University:
Felician University
Course:
BIO-209 | Evolution
Academic year:

2020
Views:

500

Pages:

1
Author:

Clint W.

Chromosomes, Genes, Alleles and Mutations Define the following terms Gene: A heritable factor that controls a specific characteristic Allele: One specific form of a gene, occupying the same gene locus as other alleles of the gene Genome: The whole of the genetic information of an organism Gene Mutation: A change in the nucleotide sequence of a section of DNA coding for a polypeptide Homologous Chromosomes: Chromosomes that have the same structural features and the same genes Genotype: The alleles of an organism Phenotype: The characteristics of an organism (combination of genotype and environmental factors) Dominant Allele: An allele that is expressed in the phenotype in a homozygous or heterozygous state Recessive Allele: An allele that is only expressed in the phenotype in a homozygous state Codominant Alleles: A pair of alleles which both affect the phenotype in a heterozygote Locus: The particular position on homologous chromosomes of a gene Homozygous: Having two identical alleles of a gene Heterozygous: Having two different alleles of a gene Carrier: A heterozygote who has one copy of a recessive allele that causes a genetic disease Test Cross: Testing a suspected heterozygote by crossing with a known homozygous recessive Clone: A group of genetically identical organisms or a group of cells derived from a single parent cell Organisation of chromosomes • Eukaryotic chromosomes consist of DNA wrapped around histone proteins • This forms the basic structure of the nucleosome, which are packaged into chromatin • Chromatin containing active genes remains in an expanded form (euchromatin) • Chromatin with genes not expressed by the cell becomes condensed (heterochromatin) • Chromatin only supercoils into chromosomes during cell division (mitosis / meiosis) DNA Nucelosome Chromatin Consquences of a base substitution mutation in sickle cell anaemia Cause: • Base substitution: GAG → GTG • Amino acid change: Glu → Val • Location of change: Haemoglobin beta chain (chromosome 11) • Mode of inheritance: Autosomal recessive Consequence: • Structural effect: Haemoglobin forms strands; red blood cells to become sickle-shaped • Functional effect: Causes anaemia (low RBC count) as sickle-cells destroyed faster Blood is less effective at transporting oxygen, causing fatigue • Complications: Altered shape causes clotting, leading to organ failure (e.g. kidneys)