Question

1) How many total chromosomes will be in each gamete if a diploid cell with 24 chromosomes undergoes meiosis?

2) In a carrier of a recessive genetic disorder what's the genotype found?

Answer 1

Question 1:

Meiosis is also known as reductional division. After meiosis (which consists of meiosis I and meiosis II), one cell gives rise to four daughter cells.

Before cell division occurs, in the interphase, the DNA content is doubled. When meiosis I occur, the homologous pairs of chromosomes are separated from each other and two daughter cells are formed consisting of an equal number of chromosomes. For example, if a diploid cell has 24 chromosomes, after meiosis I, each daughter cell will have 24 chromosomes, but in the haploid state.

In meiosis II, these two daughter cells further undergo division to form a total of four daughter cells. here, the DNA content is also halved, so that now each of the daughter cells has 12 chromosomes each. (Attaintment of proper haploidy)

Question 2:

Genotype can be defined as the genetic makeup found in the individual's cells, which determines the phenotype of the organism.

For any particular trait, the genotype will be composed of two different alleles of the gene. These alleles can be the same or they can be different. A recessive genetic disorder means that you need to have two copies of the recessive allele (homozygous recessive) for expression of the disease.

For example, if we consider the dominant allele for any trait to be represented by A and the recessive trait to be represented by a, then we can have the following combinations:

AA - homozygous dominant, children who did not receive the allele from either parent

Aa, aA- heterozygous dominant, children who are carriers of the allele like their parents

aa - homozygous recessive, children who express the disease

The probability of a child to have the disease is 25% (one in four), while the chance of the children to be a carrier of the disease is 50%.

The chance of the child inheriting the disease increases when the parents are carriers of the disease, expressing the genotype Aa. This means that each parent now has a 50% chance of passing on the disease to the child.

Examples of some autosomal recessive disorders are sickle cell anaemia, Tay-Sachs syndrome, cystic fibrosis.