Download Genetics

Genetics
A summary of the facts
Genetic Code
• All living things have some form of DNA.
• The DNA (deoxyribonucleic acid)
provides all the information for the
organism.
• DNA is passed from parent organism to
offspring.
Two Types of Reproduction
• Organisms reproduce in 2 ways
– Asexual – there is only one parent and it
gives all its DNA directly to the offspring.
Offspring is a copy of the parent.
– Sexual – there are 2 parents and each
parent gives ½ of their genetic information.
The 2 halves combine to create a new
organism that is a mix of DNA from both
parents.
More on Sexual Reproduction
• Each time both parents contribute a
different set of genetic information.
• Therefore each offspring is a unique
combination of alleles.
• Makes for diversity among the members
of a species.
• This explains how siblings of the same
parents can look different.
What About Twins?
• There are two types of twins
– Fraternal – 2 of the mother’s eggs are
impregnated by 2 separate sperm from the
father, therefore the twins have very
different characteristics
– Identical – One egg is fertilized by one
sperm. During cell division, the one cell
becomes 2 with nearly identical DNA,
therefore these twins have very similar
characteristics
Genotypes
• Each trait can be traced to one or more
genes. Genes are a pair of alleles, one
from mom and one from dad (sexual).
• Alleles can be combined in different
ways. The pairing of alleles for an
organism is called its genotype.
Dominant vs. Recessive
• Some alleles overpower and mask other
alleles. These are called dominant
alleles. They are always visible on the
outside.
• Recessive alleles are only visible if they
are paired with another recessive allele.
If not they are never seen.
Phenotype
• The genotype of an organism is entirely
responsible for that organisms
phenotype.
• The phenotype is what is expressed on
an organism. In other words it is what
can be observed about that organism
(ex. color of a rose, length of dog’s fur)
Co dominance
• If a person inherits 2 different dominant
alleles they are both expressed.
– Ex. Blood type – if A type is inherited from
one parent and B is inherited from the other,
offspring will have AB blood type.
Incomplete Dominance
• Some alleles are neither dominant or
recessive to each other. This happens
often with flowers.
• A red (R) flower can be bread with a
white (W) flower and the genotype RW
will produce a pink flower, a little of each.
Punnett Squares
• Punnett Squares are used to determine
the probability a particular trait will be
passed on to an offspring given certain
genetic information about the parents.
• Let’s practice a couple.