Transcript Genetics - I Heart Science

Intro to Genetics
Why do we look
the way we do?
Review of DNA and
Chromosomes

Our DNA wind up neatly into a CHROMOSOME.

Chromosomes contain alleles. Alleles are specific
gene clusters on a chromosome.
Review of DNA and
Chromosomes

There are 46 individual chromosomes in a
human cell. When a person wants to reproduce,
half the chromosomes are passed on.


23 from mom
23 from dad
Homologous pair
You’ll
pass on
half to
your
offspring!
Chromosome
Pair 1
Chromosome
Pair 2
Inheritance of chromosomes

Egg + sperm  zygote
meiosis
egg
zygote
sperm
fertilization
mitosis &
development
Inheritance of genes

After fertilization, you now have a
chromosome from each parent.


Alleles (genes) may have same information
Alleles may be different information
eye color
(blue or
brown?)
eye color
(blue or
brown?)
Gene trait
from dad
Gene trait
from mom
Inheritance of genes

Alleles are inherited separately from each
parent

Let’s say you have one allele for brown eyes &
one allele for blue eyes. The colors are
separate & do NOT blend


either have brown or blue, no blend
Some alleles mask others


brown eye color masked blue
brown is dominant
Genes

Dominant Gene – The gene that is
expressed


Illustrated by a capitol letter
Recessive Gene – The gene that is
hidden

Illustrated by a lower case letter
Genes

If both parents give you the same
gene, we call it homozygous.


Purebred
Example – Two blue eye genes (bb)
Genes

If parents give you two different genes on
the alleles, we call it heterozygous.



Hybrid
Example – a brown and a blue (Bb)
BUT….which of the two traits will be
expressed?
Punnett Squares

To determine the odds of that traits might
be passed on to the offspring, we can do
Punnett Square.

To do a Punnett Square, you have to know
what alleles the parent has.

In our example, we will cross two heterozygous
people. (Bb)
Punnett squares
x
Bb
male / sperm
X
female / eggs
Bb
B
b
BB
Bb
Bb
bb
B
b
Genetics vs. appearance

There can be a difference between
how an organism looks & its genetics

appearance or trait = phenotype
 brown

eyes vs. blue eyes
genetic makeup = genotype
 BB,
Bb, bb
2 people can have the same appearance but
have different genetics: BB vs Bb
Genetics vs. appearance
How were these
brown eyes made?
eye color
(brown B)
eye color
(brown B)
eye
color
(blue b)
eye color
(brown B)
vs.
B
BB
B
Bb
B
b
Karyotype


A kayrotype is the number
and visual appearance of the
chromosomes in the cell
nuclei of an organism or
species.
By studying karyotypes, you
can determine what traits are
inherited.
In other words…

Chromosomes are digitally arranged
so that they are matched with their
homologue or “partner”
chromosome.

Homologue chromosomes are the
same size, shape, and carry the
same genes, and one is inherited
from each parent.

They are numbered according to
size.
Sex determination with
karyotype

This karyotype has 23
exact pairs.

Note that #23
chromosomes are
both X. Therefore this
is a female.
Normal human male

Note that #23
chromosomes
are X and Y.
Is this person female or male?
Trisomy 21



Abnormality
shown in
karyotype
Note that there
are three copies
of #21
chromosome.
This person has
Down Syndrome.
Photos of Down Syndrome
patients from the National Down
Syndrome Society
Correlation between mother’s
age and Trisomy 21 incidence
Monosomy X

Abnormality
shown in
karyotype

Note this
person only has
1 copy of the X
chromosome.

This female has
Turner’s
syndrome.
Turners Syndrome
XXY Male (Extra X)

Abnormality
shown in
karyotype

Note this
person has 3
sex
chromosomes.

This male has
Klinefelter's
Syndrome.
XXY Male (Extra X)
How are DNA samples
obtained for karyotypes?
Amniocentesis: obtaining amniotic
fluid which has cells from the fetus
Chorionic villi sampling: removing
cells from the chorion with fetal
tissue
If there are chromosomal
number abnormalities, how
do they form?

Meiosis: the process of creating sperm or
egg from a diploid cell

If there is a mistake when chromosomes are
separating, then the resulting sperm or egg
will have too many or too few chromosomes.
The Human Genome Project

An international research effort to determine
the DNA sequence of the entire human
genome.

http://www.youtube.com/watch?v=nhoEvAY0ToM