Download Notes PPT pg. 11: Alleles & Mendel Gregor

EQ1: How do we inherit traits from our parents?
EQ2: Is inheritance predictable?
What is Genetics?
Genetics is the scientific study of
heredity
What are Genes?
 Genes are the
sequence of DNA (A, T,
C, G) that codes for a
protein and thus
determines a trait.
 Ex. Hair color
What is a Trait?
 A trait is a specific characteristic that varies
from one individual to another, one of
several options for a gene.
 Examples:



Brown hair
Tongue rolling
Free earlobes
What is an Allele?
 Alleles are the different possibilities for a
given trait. Scientists give them a letter to
represent the possibilities (1 letter represents 1
whole gene- a loooong piece of DNA ex. Your eye color).
 The letter chosen doesn’t matter
 Capital or lowercase DOES matter [make sure they look
different!]
 Every trait has two alleles (one from the
mother and one from the father)
 Example: Can roll tongue = Rr
Mom’s egg gave you a R allele (Can roll) and
Dad’s sperm gave you a r allele (Can’t roll) so you
probably have “Rr” (Can roll- R wins over r)
Examples of Alleles:
B = Brown Hair
b = Blonde Hair
If my dad has brown eyes, why
do I have blue eyes?
Practice: Gene, Trait or Allele?
r = can’t roll tongue
Allele!
Practice: Gene, Trait or Allele?
Eye color
Gene!
Practice: Gene, Trait or Allele?
F = free earlobes
Allele!
Practice: Gene, Trait or Allele?
Blue eyes
Trait!
Practice: Gene, Trait or Allele?
B = Brown eyes
Allele!
Gregor Mendel
 Father of Genetics
 1st important studies of
heredity
 Identified specific traits in the garden pea
and studied them from one generation to
another
Mendel’s
Conclusions
1. Law of Segregation – Two alleles for each
trait separate when gametes form; Parents
pass only one allele for each trait to each
offspring
2.Law of Independent Assortment – Genes
for different traits are inherited
independently of each other
 Just because you got your mom’s hair doesn’t mean you have to get
all the traits of mother
Dominant vs. Recessive
 Dominant – Masks (covers) the other trait; the
trait that shows if present. Usually more
common
 Represented by a capital letter
R
 Recessive – Less common. An organism with a
recessive allele for a particular trait will only
exhibit that trait when the dominant allele is not
present; Will only show if both recessive alleles
are inherited
 Represented by a lower case letter
r
Dominant & Recessive Example
T – straight hair
t - curly hair
 TT - Represent offspring with straight hair
 Tt - Represent offspring with straight hair
*T still wins, but your children could get curly hair!
 tt - Represents offspring with curly hair
Genotype vs. Phenotype
 Genotype – The genetic makeup of an organism;
The gene (or allele) combination an organism has.
 Example: Tt, ss, GG, Ww
 Phenotype – The physical characteristics of an
organism; The way an organism looks
 Example: Curly hair,
straight hair, blue eyes,
tall, green peas
Genotype vs. Phenotype
 Genotype: The allele combination inherited from the
parents.
 Ex: Genotype (Genetics say) = Bb
 Phenotype: The observable characteristics of the genotype
inherited. The organism’s appearance or trait expressed.
 Ex: Phenotype (PHysical appearance for Bb)= Brown hair
Practice: Genotype or
Phenotype?
Brown hair
Phenotype!
Practice: Genotype or
Phenotype?
Rr
Genotype!
Practice: Genotype or
Phenotype?
bb
Genotype!
Practice: Genotype or
Phenotype?
Hitchhiker’s thumb
Phenotype!
Practice: Genotype or
Phenotype?
Straight hair
Phenotype!
Practice: Genotype or
Phenotype?
Tt
Genotype!
Homozygous vs. Heterozygous
 Homozygous (purebred) –
Term used to refer to an
organism that has two identical
alleles for a particular trait (TT
or tt)
 Heterozygous (hybrid) - Term
used to refer to an organism that
has two different alleles for the
same trait (Tt)
RR
rr
Rr
Homozygous vs. Heterozygous
 Homozygous Dominant:
RR
 Homozygous Recessive:
rr
 Heterozygous:
Rr
Practice: Homozygous
dominant, homozygous
recessive, or Heterozygous?
HH
Homozygous
dominant!
Practice: Homozygous
dominant, homozygous
recessive, or Heterozygous?
Ee
Heterozygous
(one dominant
& one
recessive
allele)!
Practice: Homozygous
dominant, homozygous
recessive, or Heterozygous?
bb
Homozygous
recessive!
Practice: Homozygous
dominant, homozygous
recessive, or Heterozygous?
Uu
Heterozygous
(one dominant
& one
recessive)!
Allele Practice WS pg. 12
 Let’s make sure you get how the genetic code works
before we get into using the code!