Development Ch 3

The Genetic Code

All living things composed of cells
These cells manufacture proteins according to instructions kept on molecules of DNA
DNA are found on chromosomes (23 pairs=46)
Gamete = reproductive cell

gamete

-a reproductive cell
-that is, a sperm or ovum that can produce a new individual if it combines with a gamete from the other sex to make a zygote

zygote

the single cell formed from the union of two gametes (sperm and ovum)

deoxyribonucleic acid (DNA)

the chemical composition of the molecules that contain the genes, which are the chemical instructions for cells to manufacture various proteins

chromosome

-One of the 46 molecules of DNA (in 23 pairs) that virtually each cell of the human body contains that, together, contain all the genes.
-Other species have more of fewer chromosomes

gene

-a small section of a chromosome
-the basic unit for the transmission of heredity
-a gene consists of a string of chemicals that provide instructions for the cell to manufacture certain proteins
-humans have between 18,000 and 23,000
-are located on a spe

allele

-a variation that makes a gene different in some way from other genes for the same characteristics
-responsible for the change we notice in each other
-many genes never vary; others have several possible alleles
-each parent contributes half of the geneti

RNA and DNA

surround each gene to ...
-enhance, transcribe, connect, empower, silence, alter genetic instructions
-this process is called methylation
-methylation continues throughout life and can alter a gene's expression (remember epigenetics?)
-some of this transf

genome

-entire packet of instructions to make a living organism
-the full set of genes that are the instructions to make an individual member of a certain species
-all DNA material (coding AND noncoding)

SUMMING UP

-The human genome contains approximately 20,000 genes on 46 chromosomes, using a 3 million base pairs code to make a person
-some genes, called alleles, are polymorphic
-because of small differences in their genetic codes, each person is unlike any other

genotype

-an organism's entire genetic inheritance, or genetic potential
-genes that you are born with

homozygous

-referring to two genes of one pair that are exactly the same in every letter of their code
-most gene pairs are homozygous
-code of Dad's gene is exactly the same as code of Mom's...most are

heterozygous

-referring to two genes of one pair that differ in some way
-typically, one allele has only a few base pairs that differ from the other member of the pair
-genes codes differ from it's counterpart

23rd pair

-determines sex
-by y sperm or x sperm
-XX or XY
-The other 22 pairs are autosomes, inherited equally by males and females

XX

-A 23rd chromosome pair that consists of two x-shaped chromosomes, one from the mother and the father.
-XX zygotes become females

XY

-A 23rd chromosome pair that consists of an X-shaped chromosome from the mother and a Y-shaped chromosome from the father
-XY zygotes become males

stem cells

-cells from any which other specialized type of cell can form
-cells from early division and replication, that able to produce any kind of cell the body requires to form a complete individual
-duplication and division continue, but a third process differe

monozygotic twins

-twins who originate from one zygote that splits apart very early in development (aka identical twins)
-other monozygotic multiple births (like triplets and quadruplets) can occur as well
-"maternal" twins

dizygotic twins

-twins who are formed when two separate ova are fertilized by two separate sperm at roughly the same time (aka fraternal twins)

assisted reproductive technology

-a general term for the techniques designed to help infertile couples conceive and sustain a pregnancy
-when a woman takes meds to initiate production of ova...the ova is removed and sperm injected into it, then put back into uterus (intra-cytoplasmic spe

in vitro fertilization

-fertilization that takes place outside a woman's body (as in a glass labratory dish)
-the procedure involves mixing sperm with ova that have been surgically removed from the woman's ovary.
-if a zygote is produced, it is inserted into a woman's uterus, w

intra-cytoplasmic sperm injection

an in vitro fertilization technique in which a single sperm cell is injected directly into an ovum

SUMMING UP 2

-people usually have 23 chromosomes from their mother and 23 from their father, with all the genes and chromosomes matched up into mother-father pairs, although match may not be letter perfect because of alleles
-the father's 23rd chromosome pair is XY, s

genotype 2

-when a sperm and ovum combine into a zygote, they establish the genotype
-the genotype is all the genes that the developing person has

phenotype

the observable characteristics of a person, including appearance, personality, intelligence, and all other traits
-all expressed genes

genotype to phenotype

-all the genes that you will have come from when sperm and ova come together to form zygote!
-these, along with environment, with determine what gets expressed (what you look like, act like, etc) in your phenotype
-most traits are polygenic and multifacto

polygenic

-referring to a trait that is influenced by many genes
-come from many genes

multifactorial

-many factors
-referring to a trait that is affected by many factors, both genetic and environmental that enhance, halt, shape, or alter the expression of genes, resulting in a phenotype that may differ markedly from the genotype

epigenetics

-changes in gene expression (active versus inactive genes) that does not involve changes to the underlying DNA sequence, a change in phenotype without a change in genotype
-ex: diabetes... people inherit gene putting them at risk, but may never develop it

add to this...

differential susceptibility: environmental +/- can influence development
-we NOW know the reverse is also true...if you feel depressed this can affect RNA, which can open gateways for other factors to be expressed (i.e. heart disease)
-no trait is directe

Human Genome Project

-How many genes do we have??
-18,000-23,000
-an international effort to map the complete human genetic code. this effort was essentially completed in 2001, though analysis is ongoing
-how easy is it to locate precise genes?
-they did determine that many t

dominant-recessive pattern

-another HGP discovery
-one allele is dominant and controls the expression of the other (recessive)
-the interaction of a heterozygous pair of alleles in such a way that the phenotype reflects one allele (the dominant gene) more than the other (the recess

carrier

-another HGP discovery
-if a person has the (non)expressed gene they are a "carrier" of that gene
-a person whose genotype includes a gene that is not expressed in the phenotype
-the carried gene occurs in half of the carriers gametes and thus is passed o

x-linked

-a gene carried on the x-chromosome
-if a male inherits an X-linked recessive trait from his mother, he expresses that trait because the Y from his father has no counteracting gene
-females are more likely to be carriers of X-linked traits but are less li

copy number variations

-genes with various repeats or deletions of base pairs
-these DO correlate with almost every disease and condition (heart disease, MH, CA, etc)
-these are developmental also because they are particularly influential prenatally
-copy #1 variations are abun

nature vs nurture revisited

-ETOH?? which part is nature? what are environmental causes?
-diabetes? being short?

SUMMING UP 3

-the distinction between genotype (heredity) and phenotype (manifest appearance and observed behavior) is one of the many complexities in genetics and development
-all traits are epigenetic, the product of genetic and non genetic influences, beginning wit

heritability

-a statistic that indicates what percentage of the variation in a particular trait within a particular population, in a particular context and era, can be traced to genes

SUMMING UP 4

-genes affect every trait- whether it is something wonderful, such as a wacky sense of humor; something fearful, such as a violent temper, or something quite ordinary, such as a tendency to be bored
-the environment affects every trait as well, in ways th

When things go wrong

-some females produce ova that don't have 23/23 splits, but 22/24 (older women more likely)
-sperm decrease in number and normality with age
-miscounts are not rare
-many of these that do form zygotes will not survive to birth or die within a few days of

3 factors make these relevant to human development:

1. they provide insight into the complexities of nature and nurture
2. knowing their origins helps limit their effects
3. information combats prejudice: difference is not always a deficit

Down syndrome (trisomy-21)

-a condition in which a person has 47 chromosomes instead of the usual 46, with 3 rather than 2 chromosomes at the 21st site.
-people with down syndrome typically have distinct characteristics, including unusual facial features, heart abnormalities, and l

fragile x syndrome

a genetic disorder in which part of the X chromosome seems to be attached to the rest of it by a very thin string of molecules.
-the cause is a single gene that has more than 200 repetitions of one triplet
-200 repetitions of 1 gene
-most common form of i

the 23rd chromosome

-occasionally there are babies born with 1 sex chromosome OR 3+ (instead of 2)
-most will spontaneously abort, but if they survive this usually = impaired cognition, sexual maturation
-rarely someone born with only part of 23rd chromosome missing or an ex

Genetic disorders - Dominant

-most of 7,000 known are Dominant, but rarely seen as they tend to die early
-ex: Huntington's Disease

Genetic disorders - Recessive

-more commonly seen because they are passed down
-X-linked ex's = hemophilia, Duchesne's MD, Fragile X (200+ repetitions of 1 gene)
-most recessive are in autosomes (not x-linked)

carriers

-person that has inherited a recessive allele for a genetic trait or mutation but does not display that trait or show symptoms of the disease
-1:12 Americans are carriers of various recessive diseases, but disorders themselves are rare
-the recessive gene

genetic counseling & testing

-testing that allows individuals to know about their genetic heritage, including harmful conditions that MIGHT pass along to offspring
-who is this useful for?
-people with family members with serious genetic conditions
-couples who have had miscarriages

SUMMING UP 5

-Every person is a carrier for some serious genetic conditions
-most of them are rare, which makes it unlikely that the combination of sperm and ovum will produce severe disabilites
-a few exceptional recessive-gene diseases are common because carriers we