Chapter 12

Inheritance Patterns and Human Genetics

Sex Determination-Thomas Hunt Morgan experimented with fruit flies-Each had four pairs of homologous chromosomes-X and Y chromosomes are discovered-All other chromosomes are called autosomes-XX = Female XY = Male

Chromosomes and Inheritance

Sex Linkage

-Morgan Hypothesized that more chromosomes could be carried by the X chromosome than the Y chromosome

-Genes found on the Y Chromosomes are ‘Y Linked Genes’, genes found on the X chromosome are ‘X Linked Genes’

Linkage Groups

-Linkage groups are genes located on one chromosome

-Morgan’s demonstrations the existence of linkage groups by:Crossing GGLL (Grey,Long Winged) with itself to create F1

generation.

Afterwards, he crossed heterozygous GgLl with GgLl to produce the F2 generation

Phenotypic ration turned out to be 9:3:3:1

-A few of his experiments on linkage groups came out wrong because of mutations

Chromosome Mapping

-Genes distance determines likelihood of the gene crossing over

-The more offspring showing traits, the farther apart they are located on the chromosome

-A chromosome map is a diagram that shows the linear sequence of genes on a chromosome

-A map unit is the distance for a 1 percent crossover rate and is used in making chromosome maps.

Mutation

-A mutation is a change of a cell. A germ cell mutation is a mutation occurring in a germ cell also know as a gamete.

-Somatic mutation occur in a organism body cells and can affect the organism itself.

-Lethal mutations are mutations that often cause death before birth.

-Chromosome Mutations: Change in the structure of the chromosome

-Gene Mutation: DNA is mutated

Chromosome Mutation-A deletion is the loss of a chromosome piece

-Inversion is when the chromosome detaches and reattaches itself

-Nondisjunction is the failure of a chromosome to separate from its homologue during meiosis.

-This causes the gamete to receive an extra copy of the chromosome. This will cause life challenging disorders.

Gene Mutations-Point Mutation is the substitution,

addition, or removal of a single nucleotide. This creates a new codon.

-Common examples of point mutations areSubstitution mutation is when a protein is

replaced by another one

Deletion is when one or more nucleotides are lost

Addition is the adding of a nucleotide

-Frame shift mutation the addition or removal of a continuously erroring codon.

Pedigree Analysis- A pedigree is a family record showing a single trait and

how it moves around in the family.

- Repeated phenotypes arecalled patterns of inheritance

Genetic Traits and Disorders

-Genetic Disorders are genetically based disorders-One example is Huntington disease.

Mild forgetfulness, irritable, muscle control loss, spasms, mental health degrades.

-Single allele traits are overlarge amounts of traits controlled by a single allele.

-A genetic marker is a section of DNA that has a relation to another nearby strand of DNA

-Multiple allele traits are groups are three alleles that control just one gene.

-Blood type is determined by multiple allele traits

Polygenic Traits, and X Linked Traits

-A Polygenic trait is a a trait controlled by two or more genes. Skin colour is the best example, where six different genes mix together to produce the correct pigment.

-Colour-blindness is a X linked trait.

-Haemophilia is also X linked and prevents blood clotting in its victims.

-There are many other X Linked traits that cause diseases, though most the traits are not dangerous.