Transcript Intro to Genetics

Intro to Genetics
Mendel
What is genetics?
• the study of how traits
and diseases are inherited
from one generation to
the next
through genes.
• Every living thing including
plants, animals, microbes,
etc., has a set of
characteristics inherited
from its parent(s).
Mendel (Father of Genetics)
Studied the inheritance of traits in pea
plants
Developed the laws of inheritance
Mendel's work was not recognized until
the turn of the 20th century
Gregor Mendel
(1822-1884)
• Mendel notices that there
were tall plants and short
plants.
-Tall parents produced tall
offspring
-Short produced short
offspring.
• He decided to cross pollinate,
meaning the pollen from one
flower fertilized the egg of
another. This way they would
get different traits from
each parent.
• A trait is a specific characteristic such as height or
eye color that makes organisms vary from one
another.
• Mendel called the parents the P (parental) generation.
• The offspring were called F1 or first filial. Filius is
the Latin word for son.
• The offspring F1 generation are now called hybrids
since they are a cross of parents with different
traits.
• Mendel crossed the tall plant with the short plant.
What do you think happened?
• All offspring were tall in the F1 generation.
1. Biological inheritance is determined by factors passed
from one generation (parents) to the next (babies).
Today, these factors are called genes. Different genes
of the same trait are called alleles. Ex. Tall and
shorts are alleles for height. (T t)
• 2. Mendel discovered the Law of Dominance - some
genes can overpower other genes, these genes are
called the dominant genes. The "weaker genes" are
called recessive genes.
• Any time a dominant gene is present the dominant
trait will be expressed.
•
•
•
Parents (tall and short)
F1 generation: all tall
F2 generation: 3 tall, one
short
Inheritance
Mendel stated that physical
traits are inherited as
“particles”
Mendel did not know that the
“particles” were actually
Chromosomes & DNA
Vocabulary
 Trait:- any characteristic that can be
passed from parent to offspring
 Heredity: - passing of traits from
parent to offspring
 Genetics: - study of heredity
 Purebred:- one that always produces
offspring with the same form of a trait
as the parent. (homozygous)
• Hybrid:- has both forms of a trait
(heterozygous)
• Gamete: - A sex cell, either an egg or a
sperm.
More Vocabulary
 Alleles - two forms of a gene (dominant
& recessive)
 Dominant - stronger of two genes
expressed in the hybrid; represented by
a capital letter (R)
• Recessive - gene that shows up less
often in a cross; represented by a
lowercase letter (r)
• Homozygous and purebred = BB
• Heterozygous and hybrid= Bb
Eight Pea Plant Traits
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•
•
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Seed shape --- Round (R) or Wrinkled (r)
Seed Color ---- Yellow (Y) or Green (y)
Pod Shape --- Smooth (S) or wrinkled (s)
Pod Color --- Green (G) or Yellow (g)
Seed Coat Color ---Gray (G) or White (g)
Flower position---Axial (A) or Terminal (a)
Plant Height --- Tall (T) or Short (t)
Flower color --- Purple (P) or white (p)
Generations
P-Generation (Parents)
F1 Generation (1st Generation of
Offspring)
F2 Generation (2nd Generation of
Offspring)
Probability
• The likelihood that a
particular even will occur is
call probability.
• For example: toss a coin and
it will either land on heads
or tails. The probability
that the coin will land on
heads is ½.
• The probability that it will
land on tails is also ½.
• If you flip a coin three times,
what is the probability that all
three will be heads?
• ½ x ½ x ½ = 1/8
• The principles of probability
can be used to predict the
outcomes of genetic crosses
as well.
• A Punnett square is used to do
this.
Punnett Squares
• The gene combinations
that might result from a
genetic cross can be
determined by drawing a
diagram known as the
punnett square.
Parent 2
Parent 1
Try these: Tt x TT, Bb x bb, TT x
tt , and Bb x Bb
Genotype and Phenotype
• Genotype is an organisms genetic
makeup. For example Bb or BB or bb
• Phenotype is the physical
characteristics or what they look like.
For example if we were talking about
eye color, the phenotype would be blue
or brown eyes.
• If B =brown eyes and b= blue eyes
– Bb=would have brown eyes
– BB= brown eyes
– bb = blue eyes
Let’s Practice
Genotype or phenotype
•
•
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BB
Brown
Blonde
Bb
bb
•
•
•
•
•
Blue
Tt
Tall
Tt
Short
Beyond Dominant and Recessive Alleles
• Some alleles are neither dominant or
recessive, and many traits are
controlled by multiple alleles or multiple
genes.
• Incomplete dominance: one allele is not
completely dominant over another. A
red flower crossed with a white flower,
produce pink flowers. (blending)
• Codominance: Both alleles contribute to
the phenotype of the organism. Black
chicken crossed to a white chicken
produce a black and white chicken
Incomplete Dominance
Polygenic traits
• Unfortunately, not all traits are as
easily predicted as plant height.
• Many traits living organisms have are
polygenic traits.
• Polygenic traits are traits that are
controlled by two or more genes. Poly
means many. Genic refers to genes.
Polygenic means many genes.
For example
• There are at least three genes involved in
the reddish brown pigments in the eyes of
fruit flies.
• Also, skin color in humans is controlled by
at least four different genes.
• Mendel’s principals of probability could not
be used to predict these traits.
• However they can be used in some human
and fruit fly traits.