genes

What is DNA ?

DNA is the genetic blueprint which codes for and determines the characteristics of an organism.

What is a gene?

A sequence of DNA that encodes for a specific trait.

What is a loci?

The position of a gene on a particular chromosome

What is allele?

Alleles are alternative forms of a gene that code for different variations of a specific trait - they possess similar gene sequences only differing from eachother by a few bases.

What is a gene mutation?

A gene mutation is a change in the nucleotide sequence of DNA coding for a specific trait - new alleles are formed by mutations

What are the causes of Sickle Cell Anaemia

SCA results from a change to the 6th codon for the beta chain of haemoglobin

What is a genome?

The totality of genetic information of a cell, organism or organelle -including all genes as well as all non-coding DNA sequences.

What is the HUman Genome project

The HGP was established to sequence the human genome, and showed that humans share the majority of their sequence, with short nucleotide polymorphisms contributing to diversity

What did the completion of the HGP lead to?

Mapping, Screening, Medicine, Ancestry

What are prokaryotic genetics?

• do not possess a nucleas (genetic material is found free in the cytoplasm - nucleoid)

• single chromosome consisting of a circular DNA molecule (genophore)

• DNA is naked

• may possess extra DNA - plasmids

What are Eukaryotic Genetics?

• consists of multiple linear molecules of DNA

• greatly compacted structure

• compacted during cell division

What are homologous pairs?

Organisms that possess 2 copies of each chromosomes from both parents - share the same structural features (size, banding patterns) , and the same genes at the same loci positions

What are karyotypes?

the number and types of chromosomes in an eukaryotic cell, determined via a process involving;

• harvesting cells

• chemically inducing cell division , arresting mitosis while the chromosomes are condensed

What can karyotyping be used to?

• detemine gender

• test for chromosomal abnormalities (down-sydrome)

What is meiosis?

The process by which sex cells (gametes) are made in the reproductive organs, involves the reduction division of a diploid germ-line cell into 4 genetically distinct haploid nuclei.

What are the 2 cellular divisions in meisosis?

1. seperates the homologous chromosomes

2. seperates the sister chromatids

What are the stages of meiosis 1?

P- chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs

M- Spindle fibres from opposing centromeres connect to bivalents and allign along the middle of the cell

A- Spindle fibres contract, homologous choromsomes move to opposite poles of the cell

T- chromosomes decondense, cell divides

What are the stages of meiosis 2?

P- chromosomes condesne, nuclear membrane dissolves , centrosomes move to opposite poles

M- spindle fibres from opposing centrosomes attach to centrosomes and allign at equator

A- spindle fibres contract and seperate the sister chromatids, move to oppsoite poles

T- chromsomes decondense, nuclear membrane reforms, cell divides into 4 haploid cells .

What is non-disjunction?

Chromosomes failing to seperate correctly- relulting in gametes with one extra or less choromsomes.

May occur due to;

• failure of homologues to seperate in anaphase 1

• failure of sister chromatids to seperate in anaphase 2

What is amniocentesis?

The extraction of a small amount of amniotic fluid with a needle (~16 weeks)

What is chronic villi sampling?

removing a sample of chronionic villus (placental tissue) via a tube inserted through the cervix (~11 weeks)

What are the sources of genetic variation?

• crossing over (prophase 1)

• random assortment of chromosomes (metaphase 1)

• random fusion of gametes