Patterns of inheritance and variation

Question 1

Chlorosis

Answer 1

Condition in which plat leaves look pale/yellow. This is due to environmental factors such as lack of light, mineral deficiency (eg: Mg), virus infections

Question 2

Continuous variation

Answer 2

Characteristic that can take any value within a range, cause by both genetic and environmental factors.
Polygenes
eg: skin colour, leaf surface area

Question 3

Discontinuous variation

Answer 3

Characteristic that can only appear in specific discrete values.
Monogenes or digenes
eg: blood group, albinism

Question 4

Codominance

Answer 4

When 2 different alleles occur for a gene, both equally dominant. This results in both alleles expressed in the organism’s phenotype.

Question 5

Genes with multiple alleles

Answer 5

eg: immunoglobulin codes for the production of 3 different antigens: iA, iB, i0 (iA and iB are codominant, while i0 is recessive)

Question 6

Determining sex

Answer 6

Determined by the 23rd pair of chromosomes, as the 22 first pairs are identical.
Female = XX
Male = XY

Question 7

Sex linkage

Answer 7

Characteristics determined by genes on the sex chromosomes - genes are said to be sex linked. There are some characteristics on the X chromosome that male only have one copy of, therefore they can’t be expressed if they’re recessive.
(eg haemophilia)

Question 8

Dihybrid crosses

Answer 8

Used to show the inheritance of two different characteristics caused by 2 genes, which can be located on different pairs of homologous chromosomes

Question 9

Linkage

Answer 9

The reason why the ratios observed in many dihybrid crosses differ significantly from those expected. The genes are located on the same chromosome = linkage.
Linked genes are inherited as one unit as there is no independent assortment unless they’re separated by the chiasmata.

Question 10

Autosomal linkage

Answer 10

When the genes that are linked are found on any other chromosome other than the sex chromosome.

Question 11

Recombination frequency

Answer 11

number of recombinant offspring/total number of offspring

Question 12

Recombinant offspring

Answer 12

They have different combinations of allele than either parent. The closer the genes are in terms of locus, the less likely they are to be separated during crossing over and independent assortment.

Question 13

Chi-squared test

Answer 13

Statistical test used to measure the size of difference b/n the observed results and the expected results.

Question 14

Epistasis

Answer 14

Interaction of genes at different loci. (eg: gene regulation)

Question 15

Types of epistasis

Answer 15

Dominant (dominant allele results in a gene having an effect on another gene)
Recessive (2 recessive alleles lead to a change in action eg enzyme action)

Question 16

Hardy-Weinberg principle

Answer 16

In a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next if there will be no evolution.

Question 17

Hardy-Weinberg formula

Answer 17

p^2+2pq+q^2=1
p^2 = freq of homozygous dominant genotype
2pq = freq of heterozygous genotype
q^2 = freq of homozygous recessive genotype

Question 18

Types of selections

Answer 18

Stabilising
Directional
Disruptive

Question 19

Speciation

Answer 19

Formation of new species through the process of evolution.

Question 20

Allopatric speciation

Answer 20

When some members of a population are separated from the rest by a physical barrier such as a river (geographical isolation)

Question 21

Sympatric speciation

Answer 21

Within populations that share the same habitat, when members of two different species interbreed and form infertile offspring.

Question 22

Artificial selection/Selective breeding

Answer 22

The selection is made in order to perform selective breeding, and produce desired characteristics.