1.5 Important Points
Problem 1: prenatal development
A genotype is the specific makeup of the individual, while phenotype is the individual´s
observable characteristics.
Chromosomes carry the genes that form us. All of our body cells have 46 chromosomes, except
our gametes (sperm and ova) which contain 23 chromosomes.
DNA stores genetic information and is made up of nucleotides that are held together by parallel
stands. Only bases that are compatible with each other will bond together; adenine and
thymine; cytosine and guanine.
Genes are located in particular sites of the chromosomes and they trigger the production of
proteins when a particular change in the environment signals them to active. When it is
activated, the nucleotides make a new bond with their compatible other to create a copy of the
gene called mRNA, which then travels to the cell nucleus for the protein synthesis to take place.
Alleles are single stands of chromosomes. The alleles from both parents can be homozygous
(same trait) or heterozygous (different trait). The possible outcomes when alleles are
heterozygous are codominance (combine but not blend), dominant, or recessive.
In human beings, 22 pairs of chromosomes are autosomes while one pair is a sex chromosome.
XX for females and XY for males. Y chromosomes have less genetic material than X chromosomes
so any recessive X-linked genes will automatically be expressed. Some genetic defects include:
o Phenylketonuria (PKU): caused by recessive allele and if untreated leads to mental
retardation
o Down syndrome: cause by extra full or partial chromosome 21 which leads to physical
and mental retardation
o Turner syndrome: caused by receiving only one X chromosome instead of two (only
females) which leads to underdeveloped secondary sex characteristics
o Triple X syndrome: caused by an extra X chromosome (only in females) which leads to
physical abnormalities such as menstrual irregularities, premature menopause, and
limitation in cognitive abilities
o Klinefelter´s syndrome: cause by extra X chromosome (only in males) which leads so
female physical characteristics
o XYY syndrome: cause by extra Y chromosome (only in males) which leads to attention
deficit, cognitive impairment, and unusual height.
o Fragile X syndrome: caused by breaking of X chromosome which leads to physical
abnormalities, mental retardation, psychological and social problems
Meiosis is the process were the chromosomes are halved (23 chromosomes) to produce
reproductive cells. The DNA it contains is random because of cross over (random exchange of
genetic material)
Mitosis is the process of cell duplication and division into daughter cells that contains 46
chromosomes.
During the course of prenatal development, many external agents, called teratogens, may cause
developmental deviations in the fetus. Although teratogens are environmental factors, other
factors such as the mother´s age (problems before 15 and over 35), her diet, and her emotional
Problem 1: prenatal development
A genotype is the specific makeup of the individual, while phenotype is the individual´s
observable characteristics.
Chromosomes carry the genes that form us. All of our body cells have 46 chromosomes, except
our gametes (sperm and ova) which contain 23 chromosomes.
DNA stores genetic information and is made up of nucleotides that are held together by parallel
stands. Only bases that are compatible with each other will bond together; adenine and
thymine; cytosine and guanine.
Genes are located in particular sites of the chromosomes and they trigger the production of
proteins when a particular change in the environment signals them to active. When it is
activated, the nucleotides make a new bond with their compatible other to create a copy of the
gene called mRNA, which then travels to the cell nucleus for the protein synthesis to take place.
Alleles are single stands of chromosomes. The alleles from both parents can be homozygous
(same trait) or heterozygous (different trait). The possible outcomes when alleles are
heterozygous are codominance (combine but not blend), dominant, or recessive.
In human beings, 22 pairs of chromosomes are autosomes while one pair is a sex chromosome.
XX for females and XY for males. Y chromosomes have less genetic material than X chromosomes
so any recessive X-linked genes will automatically be expressed. Some genetic defects include:
o Phenylketonuria (PKU): caused by recessive allele and if untreated leads to mental
retardation
o Down syndrome: cause by extra full or partial chromosome 21 which leads to physical
and mental retardation
o Turner syndrome: caused by receiving only one X chromosome instead of two (only
females) which leads to underdeveloped secondary sex characteristics
o Triple X syndrome: caused by an extra X chromosome (only in females) which leads to
physical abnormalities such as menstrual irregularities, premature menopause, and
limitation in cognitive abilities
o Klinefelter´s syndrome: cause by extra X chromosome (only in males) which leads so
female physical characteristics
o XYY syndrome: cause by extra Y chromosome (only in males) which leads to attention
deficit, cognitive impairment, and unusual height.
o Fragile X syndrome: caused by breaking of X chromosome which leads to physical
abnormalities, mental retardation, psychological and social problems
Meiosis is the process were the chromosomes are halved (23 chromosomes) to produce
reproductive cells. The DNA it contains is random because of cross over (random exchange of
genetic material)
Mitosis is the process of cell duplication and division into daughter cells that contains 46
chromosomes.
During the course of prenatal development, many external agents, called teratogens, may cause
developmental deviations in the fetus. Although teratogens are environmental factors, other
factors such as the mother´s age (problems before 15 and over 35), her diet, and her emotional
