Genetics Since Mendel

Incomplete Dominance

• Occurs when neither allele for a trait is dominant.

• The phenotype produced is intermediate between the two homozygous parents

• Ex. Coat color in purebred dogs

Multiple Alleles

• More than 2 alleles are multiple alleles

• Traits controlled by multiple alleles produce more than 3 phenotypes.

• In humans, blood type is controlled by 3 alleles (A,B,)- A & B are dominant. O is recessive

Polygenic Inheritance

• A group of gene pairs acts together to produce a trait, which creates more variety in phenotypes.

• Many human traits are controlled by polygenic inheritance, such as hair and eye color, height, body build, shape of eyes, lips and ears.

*Height is controlled by fourgenes working together.

*Skin color is controlled by atleast three genes, each onecontaining two different alleles.Various combinations ofalleles produce the many skincolors in humans

Mutations- genes that are altered or copied incorrectly

• A mutation can be harmful, helpful, or have no effect

• Chromosome disorders- caused by more or fewer chromosomes than normal

• Down Syndrome- caused by 3 copies of chromosome 21

Significance of Mutations• Most are neutral

• Eye color• Birth marks

• Some are harmful• Sickle Cell Anemia• Down Syndrome

• Some are beneficial• Sickle Cell Anemia immune to Malaria• Immunity to HIV

What Causes Mutations?

• There are two ways in which DNA can become mutated:– Mutations can be inherited.

• Parent to child

– Mutations can be acquired.• Environmental damage• Mistakes when DNA is copied

Chromosome Mutations

• Down Syndrome– Chromosome 21 does

not separate correctly.– They have 47

chromosomes in stead of 46.

– Children with Down Syndrome develop slower, may have heart and stomach illnesses and vary greatly in their degree of inteligence.

Chromosome Mutations

• Cri-du-chat– Deletion of material on 5th

chromosome– Characterized by the cat-like

cry made by cri-du-chat babies

– Varied levels of metal handicaps

Recessive Genetic Disorders

• Both parents have a recessive allele responsible for the disorder and pass it on to their child.

• Because parents are heterozygous, they don’t show symptoms

• Cystic Fibrosis is a homozygous recessive disorder

Recessive Genetic Cont.

• Genes that determine the sex of an organism are XX in females and XY in males. Males determine the sex of the offspring

• Females produce eggs with x chromosomes only. Males produce sperm with either an x or a y chromosome.

Sex Linked Disorders

• 1. An allele inherited on an X or Y chromosome is a sex linked gene.

• Colorblindness is a sex linked disorder caused by a recessive allele on the X chromosome. More common in males- females have to inherit it on both x’s.

Example of sex-linked traitcontrolled by a recessiveallele: red-green colorblindnessAffects moremales thanfemales

What is a pedigree chart?

• Pedigree charts show a record of the family of an individual

• They can be used to study the transmission of a hereditary condition

• They are particularly useful when there are large families and a good family record over several generations.

© 2007 Paul Billiet ODWS

Symbols used in pedigree charts

• Normal male• Affected male• Normal female• Affected female• Marriage

A marriage with five children, two daughters and three sons. The eldest son is affected by the condition.

Eldest child Youngest child

© 2007 Paul Billiet ODWS

Organising the pedigree chart

• A pedigree chart of a family showing 20 individuals

© 2007 Paul Billiet ODWS

Organising the pedigree chart

– Generations are identified by Roman numerals I

II

III

IV

© 2007 Paul Billiet ODWS

Organising the pedigree chart

• Individuals in each generation are identified by Arabic numerals numbered from the left

• Therefore the affected individuals are II3, IV2 and IV3

I

II

III

IV© 2007 Paul Billiet ODWS

Advances in Genetics

• Genetic Engineering: Genes

from one organism are

transferred into the DNA of

another organism

• Used to produce medicine(insulin),

improve crops, and cure

genetic disorders

Bright face of genetically modified corn plant: pest-infected non-GM (left) and pest-free GM plant (right)

planted side-by-side in a field trial. (photo: Dr. Yu Jialin, China Agricultural University)

                                          

                  

                                        

              

French genetic researchers created Alba for artist Eduardo Kac. Thanks to genes borrowed from a jellyfish, the albino rabbit glows green when placed under special lighting. In regular light, Alba appears like any other furry white rabbit. But place her under a black light, and her eyes, whiskers and fur glow a otherworldly green.

http://www.fluorescentpets.com/index.htm

Gene Therapy

• A normal allele is placed into a virus, which delivers the normal allele when it infects its target cell.

• May be used to control cystic fibrosis and other genetic disorders

Selective Breeding: Breeding organisms with desired traits so that their offspring will havethose traits

Hybridization: Breeding twogenetically different individuals

SELECTIVE BREEDING

• The Liger is the result of breeding a female Tiger to a male Lion.

• The liger has both stripes and spots. The stripes are inherited from its tiger parent and the spots from the lion parent.

• On their hind legs, ligers stand approximately 12 feet tall. At most, ligers may weigh up to 1,000 pounds.

The Cama is the result of breeding a Llama to a Camel.

Parents in background of picture.

The Zebroid is the result of breeding

a female Horse and a male Zebra.

The Zedonk / Zonkey is the result of breeding a female Donkey and

male Zebra.

The Mule is the result of breeding a female horse(mare) to a male donkey (jack). The

mule is superior to the horse in strength,endurance, intelligence and disease resistance.

The Human Genome Project:The main goal of the humangenome project is to identifyevery gene in human DNA.How can this help improvemodern medicine?