Transcript Genetics and Inheritance - Parma City School District

Genetics and Inheritance
The Scientific Study of Genes and the
Inheritance of Traits
• Gregor Mendel (1860) = “Father of
Genetics”
 Experimented with pea plants
 Used self-fertilization (asexual reproduction)
and cross-fertilization methods (sexual
reproduction)
 chose simple traits to follow (flower color,
height, seed color, seed texture etc.)
Key Terms To Know:
• Trait = any characteristic that can be passed from
parents to their offspring
• Gene = genetic material on a chromosome that
contains the instructions for creating a particular trait
• Allele = one of several varieties of a gene, an
alternate form of the same gene for a given trait
example: A or a (same letter, different case)
• Locus = the location on a chromosome where a
gene is located
Homologous Pairs
Every somatic (body) cell contains two copies of each
chromosome, one from each parent. This is called a
Homologous Pair. Each chromosome in the pair contains a
gene for the same trait at exactly the same loci.
Monohybrid Crosses
• Monohybrid Cross = a cross involving
only a single allele responsible for a
trait; each parent contributes
information for the trait (ex. Aa X AA)
Trait Characteristics
• Dominant trait = the trait that gets
expressed in a monohybrid cross where
the mode of inheritance is Complete
Dominance; shown by a capital letter :
A
• Recessive trait = the trait that is hidden
in a monohybrid cross where the mode
of inheritance is Complete Dominance;
shown by a lower case letter : a
Allele Pairing
• Homozygous = the two alleles for a
trait that an organism has are identical
ex: Homozygous Dominant = AA ,
Homozygous Recessive = aa
• Heterozygous = the two alleles coding
for a trait are different ex: Aa
Genotype vs. Phenotype
• Genotype = the actual genetic
information, all the alleles that an
organism possesses (the actual letters)
• Phenotype = physical appearance
based on alleles
Mendel’s First Law of Heredity
• Law of Dominance: When a trait is
Completely Dominant over another trait,
then that dominant allele controls the
gene pair. In the heterozygous form
(Aa) the dominant trait only gets
expressed. The recessive allele gets
hidden.
Mendel’s Second Law of
Heredity
• Law of Segregation: Pairs of
alleles separate during the
formation of the gametes (sex
cells) during Meiosis I.
Therefore each gamete will
contain one allele for each
gene.
Meiosis and Independent
Assortment
Mendels Third Law Of Heredity
• Law of Independent Assortment :
Gene pairs separate into the gametes
both independently and randomly of
each other.
• The rules of probability are used to
describe how the different
chromosomes and their alleles from
parents assemble into gametes and
ultimately into offspring.
PUNNETT SQUARES
•
•
•
•
Used to track a trait from parents to offspring.
Shows possible ratios for offspring outcomes.
P Generation = Parents
F1 Generation = Offspring from the cross of
the parents
• F2 Generation = Offspring produced from
crosses among
the F1
• F = filial, refers to sons and daughters
Monohybrid Cross
Monohybrid Cross ratios:
Complete Dominance = 3:1 (Aa X Aa)
4:0 (AA X aa)
2:2 (Aa X aa)
Punnett Square Rules
• 1. Make a key; show dominant and
recessive alleles
• 2. Properly label parents genotypes,
place them on the outside of the punnett
square
• 3. Correctly perform the cross
• 4. Interpret the results; determine ratios
Test Crosses
– Suppose we have two Tall pea plants
• T= tall
• t = short
What are the possible
genotypes for each plant?
• tt For A Short Plant
• TT OR Tt For a Tall Plant
To find out whether an individual showing a
dominant trait is homozygous or heterozygous,
the individual can be crossed with an individual
whose genotype is known for certain.
Test Cross: cross the tall
plant (TT or Tt) with a short
one (tt)
• If any recessive phenotypes show up in
the next generation, the unknown
genotype MUST be Heterozygous
•
Homozygous tall x short TT x tt
Heterozygous Tall x short Tt x tt
x
All Offspring Would Be Tall!!
Either TT or Tt