Organization and Transmission of Genomic Information/ Intro to Genetics and Genomics

two lessons

What is the definition of a genome?

The genome is the complete set of genetic material (DNA) in an organism, including all its genes. It contains all the instructions needed to build and maintain life.

What determines who we are as individuals?

Our genomes largely determine who we are; we are the products of the information stored in our DNA.

How precise is genomic information in humans?

The human genome is extremely precise and accurate—tiny changes can lead to major biological effects.

How is the genome similar to a book?

The genome resembles a “Book of Life”: chromosomes are volumes, genes are chapters, codons are words, and nucleotides (A, C, T, G) are the alphabet.

How large is the human genome?

About 3.1 billion nucleotides organized in 23 pairs of chromosomes and around 20,000 genes.

How many chromosome pairs are autosomes?

22 pairs of autosomes and one pair of sex chromosomes (XX in females, XY in males).

Where do humans get their genomes from?

Each person inherits one genome copy from their father and one from their mother.

How do parents pass their genome to children?

Neither full copy is passed directly—meiosis shuffles both parental copies to create a unique combination in each gamete.

What are homologous chromosomes?

A pair of chromosomes (one paternal, one maternal) carrying the same genes in the same order but possibly different versions (alleles).

What is mitosis used for?

Mitosis produces identical cells for growth and repair; no crossing-over occurs.

What is meiosis used for?

Meiosis is a special division in germ cells that makes haploid gametes (eggs or sperm) and creates genetic variation.

How many chromosomes do gametes contain?

23 unpaired chromosomes—half the number found in somatic cells.

How is gender determined?

The father’s gamete determines sex: X gives a female (XX) and Y gives a male (XY).

How many divisions occur in meiosis?

Two: Meiosis I and Meiosis II, but only one DNA replication occurs.

What causes genetic variation in meiosis?

Random assortment of chromosomes and crossing-over during Prophase I.

How many chromosome combinations are possible in humans?

2²³ = 8,388,608 possible chromosome combinations from independent assortment.

What is non-disjunction?

Failure of chromosomes to separate properly during meiosis, causing aneuploidy.

What increases the risk of meiotic errors?

Advanced maternal age (over 35 years).

What are chromosomal aberrations?

Loss, duplication, or rearrangement of parts of chromosomes that affect many genes.

Are chromosomal disorders inherited?

Usually not; most occur spontaneously during gametogenesis or early embryo development.

What are examples of common chromosomal aneuploidies?

Down syndrome (Trisomy 21), Klinefelter (XXY), Patau (Trisomy 13), Edward (Trisomy 18), Triple X (47,XXX), Turner (45,X), and Super Male (XYY).

Which is the only viable human monosomy?

Turner syndrome (45,X).

What is Cri-du-Chat syndrome?

A structural chromosomal disorder caused by a small deletion on chromosome 5.

What defines a single-gene disorder?

A disease caused by a mutation in one gene while the rest of the genome remains normal.

How many single-gene disorders exist?

Over 8,000 identified so far, with more still being discovered.

Give examples of single-gene disorders.

Cystic fibrosis, sickle-cell anemia, beta-thalassemia, polydactyly, albinism, and Swyer syndrome.

What gene causes Swyer syndrome?

A mutation in the SRY gene on the Y chromosome that makes genetically male (46XY) individuals develop as females.

What causes sickle-cell disease?

A specific mutation in the beta-globin gene (HBB).

What are the main inheritance patterns of single-gene disorders?

Autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, and Y-linked.

Are all genetic diseases inherited?

No; some occur spontaneously (de novo), such as Down syndrome or Achondroplasia.

What are multifactorial disorders?

Diseases caused by the combined effects of multiple susceptibility genes and environmental factors.

Give examples of multifactorial diseases.

Type 2 diabetes, heart disease, many cancers, and psychiatric disorders.

Why is cancer called a disease of the genome?

Because it results from mutations that accumulate in genes over time, transforming normal cells into cancer cells.

What proportion of cancer cases are hereditary?

About 5% hereditary, 10% familial, and 85% sporadic.

Does “genetic” mean “inherited”?

No—genetic simply means caused by mutations; not all genetic changes are inherited.

Summarize Dr. Bassam Ali’s view of cancer.

Cancer arises from bad luck (DNA errors), bad genes (inherited mutations), bad environment (carcinogens), and bad decisions (lifestyle).

What is genomic medicine?

The use of genome information to guide lifestyle, drug response (pharmacogenomics), prevention, diagnosis, and reproductive decisions.