Download Human Inheritance

Modern Genetics
Genetics since Mendel
Beyond Dominant and Recessive
Alleles
• Some alleles are neither dominant or recessive, and
many traits are controlled by multiple alleles or
multiple genes.
• Incomplete dominance: one allele is not
completely dominant over another. A red flower
crossed with a white flower, produce pink flowers.
(blending)
• Codominance: Both alleles contribute to the
phenotype of the organism. Black chicken crossed
to a white chicken produce a black and white
chicken
Traits controlled by many genes
• The genes act together as a group to
produce a single trait.
• At least 4 genes control height in humans
• Skin color is also controlled by many genes.
The Sex chromosomes
• The sex chromosomes are one of the 23
pairs of chromosomes in each body cell.
• The sex chromosomes carry genes that
determine whether a person is male or
female. They also carry genes that determine
other traits.
• Girl = XX
• Boy = XY
Sex-Linked Genes
• The genes for some human traits are carried
on the sex chromosome.
• Genes on the X and Y chromosomes are
often called sex-linked genes because their
alleles are passed from parent to child on a
sex chromosome.
• Traits controlled by sex-linked genes are
called sex-linked traits.
• Example: red/green color blindness
The Effect of the Environment
• Many of a person’s characteristics are
determined by an interaction between genes
and the environment.
• For example, a person’s diet could affect a
person’s height.
Causes of human genetic
disorders
• A genetic disorder is an abnormal condition
that a person inherits through genes or
chromosomes.
• Some are caused by mutations in the DNA.
• Others are caused by changes in the overall
structure or number of chromosomes.
Mutation
• A mutation is an error that occurs in the
DNA when it is copied inside of a cell.
Mutations are changes in genes.
• Not all mutation are harmful. They may
have no effect and in rare cases it may be
helpful.
Examples of Genetic Disorders
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Cystic fibrosis- Recessive genes
Color blindness
Hemophilia
Sickle cell
Celiac
Down syndrome
Pedigrees
• One of the important tools geneticists use to
trace the inheritance of traits in humans is
pedigree.
• A pedigree chart tracks which members of a
family have a particular trait.
Pedigree Charts
Circle = Female
Square = Male
Karyotypes
• A karyotype is a picture of all the
chromosomes in a cell.
• It can reveal if a person has the correct
number of chromosomes
Normal Female
Normal Male
Downs Syndrome
Advances in Genetics
Selective Breeding
• The process of selecting organisms with
desired traits to be parents of the next
generation.
Inbreeding
• The technique of inbreeding involves
crossing two individuals that have similar
characteristics.
• Inbred organisms are genetically very
similar, because of this inbreeding increases
the probability that organisms may inherit
alleles that lead to genetic disorders.
Hybridization
• In hybridization breeders cross two
genetically different individuals.
• The hybrid is bred to have the best traits
from both parents.
Cloning
• A clone is an organism that has exactly the
same genes as the organism from which it
was produced.
• www.brainpop.com
• (cloning)
Genetic Engineering
• Genes from one organism are transferred
into the DNA of another organism.
• Genetic engineering can produce medicines
and improve crops.
• Genetically engineered bacteria produce
human insulin for diabetics.
• Genetically engineered crops can resist pests
or survive in cold temperatures or poor soil.
Gene Therapy
• Someday it may be possible to use genetic
engineering to correct some genetic
disorders in humans.
• This involves inserting copies of a gene
directly into a person’s cells.
The Human Genome Project
• A genome is all the DNA in one cell of an
organism.
• The main goal of the Human Genome
Project was to identify the DNA sequence of
every gene in the human genome. It was
completed in May 2006.
• Scientists estimate that human DNA has
around 25,000 genes.
DNA Fingerprinting
• DNA from a person’s cell is broken down
into small fragments.
• Selected fragments are used to produce a
pattern called a DNA fingerprint.
• Except for idenitcal twins no two people
have exactly the same DNA fingerprint.