IB Biology: Topic 2: Genetics

ABO Bloods types

- Multiple Alleles
- Based of different sugars present on the surface of the cell
- Universal Blood Donor = O
- Universal Blood Receiver = AB
- IB i and IA i = shows dominance of one type of sugar present

ABO Bloods types: A

- A = IA IA, IA i
- One sugar present

ABO Bloods types: B

- B = IB IB, IB i
- Different sugar than A present

ABO Bloods types: AB

- AB = IA IB
- Codominance
- Both sugars present

Chi-squared

Discrete Variation

Separate categories with no intermediates; trait is influenced by one gene

Continuous Variation

The range of types possible with no distinct categories; can be influenced by environment

Genes

- A sequence of DNA
- Heritable factors that can be passed on
- Influences specific traits
- Occupies a specific position on a chromosome
- DNA= genetic blueprint
- Codes for a specific trait
- Traits may be influenced by multiple genes
- Loci/locus: the location of a gene on a chromosome

Alleles

- Alternative forms of a gene
- Codes for different variations of a trait; eye colour, hair colour

Gene Mutations

- A change in the nucleotide sequence of a section of DNA
- New alleles are formed by mutations

Gene Mutations: Substitution

- One base in the sequence is replaced by a different base

Gene Mutations: Insertion

- A nucleotide is inserted into the base sequence

Gene Mutations: Deletion

- A nucleotide is removed from the base sequence

Codons

- Three base words in creating proteins

Gene Mutations: Frameshift

- A change occurs in every codon after the mutation
- Occurs in Insertion and Deletion

Consequences of Base Substitutions

Missense Mutations
- Beneficial mutation
- Changes the gene sequence to create new variations of a trait
Nonsense Mutations
- Detrimental mutation
- Shortens the gene sequence to avaid the normal shape
Silent Mutation
- Neutral mutation
- No effect

Sickle Cell Anemia

- A base substitution mutation
- Change in base sequence of mRNA transcribed from it
- Change in the base sequence of poly peptides in hemoglobin
- Single base was changed in the gene sequence
- Insoluble hemoglobin cannot process oxygen effectively
- More susceptible to illnesses
- May cause blood clotting in arteries
- Cells are destroyed more rapidly
- Low red blood count
- Heterozygous state provides protection against malaria

Genomes

- The entire set of DNA instruction found in a cell

Linked Genes

- Genes located close together on the same chromosome

Linked Genes: Autosomal Gene Linkage

- Genes that don't assort independently
- Fall close together on the same chromosome
- Stays together since they are too close to cross over

Linked Genes: Sex-Linked Genes

- Genes controlling characteristics located on the same chromosome
- SRY: Y chromosome = sex determinations
- X= Albinism, colour blindness, hemophilia
- Inheritance pattern where ratios are different

Hemophilia

- Inability to make factor VIII clotting blood protein
- Alleles = recessive on the X-chromosome
- Males only have one copy (XY)
- Inherited from the mother
- If the mother has a copy of that alleles= male offspring= hemophilia
- Females can only be hemophiliac if the father is hemophilic
- They will also inherit the allele from the mother
- Life expectancy: 10 years
- Treatment: infusing Factor VIII purified from blood donors

Codominance

- When both alleles have an effect
- Both alleles are expressed in the phenotype

Incomplete Dominance

- Both alleles have an influence but niether is dominant = blended inheritance

Blended Inheritance

- The result of no immediate phenotype

Phenotype

- Gene mutations
- Spontaneous
- Caused by copying error during DNA replication
- Induced by exposure to external elements; Radiation/chemical

Mutagen

- Carcinogens: formation of cancer

Monogenic Traits

- Characteristics controlled by a single gene loci (location)
- Exhibits discrete variation with individuals expressing one of a number of distinct phenotypes

Polygenic Traits

- Characteristics controlled by more than two gene loci (location)
- Exhibits continuous variation with an individuals phenotype exiting somewhere along the continuous spectrum of potential phenotypes

Unlinked Genes

- Genes resided on separate chromosomes
- Independent assortment
- Chromosomes independent from each other
- Segregate independently = no effect on each other
- Occurs because chromosomes pair up and line us in metaphase 1 without concern of which chromosome is facing which pole

Crossing over

Punnet Square hemophilia