Download Genetics - LauraFlemingBiology

Genetics
What is Genetics



Genetics is the scientific study of
heredity.
Heredity is what makes each
species unique.
Heredity is the passing on of genes
from one generation to the next.
Basic Genetics Terminology


Gene
 Section of DNA on a chromosome that
determines I trait
Allele
 Different forms of a gene
 Dominant – allele masks other alleles;
represented by capital letter
 Recessive – allele is only shown
(epressed) when a dominant gene is not
presentIndividuals with identical alleles
are called homozygous
Genetics Terminology Cont…




Homozygous
 When both alleles for a trait are identical
Heterozygous
 When the alleles for a trait are different
Genotype
 Actual genetic make-up for a trait
 Homozygous dominant = DD
 Homozygous recessive = dd
 Heterozygous = Dd
Phenotype


The expression of the gene; physical characteristic
Descriptive such as tall for TT or Tt
Genetics Terminology Cont…



F1 Generation
 The first generation of offspring from two
parents
F2 Generation
 The offspring from the breeding of two F1
generation offspring
Test Cross
 an experimental cross of an individual
organism of dominant phenotype but
unknown genotype to an organism with
a homozygous recessive genotype to
determine if the dominant parent is
homozygous or heterozygous
Probability & Genetics


Probability is the likelihood that an
event will happen.
The principle of probability can be
used to predict the outcomes of
genetic crosses.
Punnett Squares

Diagram used to predict genetic
crosses.
How to use Punnett Squares
A.
B.
C.
D.
E.
F.
G.
Choose a letter to represent the alleles.
Write the genotypes of the parents.
Determine the possible gametes
(reproductive cells) of each parent.
Enter the possible gamete at the top and
side of the Punnett square.
Complete the Punnett square by writing the
alleles from the gametes in the appropriate
boxes.
Determine the phenotypes of the offspring.
Using the results of step E and F write down
the genotypic and phenotypic ratios.
More Punnett Squares
Note:
Always put
The dominant
Alleles first
In the squares
Punnett Squares Monohybrid &
Dihybrid Crosses
Gregor Mendel



Austrian Monk
Famous for his work with pea plants
He is known as the father of
genetics
Mendel
Mendel’s Work



Mendel used true-breeding plants which
means if they were left to breed with
themselves they would produce offspring
identical to themselves.
Mendel studied 7 different traits in pea
plants.
A trait is a specific characteristic that
varies from one individual to another.
The Principle of Dominance



The principle of dominance states
that some alleles are dominant and
others are recessive.
Dominant alleles are always
expressed.
Recessive alleles are only expressed
if both alleles are recessive.
Segregation & Independent Assortment


The separation of alleles during
meiosis to form gamates (sex cells).
The Law of Independent Assortment
states that genes for different traits
can segregate independently during
the formation of gamates.
Law of Segregation
Laws of Inheritance
Mendel’s Principles




The inheritance of biological
characteristics are determined by genes.
For two or more forms of a gene,
dominance and recessive forms may
exist.
Most sexually reproductive organisms
have two sets of genes that separate
during gamete formation.
Alleles segregate independently.
Genetics Practice Monohybrid
In summer squash, white colored fruit is dominant over
yellow. If you place pollen from a yellow–fruited plant
on the pistil of a hybrid white–fruited ( heterozygous )
plant, what type of seeds would you expect from the
seed which come from this cross?
Problems Continued…
In cats the gene for short hair is dominant over the
gene for long hair (angora). A short– haired tom is
mated with an Angora female. What are the
expected genotypic and phenotypic ratios?
Beyond Dominant and Recessive


Incomplete Dominance – One allele is not
completely dominant over the other. White
flower crosses with a red = pink flower.
Phenotype of a
heterozygous
individual is a blend
Beyond Dominant and Recessive


Codominance – Both alleles contribute to
the phenotype. Red cow X White Cow =
Roan Cow.
Two capital letters are
usually used in
Punnett square
Beyond Dominant and Recessive

Multiple Alleles – More than two alleles control
the phenotype. Coat color of rabbits.
Multiple Alleles – Blood Type
•Blood Type is the
phenotype
•A and B are
codominant
•Both A and B are
dominant to O
•I stands for
immunoglobulin
Beyond Dominant and Recessive

Polygenic traits –
Several genes
control the trait.
Human skin and
eye color; dark
colors are usually
dominant to lighter
colors
Evolution of Polygenic Traits