Inheritance

Question 1

Define gene

Answer 1

A unit of inheritance with specific sequence of nucleotides, as part of a DNA molecule that contains information to make polypeptide
(can be passed on from parent to offspring via chromosomes of parents’ gametes)

Question 2

Define allele

Answer 2

Allele is one of two or more different forms of gene, they occupy same locus on pair of homologous chromosomes
(Alleles of particular gene impart particular characteristic)

Question 3

Define dominant allele

Answer 3

An allele that can always be expressed in phenotype when it occurs in homozygous or heterozygous condition

Question 4

Define recessive allele

Answer 4

An allele only expressed in the phenotype when it occurs in homozygous condition

Question 5

Define homozygous dominant/recessive

Answer 5

Organisms having two identical (dominant/recessive) alleles of particular gene

(Two identical homozygous individuals that breed together will be pure breeding)

Question 6

Define heterozygous

Answer 6

Organisms having two different alleles of a particular gene, not pure breeding

Question 7

Define codominance

Answer 7

When both alleles have equal effect on phenotype of offspring.
(In heterozygote, both alleles expressed in phenotype)

Question 8

How is genotype linked to phenotype

Answer 8

Genotype of organism is its genetic make up. Phenotype is organisms physical traits or characteristics. While genotype is genetic information, phenotype is expression of this information in a tangible form

Question 9

Explain why observed ratios differ from expected ratios, especially for small numbers of progeny

Answer 9

If smaller number of plants are used, observed ratio for offspring may not be accurate. Statistically, ratios are often inaccurate when sample size is small. As ratio figures are based on chance, actual progeny would be unlikely to match expected number precisely

Question 10

What are chromosomes called when not sex-linked

Answer 10

Autosomal
(Chromosomes which determine sex of organism known as sex chromosomes)

Question 11

What are patterns of X-linked recessive

Answer 11

Usually more males than females affected
No offspring of affected male affected, making trait skip generations in pedigree, always with unaffected female in intermediate generation

Question 12

What are patterns of X-linked dominant

Answer 12

When male carries affected X chromosome, all female offspring are affected but no male offspring are affected, approximately half of the offspring of affected females are affected, regardless of sex

Question 13

Define variation

Answer 13

The differences in traits between individuals of the same species

Question 14

What are genetic factors in variation

Answer 14

Crossing over in prophase 1
Random/independent assortment of chromosomes at metaphase 1
Random fertilisation of gametes
Chromosomes and gene mutation
Mutation

Question 15

What are environmental effects which cause variation

Answer 15

Characteristics of an organism are mainly determined by genes, expression of certain genes can be affected by specific environmental factors

Question 16

Describe characteristics of continuous variation

Answer 16

Deals with a range of phenotypes, greatly affected by environment conditions, controlled by many genes, differences between individuals are quantitative, continuous range of intermediate values, every possible form between two extremes will exist

Question 17

Describe characteristics of discontinuous variation

Answer 17

Deal with few clear-cut phenotype, relative unaffected by the environmental conditions, controlled by one or few genes, differences between the individuals are qualitative, discrete groups and no intermediate forms

Question 18

Define evolution

Answer 18

The change in heritable characteristics of biological populations over successive generations

Question 19

State Darwin’s theory of evolution

Answer 19

All species of organisms arise and develop through the natural selection of small, inherited variations that increase the individual’s ability to compete, survive and reproduce

Question 20

What are 6 main principles of natural selection

Answer 20

Variation, heredity, overproduction, limited resources(selection pressure), fitness(survival of fittest), genetic composition

Question 21

Describe how natural selection works

Answer 21

Variation within the population is caused by spontaneous mutation. When there is change in environment, only the fittest will survive. Those with (genetic variation) best adapted to (environment) will be more likely to survive till maturity. They have higher chance of reproducing and passing down desirable genes to offspring. Offspring increase in proportion in population and proportion of favourable genes in gene pool of species increases. Such preservation of favourable variations and elimination of unfavourable ones known as natural selection. When repeated in every generation, more and more favourable genes are accumulated in gene pool and species better adapted to environment