Chromosomes and Genes PDF

Chromosomes and Genes By: Dr. S. Mawunyo Ayivi-Tosuh 6/6/2024 Chromosomes are structures within the cell that contain the genes Some genes give the instructions to make proteins. A protein’s job is to tell your body what types of physical characteristics you should have, like your ha...

Chromosomes and Genes By: Dr. S. Mawunyo Ayivi-Tosuh 6/6/2024 Chromosomes are structures within the cell that contain the genes Some genes give the instructions to make proteins. A protein’s job is to tell your body what types of physical characteristics you should have, like your hair Several Alleles for One Trait Sometimes more than two alleles form a given For instance, coat colour in chromosomal locus, in rabbits is controlled by four C> cch >ch >c which case a trait is alleles: controlled by multiple alleles. Inheritance by multiple Blood type in humans in alleles causes a trait to three alleles and four exhibit more than two possible phenotypes: A, B, possible phenotypes. AB, O Concept of Genotype and Environmental interaction Genotype and environmental affect the phenotype. Effects ranging from mild to extreme. Polygenic inheritance an inheritance of a single phenotypic trait controlled by multiple independent genes Several genes occupying different loci on the same homologous chromosome or different homologous pair of chromosomes. Each gene has a contributing and non-contributing allele The contributing alleles are denoted by Capital letters Non-contributing alleles are denoted by small letters Each contributing alleles have a quantitative effect on the phenotype and thus the effects of the alleles Examples Many human traits are considered polygenic. Height, hair color, eye color, and weight are all examples of polygenic traits. Some diseases like high blood pressure, diabetes, and asthma are regulated by multiple genes H. Nilsson-Ehle: Seed colour in wheat Chromosomes contain Genes The parallel behavior of genes The behavior of and chromosomes leads to the chromosomes has been Both Chromosomes and proposal of the chromosomal This theory is supported by described by mitosis and Alleles are paired in diploid theory of inheritance, which the following observations; cells meiosis. states that genes are located in the Chromosome. Both homologous Both chromosomes and Fertlization restores both chromosomes and alleles of alleles of each pair separate the diploid chromosomal each pair separate during meiosis so the number and the paired independently so that gametes have half the total condition for alleles in the gametes contain possible number zygote combinations  Sex Chromosomes Sex chromosomes carry genes that determine sex. Phenotype: B-Black hair b-Brown hair Based on Drosophila cross Chromosomes undergo mutation Permanent changes in genes or chromosomes that can be passed to offspring if they occur in cells that become gametes. Monosomy (2n-1)Nondisjunctions during meiosis(common in meiosis I than MeiosisII) Trisomy (2n+1) Occurs in both plants and animal Polypliody Turner Syndrome is a monosomy involving the sex chromosomes-the individual inherits a single X chromosome. Down Syndrome is the most common Trisomy which involves 21 chromosomes Polyploidy Some mutant eukaryotes have more than two sets of chromosomes,they are called polyploids. Polyploid organisms are named according to the number of sets of chromosomes they have. Triploids (3n) Tetraploids (4n) In plants hybridization and polyploidy is a force for change. Changes in Chromosomal structure Deletion Duplication Inversion Translocation Human Genetics The shape of the red cell in humans with sickle cell disease is disadvantageous because it leads to a myriad of body disorders.