Download Intro to Genetics

Genetics
Unit 9 - Lesson 1 Notes
Heredity

Heredity – the passing of traits from parent to
offspring.


Genes on chromosomes control the traits that show up in an
organism.
The different forms of a trait that a gene may have are alleles.
Steve’s chromosomes,
or genes
Allele
Steve
Heredity


During meiosis a pair of chromosomes separates and
the alleles move into separate cells.
Each chromosome now contains one gene for each
trait.
Steve’s
chromosomes,
one from mom, one
from dad
SPERM
from mom
from dad
from mom
from mom
from dad
from dad
from mom
from mom
from dad
from dad
sperm
Heredity

The study of how traits are inherited is genetics.
Gregor Mendel

Gregor Mendel – the
Father of Genetics.

Mendel was the first to
use mathematics of
probability to explain
heredity and to trace
one trait for several
generations.
Gregor Mendel


Purebred – receives the same genetic
information for a trait from each parent.
Hybrid – receives different genetic information
for a trait from each parent.
Labradoodle
Lab (Purebred)
Poodle (Purebred)
+
(hybrid)
=
Gregor Mendel


Dominant allele – covers up or dominates the other
trait.
Recessive allele – the trait seems to disappear.
Yellow Color is
dominant
Curly hair is
dominant
Gregor Mendel

Dominant

The gene that is expressed
IF PRESENT

When we are determining
someone’s genetic makeup,
we use a capitol letter to
illustrate the dominant
gene.

Ex. B = brown eyes

Recessive

The gene that is not
expressed in the presence
of a dominant trait

When we are determining
someone’s genetic makeup,
we use a lowercase letter to
illustrate the recessive
gene.

Ex. b = blue eyes
Punnett Squares


Probability helps you predict the chance that something will happen.
A Punnett Square can help you predict what an offspring will look
like.
 Uppercase letters stand for dominant alleles.
 Lowercase letters stand for recessive alleles.
A Punnett Square looks something like this….
Bb bb
B
b
Bb
b
bb
B = Brown
b = Blue
b
Bb
bb
BB bb
B
b
Bb
B
Bb
B = Brown
b = Blue
b
Bb
Bb
BB
B
B
BB
Bb
B
BB
B = Brown
b = Blue
b
Bb
Bb
bb
b
b
bb
bb
b
bb
B = Brown
b = Blue
b
bb
bb
Bb
B
B
BB
Bb
b
Bb
B = Brown
b = Blue
b
Bb
bb
Genotype

Remember, an allele is expressed by one letter….

Genotype – the genetic makeup of an
organism.


Homozygous – an organism with two alleles for one
trait that are the same (written BB or bb PUREBRED).
Heterozygous – an organism with two alleles for one
trait that are different (written Bb or Tt…HYBRID).
Dominant/Recessive
Homozygous/Heterozygous
TT
QQ
Pp
BB
Tt
kk
bb
T = tall
Punnett Square

t = short
Use a Punnett Square to determine the probability of each of the
offspring’s genotype and phenotype when two heterozygous, talldominant traits (Tt) are crossed with eachother.
Genotype:
25% Homozygous Tall (TT)
T
T
t
TT
Tt
t
Tt
tt
50% Heterozygous Tall (Tt)
25% Homozygous Short (tt)
Phenotype:
75% Tall (TT) and (Tt)
25% Short (tt)
Phenotype

Phenotype – the way an organism looks and
behaves as a result of its genotype.
Genotype/Phenotype

Genotype

Phenotype
Principles of Heredity
1.
Traits are controlled by alleles on
chromosomes.
Steve’s
chromosomes, or
genes
Allele
Steve
Principles of Heredity
2.
An allele’s effect is dominant or recessive.
RR Rr
Roll
rr
No
Roll
Principles of Heredity
3.
When a pair of chromosomes separates
during meiosis, the different alleles for a trait
move into separate sex cells.