Genetics and Heredity

Gene-chromosome theory

• Genes are arranged in a linear sequence on chromosomes.

• Each gene has a definite position or locus• The gene chromosome theory explains th

hereditary pattern observed by Mendel.• Every organism has at least 2 alleles that govern

every trait• Gene expression is the encoding of information

that is expressed as the traits of an organism.

Gene expression

• Body cells contain the same genetic instructions – yet cells differ in structure and function.

• Genes that are on are expressed and genes that are off are not expressed

• What switches genes on and off?– Intracellular chemicals,enzymes, regulatory proteins,

cell’s environment– genes can be inactivated depending on the needs of

the cell at the time.

Genetic Mutations

• Mutations are changes in genetic material

• Mutations in body cells can be passed on to other body cells via mitosis

• Mutations in sex cells can be passed on to the next generation.

• Chromosomal alterations( number and structure) and gene mutations

Chromosomal alterations

• Changes in chromosomal number– Nondisjunction – one or more pairs of

homologous chromosomes fails to separate normally during meiotic cell division.

– Polyploidy – complete set of chromosomes fails to undergo disjunction – 3n,4n,5n. Inheritance of one or more complete extra sets.

– Plants – larger, more vigorous – wheat, potatoes, alfalfa, apples, tobacco.

Chromosomal alterations

• Changes in chromosomal structure– Random breakage and recombination of chromosome

parts– Translocation,addition,deletion,inversion

• Translocation- segment of one chromosome breaks off and reattaches to a nonhomologous chromosome

• Addition – segment breaks off one chromosome and reattaches to the homologous chromosome

• Deletion – segment breaks off and does not reattach to any other chromosome

• Inversion – segment breaks off and reattaches in reverse on the same chromosome

Gene Mutations

• Gene mutation is a random change in the chemical makeup of the DNA.

• Albinism is a gene mutation with noticeable affects

• Inheritable gene mutations tend to be harmful

• Sickle cell anemia, Tay sachs disease are caused by gene mutations.

• Usually involve one base change

Mutagenic agents

• Some mutations occur spontaneously

• Others caused by increased exposure to chemical agents

• Radiation – x-rays, ultraviolet rays, radioactive substances, cosmic rays,

• Chemicals include formaldehyde, benzene,asbestos fibers

Heredity and the environment

• Environmental factors – temperature, nutrients, sunlight can affect the development and expression of inherited traits. – Examples of gene action and environmental

influences:• Himalayan rabbits• Chlorophyll and exposure to light• Stress and nutrition – tallness and malnutrition

Plant and animal breeding

• Genetics allows breeders to be able to produce improve and maintain new varieties of plants and animals.

• Selective breeding – – artificial selection – individuals with the most desirable

traits are crossed so hopefully offspring show these desirable traits.

– inbreeding – mating of closely related organisms- selecting organisms to mate to produce organisms with those desirable traits

– Hybridization – breeders cross two varieties each with desirable traits hoping to produce offspring showing both desirable traits – rose with large petals and sweet scent.

Human Heredity – pedigree charts

• Tracing patterns of inheritance in families use pedigree charts– Show presence or absence of traits in each

generation– Helps identify carriers of recessive genes.– See lab practice

Human genetic disorders – detection and counseling

• Detection before or after birth• Blood and urine tests – sickle cell anemia

and Tay-sachs along with PKU.• Karyotyping – photographs of homologous

chromosomes show abnormalities in structure or number

• Anmiocentesis – amniotic fluid is used to karyotype or chemical analysis. Sickle cell, Tay-sachs and downs syndrome.

One gene one polypeptide hypothesis

• One gene controls the synthesis of a single polypeptide.

• A gene is a sequence of nucleotides in a DNA molecule necessary to synthesize one polypeptide.

• Jumping genes and transposons

• Gene mutations: change in the sequence of nucleotides in a DNA molecule.

Gene mutations

• Additions

• Deletions

• Substitutions

• Cloning

• Genetic engineering

• Restriction enzymes

• Electrophoresis– See hand out – packet of review information