Lecture 5 -- Genetics from genotype to phenotype

What is DNA?

Deoxyribonucleic acid; a nucleic acid located in the nucleus that stores and transmits genetic information.

What are nucleotides?

The building blocks of DNA.

What are the three components of a nucleotide?

Phosphate group, deoxyribose sugar, nitrogenous base.

What are the four DNA bases?

Adenine (A), Thymine (T), Cytosine (C), Guanine (G).

What is complementary base pairing?

A pairs with T; C pairs with G.

Why is complementary base pairing important?

It allows each DNA strand to serve as a template for accurate replication.

When does DNA replication occur?

During cell division.

What happens during DNA replication?

The original strands separate and each serves as a template to build a complementary strand.

What is the result of DNA replication?

Two identical DNA molecules.

What is genotype?

The underlying genetic makeup (genes) of an organism.

What is phenotype?

The observable physical traits resulting from gene expression.

What are amino acids?

The building blocks of proteins.

How many amino acids are used to build proteins?

20.

What is a polypeptide chain?

A linear chain of amino acids linked together.

What is a codon?

A sequence of three nucleotide bases that codes for one amino acid.

Why are many mutations synonymous?

Because the genetic code is redundant; multiple codons can code for the same amino acid.

What is the central dogma of molecular biology?

DNA is transcribed into RNA, which is translated into protein.

What is transcription?

The process in which DNA is used as a template to synthesize complementary mRNA in the nucleus.

Where does transcription occur?

In the nucleus.

What is translation?

The process in which mRNA is read at the ribosome to assemble amino acids into a protein.

Where does translation occur?

At ribosomes in the cytoplasm.

What does tRNA do?

It matches its anticodon to the mRNA codon and brings the correct amino acid to the ribosome.

What are the differences between DNA and RNA?

DNA is double-stranded, contains deoxyribose sugar, and uses thymine; RNA is single-stranded, contains ribose sugar, and uses uracil.

What is a mutation?

An alteration in the genetic code that creates new variants.

What is a point mutation?

A change in a single nucleotide base.

What is a duplication mutation?

A segment of DNA is copied and repeated.

What is an inversion mutation?

A segment of DNA flips in orientation.

What is a frameshift mutation?

A mutation caused by insertion or deletion that shifts the codon reading frame.

When can a mutation be inherited?

If it occurs in gametes during meiosis.

What percentage of the human genome codes for protein?

About 1%.

Approximately how many protein-coding genes do humans have?

About 25,000.

What is codominance?

Both alleles are fully expressed in a heterozygote (e.g., ABO blood type).

What is sex linkage?

Traits controlled by genes on the X chromosome; often more commonly expressed in males.

What is a polygenic trait?

A trait influenced by two or more genes and showing continuous variation.

What is pleiotropy?

A single gene influences multiple traits.

What is a pseudogene?

A nonfunctional DNA sequence related to a known gene that has lost its protein-coding ability.

What are exons?

DNA sequences that remain in mRNA and code for protein.

What are introns?

DNA sequences removed during RNA processing.

What is alternative splicing?

The process in which different combinations of exons are joined to produce different mRNA transcripts.

Why do cells differ if they have the same genome?

Differences in gene expression and alternative splicing.

What is epigenetics?

Modification of gene regulation without changing the DNA sequence.

What is DNA methylation?

The addition of a methyl group (CH3) to DNA, often reducing gene expression.