2.1 In the Beginning

What is a zygote?

The single cell formed from the union of two reproductive cells, a sperm and an ovum.

What does genome refer to?

The full set of genes that are the instructions to make an individual member of a certain species.

What is an allele?

A variation that makes a gene different in some way from other genes for the same characteristics.

What is the microbiome?

The entire collection of all the microbes within another living organism.

What does the term epigenetics mean?

The study of how environmental factors affect genes and genetic expression — enhancing, halting, shaping, or altering the expression of genes.

What defines an organism's genotype?

An organism’s entire genetic inheritance, or genetic potential.

What does phenotype carrier refer to?

The observable characteristics of a person, including appearance, personality, intelligence, and all other traits.

What are X-linked traits?

A gene carried on the X chromosome, which males express if inherited as recessive from their mother.

What are monozygotic (MZ) twins?

Twins who originate from one zygote that splits apart very early in development.

What are dizygotic (DZ) twins?

Twins who are formed when two separate ova are fertilized by two separate sperm at roughly the same time.

Which chromosome pairs match and which do not?

Chromosome pairs 11 through 22 match. The sex chromosome pair (pair 23) does not match; females have two X chromosomes (XX) and males have one X and one Y chromosome (XY).

Do both biological parents determine the sex of the zygote?

The sex depends primarily on which sperm penetrates the ovum — a Y sperm (creating a boy, XY) or an X sperm (creating a girl, XX). Rarely, prenatal influences also affect sex.

What does the microbiome influence?

The microbiome influences weight, immunity, diseases, moods, and many other conditions.

What is the difference between phenotype and genotype?

Genotype represents an organism's genetic makeup, while phenotype refers to its observable traits. Genotype provides genetic instructions for phenotype, but environmental factors can influence the expression of these instructions.

When in development do epigenetic changes occur?

Epigenetic changes can occur at any stage of development, from conception through adulthood.

What is the difference between additive, dominant, and recessive genes?

In additive heredity, genes and alleles "add up" to influence the phenotype. In dominant-recessive heredity, one allele is more influential than the other, controlling a characteristic's expression even when a recessive gene is present.

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.

How are boys more likely to inherit disorders from their mother than their father?

Sons inherit a Y from their fathers and an X from their mothers. If a recessive gene is on the mother's X, the Y chromosome may have no dominant gene to counteract it, allowing the recessive gene to affect the trait. For example, more males than females have color blindness because the recessive gene for color blindness is carried by the X chromosome.

What is the difference between monozygotic and dizygotic twins?

Monozygotic twins originate from one zygote that splits, while dizygotic twins are formed when two separate ova are fertilized by two separate sperm at roughly the same time. In common language, these are identical or fraternal twins, respectively.

How do monozygotic twins, dizygotic twins, and single-born siblings differ genetically?

Monozygotic twins are genetically identical as they originate from one zygote. Dizygotic twins come from two ova fertilized by two sperm; they share prenatal influences and birth date, but are genetically no more alike than single-born siblings from the same parents.