Transcript Ch.11 Genetics

What is Genetics?
 The scientific study of
heredity.
 What is heredity?
 The passing of traits
from one generation to
the next
 Characteristics that are
inherited from each
parent
 Tall or Short
 Blonde or Brown
Hair
 Blue or Green Eyes
 Gregor Mendel and his
peas…
 Austrian Priest and teacher
who tended the gardens.
 Experimented with pea
plants
 Observed how traits are
inherited, what traits were
passed from parents to
offspring.
Mendel’s
experiment
Mendel crossed many
different traits in pea plants
and recorded his results.
He did 4 unique things in his
experiment
1. Counted only one trait at a time
2. Used large numbers of data to off
set chance
3. Did many identical experiments and
combined results
4. Used probability to analyze results
 Using your textbook (pgs 263- 274), define the
following words. Find the definition from the chapter
reading…not the glossary 
Mendel
Trait
Hybrid
Gene
Allele
Gamete
Codominance
Genetics
homozygous
heterozygous
phenotype
genotype
incomplete dominance
true-breeding (purebred)
A gene is a section of DNA
that forms a trait (protein).
For example: Hair color,
Height, ear lobes….
Alleles are different forms of
a gene.
For example: brown hair,
blonde hair or Tall and
short.
You get one allele for each
trait from your parents…
 You get one allele from each of your parents in the egg
and sperm.
 Dominant allele – the allele that “wins”. We use a
capital letter “R”
 Recessive allele – the allele that is hidden or loses .
We use a lower case letter “r”.
 Lets pretend that…
R = can roll their tongue
r = can’t roll their tongue
 RR = Dominant, Dominant - Homozygous
This person can roll their tongue
 Rr = Dominant, recessive – Heterozygous (hybrid)
 This person can roll their tongue
 rr = recessive, recessive - Homozygous
 This person can’t roll their tongue
 Each gamete (sperm or egg) cell has one allele for a
trait.
 When they fertilize, the two alleles are joined –
(remember most basic traits need two alleles)
 The dominant alleles will always be expressed
 If there are two recessive alleles, then the recessive
form of the trait will be expressed.
 On your Punnett Square, the letters (alleles) are called
the Genotype.
 Example: RR, Rr, rr
 The Phenotype is what the physical trait actually looks
like (words)
 Example: can roll tongue, blond hair, blue eyes, etc.
4 steps
1. Make a box
2. Put the
genotypes of
the parents on
the outside.
Example:
Cross Tt x tt
Steps, cont’d
3. Fill in the box
4. Figure out the genotype
and phenotype of the
offspring.
*Show as a percent or
fraction
Genotype - letters
TT 0% Tt 50%
tt 50%
Phenotype - appearance
50% Can Roll tongue
50% Can’t Roll Tongue
t
t
T
Tt
Tt
t
tt
tt
 B = Brown Hair
 b = blonde hair
 Cross a homozygous brown haired man with a
heterozygous brown haired female. What are the
genotypes and phenotypes of their possible offspring?
Genotype:
BB =
Bb =
bb =
Phenotype
Brown hair =
blond hair =