Chapter 2 Flashcards
Gamete
A reproductive cell. In humans it is a sperm or an ovum.
Zygote
The single cell formed from the union of two gametes, a sperm and an ovum.
Genome
The full set of genes that are the instructions to make an individual member of a certain species.
Allele
A variation that makes a gene different in some way from other genes for the same characteristics. Many genes never vary; others have several possible alleles.
Epigenetics
The study of how environmental factors affect genes and genetic expression — enhancing, halting, shaping, or altering the expression of genes.
Genotype
An organism’s entire genetic inheritance, or genetic potential.
Phenotype
The observable characteristics of a person, including appearance, personality, intelligence, and all other traits.
Micro biome
All the microbes (bacteria, viruses, and so on) with all their genes in a community; here the millions of microbes of the human body.
Carrier
A person whose genotype includes a gene that is not expressed in the phenotype. The carried gene occurs in half of the carrier’s gametes and thus is passed on to half of the carrier’s children. If such a gene is inherited from both parents, the characteristic appears in the phenotype.
Polygenic
Many genes
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 likely to express them.
Monozygotic twins
Twins who originate from one zygote that splits apart very early in development. (Also called identical twins.) Other monozygotic multiple births (such as triplets and quadruplets) can occur as well.
Dizygotic twins
Twins who are formed when two separate ova are fertilized by two separate sperm at roughly the same time. (Also called fraternal twins.)
How is the sex of a zygote determined?
The 23rd pair of chromosomes is crucial. Every zygote has an X from the mother and either an X or Y from the father. If the zygote has a Y, it usually becomes male
What is the influence of methylation on genes?
Methylation is the effect of methyl that surrounds each gene, and “enhances, transcribes, connects, empowers, silences, and alters genetic instructions”
What is the influence of the microbiome?
The microbes that live within each person affect almost every function of the human body, influencing moods, digestion, diseases, and the immune system
How do monozygotic twins, dizygotic twins, and single-born siblings differ genetically?
Monozygotic twins are from one zygote, and hence are genetically identical, where dizygotic twins come from two ovarian that were fertilized by two sperm at about the same time. They share prenatal influences and birth date, but genetically they are no more alike than single-born siblings from the same parents
How could a child inherit a disease neither parent has?
Both parents could carry the same recessive gene, or the alleles from each parent could combine in unfortunate ways
What is the difference between additive genes and recessive genes?
Additive genes add up their influence on the future person, with each contributing to the phenotype, whereas recessive genes are hidden and don’t affect the phenotype unless the zygote inherited a recessive gene from both parents
How are boys more likely to inherit disorders from their mother rather than their father?
Sone inherit a Y from their fathers, and an X from their mothers. If a recessive gene is on the mother’s X, it may have no dominant gene on the Y to counteract it, so it alone affects the trait
Germinal period
The first two weeks of prenatal development after conception, characterized by rapid cell division and the beginning of cell differentiation.
Embryonic period
The stage of prenatal development from approximately the third week through the eighth week after conception, during which the basic forms of all body structures, including internal organs, develop.
Fetal period
The stage of prenatal development from the ninth week after conception until birth, during which the fetus gains about 7 pounds (more than 3,000 grams) and organs become more mature, gradually able to function on their own.
In vitro fertilization
when a sperm and an ovum join to form a zygote using a laboratory dish
Embryo
The name for a developing human organism from about the third week through the eighth week after conception.
primitive streak
appears down the middle of the cell mass at day 14; it forms the neural tube 22 days after conception
cephalocaudal
head forms first and the extremities last
Fetus
The name for a developing human organism from the start of the ninth week after conception until birth.
Age of viability
The age (about 22 weeks after conception) at which a fetus might survive outside the mother’s uterus if specialized medical care is available.
apoptosis
A process that occurs in the final months of pregnancy — cell death
fontanels
which are areas on the top of newborn head where the skull bones have not fused yet
What must happen before the developing organism is called an embryo?
Not until 8 weeks after conception does the developing reason have all the body parts of the person (except sex organs). At that point it is called an embryo.
When is an embryo about 3 inches long?
About 3 months after conception