids).
Genetic influence of Development
The transmission of trait
• Mendel, an Austrian monk studies pea plans by cross breeding them for
generations and cataloging the result of these hybridization (found some traits
disappear but tend to reappear after generations). He worked on two principles:
• Principle of segregations: Each inherited trait comes from one’s parent as a
separate unit (eg: flower color, stem height).
• Principle of Independent assortment: The inheritance of various traits occurs
independently of one another (eg: inheritance of flower color has nothing to do
with inheritance of stem height).
• Allele: An alternative form of gen; typically gene had two alleles, one from mom
and one from dad. Homozygous (alleles for particular trait from each parent are
same eg: AA). Heterozygous (alleles for particular trait from each parent are
different eg: Aa).
• Intermediate: combination of 2 disssimilar allele will produce an outcome
intermediate between the traits. Eg: red flower + white flower = pink flower
2 • Co- dominance: In heterozygous combination, both alleles express trait
simultaneously and with equal force.
eg: red flower + white flower = red flowers with white spots.
• Dominant: In heterozygous combination, there is more powerful of two alleles
so, it’s trait is expressed (Aa). eg: brown eyes + blue eyes = brown eyes
• Recessive: In heterozygous combination, the weaker of two alleles. So, the
green eyes. (Aa)
Genes on the Sex chromosomes: Exception to the rule
• Genes on the sex chromosomes provide an exception to the rules because not
all genes have 2 alleles.
• X-linked genes: genes that are carried on the X chromosome (which is much
bigger than Y with more genes and therefore the Y will sometimes have no
equivalent genes comparing to it) and therefore it will be expressed. Females
have two X so, more chance that there is a normal dominant X that will inhibit the
other X (abnormal) so trait won’t be expressed. eg: Hemophilia (X-linked
recessive characteristics) is when blood is unable to clot and found more in
• Some traits (eg: intelligence) are influenced by interactions of many genes
• Modifier Genes: Genes that exert their influence indirectly, by affecting the
expression of still other genes. Forming Cataract is controlled by a dominant
gene but where in your lens it is formed is controlled by a modifier gene.
See table 2-2 (pg 51-52, table) for all genetic disorders
Phenylketonuria (pku): A disease caused by a recessive allele that fails to produce an
enzyme necessary to metabolize the protein phenylalanine (found in milk); if untreated
immediately at birth, it accumulates and toxic substance damages the nervous system
and causes mental retardations. If each of the parents has a recessive allele, there is ¼
chance they will have a child with the disorder.
Sickle cell anemia: A disorder caused by a recessive gene, in which the red blood cell
becomes distorted when low in oxygen, causing fatigue, shortness of breath and severe
pain and blocking blood vessels (threat to life). Prone to African descendents. Due to
their shape, splle keeps on removing them from blood, giving rise to chronic anemia
3 (too few blood cells). Severe combined immunodeficiency (in utero treatment (surgery)
for victim with SCA).
Down Syndrome/Trisomy 21: A form of Chromosome abnormality , in which person
suffers from disabling physical and mental development and highly susceptible to such
illness as leukemia, heart disorders and respiratory infection. At the 21st slot, there are
3 chromosomes (most likely from mom) instead of 2. Prone to mother who get pregnant
over 35 (more influence) and father over 40.
Turner Syndrome: A form of abnormalities of the sex chromosomes found in females,
in which secondary sex characteristics develop only if female hormones are
administrated and in which abnormal of internal reproductive organs leads to permanent
sterility. Occur due to father’s sperm containing neither X or Y so resulting in XO. Not
good at discriminating and recognizing facial or emotional cues.
Klinefelter’s syndrome: A form of chromosome abnormality, in which a male inherits
extra X sex chromosomes, resulting in XXY pattern, and has many feminine physical
characteristics as well as language deficits and sometimes, mental retardation. Taller
than most man.
Fragile X-chromosome: a form of chromosome abnormalities (more common in
males) in which an X chromosomes is narrowed in some areas, causing it to be fragile
and leading to a variety of physical (cleft palate, seizures), psychological (ADD,
hyperactivity, anxiety) and social problems. Males have more social interaction
problems where females are more likely be depressed and have linguistic and cognitive
Genetic counselling and genetic Engineering
• Genetic counselling: it is possible to get a sample cell from a developing fetus
to determine if the fetus carries any genes for any disorders. Genetic counselling
is a health care service that provides medical information and information about
risks to couples (often they have family history of genetic disorders), helping
them to make difficult decisions.
• Preventive Genetic counselling: Couples get tested and if they have defective
alleles, they can adopt or go t