HEREDITY AND ENVIRONMENT
DNA: long, double-stranded molecules that make up chromosomes
chromosomes: long, threadlike structures made of twisted strands of DNA
23 pairs of chromosomes
autosomes: the first 22 pairs; control physical and mental traits
(sex chromosomes): 23rd pair; determine your sex
girl – XX
boy – XY
father determines the sex of the child b/c can give an X or Y but
mom can only give X
genes: the biological blueprints that determine our hereditary traits
homozygous: both parents passed on the same gene for a trait
heterozygous: parents passed on different genes for a trait
EX:
father
mother
if heterozygous for a trait, can still pass on the recessive gene to their children
and then the children are said to be a carrier of the trait
Other EXS of
Dominant
Recessive characteristics
genotype: the genetic makeup of an individual
phenotype: the individual’s physical and behavioral characteristics, which are determined by
genetic and environmental factors.
CHROMOSOMAL ABNORMALITIES
these usually occur when the zygote’s cells have
is also a factor
the older a mother is, the likelihood of the child having chromosomal abnormalities
increases
about
of all fetuses with an abnormality will spontaneously abort and possibly
before the mother realizes she is pregnant
Down syndrome: most common chromosomal abnormality
occurs in
in
of cases, it results from a failure of the 21st pair of chromosomes
instead of having only 2 chromosomes on the 21st pair, these children have 3
chromosomes on the 21st pair, so it’s also called trisomy-21
most embryos with trisomy-21 are aborted
consequences of Down syndrome:
have distinct physical features: short, stocky build; flattened face; protruding
tongue; almond-shaped eyes
up until about 30 years ago, most of these people affected died by early adulthood
now they can live past their 60s
infants don’t smile as readily as other infants and are less likely to explore like
other infants
with encouragement from caregivers, these children can develop a lot better
benefit from infant and preschool intervention programs
however, their emotional, social, and motor skills improve more than intellectual
skills
risk rises dramatically with maternal age, from
births at age 20 to
at age 39, to
at age 44
geneticists believe that this occurs because the mother’s eggs are weakened by
then
in only
of cases is the extra genetic material coming from the father
tend to age faster than other adults; some ailments show up around age 30 and by
middle adulthood, can develop Alzheimer’s and can also develop cataracts and cancer
Turner syndrome: problem with the sex chromosome; these females are missing an X
chromosome
anatomically female but have stunted growth and are usually sterile
need hormone therapy to begin menstruation and to develop breasts
intellectually, have trouble with spatial skills (drawing pictures, telling left from
right, following travel directions, and noticing changes in facial expressions)
however, they are still at or above normal levels on verbal skills
Klinefelter syndrome: most common sex chromosome abnormality; males have an extra X
chromosome
occurs
males
look normal but have underdeveloped testes
are not mentally retarded but do have language and learning disabilities
by puberty, their penis’ may not enlarge but they do begin to develop breasts
GENETIC ABNORMALITIES
abnormality with genes and all of us carry some type of abnormal gene that may have the
potential to develop into a serious disease or handicap for the next generation
the genes are usually recessive and may not show up for a couple or a few generations, but
mainly if it ends up paired with another recessive gene
dominant genetic abnormalities do occur but usually those carrying the genes don’t have
children that they pass on the genetic abnormality to or if it’s debilitating enough, the person
may die an early death
Huntington’s disease: a dominant disorder that causes the brain to deteriorate and affects
psychological and motor functioning.
usually diagnosed
it used to be where the children of these people had to wait until they were adults to see
if they had it also; if they became sick
now they are able to do blood tests to identify the Huntington gene
Tourette syndrome: a dominant disorder characterized by uncontrollable tics and explosive
outbursts of verbal obscenities although the obscenities are rare
of those who carry the gene will develop a severe case of Tourette’s while
will be able to have more control over the tics
fragile X syndrome: there is a fragile or damaged spot on an X chromosome
can cause mental retardation that becomes progressively worse as the child gets older
affects
males and
females
BEHAVIOR GENETICS
behavior genetics: the study of the genetic origins of psychological characteristics, such as
personality patterns, psychological disorders, and intellectual abilities
What are some personality traits that are genetically linked?
What are some psychological disorders that are genetically linked?
CONCEPTION
For conception to take place, the male reproductive cell, or sperm, must penetrate the
membranes of a female reproductive cell, or ovum
Each reproductive cell is called a gamete and each contains 23 chromosomes
After the sperm travels thru the fallopian tubes, the nuclei of each cell come together to
form one cell
The chromosomes pair up to make 46 in all (23 pairs)
After the sperm penetrates the ovum, the cell is now called a zygote: the fertilized cell
formed by the union of the sperm and ovum
Not long after conception, the zygote begins the processes of duplication and division
Duplication: the 23 pairs of chromosomes duplicate to form 2 sets of the genetic code for
that individual
Division: the cells continually divide themselves, starting by dividing into 2, then 4, then 8
Each of the new cells contains the person’s genetic material
These new cells also will form different parts of the individual’s body; part of those cells will
form the amniotic sac
This process of forming different parts of the body and the amniotic sac is called
differentiation
If the cells of the zygote split during the very early stages of development, can have multiple
zygotes; can split into 2, 4, etc. so leads to multiple births
If one zygote splits into two separate clusters of cells, will have monozygotic twins or
identical twins
Have same genotype, identical genetic instructions for physical appearance, psychological
traits, vulnerability to diseases, etc.
Frequency of identical twins is about
births
Dizygotic or fraternal twins occur when 2 ova are released and fertilized separately
Most common type of multiple birth and occurs about
births
Are no more alike than ordinary siblings
May not look alike and can look extremely different
What is a factor that can contribute to the rise in multiple births?