BIOL1020 Week 7 : Sexual Reproduction, Meiosis and Inheritance

Genetics

Study of inheritance patterns. Physical and biochemical characteristics can be inheritable

Alleles

Variants of the same gene. Caused by gene mutation

Genotype

Combination of alleles that an individual possesses for a specific gene

Inherited by the parents

Phenotype

The sum of an organism’s observable appearance

Can be influenced by external factors like environment and lifestyle factors

Cannot be inherited by parents

Mutations of Genomic DNA

Creates different alleles of a genotype

Occurs in both the coding and non-coding regions of the DNA

Occurs in both the somatic and/or germ cells

Are spontaneous and can be induced (e.g. UV light)

3 Categories of Genomic DNA Mutations

1) Loss-of-function Mutation: reduces the activity of a gene, either by preventing its production or by decreasing the activity of a product)

2) Gain-of-function Mutation: the normal product of a gene to be expressed inappropriately (high level, wrong time, wrong location), or acquire an abnormal function

3) Silent Mutation: have no effect on the amino acid sequence coded for that gene

3 Types of Genomic DNA Mutations

1) Point Mutations: a single nucleotide base is changed, inserted or deleted

2) Insertion/Deletion Mutations: the addition or removal of a single or group of nucleotides

3) Translocation/Duplication Mutations: a section of a chromosome is added to another or multiple copies of the same segment are produced

Bacteria Genetically Diverse Causes

They are genetically diverse in the absence of sexual reproduction due to

1) Higher mutation rate

2) Rapid reproduction

3) Horizontal DNA transfer

4) Genetic recombination

Bacteria : Conjugation

Direct cell to cell transfer via sex pilus (hair like appendage on the surface of bacteria)

Bacteria : Transformation

Uptake and incorporation of naked DNA from the environment

Bacteria : Transduction

Transfer of DNA via intermediary bacteriophage

Meiosis

Special type of cell division that only occurs in gametes

Process ensures that the fusion of an egg and sperm during sexual reproduction does not lead to an increase chromosome number

Leads to genetic variation via DNA recombination, segregation of homologous chromosomes and independent assortment of non-homologous chromosomes

Consists of Meiosis I and Meiosis II

Unlike Mitosis, produced 4 daughter cells that are genetically different

Meiosis I

Homologous chromosomes are separated

Follows the same steps are mitosis, Prophase I, Prometaphase I, Metaphase I, Anaphase I, Telophase I, Cytokinesis

Meiosis II

Continued from Meiosis II

No DNA replication occurs, therefore the daughter cells have half the number of chromosomes (23 chromosomes)

Follows similar steps except it is occurring twice, Prophase II, Prometaphase II, Metaphase II, Anaphase II, Telophase II and Cytokinesis

DNA Recombination

Occurs during Prophase I when the two homologous chromosomes are in a tetrad

Homologous chromosomes can overlap and swap part of their DNA, forming a unique genetic variation

Segregation of Homologous Chromosomes

Paired homologous chromosomes are separated from each other and migrate to opposite sides of the nucleus

Independent Assortment of Non-Homologous Chromosomes

The random orientation of homologous chromosomes pairs during Metaphase I allow for the production of gametes with many assortments of homologous chromosomes

Aneuploidy

The presence of an abnormal number of chromosomes in the cell

Common example is Down Syndrome where there is an extra Chromosome