Chapter 2 Flashcards
DNA (deoxyribonucleic acid)
The Beginning of Life
- Molecule that contains the chemical instructions for cells to manufacture various proteins
- Promotes growth and sustains life
- All living things are composed of DNA molecules
Chromosome
The Beginning of Life
One of the 46 molecules of DNA (in 23 pairs) that almost every cell of the human body contains and that, together, contain all the genes.
- Each molecule of DNA is called a chromosome.
- Chromosomes contain units of instructions called genes
- Consists of 46 chromosomes arranged in 23 pairs.
Zygote
The Beginning of Life
The single cell that is formed from the fusing of two gametes, a sperm and an ovum.
• Every person starts life as a single cell, called a zygote
• The zygote contains genes that have been passed down for hundreds of thousands of years
• The first hours of development are:
– universal to all humans yet
– provide characteristics that are unique to each human
Genes
- Chromosomes contain units of instructions called genes (which code for proteins)
- Each gene is located on a particular chromosome
Genotype
– An organism’s genetic inheritance / genetic potential
– Unique for each organism
– Genes are passed down from generation to generation
Phenotype
The observable characteristics of an organism, including appearance, personality,
intelligence, and all other traits
The Human Genome
the complete set of nucleic acid sequence for humans encoded as DNA
• It is made up of 23 chromosome pairs in cell nuclei
• Involves the full set of genes that are the instructions that make an individual who they are
Similarity between two people
The Human Genome
99.5%
Similarity between humans and chimpanzees
The Human Genome
98%
Similarity between humans and every other mammals
The Human Genome
90%
Human Genome Project
international effort to map the complete genetic code
• About 18,000 – 23,000 shared genes in humans
• The regulator genes and the “junk” around the genes are responsible for differences among species
Genomic DNA
Junk DNA that does not encode proteins and whose function, if it has one, is not well understood.
• Junk. Barren. Non-functioning. Dark matter. That’s how scientists described the 98% of human genome that lies between our 20,000+ genes (DNA) a decade ago
Sex/Gender
Humans usually possess 46 chromosomes: 44 autosomes and 2 sex chromosomes
– Females: XX and Males: XY
How is sex determined?
By the father:
• Sex of offspring depends on whether the father’s Y sperm or X sperm fertilizes the ovum (50% chance for either sex)
Gametes
The Beginning of Life
Sperm and ovum/egg reproductive (SEX) cells
• Each gamete consists of 23 chromosomes
Zygote
Two gametes (sperm and ovum) combine and produce a new individual with 23 chromosomes from each parent. – the two nuclei will fuse, bringing together about 20,000 genes to guide development
Fertilization
Sperm and ovum fuse to create zygote
Intersex**
Child born with genetilia of both sexes
o Every now and then, a baby is born with “ambiguous genitals,” meaning that the child’s sex is not abundantly clear.
o When this happens, a quick analysis of the chromosomes is needed to make sure there are exactly 46 and to see whether the 23rd pair is XY or XX.
Monozygotic twins
Identical twins
• Originate from one zygote that splits apart very early in development.
• Incomplete split results in conjoined twins.
• Same genotype but slight variations in phenotype are possible due to environmental influences.
Dizygotic twins
Fraternal twins
• Result from fertilization of two separate ova by two separate sperm.
• Dizygotic twins have half their genes in common and occur twice as ofen as monozygotic twins.
• Incidence is genetic and varies by ethnicity and age.
Prenatal development
Is the process of which a single cell develops after conception into an embryo and later into a fetus /offspring (full-term baby)
o Takes about 38 weeks to complete
o Takes place in the mother’s womb
o Consists of 3 main periods
Three main periods of Prenatal Development
- Germinal Period
- Embryonic Period
- Fetal Period
Germinal Period
Prenatal development
The first two weeks of development after conception, characterized by rapid cell division and the beginning of cell differentiation.
Conception is the beginning of the germinal period.
This stage occurs during the first 2 weeks of zygote development
Embryonic Period
Prenatal development
This stage lasts from implantation until ~8 weeks from the time of conception
– This is the most important time of prenatal development bc the embryo is developing the foundations for a healthy baby
Fetal Period
Prenatal development
Final stage of development. – From the end of the embryonic stage (week 9) until birth
Fetus (scientifically)
Not a fetus until brain has developed
First 14 Days
First Stages of the Germinal Period
Zygote begins duplication and division within hours of conception
• Development of the placenta
• Implantation (about 10 days after conception)
• Organism grows rapidly
Occasionally at this early stage, the cells separate completely, forming the beginning of monozygotic twins, quadruplets, or octuplets.
From the 3rd Through 8th Week - EMBRYO
The Embryonic Period
• Primitive streak becomes the neural tube and later forms the brain and
spine of the CNS.
• Head takes shape
• Eyes, ears, nose, and mouth form
• Heart begins to pulsate
• Extremities develop and webbed fingers and toes separate
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From 9th Week Until Birth - FETUS
The Fetal Period
- Genitals form and sex hormones cause differences in fetal brain organization
- At 3 months, the fetus weighs about 3 ounces
- Experiences the period of greatest brain growth during the 4th, 5th,and 6th months
Age of viability
The Fetal Period
• Age at which a preterm newborn may survive outside the mother’s uterus if medical care is available
– About 22 weeks after conception
• Brain is able to regulate basic body functions: breathing, heart beat