Download Introduction to Genetics

Genetics
&
Heredity
Who was Gregor Mendel?
• “Father of Genetics”
Who was Gregor Mendel?
• Austrian monk who studied
mathematics and science
• As a boy he could predict the possible
types of flowers and fruits that
would result from crossbreeding two
plants in his father’s garden
Who was Gregor Mendel?
• Curiosity about the connection between the
color of a pea flower and the type of seed
that same plant produced inspired him to
begin experimenting with garden peas in
1856.
• Made careful use of scientific methods,
which resulted in the first recorded study
of how traits pass from one generation to
the next.
What is GENETICS?
The study heredity of how traits
(characteristics) are inherited
through the interactions of genes.
What is a GENE?
• The material that controls which
traits are expressed in an organism
• Genes come in pairs and offspring
inherit one copy of each gene from
each parent
Define HEREDITY
The passing of traits from parent
to offspring
Define ALLELE
• Either member of a pair of genes
that determine a trait.
• The different forms of a trait that
a gene may have
• One form of a gene
Define TRAIT
• Ways of looking, thinking, or being
• Traits that are genetic are passed
down through the genes from
parents to offspring
Describe RECESSIVE
(weak)
• A trait that is covered over, or
dominated, by another form of
that trait and seems to disappear
• Hidden when the other copy of the
gene contains the dominant allele.
• A recessive allele shows up only
when there is no dominant allele
present
• Shown with a lower-case letter
HOMOZYGOUS or Pure
(same)
• Both alleles [forms of the gene] are the
same ex. BB, bb, TT, tt
• When offspring inherit two dominant
genes, (one dominant gene from each
parent) they are said to be homozygous
dominant
• When offspring inherit two recessive
genes, (one recessive gene from each
parent) they are said to be homozygous
recessive
HETEROZYGOUS or Hybrid
(different)
• When alleles occur in different
forms ex. Tt, Bb, Rr
• When offspring inherit one
dominant gene and one recessive
gene, they are said to be
heterozygous
• Since the dominant gene will be
expressed, they are said to be
heterozygous dominant
INCOMPLETE DOMINANCE
p. 316 snap dragons
•
A blend of 2 traits,
resulting in a cross
•
of homozygous.
•
P1 RR x WW
No dominance or recessive,
all offspring are pink
Describe CO-DOMINANCE
• When an organism has two different
alleles for a gene that does not
follow the dominant/recessive
pattern
• The organism shows a trait that is a
blend of the traits represented by
the two alleles
• Also called INCOMPLETE
DOMINANCE
Describe CO-DOMINANCE
P. 317 (checkered chicken)
For example:
P1 BB x WW
Both traits are displayed
All the offspring are black and white
Describe DOMINANT
(strong)
• A trait that covers over, or
dominates, another form of that
trait
• Trait that always shows up, even
when only one of the two alleles is
in the dominant form
• Shown by a capital letter
Define GENOTYPE
An organism's genetic makeup
Think……(letters)
Ex. TT, Tt, tt, RR, rr, Rr
Define PHENOTYPE
Outward physical appearance and
behavior of an organism
think…”what does looks like”
Ex. green, round, tall …
What is a PUNNETT SQUARE?
• A tool to predict the probability of
certain traits in offspring that shows
the different ways alleles can combine
• A way to show phenotype & genotype
• A chart that shows all the possible
combinations of alleles that can result
when genes are crossed
What is a PUNNETT SQUARE?
• Letters stand for dominant and
recessive alleles
• An uppercase letter stands for a
dominant allele
• Lowercase letters stand for
recessive alleles
3 Principles of Heredity
• Principle of Dominance and Recessive
(one trait is masked or covered up by
another trait)
• Principle of Segregation
(two alleles (pair of genes) for a trait
separate during gamete formations)
• Principle of Independent Assortment
( each trait is independently
inherited)
MULTIPLE ALLELES
• Traits controlled by more than
two alleles
• Traits controlled by multiple
alleles produce more than
three phenotypes of that trait
What is meant by MULTIPLE
ALLELES?
For Example: Blood Types
4 types
Genotype
phenotype
A
AA, AO, IAIA, IAi
B
BB, BO, IBIB, IBI
AB
AB, IAIB
OO
OO, ii
Universal
Recipient
Universal
Donor
What is POLYGENIC
INHERITANCE?
• Occurs when a group of gene pairs
acts together to produce a trait.
• The effects of many alleles produces
a wide variety of phenotypes .
• Ex. Hair color, eye color