Chapter 4 Flashcards, Genes and Genetic Diseases

Question 1

What are genes?

Answer 1

Genes are the basic units of inheritance, composed of DNA and located on chromosomes.

Question 2

What are the four types of nitrogenous bases in DNA?

Answer 2

The four types of nitrogenous bases in DNA are A, C, G, and T.

Question 3

What is the physical structure of DNA?

Answer 3

The physical structure of DNA is a double helix.

Question 4

How do DNA bases relate to proteins?

Answer 4

DNA bases code for amino acids, which make up proteins, specified by triplet codons of nitrogenous bases.

Question 5

What is DNA replication based on?

Answer 5

DNA replication is based on complementary base pairing.

Question 6

What is the role of DNA polymerase?

Answer 6

DNA polymerase is the primary enzyme involved in replication, adding bases to the new DNA strand and performing proofreading functions.

Question 7

What is a mutation?

Answer 7

A mutation is an inherited alteration of genetic material (i.e., DNA).

Question 8

What are mutagens?

Answer 8

Substances that cause mutations are called mutagens.

Question 9

What is the mutation rate in humans?

Answer 9

The mutation rate in humans varies from locus to locus and ranges from 10−4 to 10−7 per gene per generation.

Question 10

What are the two basic processes involving RNA?

Answer 10

Transcription and translation are the two basic processes in which proteins are specified by DNA.

Question 11

How is RNA chemically different from DNA?

Answer 11

RNA is single stranded and has uracil rather than thymine as one of its four nitrogenous bases.

Question 12

What is transcription?

Answer 12

Transcription is the process by which DNA specifies a sequence of mRNA.

Question 13

What happens to RNA sequences before mRNA leaves the nucleus?

Answer 13

Much of the RNA sequence is spliced from the mRNA before it leaves the nucleus.

Question 14

What are introns and exons?

Answer 14

Introns are excised sequences, while exons are the sequences that remain to code for proteins.

Question 15

What are microRNAs (miRNAs)?

Answer 15

MicroRNAs are small RNA sequences, 17 to 27 nucleotides in length, that bind to specific mRNA sequences and down-regulate their expression.

Question 16

What is long noncoding RNA (lncRNA)?

Answer 16

Long noncoding RNA (lncRNA) is a nontranslated RNA greater than 200 nucleotides in length, with at least 10,000 lncRNAs in the genome.

Question 17

What do transcription factors do?

Answer 17

Transcription factors bind to DNA sequences called transcription factor binding sites to regulate the timing of transcription.

Question 18

What is translation?

Answer 18

Translation is the process by which RNA directs the synthesis of polypeptides.

Question 19

Where does translation take place?

Answer 19

Translation takes place in the ribosomes.

Question 20

What is the role of tRNA during translation?

Answer 20

During translation, mRNA interacts with tRNA, which has an attachment site for a specific amino acid.

Question 21

What types of cells do humans have?

Answer 21

Humans consist of diploid somatic cells (body cells) and haploid gametes (sperm and egg cells).

Question 22

How many pairs of chromosomes do humans have?

Answer 22

Humans have 23 pairs of chromosomes: 22 pairs are autosomes and 1 pair are sex chromosomes.

Question 23

What are the sex chromosomes for females and males?

Answer 23

Females have two homologous X chromosomes; males have an X and a Y chromosome.

Question 24

What is a karyotype?

Answer 24

A karyotype is an ordered display of chromosomes arranged according to length and the location of the centromere.

Question 25

What can be used to make chromosome bands more visible?

Answer 25

Various types of stains can be used to make chromosome bands more visible.

Question 26

What is the prevalence of major diagnosable chromosome abnormalities?

Answer 26

About 1 in 150 live births has a major diagnosable chromosome abnormality.

Question 27

What are the leading known causes of intellectual disability and miscarriage?

Answer 27

Chromosome abnormalities are the leading known cause of intellectual disability and miscarriage.

Question 28

What is polyploidy?

Answer 28

Polyploidy is a condition in which a euploid cell has some multiple of the normal number of chromosomes.

Question 29

What are triploidy and tetraploidy?

Answer 29

Triploidy is having three copies of each chromosome; tetraploidy is having four copies of each chromosome. Both conditions are lethal.

Question 30

What are aneuploid cells?

Answer 30

Somatic cells that do not have a multiple of 23 chromosomes are aneuploid.

Question 31

What causes aneuploidy?

Answer 31

Aneuploidy is usually the result of nondisjunction.

Question 32

What is trisomy?

Answer 32

Trisomy is a type of aneuploidy in which one chromosome is present in three copies in somatic cells.

Question 33

What is partial trisomy?

Answer 33

A partial trisomy is one in which only part of a chromosome is present in three copies.

Question 34

What is monosomy?

Answer 34

Monosomy is a type of aneuploidy in which one chromosome is present in only one copy in somatic cells.

Question 35

How do monosomies compare to trisomies in terms of physical defects?

Answer 35

In general, monosomies cause more severe physical defects than do trisomies.

Question 36

What is Down syndrome?

Answer 36

Down syndrome is a trisomy of chromosome 21 and affects 1 in 800 live births.

Question 37

Who is more likely to have a child with Down syndrome?

Answer 37

Down syndrome is much more likely to occur in the offspring of women older than 35 years of age.

Question 38

How do sex chromosome aneuploidies compare to autosome aneuploidies?

Answer 38

Most aneuploidies of the sex chromosomes have less severe consequences than those of the autosomes.

Question 39

What are the most commonly observed sex chromosome aneuploidies?

Answer 39

The most commonly observed sex chromosome aneuploidies are 47,XXX; 45,X (Turner syndrome); 47,XXY (Klinefelter syndrome); and 47,XYY.

Question 40

What are some abnormalities of chromosome structure?

Answer 40

Abnormalities of chromosome structure include deletions, duplications, inversions, and translocations.

Question 41

What are Mendelian traits?

Answer 41

Mendelian traits are caused by single genes, each occupying a position, or locus, on a chromosome.

Question 42

What are alleles?

Answer 42

Alleles are different forms of genes located at the same locus on the chromosome.

Question 43

What does an individual have at any given locus in a somatic cell?

Answer 43

An individual has two genes, one from each parent, and may be homozygous or heterozygous for a locus.

Question 44

What is an individual's genotype and phenotype?

Answer 44

An individual's genotype is their genetic makeup, while the phenotype reflects the interaction of genotype and environment.

Question 45

What happens at a heterozygous locus?

Answer 45

At a heterozygous locus, a dominant gene's effects mask those of a recessive gene.

Question 46

When is a recessive gene expressed?

Answer 46

The recessive gene is expressed only when it is present in two copies.

Question 47

What modes of inheritance do genetic diseases caused by single genes usually follow?

Answer 47

Autosomal dominant, autosomal recessive, or X-linked recessive.

Question 48

What is an important tool in the analysis of modes of inheritance?

Answer 48

Pedigree charts.

Question 49

What do recurrence risks specify?

Answer 49

The probability that future offspring will inherit a genetic disease.

Question 50

What is the recurrence risk for autosomal dominant diseases?

Answer 50

Usually 50%.

Question 51

How can germline mosaicism alter recurrence risks?

Answer 51

Unaffected parents can produce multiple affected offspring due to a mutation in the germline.

Question 52

Are skipped generations seen in classic autosomal dominant pedigrees?

Answer 52

No.

Question 53

Are males and females equally likely to exhibit autosomal dominant diseases?

Answer 53

Yes.

Question 54

What is incomplete penetrance?

Answer 54

A gene that is not always expressed phenotypically.

Question 55

Is penetrance age-dependent?

Answer 55

Yes, as seen in Huntington disease and familial breast cancer.

Question 56

What is variable expressivity?

Answer 56

A characteristic of many genetic diseases.

Question 57

What is the recurrence risk for autosomal recessive diseases?

Answer 57

25% when both parents are heterozygous carriers.

Question 58

Are males and females equally likely to be affected by autosomal recessive diseases?

Answer 58

Yes.

Question 59

What is the relationship between consanguinity and autosomal recessive diseases?

Answer 59

Consanguinity is sometimes present and becomes more prevalent with rarer recessive diseases.

Question 60

What is available for an increasing number of autosomal recessive diseases?

Answer 60

Carrier detection tests.

Question 61

How does the frequency of genetic diseases change in the offspring of first-cousin matings?

Answer 61

It approximately doubles.

Question 62

What happens to one of the two X chromosomes in each normal female somatic cell?

Answer 62

One is inactivated early in embryogenesis.

Question 63

What is X inactivation?

Answer 63

Random, fixed, and incomplete inactivation of one X chromosome.

Question 64

How is gender determined embryonically?

Answer 64

By the presence of the SRY gene on the Y chromosome.

Question 65

What are X-linked genes?

Answer 65

Genes located on the X chromosome.

Question 66

Why are X-linked recessive diseases seen more often in males?

Answer 66

Males need only one copy of the gene to express the disease.

Question 67

Can fathers pass X-linked genes to their sons?

Answer 67

No.

Question 68

Are skipped generations often seen in X-linked recessive disease pedigrees?

Answer 68

Yes, due to transmission through carrier females.

Question 69

What do recurrence risks for X-linked recessive diseases depend on?

Answer 69

The carrier and affected status of the mother and father.

Question 70

What is a sex-limited trait?

Answer 70

A trait that occurs in only one of the sexes.

Question 71

What is a sex-influenced trait?

Answer 71

A trait that occurs more often in one sex than in the other.

Question 72

What occurs during meiosis I that can cause recombinations of alleles?

Answer 72

Crossing over occurs and can cause recombinations of alleles located on the same chromosome.

Question 73

How can the frequency of recombinations be used in genetics?

Answer 73

The frequency of recombinations can be used to infer the map distance between loci on the same chromosome.

Question 74

What is the role of a marker locus in genetic disease prediction?

Answer 74

A marker locus, when closely linked to a disease-gene locus, can be used to predict whether an individual will develop a genetic disease.

Question 75

What will facilitate gene identification, diagnosis, and disease treatment?

Answer 75

The complete human genome sequence will facilitate gene identification, diagnosis, and disease treatment.