Transcript Introduction to Genetics PPTx

Introduction
to Genetics
Chapter 11
Genetics
 The
study of how traits are passed on from
parents to offspring.
 Trait:

Physical characteristic
Ex: hair color, seed color, height
Gregor Mendel (1822-1884)
 “Father
of genetics”
 A monk from Austria
 Lived in a monastery where he was a
priest and a school teacher
 Experimented with pea plants in the
garden
 Mendel

studied 7 different pea plant traits
Pea color, plant height, flower color, etc…
 He
wanted to know how the traits were
passed
 So he crossed (bred) two different plants to
see what the offspring would look like
Mendel believed that the
characteristics of pea plants
are determined by the:
a) inheritance of units or factors from
both parents
 b) inheritance of units or factors from
one parent
 c) relative health of the parent plants at
the time of pollination

 Crossed
a tall pea plant with a short pea
plant
 What did the offspring look like?
Where did the short trait go?
 Then
he crossed the F1 offspring
 What
happened?
 Short
trait reappeared!
Mendel concluded:
 Allele Ex:
form of a trait (written as letters)
Tall pea plant = TT or Tt
A
trait has two alleles
 1 from mom, 1 from dad
 Some
traits are dominant and others are
recessive.
(Why some of us look more like 1 parent
than the other)
An allele is…
 a)
another word for a gene
 b) a homozygous genotype
 c) a heterozygous genotype
 d) one of several possible forms of a
gene

Dominant- Capital letter allele overpowers
small letter, and the dominant trait is shown.


Ex: Tt = Tall plant
Recessive- lowercase allele that is masked by
dominant one, must have two recessive
alleles to show the recessive trait.

Ex: tt = short plant
 Traits
can be described in 2 ways:
 Genotype-
Genetic makeup (Tt, TT or Tt)
 Phenotype- Physical appearance (Tall or
short)
 Homozygous-
Two of the SAME alleles
(both dominant OR both recessive)
 TT
or tt
 Heterozygous-
One dominant allele and
one recessive allele
 Tt
 Sex
cells (sperm and eggs) can only carry
1 allele at a time for each trait.
 If mom has a trait Gg
 Her eggs can only have a G or g
 If dad is GG, his sperm all have one G
 Those
sex cells mix to form the offspring’s
genotype.
 Those offspring can either be GG or Gg
When the genotype consists of
a dominant and a recessive
allele, the phenotype will be
like _________________ allele.
 a)
the dominant
 b) the recessive
 c) neither
 Stop
 Do
activity
 Problem:
Cross a heterozygous tall pea
plant with a heterozygous tall pea plant.
 Step
1: What are the parents (P)
genotypes?
 Tt
x Tt
 Step
2: Set-up your Punnett square.
 Step
3: Fill-in genotypes of offspring
 Step
 Step
4: Make table to organize data
5: Answer any questions asked of you
about the results
 Genotypic ratio:
 Phenotypic ratio:
 %chance having tall offspring:
 % chance having short offspring:
 Freckles
(F) is a dominant trait. Patty is
homozygous for freckles while her hubby
Harry is heterozygous for freckles.
 What are the chances of their children
having freckles ?
 What is the phenotypic ratio?
Practice:

Two dogs mate and have puppies. The male
dog is homozygous for black fur and the
female is homozygous for yellow fur. Black is
dominant and yellow is recessive.
Parents: ____ x ____
How many puppies will
have black fur?
What percent of the
offspring have yellow fur?
Is it possible for these dogs to
have a puppy with yellow fur?
Why/Why not?
Genotype
#
Phenotype