Download Intro to Genetics PPT

INTRODUCTION TO GENETICS
TRAITS
• Traits are the different forms of a characteristic
that you may exhibit
• Ex: Blue or Brown Eyes
• Traits are inherited from our parents – mother
and father
• Therefore, when we talk about genetics, we are
talking about sexual reproduction
Chromosomes
• Every cell in a human body has 23 pairs of
chromosomes – half from our mother, half from our
father
• Genes are found on chromosomes
• We have about 20,000-25,000 genes
• Each gene holds a code that tells our body to make
a certain protein
• The protein that is made determines a
Specific trait.
Ex: Blue eye pigment or Brown eye pigment
•
Alleles
• The different forms of a gene that can exist
• Ex: Curly hair gene or straight hair gene
•
Dominant – ‘Strongest Allele’ – If it is present,
you will have that trait. We use upper case
letters for dominant alleles
• Recessive – ‘Weakest Allele’ – This won’t
show up unless there are two of them. We
use lower case letters for recessive alleles
Human cells contain ____
chromosomes
1.
2.
3.
4.
23
46
12
2
25%
1
25%
25%
2
3
25%
4
DNA contains a code that tells your
body to make _____________
1. fat
2. carbohydrate
3. protein
33%
1
33%
2
33%
3
______________ traits won’t show up
unless you have two copies of the
gene.
25%
1.
2.
3.
4.
25%
25%
25%
Recessive
Dominant
Generic
Terrific
1
2
3
4
Genotype
• The actual alleles you have for a trait
• Ex: For eye color, you inherit B from dad
and b from Mom
• Your genotype is Bb
• If there is a dominant allele, the genotype is
written with the upper case first. (Never write
bB)
• Always use the same letter for both alleles
• Your genotype is the genes you have
Genotype (cont’d)
• If you have two copies of the same
allele for a trait (BB or bb), then you
are HOMOZYGOUS for that trait.
• If you have two different alleles for a
trait (Bb), then you are
HETEROZYGOUS for that trait
Phenotype
•How the genes actually show up, or how they
are expressed
•So, if your genotype is Bb,
• Where B is brown
• And
b is blue
•The phenotype would be Brown eyes
•Phenotype is the physical appearance
BB
1. Heterozygous
2. Homozygous
50%
1
50%
2
Rr
1. Heterozygous
2. Homozygous
50%
1
50%
2
You inherit the gene for freckles (F) from your
mother, and the gene for no freckles (f) from your
father. What is your genotype?
1.
2.
3.
4.
Freckles
No freckles
Ff
FF
25%
1
25%
2
25%
3
25%
4
You inherit the gene for freckles (F) from your mother, and the gene
for no freckles (f) from your father. What is your phenotype?
25%
1.
2.
3.
4.
25%
25%
2
3
25%
Freckles
No freckles
Ff
FF
1
4
Blue is dominant to white. What
would the genotype be for a white
flower?
25%
1.
2.
3.
4.
25%
25%
25%
BB
Bb
bb
0
1
2
3
4
Blue is dominant to white. What would
the genotype be for a heterozygous blue
flower?
1.
2.
3.
4.
BB
Bb
Bb
0
25%
1
25%
2
25%
3
25%
4
Karyotype – Normal/Male
A picture of the chromosomes found in an individual. Used to determine
abnormalities.
Karyotype – Abnormal/Female
There are three copies of chromosome 21 – there should only be
two copies. This is a karyotpe of a female with Down’s Syndrome.