3C1 Heredity

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

Which base is unique to RNA?

Answer 5

Uracil

Uracil replaces thymine in RNA and pairs with adenine during 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 four nitrogenous bases in DNA?

Answer 7

• Adenine
• Thymine
• Cytosine
• Guanine

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

Question 8

What are the building blocks of DNA?

Answer 8

Nucleotides

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

Question 9

Fill in the blank:

In DNA, adenine pairs with _______.

Answer 9

Thymine

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

Question 10

What is the function of DNA?

Answer 10

Storing genetic information.

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

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

Fill in the blank:

DNA replication occurs in the ________ of eukaryotic cells.

Answer 12

nucleus

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

Question 13

What is transcription?

Answer 13

The process of creating RNA from a DNA template.

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

Question 14

What are the three types of RNA?

Answer 14

• mRNA
• tRNA
• rRNA

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

Question 15

What is the function of mRNA?

Answer 15

It carries the genetic code for protein synthesis.

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

Question 16

Where does transcription occur in eukaryotic cells?

Answer 16

In the nucleus.

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

Question 17

What enzyme catalyzes transcription?

Answer 17

RNA polymerase

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

Question 18

True or False:

Transcription occurs in the cytoplasm of prokaryotes.

Answer 18

True

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

Question 19

What are the three main stages of transcription?

Answer 19

1. Initiation
2. Elongation
3. Termination

Initiation begins the process, elongation builds the RNA strand, and termination ends transcription.

Question 20

Fill in the blank:

RNA polymerase binds to the _______ during transcription initiation.

Answer 20

promoter

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

Question 21

What is the central dogma of molecular biology?

Answer 21

DNA → RNA → Protein

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

Question 22

Why is the central dogma important?

Answer 22

It explains how genetic information leads to protein synthesis.

The central dogma outlines the essential flow of information needed for gene expression and protein production.

Question 23

Fill in the blank:

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

Answer 23

tRNA

(transfer RNA)

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

Question 24

Define:

codon

Answer 24

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 25

What is the start codon in **mRNA**?

Answer 25

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

Question 26

What **molecule** provides energy for translation?

Answer 26

GTP | (Guanosine triphosphate) ## Footnote **GTP** provides energy for various steps in the translation process, such as tRNA binding and ribosome movement.

Question 27

What are **chromosomes**?

Answer 27

**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 28

What is a **karyotype**?

Answer 28

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

Question 29

# Define: Gene

Answer 29

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 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

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

Answer 31

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

Question 32

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

Answer 32

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

Question 33

What are **autosomes**?

Answer 33

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

Question 34

What are **sex chromosomes**?

Answer 34

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 35

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

Answer 35

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 36

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

Answer 36

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

Question 37

What are **chromosomal** mutations?

Answer 37

**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 38

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

Answer 38

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

Question 39

What is an **allele**?

Answer 39

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 40

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

Answer 40

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

Question 41

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

Answer 41

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 42

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

Answer 42

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 43

List **three advantages** of sexual reproduction.

Answer 43

1. Genetic Variation 2. Better Disease Resistance 3. Elimination of Harmful Mutations ## Footnote **Genetic Variation** – Increases adaptability and evolution potential. **Better Disease Resistance** – Inheriting diverse genes may improve survival. **Elimination of Harmful Mutations** – Genetic recombination can help remove deleterious traits.

Question 44

List **three disadvantages** of sexual reproduction.

Answer 44

1. Requires finding a mate. 2. Slower reproductive cycle. 3. High energy investment in offspring. ## Footnote Mating can be **difficult**, especially in isolated populations. The process is time-consuming, and energy is spent on producing and nurturing offspring, making it less efficient in rapid population expansion.

Question 45

What makes **asexual reproduction** efficient?

Answer 45

It allows **rapid** population growth. ## Footnote Since offspring are *clones* of the parent, no time is wasted on finding a mate. This is beneficial in environments where survival depends on quickly increasing numbers.

Question 46

List **three types** of asexual reproduction.

Answer 46

1. Binary fission 2. Budding 3. Fragmentation ## Footnote **Binary fission** – Cell splits into two (e.g., bacteria). **Budding** – Offspring grows from the parent (e.g., yeast, hydra). **Fragmentation** – Body parts regenerate into new organisms (e.g., starfish).

Question 47

# True or False: Sexual reproduction results in **faster population growth** than asexual reproduction.

Answer 47

False ## Footnote *Sexual reproduction* requires finding a mate and has a longer reproductive cycle, whereas *asexual reproduction* allows for rapid cloning and exponential growth.

Question 48

# Fill in the blank: Sexual reproduction **increases** ____ ____ within a population.

Answer 48

genetic variation ## Footnote This variation helps species **survive** environmental changes, as some individuals may have traits that offer a *survival advantage*.

Question 49

What does a **Punnett square** show?

Answer 49

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 50

# Define: homozygous genotype

Answer 50

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

Question 51

What is **genotype**?

Answer 51

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 52

# Define: phenotype

Answer 52

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 53

What is a **dominant** trait?

Answer 53

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 54

What is a **recessive** trait?

Answer 54

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 55

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

Answer 55

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

Question 56

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

Answer 56

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

Question 57

# Define: heterozygous genotype

Answer 57

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

Question 58

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

Answer 58

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

Question 59

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

Answer 59

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

Question 60

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

Answer 60

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 61

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

Answer 61

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

Question 62

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

Answer 62

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 63

# 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 63

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 64

What does a **pedigree chart** represent?

Answer 64

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 65

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

Answer 65

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

Question 66

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

Answer 66

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

Question 67

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

Answer 67

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

Question 68

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

Answer 68

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

Question 69

# Define: Incomplete dominance

Answer 69

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 70

What is **codominance**?

Answer 70

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 71

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

Answer 71

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 72

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

Answer 72

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

Question 73

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

Answer 73

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

Question 74

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

Answer 74

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 75

What is a **mutation**?

Answer 75

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 76

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

Answer 76

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 77

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

Answer 77

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 78

What is a **point mutation**?

Answer 78

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 79

# Define: Frameshift mutation

Answer 79

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 80

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

Answer 80

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

Question 81

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

Answer 81

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