When a stem cell divides, each new cell can either stay a stem cell or become a specialized cell, such as a muscle cell, a red blood cell, or a brain cell.
Answer:
1. The difference between the normal hemoglobin protein DNA sequence and the sickle cell hemoglobin DNA sequence is a base to base shift, in this case adenine (GAG) to thymine (GTG).
2. The difference affects the amino acid sequence of the protein by replacing glutamic acid (Glu) with valine (Val).
Explanation:
In sickle cell anemia, a change in the DNA nucleotide sequence is observed, where adenine is substituted by thymine, whose expression is the change in the amino acid sequence of globine β, incorporating valine instead of glutamic acid. This represents a molecular mutation - point mutation - by subtitution, which corresponds to missense mutation.
<u>Normal hemoglobin protein in a RBC</u>
DNA CTG ACT CCT GAG GAG AAG TCT
Amino acids Leu Thr Pro Glu Glu Lys Ser
<u>Sickle cell hemoglobin protein in a RBC</u>
DNA CTG ACT CCT <em>GTG</em> GAG AAG TCT
Amino acids Leu Thr Pro <em>Val</em> Glu Lys Ser
When GAG is transcribed to mRNA, the CUC codon is obtained, which codes for glutamic acid. Thymine substitution causes the DNA sequence to change to GTG, which is transcribed as CAC, the codon that encodes the amino acid valine. The <u>change from glutamic acid to valine in β-globin causes an altered hemoglobin, giving the abnormal erythrocytes observed in sickle cell disease</u>.
Answer:
If the two organisms are heterozygous for the dominant trait.
Explanation:
For every trait, a diploid organism receives two forms of gene called ALLELE, from each parent. Allele is the variant form of a gene.
According to Mendel's law of dominance, for a particular trait, an allele is capable of masking the expression of another allele in a gene. The expressed allele is called the DOMINANT allele while the masked allele is called the RECESSIVE allele. Due to this, an organism can express a dominant trait even in a combined or heterozygous state i.e. different alleles.
When the two heterozygous organisms mate or are crossed, they undergo meiosis and their alleles are separated into GAMETES according to Mendel's law of segregation. For example; an organism with genotype (genetic make-up) Aa will produce gametes with A and a alleles.
Note that, a recessive trait can only be expressed in a homozygous state i.e. same allele. Hence, the two heterozygous organisms will produce gametes containing the recessive allele, which will likely combine to produce a recessive phenotype or trait.
The plants that use photosynthesis would die because the plants would not create food. They would die of hunger. Without another source of food, most of the animals would likewise die off to.
