Genetics and Inheritance

Question 1

Hereditary

Answer 1

Refers to the transmission of characteristics from parents to the offspring

Question 2

Inheritance

Answer 2

Refers to the set of characteristics that have been passed from parents to the offspring

Question 3

Genetics

Answer 3

Refers to the study of hereditary and the variations that occur in the transmission of hereditary characteristics.

Question 4

Genes

Answer 4

The chromosomes are made up of genetic material called DNA, tightly wrapped around proteins
A particular length of DNA at a particular location on the chromosome that influences a particular characteristic is called gene
Each gene has a particular position called its locus on a particular chromosome
Some characteristic are controlled by as single gene found at a single position (locus) on the chromosome- this is called monogenic inheritance
Other characteristics may be controlled by more than one gene found at different positions (loci) on one or more chromosomes- this is called polygenic inheritance

Question 5

Phenotype and Genotype

Answer 5

The external appearance of an organism is referred to as its phenotype
The genetic composition of the individual is known as its genotype

Question 6

Alleles

Answer 6

Alternative forms of a gene found at the same locus, and providing different expressions of a characteristic, are called alleles
Flower colour is controlled by a single gene with two alleles: an allele for red flower and colour and an allele for white flower colour
A diploid organism may have any combination of these two alleles as follows:
2 alleles for red flower colour
2 alleles for white flower colour
2 alleles for red flower colour and 1 allele for white flower colour

Question 7

Define genotype as the combination of alleles that an individual possesses for a particular characteristic

Answer 7

During the formation of gametes by meiosis, homologous chromosomes containing the alleles for each characteristic separate during Anaphase 2. As a result only one allele ends up in each new cell. The haploid gametes therefore will only have one allele for each characteristic. When a male and female gamete fuses, the offspring will have a combination of the alleles from both parents carried by gametes

Question 8

Dominant and Recessive

Answer 8

The alleles of a gene may interact with each other in three different ways (Complete Dominance, Incomplete Dominance, Co-Dominance) which may lead to different phenotypic expressions of a characteristic

In Complete Dominance, one allele is dominant over the other allele. The other allele is said to be recessive. When a dominant allele and a recessive allele together makes up the genotype of an individual, then the dominant allele determines the phenotype. the effect of the recessive allele is masked. Only when two recessive alleles make up the genotype of an individual (In other words, there is no dominant allele), do the recessive alleles influence the phenotype

Question 9

Complete Dominance

Answer 9

One allele is dominant over the other allele. The other allele is said to be recessive. When a dominant allele and recessive allele together make up the genotype of an individual, then the dominant allele determines the phenotype

Question 10

Complete Dominance (Genotype and Phenotype)

Answer 10

RR-Red flower colour (since the allele for red flower colour (R) is dominant)
rr-White flower colour (since the dominant allele for red flower colour (R) is absent, the alleles for white flower colour (r) express themselves in the phenotype)
Rr-Red flower colour (since the allele for red flower colour (R) is dominant

Question 11

Incomplete Dominance

Answer 11

No one allele is dominant over the other. we therefore cannot refer to alleles as being recessive or dominant. When in combination with each other the alleles produce a new, third phenotype

Question 12

Incomplete Dominance (Genotype and Phenotype)

Answer 12

RR-Red flower colour (since both alleles are for red flower colour)
WW-White flower colour (since both alleles are for white flower colour)
RW-Pink flower colour (since neither allele is dominant, the flower colour cannot be either red or white; Pink flowers produced represent a phenotype intermediate between red and white

Question 13

Co-Dominance

Answer 13

Both alleles are equally dominant. When in combination with each other, both alleles will influence the phenotype

Question 14

Co-Dominance (Genotype and Phenotype)

Answer 14

RR-Red flower colour (since both alleles are for red flower colour)
WW-White flower colour (since both alleles are for white flower colour)
RW-Flowers with equal distribution of red and white colour (since both alleles are equally dominant, the flower colour is a combination of the two phenotypes, red and white, each flower will be partly red and partly white

Question 15

Homozygous

Answer 15

When an individual has two copies of the same allele for a particular characteristic, the individual is said to be homozygous (Pure breeding/ true breeding) characteristic

Question 16

Heterozygous

Answer 16

when an individual has two contrasting or different alleles for a characteristic, the individual is said to be heterozygous (Hybrid)