3A4 Genetics and Protein Synthesis

Question 1

What does DNA stand for?

Answer 1

Deoxyribonucleic acid

DNA is a molecule that carries genetic instructions for the development, functioning, growth, and reproduction of all known living organisms.

Question 2

What does RNA stand for?

Answer 2

Ribonucleic acid

RNA plays a role in protein synthesis and can act as genetic material in some viruses.

Question 3

What is the shape of the DNA molecule?

Answer 3

Double helix

DNA’s double-helix structure was discovered by James Watson and Francis Crick, supported by Rosalind Franklin’s X-ray diffraction data.

Question 4

What sugar is found in DNA?

Answer 4

Deoxyribose

Deoxyribose is a 5-carbon sugar that lacks an oxygen atom at the 2’ position, distinguishing it from ribose in RNA.

Question 5

What are the four nitrogenous bases in DNA?

Answer 5

• Adenine
• Thymine
• Cytosine
• Guanine

Adenine pairs with thymine, and cytosine pairs with guanine through complementary base pairing.

Question 6

True or False:

Thymine is found in RNA.

Answer 6

False

Thymine is found only in DNA, whereas RNA contains uracil instead.

Question 7

What are the building blocks of DNA?

Answer 7

Nucleotides

Each nucleotide consists of a phosphate group, deoxyribose sugar, and a nitrogenous base.

Question 8

Fill in the blank:

In DNA, adenine pairs with _________.

Answer 8

Thymine

Adenine pairs with thymine through two hydrogen bonds, maintaining the double-helix structure.

Question 9

What is the function of DNA?

Answer 9

Storing genetic information.

DNA serves as the blueprint for all cellular processes and is passed from parent to offspring.

Question 10

Which base is unique to RNA?

Answer 10

Uracil

Uracil replaces thymine in RNA and pairs with adenine during base pairing.

Question 11

True or False:

RNA is double-stranded like DNA.

Answer 11

False

RNA is typically single-stranded, although it can fold into complex shapes for specific functions.

Question 12

What are the three types of RNA?

Answer 12

• mRNA
• tRNA
• rRNA

mRNA carries genetic code, tRNA brings amino acids, and rRNA forms ribosomes.

Question 13

Fill in the blank:

DNA replication occurs in the ________ of eukaryotic cells.

Answer 13

nucleus

DNA replication takes place during the S-phase of the cell cycle in the nucleus.

Question 14

What is the function of mRNA?

Answer 14

Carrying the genetic code for protein synthesis.

Messenger RNA (mRNA) transfers genetic information from DNA to ribosomes for translation.

Question 15

What is transcription?

Answer 15

The process of creating RNA from a DNA template.

This occurs in the nucleus where RNA polymerase synthesizes messenger RNA (mRNA).

Question 16

Fill in the blank:

During translation, amino acids are brought to the ribosome by _______.

Answer 16

tRNA

(transfer RNA)

tRNA contains anticodons that pair with mRNA codons, allowing amino acids to assemble into proteins.

Question 17

What is the central dogma of molecular biology?

Answer 17

DNA → RNA → Protein

The central dogma explains the flow of genetic information: DNA is transcribed into RNA, which is then translated into proteins.

Question 18

Where does transcription occur in eukaryotic cells?

Answer 18

In the nucleus.

In eukaryotes, DNA is located in the nucleus, so transcription must occur there.

Question 19

What enzyme catalyzes transcription?

Answer 19

RNA polymerase

This enzyme binds to the DNA template strand and synthesizes complementary RNA.

Question 20

True or False:

Transcription occurs in the cytoplasm of prokaryotes.

Answer 20

True

In prokaryotes, transcription occurs in the cytoplasm because they lack a nucleus.

Question 21

Fill in the blank:

RNA polymerase binds to the ______ during transcription initiation.

Answer 21

promoter

The promoter is a DNA sequence that signals the start of transcription.

Question 22

Define:

codon

Answer 22

A sequence of 3 nucleotides that code for a specific amino acid.

Also referred to as triplet code, these sequences exist in both DNA and RNA.

For example, the codon “CAG” codes for the synthesis of the amino acid glutamine.

Question 23

What is the start codon in mRNA?

Answer 23

AUG

AUG codes for the amino acid methionine, and signals the beginning of translation.

Question 24

What molecule provides energy for translation?

Answer 24

GTP

(Guanosine triphosphate)

GTP provides energy for various steps in the translation process, such as tRNA binding and ribosome movement.

Question 25

Why is the central dogma **important**?

Answer 25

It explains how genetic information **leads** to protein synthesis. ## Footnote The *central dogma* outlines the essential flow of information needed for gene expression and protein production.

Question 26

What are **chromosomes**?

Answer 26

**Structures** made of DNA and proteins that carry genetic information. ## Footnote Chromosomes are found in the nucleus of eukaryotic cells and contain **genes** that determine traits.

Question 27

How **many** chromosomes do humans have in each somatic cell?

Answer 27

46 chromosomes (23 pairs) ## Footnote Humans inherit 23 chromosomes from *each parent*, resulting in 23 pairs of homologous chromosomes.

Question 28

# Define: Gene

Answer 28

A **segment of DNA** that codes for a specific protein or trait. ## Footnote They are the basic units of heredity and determine specific characteristics, such as eye color or blood type.

Question 29

What are the three main **stages** of transcription?

Answer 29

1. Initiation 1. Elongation 1. Termination ## Footnote Initiation begins the process, elongation builds the RNA strand, and termination ends transcription.

Question 30

Where are genes **located**?

Answer 30

On chromosomes. ## Footnote Genes occupy specific positions called **loci** on chromosomes. Each gene carries instructions for a trait.

Question 31

# True or False: All chromosomes are **identical** in structure and function.

Answer 31

False ## Footnote Chromosomes vary in size, shape, and the genetic information they carry. Autosomes and sex chromosomes have different roles.

Question 32

What is an **allele**?

Answer 32

A **variant** form of a gene. ## Footnote Alleles are different versions of the same gene that can result in variations in a trait, such as blue or brown eyes.

Question 33

Generally, how **many** alleles for a gene does an individual inherit?

Answer 33

**Two**—one from each parent. ## Footnote For *most* traits, individuals inherit one allele from the mother and one from the father.

Question 34

# Fill in the blank: Chromosomes are **made** up of \_\_\_\_\_ and proteins.

Answer 34

DNA ## Footnote Chromosomes consist of tightly packed DNA molecules wrapped around proteins called histones.

Question 35

What are **sex chromosomes**?

Answer 35

Chromosomes that **determine the biological sex** of an organism. ## Footnote Humans have **two** sex chromosomes—XX in females and XY in males. There are some genetic conditions where people inherit more than two sex chromosomes, such as Klinfelter (XXY) and Triple X Syndrome (XXX).

Question 36

What is **genotype**?

Answer 36

The genetic **makeup** of an organism. ## Footnote Genotype refers to the *combination* of alleles (e.g., AA, Aa, or aa) inherited from both parents that determine an organism's traits.

Question 37

# Define: phenotype

Answer 37

The **outward presentation** of an individual based on the genotype. ## Footnote Phenotypes can be easily observed, such as eye color. Phenotypes are determined by the genotype, or genetic allele combination, of someone's DNA.

Question 38

What is a **dominant** trait?

Answer 38

A trait where **only 1 copy of the allele is needed** to express the trait. ## Footnote Dominant traits are expressed in both homozygous dominant (AA) and heterozygous (Aa) individuals, masking the recessive trait.

Question 39

What is a **recessive** trait?

Answer 39

A trait expressed only when **both alleles are recessive**. ## Footnote A recessive trait will not be observed in the presence of a dominant allele (Aa or AA) but will be expressed in homozygous recessive individuals (aa).

Question 40

# Define: homozygous genotype

Answer 40

Having **two identical alleles** for a gene. ## Footnote A homozygous genotype can be **either** dominant (AA) or recessive (aa).

Question 41

# Define: heterozygous genotype

Answer 41

Having **two different alleles** for a gene.

Question 42

# True or False: **Mutations** in genes can lead to changes in traits.

Answer 42

True ## Footnote Mutations are changes in the DNA sequence that can **alter** the structure or function of proteins, resulting in new traits.

Question 43

What are **autosomes**?

Answer 43

Chromosomes that **do not** determine sex. ## Footnote Humans have *22 pairs* of autosomes, which carry genes for most traits.

Question 44

What is a **karyotype**?

Answer 44

A **visual representation** of all the chromosomes in a cell. ## Footnote They are used to *study* chromosome structure, number, and abnormalities.

Question 45

# Fill in the blank: The complete **set** of an organism's genetic material is called its \_\_\_\_\_\_\_\_.

Answer 45

genome ## Footnote The **genome** includes all the DNA in an organism, including all its genes and chromosomes.

Question 46

What is the **genotype** of an individual with a recessive trait?

Answer 46

Homozygous recessive (aa) ## Footnote A recessive trait can only be observed when both alleles are recessive, meaning the genotype must be **aa**.

Question 47

What is the **genotype** of a homozygous dominant individual?

Answer 47

AA ## Footnote Homozygous dominant individuals have two copies of the dominant allele, ensuring the dominant trait is expressed.

Question 48

# True or False: Heterozygous individuals express the **recessive** trait.

Answer 48

False ## Footnote Heterozygous individuals (Aa) express the **dominant** trait, as the dominant allele masks the recessive allele.

Question 49

What is the **result** of a homozygous dominant x homozygous recessive cross?

Answer 49

All offspring will be **heterozygous**. ## Footnote A cross between homozygous dominant (AA) and homozygous recessive (aa) parents produces offspring with the genotype **Aa**, all expressing the dominant trait.

Question 50

# True or False: Two homozygous recessive parents can produce offspring with a **dominant** trait.

Answer 50

False ## Footnote Two homozygous recessive parents (aa x aa) can only pass on **recessive** alleles, so all offspring will express the recessive trait.

Question 51

What does a **Punnett square** show?

Answer 51

It shows the **probability** of offspring genotypes. ## Footnote Punnett squares help *visualize* how alleles from both parents combine, providing a probability of different genotype combinations in the offspring.

Question 52

What is the **probability** of offspring having a dominant phenotype in a cross between a heterozygous (Aa) and a homozygous recessive (aa) organism?

Answer 52

50% ## Footnote The Punnett square shows that **50%** of the offspring will inherit the dominant allele (A) from the heterozygous parent, resulting in a dominant phenotype (Aa).

Question 53

What is a **sex-linked** trait?

Answer 53

A trait controlled by **genes located on the X or Y chromosome**. ## Footnote Sex-linked traits are often more **common** in males because they have only one X chromosome. An example is red-green color blindness, which is X-linked.

Question 54

Why are sex-linked traits more common in **males** than in females?

Answer 54

Males have only **one** X chromosome. ## Footnote Males inherit their X chromosome from their mother and the Y chromosome from their father. A recessive allele on the X chromosome will be expressed in males because they lack a second X chromosome to mask it.

Question 55

# True or False: Females must inherit **two** copies of a recessive allele on the X chromosome for the recessive sex-linked trait to be expressed.

Answer 55

True ## Footnote Females have two X chromosomes, so they need two copies of the recessive allele (one on each X) to express the recessive sex-linked trait, such as color blindness.

Question 56

What does a **pedigree chart** represent?

Answer 56

A family tree that shows the **inheritance of traits across generations**. ## Footnote Pedigrees are used to track the *inheritance* of specific traits, showing the genotypes of family members and how traits are passed through generations.

Question 57

What is the **probability** of a child inheriting a recessive trait from two heterozygous (Aa) parents?

Answer 57

25% ## Footnote The Punnett square shows a **25%** chance (aa) of inheriting two recessive alleles, resulting in the expression of the recessive trait.

Question 58

# Fill in the blank: A \_\_\_\_\_\_\_\_ cross is a genetic cross involving **two** traits.

Answer 58

Dihybrid ## Footnote A *dihybrid cross* tracks two traits, such as seed color and shape, to observe how they assort independently.

Question 59

# True or False: In a monohybrid cross, **two** traits are observed.

Answer 59

False ## Footnote A monohybrid cross focuses on a **single** trait, while a dihybrid cross examines the inheritance of two traits simultaneously.

Question 60

What is the **probability** of offspring inheriting a dominant trait from a homozygous dominant (AA) and heterozygous (Aa) parent?

Answer 60

100% ## Footnote All offspring will inherit at least **one** dominant allele (A), resulting in the expression of the dominant trait.

Question 61

# Define: Incomplete dominance

Answer 61

A genetic scenario where the heterozygote displays an **intermediate phenotype**. ## Footnote In incomplete dominance, *neither* allele is completely dominant over the other, leading to an intermediate expression of traits. For example, crossing red and white flowers may result in pink flowers.

Question 62

What is **codominance**?

Answer 62

Inheritance where **both** alleles are expressed in the heterozygote. ## Footnote Codominance occurs when both alleles contribute equally and visibly to the phenotype. An example is the AB blood group, where both A and B alleles are expressed.

Question 63

# True or False: In incomplete dominance, the heterozygote phenotype is a **blend** of the two homozygotes.

Answer 63

True ## Footnote In *incomplete dominance*, the offspring’s phenotype is a blend of the parental traits, such as pink flowers from red and white flower parents.

Question 64

What would be the **phenotype** of a red-flowered (RR) and white-flowered (WW) snapdragon cross in incomplete dominance?

Answer 64

Pink flowers (RW) ## Footnote Since neither allele is dominant, the resulting phenotype is a **blend** of the two homozygotes, resulting in pink flowers.

Question 65

In the case of a black (BB) chicken and a white (WW) chicken, what would be the **phenotype** of their offspring?

Answer 65

Black and white feathers. ## Footnote In *codominance*, both black and white alleles would be expressed equally in the offspring, resulting in speckled feathers.

Question 66

# True or False: In a cross between two pink (RW) snapdragons, the expected phenotypic **ratio** is 1 red, 2 pink, and 1 white.

Answer 66

True ## Footnote The Punnett square for two RW parents shows a 1:2:1 phenotypic ratio: 25% red (RR), 50% pink (RW), and 25% white (WW).

Question 67

What is a **mutation**?

Answer 67

A **change** in the DNA sequence. ## Footnote Mutations can occur naturally or due to environmental factors like radiation, chemicals, or viruses. These changes can lead to genetic variation, which may or may not affect an organism’s *traits*.

Question 68

What are the **two** main types of mutations?

Answer 68

1. Gene mutations 2. Chromosomal mutations ## Footnote Gene mutations affect a single gene, while chromosomal mutations involve changes to the structure or number of chromosomes.

Question 69

# True or False: Mutations **always** result in harmful effects.

Answer 69

False ## Footnote While mutations can be harmful, beneficial, or neutral, not all mutations result in negative outcomes. Some mutations may even provide advantages in certain environments.

Question 70

What is a **point mutation**?

Answer 70

A mutation that **affects** a single nucleotide in DNA. ## Footnote Point mutations can change one base pair in the gene sequence, potentially altering the protein product. Examples include silent mutations, missense mutations, and nonsense mutations.

Question 71

# Define: Frameshift mutation

Answer 71

A mutation that **shifts** the reading frame of the gene. ## Footnote Frameshift mutations *occur* when nucleotides are inserted or deleted, causing the sequence to shift and change the downstream codons, which can significantly affect the protein’s function.

Question 72

What are **chromosomal** mutations?

Answer 72

**Changes** in the structure or number of chromosomes. ## Footnote Chromosomal mutations can include deletions, duplications, inversions, and translocations. They can lead to disorders such as Down syndrome or Turner syndrome.

Question 73

# Fill in the blank: \_\_\_\_\_\_\_\_\_ mutations **result** in the loss or addition of one or more nucleotides in the DNA sequence.

Answer 73

Frameshift ## Footnote Frameshift mutations can have severe effects, potentially leading to a completely different protein being made or no protein at all.

Question 74

What genetic disorder is characterized by an extra copy of **Chromosome 21**?

Answer 74

Down Syndrome ## Footnote Down syndrome, or *trisomy 21*, occurs when there is a third copy of chromosome 21 instead of the usual two, leading to developmental and intellectual disabilities.

Question 75

What is the most **common genetic disorder** caused by a mutation in a single gene?

Answer 75

Cystic fibrosis ## Footnote *Cystic fibrosis* is caused by mutations in the CFTR gene, leading to the production of thick, sticky mucus that affects the lungs and digestive system.

Question 76

# Fill in the blank: \_\_\_\_\_\_\_\_ \_\_\_\_\_\_\_\_\_ is a chromosomal **abnormality** characterized by an extra chromosome 13.

Answer 76

Patau syndrome ## Footnote *Patau syndrome* (trisomy 13) leads to severe intellectual disability, physical abnormalities, and a shortened life expectancy.

Question 77

What is the genetic basis of **sickle cell anemia**?

Answer 77

A point mutation in the **hemoglobin** gene. ## Footnote The mutation causes the hemoglobin protein to form abnormally, leading red blood cells to become sickle-shaped, which can block blood flow and cause pain.

Question 78

What is **genetic screening**?

Answer 78

A **test** to detect genetic disorders or risk factors in individuals. ## Footnote Genetic screening helps identify people who carry genes for genetic disorders, those who might be at risk for conditions like breast cancer, or those who may pass on a genetic condition to their children.

Question 79

What is the role of **genetic counseling**?

Answer 79

To support and **educate** about genetic conditions. ## Footnote It helps people understand the risk of inherited genetic disorders, make informed decisions, and manage potential health issues. It is useful in cases of inherited diseases, pregnancy, and family planning.

Question 80

# True or False: Genetic counseling can **only** be done before pregnancy.

Answer 80

False ## Footnote Genetic counseling can be beneficial before and during pregnancy, as well as for individuals with existing genetic conditions or concerns about inherited diseases.

Question 81

What is the purpose of **prenatal genetic testing**?

Answer 81

To **assess the risk of genetic disorders** in a fetus. ## Footnote Prenatal genetic testing, such as amniocentesis or chorionic villus sampling (CVS), helps detect conditions like down syndrome, cystic fibrosis, and sickle cell anemia in unborn children.