Transcript Genetics Since Mendel

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 four
genes working together.
*Skin color is controlled by at
least three genes, each one
containing two different alleles.
Various combinations of
alleles produce the many skin
colors 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 malesfemales have to inherit it on both x’s.
Example of sexlinked trait
controlled by a
recessive
allele: red-green
color
blindness
Affects more
males than
females
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: pestinfected 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 have
those traits
Hybridization: Breeding two
genetically 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 human
genome project is to identify
every gene in human DNA.
How can this help improve
modern medicine?