Download Genetics

Genetics
A. Definition =
The study of how genes are
passed from parent to
offspring (heredity) and
how genes cause variation
in the traits of organisms.
B. The Father of Genetics
1. The first individual to conduct
extensive research on how genes
work was
Gregor Mendel
*Between 1856 and 1863, Mendel cultivated
and tested approx. 29,000 pea plants to
discover how certain traits were passed
from one generation to another.
* Some of the traits he studied in peas
were the height of the plants, the
color of the flowers, and the shape of
the seeds (peas).
Mendelian Genetics
2. Based on his research, Mendel
proposed several genetics theories,
one being :
The Law of Dominance and Recessive
in genes for a trait.
*A pattern of heredity in which 1
gene/allele is expressed = the
Dominant gene.
Mendelian Genetics
3. Also proposed the
Law of Independent Assortment =
if the genes for two different traits
are located in different non-homologous
chromosomes, they separate randomly
during meiosis and are inherited
independent of each other
C. The Role of DNA
and Chromosomes
REVIEW:
1. During cell division, DNA forms
chromosomes.
2. Each chromosome contains millions of
nitrogen base pairs which serve as genes.
3. Each gene controls the production of a
protein in the organism which creates a
trait (characteristic).
Chromosomes
4.The chromosomes in a diploid cell
can be organized into
Homologous pair = matched sets
of chromosomes.
Pairs are matched on the basis of:
*Overall length of the chromosomes
*Banding pattern on the chromosomes
*Location of the centromere
Homologous Chromosomes
Human Chromosomes
5.The 46 chromosomes in a diploid
human cell create 23 homologous
pairs of chromosomes.
*Pairs 1-22 are referred to as
AUTOSOMES
6. Pair #23 = the Gender Determining
Chromosomes (Sex Chromosomes)
*may or may not match exactly.
*referred to as the X sex
chromosome and the Y sex
chromosome.
*The Y sex chromosome carries the Sex
Determining Gene (SRY gene) which is
the master switch to the male gender.
7. If the 23rd pair of chromosomes
matches exactly, then the
combination is referred to as
XX = Female
23rd pair of
chromosomes
match =
female
8.If the 23rd pair of chromosomes
does not match, then the
. combination is referred to as
XY = Male
23rd pair of
chromosomes
do not match
= male
Karyotype
9. A Karyotype is a test to
identify and evaluate the size,
shape, and number of
chromosomes in a sample of body
cells.
*Extra, missing, or abnormal positions
of chromosome pieces can be
determined.
*The gender of the organism can also
be determined.
Example: Normal Human Karyotype:
Example: Abnormal Human Karyotype:
Example: Abnormal Human Karyotype:
D. Chromosomes and Genes
1. Many genes can be found on a
single chromosome, but most traits
are controlled by 2 genes.
* One of the genes was passed to
you on a chromosome you inherited
from your mother, while the other
gene was passed to you on a
chromosome you inherited from your
father.
* The genes for a single trait can
occur in different versions,
called ALLELES.
* Different alleles can result in
slightly different proteins which
can then result in different
effects on the trait.
Example: Brown eye allele = brown eye protein
Blue eye allele = blue eye protein
VOCABULARY
*Homozygous = the alleles for the
trait result in the production of
the same proteins.
Examples of symbols for
homozygous genes :
HH
tt
BB
X HX H
*Heterozygous = different alleles
for the trait result in the
production of the different
proteins.
Examples of symbols for
heterozygous genes :
Hh
Tt
CS
X hX H
*Phenotype = a description of the
effects of the alleles on a trait.
Examples:
Blue eyes
Tall Height
Has Cystic Fibrosis
*Genotype = an identification of
the exact alleles an individual has
for a trait.
Examples:
Eye color = bb
Height = Tt
Disease = NN
XhY
Go to packet for traits and
Punnett Squares
E. Dihybrid Cross
A cross showing the inheritance of two
different traits at the same time.
*each parent genotype will have 4 alleles,
two for each trait
*One allele for each trait will occur in the
gametes each parent creates. All
possibilities must be determined. (= 4
possibilities per parent)
*requires a 16 box Punnett Square
**SEE EXAMPLE with pea plant traits**
F. Multiple alleles
A trait having more than 2 versions
(alleles) of the genes for a trait
Example:
*Human ABO Blood Type Trait
Rabbit Fur Color
•
•
•
•
•
Example is the color of rabbit fur,
conditioned by four different alleles
C = brown-red fur (wild type)
g = gray fur (chinchilla color)
h = black and white (Himalayan)
a = albino
In this case the dominance relations are
C>g>h>a
(the symbol > means “dominates over”).
G. Polygenic Traits
Traits controlled by more than two
genes (usually by many different genes)
on different chromosomes described as
polygenes. Each has its own alleles.
Examples:
Human
Human
Human
Human
height
weight
skin color
eye color
Human eye color
H. Epistasis =
The suppression of the effects of a
gene by the presence of a completely
different gene.
Coat color in Labrador Retrievers:
*Allele of coat color gene:
B = dominant = Black
b = recessive = brown
*Alleles of epistasis gene:
EE or Ee = does not suppress the black or brown allele
ee = suppresses both the black and brown alleles
Key:
BB = black Lab, no chocolate gene
Bb = black Lab, carries chocolate gene
bb = chocolate Lab, no black gene
Yellow is produced by the presence of a
recessive epistatic gene which has the effect
of masking the the black or chocolate genes.
EE = no yellow gene
Ee = yellow carrier but appears
chocolate
ee = yellow Lab
either black or
So....
EEBB
EEBb
EeBB
EeBb
=Black
=Black
=Black
=Black
eeBB =Yellow
eeBb =Yellow
eebb =Yellow
EEbb =Chocolate
Eebb =Chocolate
H. Sex Influenced Trait
Autosomal traits where the phenotypes
are affected by whether they appear in
a male or female body.
Example:
Baldness in humans.
XY –
BB =
Bb =
bb =
male
bald
bald
not bald
XX –
BB =
Bb =
bb =
female
bald
not bald
not bald
White
African/
American
Hispanic
Asian
O+
37%
47%
53%
39%
O-
8%
4%
4%
1%
A+
33%
24%
29%
27%
A-
7%
2%
2%
0.5%
B+
9%
18%
9%
25%
B-
2%
1%
1%
0.4%
AB +
3%
4%
2%
7%
AB -
1%
0.3%
0.2%
0.1%