What is a recessive allele?

Biology

2 answers:

irinina [24]3 years ago

7 0

An allele that can only be expressed when no dominant allele is present

tangare [24]3 years ago

7 0

Answer:

B/2. An allele that is only expressed when no dominant allele is present.

Explanation:

Alleles always come in pairs, and we represent them with letters. Uppercase letters represent dominant alleles, and recessive alleles are represent by lowercase letters.

A recessive trait can only appear when the pair of alleles contains 2 lowercase letters, otherwise, if there are 2 uppercase letters or 1 of each, a dominant trait will be seen.

So:

AA - a pair of 2 dominant alleles (here we get a dominant trait).

Aa - a pair of 1 dominant and 1 recessive allele (here we get a dominant trait)

aa - a pair of 2 recessive alleles (here we get a recessive trait).

→ As we can see, we only get a recessive trait when there is a pair of 2 recessive alleles, therefore no dominant alleles in the pair.

Hope it helped,

BiologiaMgaister

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Which of the following best explains how the expression of a eukaryotic gene encoding a protein wil differ if the gene is expres

Ivan

Answer: c. The protein will be made but will not function, because prokaryotes cannot remove introns.

Explanation:

Eukaryotic cells are cells that have membrane-surrounded organelles, such as a nucleus which is an organelle that stores the DNA, the genetic material. On the other hand, prokaryotic cells do not have a nucleus, and the genetic material is a single molecule, usually circular and closed and double-stranded, which is located in a sector of the cell known as the nucleoid (meaning "similar to the nucleus"), which does not imply the presence of a nuclear membrane.

<u>A gene is a unit of information at a DNA locus that codes for a protein. To synthesize that protein, DNA must be transcribed into messenger RNA (mRNA), and that mRNA is read by ribosomes in a process called translation or protein synthesis</u>. The difference between protein synthesis in prokaryotic and eukaryotic cells is that in prokaryotes, transcription and translation take place directly in the cytoplasm since there is no nucleus. In eukaryotes, transcription takes place inside the nucleus, to generate mRNA. This mRNA molecule is then directed to the cytoplasm where translation happens.

a. In prokaryotic cells, ribosomes are produced in the cytoplasm, whereas in eukaryotic cells they are generated in the nucleolus within the cell nucleus. So they both have ribosomes and they are used to make proteins, then this option is true.

b. RNA polymerase initiates transcription of all different types of RNA (mRNa, ribosomal RNA and transfer RNA). However, there are three RNA polymerase variations, each one translate a different type of gene. But, prokaryotic RNA polymerase can translate eukaryotic genes. Then this option is not true.

c. Prokaryotic cells don't have introns because those cells do not perform a post-transcriptional RNA modifications, only done by eukaryotic cells. One of the modifications is the excision of introns in RNA. An intron is a region of DNA that is part of the primary RNA transcript, but unlike exons, they are removed from the mature transcript prior to translation. <u>So, this remotion does not happen in prokaryotes because they just don't have introns</u>. Also, in prokaryotic cells. the translation and transcription machinery is coupled. So, the transcription and translation occurs simultaneously, there will be no remotion of introns then the protein will be synthesized differently, since the reading frame is changed. Remember that each codon (set of three nucleotides) codes for an amino acid. So if the gene sequence is different because certain sections of the gene have not been removed, the protein will be different, and probably it will not function. This option explains how the expression of an eukaryotic gene encoding a protein will differ if the gene is expressed in prokaryotic cells.

d. The genetic code is the set of rules that defines how a sequence of nucleotides in RNA is translated into a sequence of amino acids in a protein. This code is common to all living organisms, although there are small variations, and it has a unique origin and is universal. So, the code defines the relationship between each sequence of three nucleotides, called a codon, and each amino acid. The sequence of genetic material is composed of four distinct nitrogenous bases, which are represented by letters in the genetic code:

Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
Uracil (U), only in RNA (instead of T)

So, the genetic code is the same for eukaryotes and prokaryotes. So this option is not true.

7 0

3 years ago

Contractions per M

Andreyy89

To make Paramecium Contractile vacuole concentration graph useful the salt concentrations descriptions should replaced with actual values.

Thus, option "A" is correct.

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"It is a sub-cellular structure (organelle) involved in osmoregulation."

<h3>What is a graph?</h3>

"A diagram (such as a series of one or more points, lines, line segments, curves, or areas) that represents the variation of a variable in comparison with that of one or more other variables."

<h3>What does the graph in the given question depict?</h3>

It shows that the Paramecium Contractile Vacuole concentration per minute decreases as salt concentration increases.

But the concentration of salt is not mention in quantity so its not clear what are the lowest and highest concentration affecting Paramecium Contractile Vacuole.

Hence, the Paramecium Contractile Vacuole concentration graph can be more useful if the actual values of salt concentration will be mentioned.

To know more about Paramecium Contractile Vacuole here

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