Chapter 18: Inheritance

Question 1

Define inheritance.

Answer 1

Inheritance refers to the transmission of traits from one generation to another.

Question 2

What is a hereditary trait?

Answer 2

A hereditary trait is a characteristic that can be passed on from one generation to another.

Question 3

What are some examples of hereditary traits?
(8 pts.)

Answer 3

• Hair type
• Shape of earlobe
• Eye color
• Face shape
• Chin shape
• Ability to roll tongue
• Skin colour
• Blood type

Question 4

What is monohybrid inheritance?

Answer 4

Monohybrid inheritance refers to the inheritance of one characteristic with two contrasting forms.

Each characteristic is controlled by a single gene, consisting of a pair of alleles.

Question 5

Define the term ‘allele’.

Answer 5

Alleles are:
- different forms of a gene that
- occupy the same relative positions on a pair of homologous chromosomes

Question 6

Define the term ‘gene’.

Answer 6

A gene is a:
- unit of inheritance, born on a particular locus of a chromosome
- segment of DNA containing a sequence of nucleotides which code for a single polypeptide

Question 7

How do alleles affect genetic variation?

Answer 7

Different alleles can lead to variations in traits among individuals.They contribute to the genetic diversity within a population.

Question 8

Describe a chromosome.

Answer 8

• rod-like structures visible in the nucleus during cell division
• made up of DNA molecule

Question 9

What is phenotype in genetics?

Answer 9

• observable traits
• influenced by the organism’s genotype and environmental factors.

Question 10

What is genotype in genetics?

Answer 10

• genetic makeup of an organism inherited from its parents
• determines the specific traits that can be expressed in the phenotype.

Question 11

What is homozygous in genetics?

Answer 11

Homozygous refers to having two identical alleles for a particular gene.

Question 12

What is heterozygous in genetics?

Answer 12

Heterozygous refers to having two different alleles for a particular gene.

Question 13

Explain the term ‘dominant allele’.

Answer 13

A dominant allele is an allele that expresses itself in both homozygous dominant and heterozygous conditions.

Question 14

Explain the term ‘recessive allele’

Answer 14

A recessive allele is an allele that will only express itself in a homozygous recessive genotype.

Question 15

Define co-dominance.

Answer 15

Co-dominance refers to when two different alleles of the same genotype are equally expressed in its phenotype.

Question 16

With reference to ABO blood group phenotypes, explain what is meant by co-dominance.

Answer 16

• co-dominance is when two different alleles of the genotype are both expressed evenly in its phenotype
• in the ABO blood group, the alleles IA and IB are codominant
• in an individual with both of these alleles, with a heterozygous IA IB genotype
• both alleles are expressed in its phenotype
• both the antigens A and B are found on the red blood cells
• both of these alleles IA and IB are dominant over the IO allele and will be expressed over the IO allele in the heterozygous individual;

Question 17

What is the Law of Segregation?

Answer 17

Each gamete will only contain one factor for a characteristic

Question 18

How do dominant and recessive alleles affect phenotype?

Answer 18

Dominant alleles can mask the expression of recessive alleles in the phenotype.The presence of at least one dominant allele typically results in the dominant trait being expressed.

Question 19

What are the key differences between discontinuous and continuous variation?

Answer 19

Discontinuous variation: involves a few clear-cut phenotypes
Continuous variation: involves a range of phenotypes

Discontinuous variation: controlled by one or a few genes
Continuous variation: controlled by many genes

Discontinuous variation: not affected by environmental conditions
Continuous variation: affected by environmental conditions

Question 20

What are the sources of genetic variation?

Answer 20

1. Meiosis
   - produces genetically dissimilar gametes with different combinations of parental chromosomes.
2. Random fertilization
   - allows any sperm to fuse with an egg, creating genetic diversity
3. Mutation
   - a change in the sequence of a gene or in chromosome number or structure.

Question 21

Define mutation.

Answer 21

A mutation is a sudden, random change in the DNA structure or chromosomal structure.

Question 22

What are the main causes of mutations in biology?

Answer 22

• Errors during the replication of genes or chromosomes
• Dominant mutations are easily detected, while recessive mutations may remain undetected for generations.

Question 23

What are the two main types of mutations?

Answer 23

• Chromosome mutation
• Gene mutation

Question 24

What is a chromosome mutation and what condition can it cause?

Answer 24

• Change in the structure or number of chromosomes
• Condition:
  -Down syndrome, where individuals have a third copy of chromosome 21.

Question 25

What is **gene mutation** and what are some examples of conditions it can cause?

Answer 25

- Change in the structure of DNA. - Condition: -albinism -sickle-cell anaemia,

Question 26

What are the characteristics of albinism caused by gene mutation?

Answer 26

- Caused by a mutation in a recessive allele. - Results in reddish-white skin, white hair, and pink eyes due to the absence of melanin.

Question 27

What are the causes and effects of sickle-cell anaemia?

Answer 27

- Caused by a mutation in the gene controlling haemoglobin production. - The mutated gene is recessive, expressed only in homozygous recessive individuals. - Sickle-shaped red blood cells have low oxygen carrying capacity and tend to clump together. - This disease is fatal, with sufferers usually dying young - Heterozygous individuals are more resistant to malaria

Question 28

Describe the harmful effects on the body of having red blood cells which become sickle-shaped.

Answer 28

- fewer normal red blood cells - less flexible red blood cells - less haemoglobin, less efficient at transporting oxygen-> less respiration-> less energy / fatigue / exhaustion - blood capillaries are blocked-> increased chance of thrombosis-> death of tissues linked to oxygen supply - poor, growth - reduced life span

Question 29

What role do mutagenic agents play in gene mutations?

Answer 29

Mutagens can greatly increase the rate of mutations. In the absence of mutagens, the rate of spontaneous mutation is extremely low.

Question 30

How do mutations influence natural selection?

Answer 30

- Mutations can be harmful or beneficial to individuals. - Harmful mutations lead to elimination - Beneficial mutations may result in more offspring.

Question 31

What are the main causes of variations in organisms?

Answer 31

- Crossing over and independent assortment of chromosomes during meiosis - Mutations in genetic material that introduce new alleles to the gene pool.

Question 32

Why is genetic variation important for organisms?

Answer 32

- Helps organisms adapt to changing environments - Increases the chances of survival and reproduction in a population

Question 33

Define natural selection.

Answer 33

A process that ensures the best adapted organisms survive to reproduce and pass on their genes to the next generation.

Question 34

What characteristics do organisms selected by nature typically have?

Answer 34

- Resistance to diseases - Better adaptation to changes in the environment

Question 35

What is evolution in the context of natural selection?

Answer 35

The **gradual change** in **inheritable characteristics** of a population over time, driven by the process of **natural selection** acting on **variations**.

Question 36

What are the mechanisms of evolution by natural selection?

Answer 36

_1. Variation and competition for survival_ - Mutations cause organisms to show variation - Changes in environmental factors may result in competition for food, diseases, and possibility of being eaten up by predators. _2. Survival of the fittest_ - Organisms with favourable genes and characteristics that make them better adapted to the environmental conditions are most likely to survive. _3. Reproduction and passing down favourable genes_ - Organisms that survive reproduce and pass down their favourable genes to their offspring. - Over time, more beneficial genes or alleles accumulate in a species.

Question 37

What is the process by which the characteristics of a population change over time?

Answer 37

Evolution

Question 38

What role do mutations play in the survival of bacteria?

Answer 38

- Mutations can lead to genetic variations in bacteria. - Bacteria with mutations that confer antibiotic resistance are more likely to survive and reproduce.

Question 39

What are some examples of mutagenic agents?

Answer 39

Radiation: - UV light, X-ray - alpha and beta radiation - gamma rays Chemicals: - mustard gas - formaldehyde - lysergic acid diethylamide (LSD)

Question 40

Suggest how radiation and chemicals could influence the evolution of a population.

Answer 40

1. Radiation and chemicals are mutagens which cause mutations 2. leading to variations in phenotypes in a population 3. When environment changes, some individuals are more likely to be able to adapt to survive 4. Individuals with a beneficial allele will be selected for + survive + reproduce 5. Individuals pass on their beneficial allele to next generation + an increase in the frequency of that allele in that population 6. Individuals with harmful mutations disappear from population