Monohybrid Crosses

Question 1

What is a Monohybrid Cross

Answer 1

A Monohybrid Cross refers to reproduction between two individuals where we are concerned with the inheritance of only one characteristic or trait. For example, one characteristic: height of an individual

Question 2

Mendel’s Experiments

Answer 2

Gregor Mendel, an Austrian monk, carried out breeding experiments with garden peas from 1857 to 1864

Question 3

Mendel’s Law of Dominance

Answer 3

When a homozygous tall plant is crossed with a heterozygous short plant, all the offspring produced will be tall

Question 4

Mendel’s Law of Segregation

Answer 4

For each characteristic, a plant possesses two ‘factors’ which separate or segregate so that each gamete contains only one of these factors. This is known as Mendel’s Law of Segregation

Question 5

Explanation of Mendel’s Monohybrid Crosses in terms of Genes, Chromosomes and Alleles

Answer 5

Each characteristic is controlled by one gene, consisting of two alleles; one for tallness and one for shortness
The homozygous tall plant had two copies of the same allele for tallness and these can be shown as T and T
The homozygous short plant had two copies of the same allele for shortness and these can be shown as t and t
As a result of meiosis taking place during gamete formation, the gametes from the tall plant have only a T allele and the gametes from the short plant have only a t allele

Question 6

Genotype of parents and gametes

Answer 6

A parent with the genotype TT can only produce gametes containing the T allele
A parent with the genotype tt can only produce gametes containing the t allele
A parent with the genotype Tt will produce gametes containing the T allele as well as gametes containing the t allele

Question 7

Multiple Alleles

Answer 7

The three alleles for blood grouping are able to produce six possible genotypes leading to 4 possible phenotypes. This increases the variation amongst individuals of the same species

Question 8

Blood Grouping

Answer 8

Among humans there are four blood types: blood type A, blood type B, blood type AB and blood type O. These are regarded as the phenotypes
In the human population there are three alleles controlling these four blood types viz. alleles IA; IB; and i
An individual can only have two of these three alleles making up his/ her genotype
The i allele recessive to IA and IB alleles. The IA allele and IB allele are co-dominant to each other