IB Biology SL - Genes

What is a gene?

A heritable factor that consists of a length of DNA and influences a specific characteristic

What is genetics?

The storage of information, passing from parents to progeny. Something causes a feature to be passed on to offspring, like eye color or hair color.

Fill in the blank: The DNA of humans, __ chromosomes contain _______(s) of genes

The DNA of humans, 46 chromosomes contain thousand(s) of genes

What is a locus?

Location of a gene on a chromosome

Fill in the blank: Breeding experiments show that genes are linked into ______, and those _______ of genes are located on a specific _______

Breeding experiments show that genes are linked into groups, and those groups of genes are located on a specific chromosome

What led to more detailed gene maps?

Crossing experiments, and the discovery of gene order on chromosomes, leading to the sequencing of genomes

Note: More complex organisms do not necessarily have more genes, but the number of genes in humans can be compared with other species

What are the various specific forms of genes called?

Alleles

Describe Gregor Mendel's experiment.

(1)He crossed varieties of pea plants, green and yellow (2)Then he deduced differences due to different heritable factors, one from each parent (3) Pair of factors, that are alternate forms of the same genes were determined as alleles (4) Multiple, two or more alleles can occur, like blood types (5) Alleles occupy the same locus on a chromosome (6) There are two copies of each chromosome, 2 of the same kind of allele, or 2 different.

Fill in the Blank: Alleles differ from each other by one or only a few _____

Alleles differ from each other by one or only a few bases

How are new alleles formed?

Mutation

Note: Most mutations aren't beneficial, they're mostly neutral or harmful, even lethal

What are the most significant types of mutation caused by?

Change in base, one base for another, cytosine - thymine, guanine instead of adenine

Fill in the Blank: Mutations in _____ cells may kill the cell or organism and aren't passed on. Mutations in ______ that don't kill the cell or organism are passed on.

Mutations in body cells may kill the cell or organism and aren't passed on. Mutations in gametes that don't kill the cell or organism are passed on.

What causes Sickle Cell Anemia?

A mutation of hemoglobin, it's the most common genetic disease in the world. In the sixth codon in the gene for alpha-globin chain changes, CTC to CAC

How is the change of the CTC to CAC reflection in the processes of transcription and translation? (4)

(1) The base sequence of mRNA transcribed is altered, GAG to GUG (2) The sequence of the polypeptide now has valine instead of glutamic acid (3) The altered amino acid sequence causes hemoglobin proteins to polymerize in low oxygen conditions forming chains (4) The hemoglobin chains are rigid, and deform the red blood cells, hence sickle shaped cell

How does sickle cell cause damage? (5)

(1) They get trapped in capillaries, and reduce blood flow (2) They then return to normal as they circulate and become oxygenated in the lungs (3) Over time they damage hemoglobin and membranes of cells (4) Sickle cells can die within four days, faster than they can be replaced (5) Small change in DNA sequence can have harmful consequences.

What's the frequency of sickle cell anemia in the middle east?

Quite high, 5% of babies have 2 copies, therefore having severe anemia. 35% have one copy, some normal and some mutant, mid anemia

How does sickle cell anemia interact with malaria?

Due to carriers of sickle cell anemia being resistant to malaria.

What is the human genome? (3)

Whole of the genetic information of an organism, the entire base sequence of DNA not the number of genes. Humans have DNA in 46 chromosomes plus DNA in mitochondria. Similar pattern, different number in other animals.

How does DNA work in plants?

They have DNA in chromosomes and mitochondria, plus DNA in chloroplasts.

How does DNA work in prokaryotes?

They have DNA in single chromosome, plus plasmids

What was the Human Genome Project?

An international cooperative venture that began in 1990 established to sequence the complete human genome (2013)

What was the outcome of the Human Genome Project?

Knowledge of the number of human genes, which is 23,000 total. Not all of the genome is transcribed though, satellite DNA affects gene expression, repetitive sequences. Since then, other species sequences have been completed, revealing previously unknown evolutionary relationships.

What can be used to determine differences in the base sequence of a gene in two species?

Databases like Genbank that use cytochrome oxidase I comparison.