everything you need to know about genetics. what is genetics? genetics is the science of heredity ...
TRANSCRIPT
Everything you need to know about
Genetics
What is GENETICS?
Genetics is the science of heredity
Heredity is the passing of a trait from parent to offspring
Some definitions
Allele - different forms of a geneGenotype - the genetic makeup of
an organism; expressed by two letters
Phenotype - The physical appearance of an organism (determined by the genotype)
it’s what you see
Law of Segregation
This law states that each pair of genes is segregated, or separated, during the formation of gametes (meiosis)
This occurs during anaphase I, when the homologous chromosomes separate
The Law of Independent Assortment Genes for different traits are
distributed to gametes independently of each other In other words, green eyes doesn’t
always sort with red hair.
Here’s another example…
Mendel and the gene theory
Mendel worked with the common pea plant and studied 7 different traits. He studied the offspring of plants for many generations, determining that some traits were dominant and some were recessive. He used his experiments to come up with the laws of segregation and independent assortment.
Mendel's Results One trait he studied was flower color. He
crossed a purple flower with a white flower All the offspring were purple
He then crossed two of these purple offspring Every time he did this he got a 3 to 1 ratio of
purple to white flowers! He developed the idea that purple must be
dominant over white Now lets explore dominance…
Mendelian Genetics Video
Dominant and Recessive Genotypes
There are three kinds of genotypes that one can have for any trait: Homozygous Dominant – both genes
are dominant (AA or GG) Homozygous Recessive – both genes
are recessive (aa or gg) Heterozygous – one dominant and one
recessive gene are present (Aa or Gg)
Dominant and Recessive traits continued…
The dominant allele will always be represented by a capital letter (A,B,C etc…)
The recessive allele will always be represented by a lowercase letter (a,b,c etc…)
Now lets assume that Black-haired rabbits are dominant to white-haired rabbits B = black hair and b = white hair BB – homozygous dominant = black hair Bb – heterozygous = black hair (a carrier for the
white hair gene) bb – homozygous recessive= white hair
Punnett squares
Lets cross a homozygous dominant (black-haired) rabbit with a white rabbit…what are the offspring?
MORE Punnett squares
Now lets cross the offspring from the previous cross
The offspring Are 75% blackAnd 25% whiteOr a 3:1 ratio ofBlack-haired to White-haired rabbits
Punnett Squares are FUN!!
Lets try doing this new cross using a PUNNETT SQUARE
Lets cross a Heterozygous black rabbit with a white rabbit
What are the offspring?
Punnett squares continued
The offspring will be… Two heterozygous black
rabbits and two white rabbits
Remember the Law of
Independent Assortment???? Genes for different characteristics are distributed to gametes independently
This means that traits produced by dominant genes are not necessarily shown together
Here’s a good example…
Independent assortment
Why don’t all traits follow the
rules??? Some traits (like eye color, hair color, skin color, and height) are harder to predict
This is due to a few other patterns of inheritance
Let’s take a look at some!!
Co-dominanceA mix of both phenotypes!
To explore codominance, we are going to use horses. Hair color in horses is codominant… one color does not dominant over the other, but both phenotypes are present. A roan horse will have red and white hair, instead of being all white, or all red.
Roan color in horses
Incomplete DominanceA blend of both phenotypes!!
Incomplete dominance is when the heterozygote phenotype (what you see) seems to be an intermediate, or blend of the traits shown by the parents. A good example is snapdragon flowers. A red flower crossed with
a white flower will produce 100 % pink flowers.
Multiple Alleles Three or more possible alleles for a
single trait like tall, short & medium for plant
height The best example is blood type, in
which the three alleles are IA, IB and i IA and IB are Codominant (remember
that?) and i is the recessive allele
Blood TypesThere are four blood types; A, B, AB
and OBlood type A is represented by IAIA or
IAiBlood type B is represented by IBIB or
IBiBlood type AB is represented by IAIB
Blood type O is represented by ii
Sex-Linked traits Some traits are SEX-LINKED, or found on the sex
chromosomes the trait will be determined by the mother
The sex of the offspring is determined by the presence or absence of the Y, determined by the father If the offspring is XX, it is a female, if it is XY, it is a male
Examples of traits that are sex-linked are baldness and color blindness
Sex-linked punnett squares
Lets assume that XA = normal and Xa = colorblind
So… to be colorblind, the genotype is XaY or XaXa
How many children will be colorblind?
Sex Linked Karyotypes Video
Genetic Disorders Genetic disorders are a mutation in the code for
a gene. Some mutations are chromosomal (when one of
the chromosomes is altered, added or missing) Some are single gene mutations (protein of a
single gene is altered or missing). It is difficult to find a cure for these diseases
because your cells divide rapidly, and since cells make exact copies of themselves, the mutation will be copied over and over again.
Types of Genetic Disorders
Cystic Fibrosis Huntington’s disease Sickle-cell Anemia Hemophilia Down syndromeBut these aren't all of them… go to
http://www.icomm.ca/geneinfo/ for a very complete list of genetic disorders.
The Karyotype
This karyotype is a picture of homologous chromosomes lined up with their pair