Chapter 18: Inheritance

Question 1

Inheritance

Answer 1

• the transmission of traits from one generation to another

Question 2

Gene

Answer 2

• a sequence of DNA nucleotides that controls the formation of a single polypeptide. it is also a unit of inheritance

Question 3

Alleles

Answer 3

• different forms of the same genes
• alleles occupy the same relative position on a pair of homologous chromosomes

Question 4

Genotypes

Answer 4

• the combination of alleles for a particular gene

Question 5

Phenotype

Answer 5

• expressed trait or outwards appearance is called phenotype

Question 6

Homozygous

Answer 6

• refers to having 2 identical alleles of a particular gene

Question 7

Heterozygous

Answer 7

• refers to having 2 different alleles of a particular gene

Question 8

Codominant alleles

Answer 8

• in codominance, both alleles express themselves in the heterozygote, which has a phenotype intermediate between that of its pure-bred parents. Alleles are said to be codominant

Question 9

Chromosomes in human body

Answer 9

• there is 1 pair of sex chromosomes and 22 pairs of non-sex chromosomes called autosomes
• human body cells are diploid with 23 pairs of chromosomes (46 chromosomes in total)
• in males, there is one X and one shorter Y chromosome in each body cell
• in females, there is a pair of X chromosomes in each normal body cell

Question 10

Variation

Answer 10

• refers to the differences in traits between individuals of the same species

Question 11

Discontinuous variation

Answer 11

• traits show clear-cut phenotypes with no intermediate form between the traits
• traits are easily distinguishable and are not affected by environmental conditions
• controlled by one or a few genes
• genes do not shows addictive effect
• relatively unaffected by environmental conditions
• ex: blood group

Question 12

Continuous variation

Answer 12

• brought about the combined or addictive effects of many genes
• involves a range of phenotypes
• controlled by many genes
• genes show addictive effects
• greatly affected by environmental conditions
• ex: skin colour

Question 13

Sources of genetic variation

Answer 13

• meiosis, since they produce genetically dissimilar gametes with different combinations of parental chromosomes
• random fertilisation
• mutation

Question 14

Mutation

Answer 14

• a change in the sequence of a gene or in the chromosome number

Question 15

Albinism

Answer 15

• example of gene mutation
• when they are homozygous for the albinism allele are albinos
• they have reddish-white skin and white hair
• the iris does not contain any pigment, so it will appear red because of the colour of the blood vessels in it

Question 16

Sickle cell anaemia

Answer 16

• example of gene mutation, which results in a change in the structure of gene, it involves a change in the sequence of bases or nucleotides in the DNA
• Results into the change in structure of gene that encodes for haemoglobin S protein in red blood cell
• Causes a change in the 3D shape of the haemoglobin molecules, causing them to clump together
• When oxygen concentration in blood decreases, red blood cells becomes sickle shaped and lose ability to transport oxygen and can get stuck in narrow blood vessels, slowing or blocking flow of oxygen to parts of the body

Question 17

Down syndrome

Answer 17

• when a person has 47 instead of 46 chromosomes
• this happens when zygotes when zygotes has an extra copy of copy chromosome 21
• occurs when there is an error during gamete formation of sperm or egg where copies of chromosome 21 do not separate

Question 18

Mutagens

Answer 18

• rate of spontaneous mutation is usually very low
• rate of mutation can be increases with the presence of some chemicals and ionising radiation

Question 19

Natural selection

Answer 19

• refers to a process in which organisms with desirable genes and characteristics are selected or favoured to survive and pass on their genes to their offsprings

Question 20

Evolution

Answer 20

the gradual chance in the inheritable characteristics of a population over time

Question 21

Evolution by natural selection

Answer 21

Variation and competition for survival: mutation causes organisms to show variation. Variation and competition lead to differential survival and reproduction by those organisms best fitted to the envrionment
Survival of fittest: organisms with favourable genes and characteristics that make them better adapted to environmental conditions are more likely to survive
Reproduction and passing down of favourable genes: over time, beneficial qualities may accumulate in species, making it more adaptable to their new envrionment