What phenotypic ratio would you expect as a result of a test cross between a dihybrid organism and one that is homozygous recessive for alleles at two independent loci?
a. 3:1
b. 9:3:3:1
c. 1:1:1:1
d. 1:2:1
e. 9:4:2:1
Answer:
c. 1:1:1:1
Explanation:
When a heterozygous individual for two genes is test crossed with a double homozygous recessive individual, the progeny is obtained in 1:1:1:1 phenotypic ratio. This occurs as the heterozygous dominant individual forms four types of gametes in 1:1:1:1 ratio while the homozygous recessive individual would form only one type of gamete having one recessive allele for each gene.
For example, a test cross between TtRr (tall and red) and ttrr (short and white) would produce a progeny in following ratio=
1 tall, red: 1 tall, white: 1 short, red: 1 short, white
Here, T= tall, t= short, R= red, r= white
Answer:
Purpose: Meiosis is a special version of cell division that occurs only in the testes and ovaries; the organs that produce the male and female reproductive cells; the sperm and eggs. ... Therefore the purpose of meiosis is to produce gametes, the sperm, and eggs, with half of the genetic complement of the parent cells.
Genetic variability is a measure of the tendency of individual genotypes in a population to vary (become different) from one another. Variability is different from genetic diversity, which is the amount of variation seen in a particular population.
Meiosis generates genetic diversity through a process called crossing over which allows new combinations of variations to appear in gene pool. ... Chiasmatal points appear randomly on homologous chromosomes, hence amount of genetic material exchanged in every case/cell could be different.
Explanation:
<h2><em>the DNA that is packaged into chromosomes must be fully copied. Previous to replication, a germ cell contains two copies of each chromosome, a maternal copy, and a paternal copy. ... DNA replication occurs in the same fashion as it does during mitosis.</em></h2>
Not for long. We use oxygen for cellular respiration and plants make oxygen so if all the plants died, we would only have so long to live
