Transcript Introduction to Genetics

Introduction to Genetics
Chapter 9
Heredity
Transmission of characteristics form
parents to offspring
Gregor Mendel
Austrian Monk
Studied heredity in pea plants
Studied 7 characteristics of peas
Traits
characteristic
occur in two forms
7 Characteristics of Pea Plants
Plant height (long or short)
Flower Position along the stem (axial or
terminal)
Pod Color (green or yellow)
Pod appearance (inflated or constricted)
Seed texture (smooth or wrinkled)
Seed color (yellow or green)
Flower color (purple or white)
Chromosomes
Humans have 46 chromosomes
arranged in 23 pairs (44 autosomes and
2 sex chromosomes)
Chromosomes are made up of DNA and
Proteins
Chromosomes and therefore the DNA
can be divided into genes
Genes are short segments of DNA
Chromosome with genes
Allele – alternate form of a
gene
Example: Brown/blue, tall/short
can be represented by a letter
Example: Brown – B
Blue - b
Homologous Chromosomes
Determines eye
color
Determines hair
color
Genes
Blue Alleles
b
b
One pair of your chromosomes
for eye color
Blue Allele
b
Brown Allele
B
One pair of your chromosomes
for eye color
b
Blue alleles
Blue Allele
b
b
Homozygous – alleles are the same
Brown Allele
B
Heterozygous – alleles are
different
Homozygous (pure)
The two alleles are the same
The two letters are the same
BB or bb
Homozygous Dominant – BB
Homozygous Recessive - bb
Heterozygous (hybrid)
The two alleles are different
The two letters are different
Bb
Dominant Gene
A gene that will be expressed if it is
present
Examples – brown, tall, green, purple
Written as a capital letter
Recessive Gene
A gene that will only be expressed if
there are two alleles present
Recessive genes are not expressed if
there is a dominant gene present
Short, blue, yellow, white
Written as a lower case letter
Genotype
The two alleles an organism has
What the genes “say”
Ex. BB, Bb, bb
Phenotype
Physical appearance of an organism
The result of the expression of the
genes
Example: tall, short, brown, blue
The Goal
The goal of genetics is to determine the
possible offspring that can be produced
from two parents
The likelihood of an outcome is
determined through the laws of
probability
Probability
The likelihood that a specific event will
occur
Can be expressed as a decimal, percent
or a fraction
Equation for Probability
Number of times an event
is expected to happen
Probability =
The number of opportunities
for an event to happen
Probability Example
You flip a coin once
The probability of getting tails is ½
You flip a coin twice
The probability of getting tails twice is
1/4
1
1
1
=
X
2
2
4
First Flip
H
or
T
Second Flip
If I got Tails on the first flip I can either get heads or tails
On the second flip
H
T
First
Second
Probability of getting:
H
1/4
T
1/4
H
1/4
H
T
T
1/4
Gametes
Egg or sperm
Haploid
Contains half the number of
chromosomes
One gene from each homologous pair
Genetic Crosses
When doing genetic crosses it is
important to keep tract of the
generations
P1 – parents
F1 – children of the parents (P1)
F2 – Children of the F1’s
GG
gg
Gg
gg
GG
Gg
A Genetic Cross
Punnett Square – used to predict the possible outcomes
of a cross
AA
Male produces one
type of sperm with
the gene A
aa
aa
Female produces one
type of egg with
the gene a
The Baby Elephants will be..
Aa
Aa
Aa
Aa
Monohybrid Cross
a
a
A
Aa
Aa
A
Aa
Aa
How to fill in the Punnett
Square
Monohybrid Cross
Cross where one trait is looked at
Dark elephant vs. light elephant
Aa
Male produces two
types of sperm with
the gene A or a
Aa
Female produces two
type of eggs with
the gene A or a
The Baby Elephants will be..
AA
Aa
Aa
aa
Genotypic Ratio
Ratio of the offspring's genotypes
Genotypic Ratio:
1:2:1
EE – 1
Ee – 2
ee – 1
Phenotypic Ratio
Ratio of the offspring's phenotypes
Phenotypic ratio:
3:1
3 – smooth
1- wrinkled
Phenotypes?
Genotypic Ratio?
Genotypes?
Phenotypic Ratio?
Law of Segregation
A pair of genes is segregated or
separated during the formation of
gametes
Law of Independent
Assortment
Genes for different characteristics are
not connected
They are inherited independently
Dihybrid Cross
A cross between individuals that
involves two pairs of contrasting traits
Look at hair color and eye color at the
same time
Look at height and color at the same
time
Dihybrid Cross Punnett Square
AABB
AB
AB
AB
AB
aabb
ab
ab
ab
ab
Sperm
Egg
ab
AB
Fertilization
AB ab
Genes in the fertilized egg
AaBb
ab
ab
ab
ab
AB
AaBb
AaBb
AaBb
AaBb
AB
AaBb
AaBb
AaBb
AaBb
AB
AaBb
AaBb
AaBb
AaBb
AaBb
AaBb
AaBb
AaBb
AB
AaBb
Genotypic Ratio:
Phenotypic Ratio:
1
1
What if the Dihybrid cross has
heterozygous parents?
How do you find the gametes?
How to find genes for the gametes
of a dihybrid cross
B
AB
b
Ab
B
aB
b
ab
A
a
AaBb
AaBb
AB
Ab
aB
ab
AB
Ab
aB
ab
Dihybrid Heterozygous Cross
Genotypic Ratio
1:2:1:2:4:2:1:2:1
Testcross
When an individual of unknown
genotype is crossed with a homozygous
recessive individual
B? x bb