Transcript Human Growth and Development

Human
Growth
and
Development
Day #5
March 22, 2012
Fort Omaha 12 – 1:55 p.m.
Agenda for Day #5
• Continue genetics, prenatal development
• Begin DVD
• Distribute test and return papers
Genetics and
Genetics and
Human
Development,
continued
DNA Molecule
For more detail: http://www.youtube.com/watch?v=CkcFqif7H5k&feature=related
Genes
• Genes - units of hereditary information
– short segments of DNA
• Genes direct cells to reproduce
themselves and to assemble proteins
• Proteins
– the building blocks of cells
– the regulators that direct the body’s
processes
(Mader, 2008)
Human Genome Project
• Preliminary map of the human genome
• the complete set of developmental
instructions for creating proteins that
initiate the making of a human organism
• Each human has 20,000 – 30,000 genes
Enduring Nature of Genes
• Three processes by which cells split
and are formed
–Mitosis
–Meiosis
–Fertilization.
Mitosis
• All body cells, except the sperm and egg, have
46 chromosomes arranged in 23 pairs
• These cells reproduce by a process called
mitosis
• During mitosis, the cell’s nucleus—including
the chromosomes—duplicates itself and the
cell divides
• Two new cells are formed, each containing the
same DNA as the original cell.
http://www.youtube.com/watch?v=rgLJrvoX_qo&feature=related
Meiosis
• Sex cell division is different type of cell
division
• Eggs and sperm (or gametes) are formed in
meiosis
• A cell of the testes (in men) or ovaries (in
women) duplicates its chromosomes but then
divides twice, thus forming four cells
• Each of these has only half of the genetic
material of the parent cell.
• By the end of meiosis, each egg or sperm has
23 unpaired chromosomes.
Fertilization
• During fertilization, an egg and a sperm
fuse to create a single cell, called a zygote
• In the zygote, the 23 unpaired
chromosomes from the egg and sperm
combine to form one set of 23 paired
chromosomes
• One chromosome of each pair is from the
mother’s egg and the other from the
father’s sperm.
• Each parent contributes half of the
offspring’s genetic material.
•
http://www.youtube.com/watch?v=vXNaTRs83hE&NR=1
The 23rd Pair of Chromosomes
• Ordinarily, in females the 23rd pair
consists of two chromosomes called X
chromosomes
• In males the 23rd pair consists of an X
and a Y chromosome
• The presence of a Y chromosome is what
makes an individual male
So, is this the karotype of a girl or a boy?
Sources of Variability
• Combining genes of two parents
increases genetic variability in the
population
• chromosomes in the zygote are not exact
copies of the parents
• Another source of variability comes from
DNA
– a mutated gene, which is a permanently
altered segment of DNA
http://www.youtube.com/watch?v=vNWwSL55gUM
Genotype and Phenotype
• Genotype -- all of a person’s genetic
material
• Phenotype -- observable characteristics
• Phenotypes include
– physical characteristics (such as height,
weight, and hair color)
– psychological characteristics (such as
personality and intelligence)
Genetic Principles
•
•
•
•
Dominant-recessive genes
Sex-linked genes
Genetic imprinting
Polygenically determined characteristics
Dominant-Recessive Genes Principle
• Dominant -- one gene of a pair always
exerts its effects
• Recessive gene – exerts its influence only
if the two genes of a pair are both
recessive
– may be overridden by a dominant gene
– May be carried from generation to
generation but not expressed in phenotype
Sex-Linked Genes
• X-linked inheritance -- mutated gene is carried
on the X chromosome
– very different implications for males than females
(Turner, 2006)
– males have no “backup” copy to counter the
harmful gene
– females have a second X chromosome, which is
likely to be unchanged
• Females who have one changed copy of the X gene are
known as “carriers”
Polygenic Inheritance
• Genetic transmission is usually quite
complex
– Few characteristics reflect the influence of
only a single gene or pair of genes
• polygenically determined characteristics - determined by the interaction of many
different genes
Chromosome Abnormalities
• Down syndrome -- caused by the
presence of an extra copy of
chromosome 21
– once in every 700 live births
– Women aged 16 - 34 are less likely to give
birth to a child with Down syndrome
• Sex-Linked Chromosome Abnormalities
Sex-Linked Chromosome
Abnormalities
• Klinefelter syndrome – extra X
chromosome
• Fragile X syndrome -- results from an
abnormality in the X chromosome
– X chromosome becomes constricted and
often breaks
• Turner syndrome -- females have either
an X chromosome missing or part of one
X chromosome is deleted
• XYY syndrome – male has extra Y
Gene-Linked Abnormalities
• Phenylketonuria (PKU) – individual
cannot properly metabolize
phenylalanine, an amino acid
– once in every 10,000 to 20,000 live births
– left untreated, phenylalanine builds up in
the child, producing mental retardation and
hyperactivity
• Sickle-cell anemia -- genetic disorder that
impairs the body’s red blood cells
– most often in African Americans
– red blood cell becomes a hook-shaped
“sickle” that cannot carry oxygen properly
– 1 in 400 African American babies is affected
• 1 in 10 African Americans is a carrier
• 1 in 20 Latin Americans is a carrier
• Other diseases that result from genetic
abnormalities
– cystic fibrosis
– diabetes
– hemophilia
– Huntington disease
– spina bifida
– Tay-Sachs disease
PRENATAL DEVELOPMENT AND
BIRTH
The Fetal Period
• Fetal period begins two months after
conception and lasts for seven months
• Three months after conception-- fetus is about
3 inches long; weighs about 3 ounces
• At birth, the average American baby weighs 7
½ pounds and is about 20 inches long
Three Trimesters
• The germinal and embryonic periods occur in
the first trimester
• The fetal period begins toward the end of the
first trimester and continues through the
second and third trimesters
• Viability (the chances of surviving outside the
womb) occurs at the beginning of the third
trimester.
• Age of viability – about 23-24 weeks on
average
DVD: The biology of prenatal
development
http://www.cerebralpalsyinfo.com/CP1.jpg
Assignment
• Finish reading Chapters 1 – 2
• Take Home Test
• Test is due March 29