Chapter 3

Question 1

DNA

Answer 1

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

Question 2

chromosome

Answer 2

• one of the 46 molecules of DNA (in 23 pairs) that virtually each cell of the human body contains and that, together contain all the genes
• other species have more or fewer

Question 3

gene

Answer 3

• a small section of a chromosome; basic unit for the transmission of heredity
• consists of a string of chemicals that provide instructions for the cell to manufacture certain proteins

Question 4

allele

Answer 4

• a variation that makes a gene different in some way from other genes for characteristics
• many genes never vary; others have several possibilites

Question 5

genome

Answer 5

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

Question 6

gamete

Answer 6

-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

Question 7

zygote

Answer 7

-the single cell formed from the union of two gametes, a sperm and an ovum

Question 8

genotype

Answer 8

-an organism’s entire genetic inheritance, or genetic potential

Question 9

homozygous

Answer 9

• referring to two genes of one pair that are exactly the same in every letter of their code
• most genes are _______

Question 10

heterozygous

Answer 10

• 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

Question 11

23rd Pair

Answer 11

• the chromosome pair that determines sex in humans
• the other 22 pairs are autosomes–inherited equally by males and females

Question 12

XX

Answer 12

• a 23rd chromosome pair that consists of two X-shaped chromosomes, one each from the mother and the father
• ___zygotes become females

Question 13

XY

Answer 13

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

Question 14

stem cells

Answer 14

-cells from which any other specialized type of cell can form

Question 15

monozygotic (MZ) twins

Answer 15

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

Question 16

dizygotic (DZ) twins

Answer 16

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

Question 17

ART

Answer 17

• assisted reproductive technology
• a general term for the techniques designed to help infertile couples conceive and then sustain a pregnancy

Question 18

IVF

Answer 18

• in vitro fertilization
• fertilization that takes place outside a woman’s body (as in a glass laboratory dish)
• 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, where it may implant and develop into a baby

Question 19

phenotype

Answer 19

-the observable characteristics of a person, including appearances, personality, intelligence, and all other traits

Question 20

polygenic

Answer 20

-referring to a trait that is influenced by many genes

Question 21

multifactorial

Answer 21

-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

Question 22

epigenetic

Answer 22

-referring to environmental factors that affect genes and genetic expression–enhancing, halting, shaping, or altering the expression of genes and resulting in a phenotype that may differ markedly from the genotype

Question 23

Human Genome Project

Answer 23

• an international effort to map the complete human genetic code
• essentially completed in 2001, though analysis is ongoing

Question 24

dominant-recessive pattern

Answer 24

-the interaction of a heterozygous pair of alleles in such a way that the phenotype reflects one allele (dominant gene) more than the other (recessive gene)

Question 25

carrier

Answer 25

• 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

Question 26

X-linked

Answer 26

-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

Question 27

copy number variations

Answer 27

-genes with various repeats or deletions of base pairs

Question 28

heritability

Answer 28

-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

Question 29

down syndrome

Answer 29

• 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 distinctive characteristics, including unusual facial features, heart abnormalities, and language difficulties
• aka trisomy-21

Question 30

fragile X syndrome

Answer 30

• 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

Question 31

genetic counseling

Answer 31

-consultation and testing by trained experts that enable individuals to learn about their genetic heritage, including harmful conditions that they might pass along to any children they may conceive

Question 32

PKU

Answer 32

• a genetic disorder in which a child’s body is unable to metabolize an amino acid called phenylalanine
• unless the infant immediately begins a special diet, the resulting buildup of phenylalanine in body fluids causes brain damages, progressive mental retardation, and other symptoms