(Paper 2) 6.2 Inheritance, Variation, and Evolution: Genetic inheritance

Question 1

What is a gene?

Answer 1

A small section of DNA on a chromosome that codes for a particular protein.

Question 2

What are alleles?

Answer 2

Different versions of the same gene (e.g., blue eye allele, brown eye allele).

Question 3

What does homozygous mean?

Answer 3

Having two identical alleles for a characteristic (e.g., AA or aa).

Question 4

What does heterozygous mean?

Answer 4

Having two different alleles for a characteristic (e.g., Aa).

Question 5

What is a dominant allele?

Answer 5

An allele that is always expressed if present. Represented by a capital letter (e.g., A).

Question 6

What is a recessive allele?

Answer 6

An allele that is only expressed if two copies are present. Represented by a lowercase letter (e.g., a).

Question 7

What is a genotype?

Answer 7

The genetic makeup (the combination of alleles, e.g., Aa, AA, aa).

Question 8

What is a phenotype?

Answer 8

The physical characteristics resulting from the genotype (e.g., blue eyes).

Question 9

How are chromosomes inherited?

Answer 9

In pairs – one from each parent.

Question 10

Can some characteristics be controlled by a single gene? Give examples.

Answer 10

Yes – e.g., fur colour in animals and red-green colour blindness in humans.

Question 11

What is a monohybrid cross?

Answer 11

A genetic cross that examines the inheritance of one gene with two alleles.

Question 12

What tool is used to show genetic crosses and predict offspring combinations?

Answer 12

A Punnett square.

Question 13

In a Punnett square, what do capital letters represent?

Answer 13

Dominant alleles (e.g., T for tall plants).

Question 14

In a Punnett square, what do lowercase letters represent?

Answer 14

Recessive alleles (e.g., t for short plants).

Question 15

What are the offspring genotypes if a TT (tall) plant is crossed with a tt (short) plant?

Answer 15

All offspring are Tt (heterozygous, tall).

Question 16

What is the phenotype of Tt offspring (tall × short)?

Answer 16

All are tall (because T is dominant).

Question 17

What are the genotypes and ratios if Dd is crossed with dd?

Answer 17

2 Dd : 2 dd → 1:1 ratio

Question 18

How do you express outcomes of a genetic cross?

Answer 18

As direct proportion, probability, or ratio.

Question 19

What is the probability of getting each genotype in a 1:1 Punnett square?

Answer 19

50% for each genotype (e.g., 50% Dd, 50% dd).

Question 20

Why do we use probability when predicting inheritance?

Answer 20

Because fertilisation is random and outcomes are not guaranteed.

Question 21

How many pairs of chromosomes do humans have?

Answer 21

23 pairs.

Question 22

What are the first 22 pairs of chromosomes called?

Answer 22

Autosomes – they control most characteristics.

Question 23

What is the 23rd pair of chromosomes called?

Answer 23

The sex chromosomes – they determine biological sex.

Question 24

What are the sex chromosomes in males?

Answer 24

XY

Question 25

What are the sex chromosomes in females?

Answer 25

XX

Question 26

Which parent determines the sex of the baby?

Answer 26

The father, because he can pass on either an X or a Y chromosome.

Question 27

What sex results from an X from the mother and an X from the father?

Answer 27

Female (XX)

Question 28

What sex results from an X from the mother and a Y from the father?

Answer 28

Male (XY)

Question 29

What is the ratio of male to female offspring?

Answer 29

1:1 or 50% male, 50% female.

Question 30

What does a Punnett square show in sex determination?

Answer 30

The possible combinations of X and Y chromosomes and the resulting probabilities of male or female offspring.

Question 31

What type of disorder is cystic fibrosis?

Answer 31

A recessive inherited disorder affecting cell membranes.

Question 32

What organs are mainly affected by cystic fibrosis?

Answer 32

The lungs and digestive system.

Question 33

Which allele causes cystic fibrosis, and how is it represented?

Answer 33

A faulty recessive allele, shown as f.

Question 34

What genotype causes someone to have cystic fibrosis?

Answer 34

ff (homozygous recessive).

Question 35

What genotype makes a person a carrier of cystic fibrosis without symptoms?

Answer 35

Ff (heterozygous).

Question 36

What is the genotype of a person who is unaffected and not a carrier of CF?

Answer 36

FF (homozygous dominant).

Question 37

If two carriers (Ff and Ff) have a child, what is the chance the child will have CF?

Answer 37

25% or 1 in 4.

Question 38

If one parent is a carrier (Ff) and the other is unaffected (FF), can their child have CF?

Answer 38

No, but there's a 50% chance the child will be a carrier.

Question 39

What is polydactyly?

Answer 39

A condition where a person has extra fingers or toes.

Question 40

Is polydactyly caused by a dominant or recessive allele?

Answer 40

A dominant allele, shown as P.

Question 41

What genotypes result in polydactyly?

Answer 41

PP (homozygous dominant) or Pp (heterozygous).

Question 42

Can someone with polydactyly pass the condition to their child if the other parent is unaffected?

Answer 42

Yes – there’s a 50% chance if the affected parent is Pp.

Question 43

What is genetic testing?

Answer 43

The analysis of a person’s DNA to detect alleles for genetic disorders.

Question 44

What is antenatal testing?

Answer 44

Genetic testing of a foetus before birth, to check for inherited disorders.

Question 45

What is neonatal testing?

Answer 45

A newborn blood spot test, used to detect inherited disorders soon after birth.

Question 46

What is Pre-implantation Genetic Diagnosis (PGD)?

Answer 46

Testing embryos for genetic disorders before implantation during IVF.

Question 47

How is PGD done?

Answer 47

A single cell is removed from an embryo created via IVF and tested for faulty alleles. Only healthy embryos are implanted.

Question 48

Are genetic tests available for all inherited disorders?

Answer 48

No, genetic tests are not available for every disorder.

Question 49

Are genetic tests always reliable?

Answer 49

No, they can give false positives or false negatives.

Question 50

What is a false positive in genetic testing?

Answer 50

A result that wrongly detects a faulty allele, suggesting the person has a disorder when they do not.

Question 51

What is a false negative in genetic testing?

Answer 51

A result that misses a faulty allele, wrongly suggesting the person does not have a disorder when they do.

Question 52

Why are false negatives especially serious in genetic testing?

Answer 52

Parents may not prepare for a child with an inherited disorder, impacting care and support plans.

Question 53

What is gene therapy?

Answer 53

A technique to insert normal alleles into cells of people with faulty alleles to treat genetic disorders.

Question 54

What are the basic steps of gene therapy?

Answer 54

Identify the faulty gene Use restriction enzymes to cut out the normal allele Make copies of the normal allele Insert the normal allele into target cells

Question 55

What are three problems with gene therapy?

Answer 55

Alleles may not reach every target cell Alleles may insert into the wrong place in DNA Treated cells may be replaced by untreated ones through mitosis

Question 56

Name three delivery methods used in gene therapy.

Answer 56

Nose sprays Modified cold viruses Direct DNA injection

Question 57

Why do some people support gene therapy?

Answer 57

It can prevent suffering and treat genetic disorders.

Question 58

Why do some people oppose gene therapy?

Answer 58

They believe it is unnatural or has ethical concerns.

Question 59

Does gene therapy affect future generations?

Answer 59

No, it only affects the individual treated, not their offspring.

Question 60

Who was Gregor Mendel?

Answer 60

A 19th-century scientist who studied inheritance in pea plants and is known as the father of genetics.

Question 61

What did Mendel discover about red and white flower colour in pea plants?

Answer 61

Red flower allele is dominant; white is recessive.

Question 62

What happened when Mendel crossed red-flowered plants with white-flowered ones?

Answer 62

All offspring had red flowers (Ff – heterozygous).

Question 63

What happened when Mendel bred two heterozygous (Ff) red-flowered plants?

Answer 63

75% had red flowers (FF or Ff), 25% had white (ff).

Question 64

What ratio did Mendel find in his second cross?

Answer 64

1 FF : 2 Ff : 1 ff

Question 65

What did Mendel call the factors passed from parent to offspring?

Answer 65

Units – now known as genes.

Question 66

Why was Mendel’s work not accepted during his lifetime?

Answer 66

Poor communication Published in an obscure journal He couldn’t explain the biological mechanism of inheritance

Question 67

When did scientists start accepting Mendel’s ideas?

Answer 67

In the early 20th century, when scientists discovered chromosomes.

Question 68

What discovery in the late 19th century helped validate Mendel’s ideas?

Answer 68

Scientists observed that chromosomes behaved like Mendel’s units during cell division.

Question 69

When was the structure of DNA discovered?

Answer 69

In the mid-20th century by Watson and Crick, using Franklin and Wilkins’ data.

Question 70

What structure did Watson and Crick discover?

Answer 70

The double helix structure of DNA with base pairing.

Question 71

What did the discovery of DNA’s structure help scientists understand?

Answer 71

How genes code for proteins.

Question 72

How did Mendel’s work contribute to gene therapy today?

Answer 72

It laid the foundation for understanding inheritance, leading to modern genetic research and gene therapy.