Transcript Introduction to Genetics

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Looking at chromosomes
Karyotyping – 22 autosomal pairs, 1 sex pair
Recognizing abnormalities in karyotypes
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To genetics!!!!
What is a gene?
A gene is a unit of heredity that is passed down
from parent to child. Genes are located on
chromosomes that are in all of our cells,
including the sperm and egg that make a baby.
Genes are made of molecules or chemicals
called DNA. The pattern of DNA will
determine if the gene is working properly. The
DNA has to be in a certain pattern or order,
like the numbers in a phone number.
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I can describe the evidence Mendel obtained for
dominance, segregation, and the independent
assortment of genes on different chromosomes.
I can summarize Mendel’s laws of segregation and
independent assortment
I can calculate & compare ratios and probabilities of genotypes
and phenotypes for genetic crosses with the following inheritance
patterns:
- Dominant / Recessive
-Testcrosses
- Multiple Dominance / Multiple Alleles
- Incomplete Dominance
- Codominance
- Sex-Linked
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I can use / interpret pedigrees which
graphically illustrate the inheritance patterns
above.
I can explain the effect that gene linkage and
crossing over have on the variability of
organisms.
I understand that traits can be controlled by
one pair of genes or they may be polygenic
meaning they are controlled by many genes (ex.
skin colour, height)
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What is genetics?
Who is Gregor Mendel (and what did he
discover about passing on of traits)?
What are the basic genetic terminology that I
need to know?
Phenotype
Genotype
Dominant
Recessive
Genetics – the study of heredity
which is the transmission of
characteristics from parents to
offspring
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the transmission or
passing of traits from
parent to offspring.
“Heredity: the thing a
child gets from the
other side of the
family” –
Marcelene Cox
Small sections of DNA are responsible for a
“trait”. These small sections are called
“Genes”.
Gene - A segment of DNA that codes for a specific
trait
 Trait - A characteristic an organism can pass on to
it’s offspring through DNA
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born on July 22, 1822
to peasant parents in a
small agrarian town in
Czechoslovakia
In 1843 he entered an
Augustinian monastery
in Czechoslovakia
He was later sent to the
University of Vienna to
study
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The pea flower
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Pistil
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Stamen
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The male part of the
flower (stamen) was
easily removed to
prevent self-pollination.
Pea flowers are easy to
cross-pollinate (he could
control the pollination)
They were easy to grow.
Dominant Recessive
Round
wrinkled
Yellow
seed
Green
seed
Purple
flower
White
flower
Inflated
pod
Constricted
pod
Green pod Yellow pod
Tall is dominant over short.
Flower postion:
Axial is dominant over terminal
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Mendel tested all 34 varieties of peas available to
him through seed dealers. The garden peas were
planted and studied for eight years.
Mendel's experiments used some 28,000 pea
plants.
So just imagine what life would have been like
living in the same monastery as Brother Gregor??
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Phenotype - Characteristics that can be
observed. Tall and short are phenotypes
Genotype – Actual coding of the gene.
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Examples of genotypes are: TT, Tt, tt
TT is tall, Tt is hybrid tall, tt is short
Allele – An allele is one of two or more
versions of a gene. Tall and short are the alleles
for height in pea plants.
Dominant – Tall is stronger over short so the
tall allele will be expressed
Recessive – Short is the weaker allele and
won’t show unless both alleles for short are
present
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Homozygous – pure
a genotype in which
both alleles of a pair
are the same
Heterozygous –
hybrid
a genotype in which
the alleles of a pair
are different
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two or more alternate forms of a gene.
The alleles are located at the same position on
one of the pairs of homologous chromosomes
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Filial generation one
A term Mendel used
for the first generation
in his experiements.
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The second
generation.
A term Mendel used
for the offspring of the
F1 generation.
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the alleles an
organism contains
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the observable
traits of an
organism that
arise because of
the interaction
between genes
a chart used by
geneticists to show the
possible combinations of
alleles in offspring AND
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Used to calculate the
probability of inheriting
a particular trait
 Probability – The
chance that a given event
will occur
Parent
Parent
Offspring
Y-Yellow
y-white
Genotype:
1:2:1
(YY:Yy:yy)
Phenotype:
3 Yellow
1 White
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Give the genotype and phenotype for the
following cross: TT x tt (T = Tall and t = Short)
Step One: Set Up Punnett Square (put one parent on
the top and the other along the side)
T
t
t
T
Step Two: Complete the Punnett Square
T
T
t
Tt
Tt
t
Tt
Tt
Step Three: Write the genotype and phenotype
T
T
t
Tt
Tt
t
Tt
Tt
Genotype:
4 – Tt
4:0:0
Phenotype:
4:0 tall
Remember: Each box is 25% 100% Tall
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a cross that involves
one allele pair of
contrasting traits
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When studying genetics you are examining the
inheritance of biological traits which are passes
from parents to offspring.
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Mendel proved over and over that a blend is not
always the result of the crossing of traits. He found
that when he crossed two traits that one trait always
dominated the other trait no matter what method of
cross-fertilization he used.
For example, when he crossed a plant that produced
round seeds with a plant that produced wrinkled
seeds he always saw offspring with round seeds.
This was also proved true with other characteristics
of the pea plant. He reasoned that factors (now
known as genes) control the traits of plants and that
there were alternate forms of these factors.
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A dominant trait is the trait that is expressed
most often. A dominant trait will overrule or
mask a recessive trait.
For example, in garden peas purple flowers are
dominant over white flowers. If a pea plant
receives one allele for purple and one allele for
white, the flower will be purple.
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Mendel created a system of symbols he used to
record the results of his experiments. Upper
case letters are used for the dominant traits
while lower case letters are used for the
recessive traits.
For example, yellow seeds are dominant over
green seeds so the allele for yellow seeds is
represented by (Y) and the allele for green
seeds is represented by (y).
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A hybrid parent contains one dominant allele
and one recessive allele. For example, a round
hybrid parent would be (Rr). R is the allele for
round while r is the allele for wrinkled.
Mendel discovered that when he crossed two
hybrid parents 75% of the offspring expressed
the dominant trait (round) while 25%
expressed the recessive trait (wrinkled).
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Purple 75 %
White 25 %
Genotype Ratio
D:H:R
1:2:1
Phenotype Ratio
D:R
3:1 Purple