Basic Genetics

A comprehensive set of practice questions and answers covering basic genetics, including historical theories, molecular biology, inheritance patterns, and genetic disorders based on the provided lecture notes.

What is genetics?

The scientific study of heredity and variation.

According to Charles Darwin's pangenesis theory, what are 'gemmules'?

Units involved in the inheritance of traits as proposed in Darwin's pangenesis theory.

Who is known as the father of modern taxonomy?

Carl Linnaeus.

What is the 'Homunculus' in the context of Preformationism?

The idea that there are preformed bodies within the sperm or egg.

Which two laws of inheritance were published by Gregor Mendel?

1. Law of Segregation and 2. Law of Independent Assortment.

Who were the three scientists who independently worked out the laws of heredity around the same time as the rediscovery of Mendel's work?

Hugo de Vries, Carl Correns, and Erich von Tschermak-Seysenegg.

What contribution did Rosalind Franklin make to the study of DNA?

She provided the idea that the structure of DNA is a helical structure.

Who came up with the double helical structure of DNA?

Crick and Watson.

What is the definition of a gene?

The unit of heredity that occupies a specific locus on the chromosome and is a DNA sequence that directs synthesis of a specific polypeptide chain.

What is the function of a regulatory gene?

They code for proteins that turn other genes ON or OFF.

Define genome.

The total number of genes contained in one cell.

What are alleles?

Alternative forms of a gene that occupy a specific locus on a specific chromosome.

What is the difference between homozygous and heterozygous?

Homozygous means having two identical alleles for a given gene, while heterozygous means having two different alleles.

Describe the genotype of an individual.

The complete genetic constitution of an individual for a particular trait.

What is a carrier?

A heterozygous individual who does not display symptoms of a recessive genetic disorder but can transmit the disorder to his or her offspring.

What is the difference between dominant and recessive traits?

A dominant trait is expressed in both homozygous and heterozygous forms, while a recessive trait is only expressed in homozygous form and is masked in the heterozygous form.

Define incomplete dominance.

A pattern of inheritance in which a heterozygous genotype expresses a phenotype intermediate between dominant and recessive phenotypes.

What is a phenotype?

The physical appearance of an individual produced by the interaction of his genes and the environment.

How is a karyotype defined?

A systematic arrangement of images of chromosomes into homologous pairs.

What are autosomal chromosomes?

In humans, the 22 pairs of chromosomes that are not the sex chromosomes ($XX$ or $XY$).

What is transcription?

The process of copying DNA sequences into messenger RNA ($mRNA$).

What is translation?

The process of copying $mRNA$ sequences into protein.

Which enzyme facilitates the production of $mRNA$ during transcription?

DNA-dependent RNA polymerase.

What are the three processes involved in post-transcriptional modifications?

1. Splicing (cleavage of introns and ligation of exons), 2. Capping (addition of a cap to the $5'$ end), and 3. Tailing (addition of poly A tail to the $3'$ end).

What are 'housekeeping genes'?

Genes typically expressed in all cell types that are required for cell replication, metabolism, and/or maintenance, such as actin, tubulin, DNA polymerase, and RNA polymerase.

What is the genetic code?

The informational relationship between nucleotide and amino acid sequences, consisting of a triplet code of nucleotides called codons.

Explain 'degeneracy' in the genetic code.

A property where an amino acid can be specified by multiple codons, though a given codon still specifies only one amino acid.

What is the start codon and which amino acid does it specify?

The start codon is $AUG$, which specifies methionine.

What are the three termination or stop codons?

$UAA$, $UAG$, and $UGA$.

What is the 'wobble base'?

The third base in a codon, which is often the degenerate base.

According to Table 6-1, what is the function of $miRNAs$?

MicroRNAs regulate gene expression typically by blocking translation of selective $mRNAs$.

In mitochondrial inheritance, from which parent does an embryo receive all its mitochondria?

The mother, through the egg cell.

What are sex-limited genes?

Genes present in both sexes but normally expressed only in the gender having the appropriate hormonal determiner.

Give examples of sex-influenced traits.

Male Pattern Baldness, length of index finger, body hair, muscle mass, and milking characteristics.

How is co-dominance different from incomplete dominance?

In co-dominance, both alleles are independently and equally expressed (e.g., roan color), while in incomplete dominance, an intermediate phenotype is produced (e.g., pink flowers).

What symbols are used for male and female in a pedigree?

Square for male and circle for female.

What are the characteristics of an autosomal dominant pedigree?

Heterozygotes are affected, affected children usually have affected parents, and two unaffected parents will not produce affected children.

Name three examples of autosomal recessive disorders.

Albinism, Sickle Cell anemia, and Phenylketonuria ($PKU$).

What is Progeria?

An autosomal dominant disorder characterized by drastic premature aging, limited growth, wrinkled skin, and atherosclerosis, where individuals often die by age 13.

What causes Tay Sachs Disease?

A lack of an enzyme needed to break down lipids necessary for normal brain function, resulting in nervous system destruction.

What are the traits associated with Duchenne Muscular Dystrophy?

Progressive weakness and degeneration of skeletal muscles due to the absence of dystrophin, mainly affecting boys.

Define mutation.

A change in the genetic material caused by exposure to mutagenic agents or occurring spontaneously through errors in DNA replication and repair.

What is a silent mutation?

A point mutation where a changed base codes for the same amino acid, resulting in no difference in the polypeptide chain.

What is the result of a nonsense mutation?

The changed base becomes a termination (stop) codon, leading to the termination of translation and a shortened protein.

What is a frameshift mutation?

The deletion or addition of one or two bases to a sequence, leading to a change in the reading frame and a completely different amino acid sequence from that point.

Describe Klinefelter Syndrome.

A sex chromosomal disorder where an individual is $XXY$, having underdeveloped testes, no facial hair, possible breast development, and long limbs.

What is the cause of Down syndrome?

Trisomy 21, usually due to nondisjunction, or in 2-3% of cases, due to translocation of chromosome 21 to 14.

What is Fragile X syndrome?

An inherited cause of intellectual disability due to a mutation of the fragile X mental retardation 1 ($FMR1$) gene.

What is Achondroplasia?

A common genetic cause of dwarfism caused by a mutation in the fibroblast growth factor receptor 3 ($FGFR3$).

Define 'Cri du chat' syndrome.

A condition caused by the deletion of a portion of the short arm of chromosome 5, leading to a cat-like cry, mental retardation, and microcephaly.

What is Turner syndrome?

A condition caused by the deletion of part of the short arm of one X chromosome ($XO$), resulting in short stature, webbed neck, and rudimentary ovaries.

What is the difference between paracentric and pericentric inversion?

Paracentric inversion does not include the centromere, while pericentric inversion includes the centromere.

What is translocation?

The transfer of a part of a chromosome or a set of genes to a non-homologous chromosome.