Download Intro to Genetics

Introduction to Genetics
Learning Targets
 I can define and provide an example
of the following: genotype,
phenotype, dominant allele,
codominant alleles, incompletely
dominant alleles, homozygous,
heterozygous, and carrier.
Genetics Terms
 Heredity is the passing of traits from
parents to offspring
 Traits are inherited characteristics
such as eye color, height, hair color
 Fertilization is the uniting of male
and female gametes
 Pollination is plant fertilization
More Terms
 Gametes-specialized cells involved in
sexual reproduction; sperm or egg;
pollen or ovum
 Gene-sequence of DNA that codes for
a protein and thus determines a trait
 Probability-likelihood that a
particular event will occur
More terms
 Alleles are the various genes for the
same trait
 Dominant traits are those that are
always expressed when present
(brown eyes)
 Recessive traits are only expressed
if the dominant trait is absent (blue
eyes)
More terms
 Homozygous means possessing a
pair of identical alleles for a trait; can
be dominant or recessive. Shown by
AA or aa
 Heterozygous means possessing a
pair of unlike alleles; dominant trait is
expressed; recessive trait is carried;
Aa
More Terms
 Phenotype is the physical
appearance of a trait
 Genotype is the actual genetic
makeup; XX for females; XY for
males
Even more terms
 True breeders -organisms that
produce offspring identical to
themselves if allowed to self-pollinate
 Hybrids – offspring of crosses
between parents with different traits
Learning Targets
 I can define and provide an example
of the following: genotype,
phenotype, dominant allele,
codominant alleles, incompletely
dominant alleles, homozygous,
heterozygous, and carrier.
Gregor Mendel
 http://science.discovery.com/tvshows/greatestdiscoveries/videos/100-greatestdiscoveries-shorts-genetics.htm
Gregor Mendel
 Father of genetics
 Born 1822 on farm
in Austria (now Czech
Republic)
 Entered monastery
in 1843
Mendel
 Sent to University of Vienna; studied
botany and other subjects
 Became chief gardener at the
monastery
 Monks helped feed not only
themselves but their community
Mendel
 Mendel sought to increase production
and yield of their crops
 Mendel started breeding peas in 1857
to study inheritance
 His study took 10 years to complete
 His methods are still used today
because he kept meticulous records
Why Peas?
• Many varieties have two clearly
different traits
 Flower color
 Seed color
 Seed shape
• Plants are easy to control
 Male and female parts on same flower
(dioecious)
 Pollen is male ; ovule is female
Learning Targets
 I can describe the basic mechanisms
of plant processes, especially
movement of materials and plant
reproduction.
 I can explain the functions of unique
plant structures.
Flowers
http://studyjams.scholastic.com/studyjams/jams/science/plants/flowers.htm
Parts of a Flower

Sepals-outermost circle
of floral parts; usually green
and look like leaves

Petals-often brightly colored;
found just inside the sepals

Leaf-photosynthetic organ
that contains one or more
Bundles of vascular tissue
Parts of a Flower Terms

Stamen-male part of the
flower; made of filament
and anther

Filament-a long thin structure
that supports the anther

Anther-flower structure in
which haploid male gametes
are produced
Parts of a Flower Terms





Pistils (Carpels)-innermost
part of a flower that produces
the female gametes
Stigma- sticky portion at the
top of the style where pollen
grains land
Style-narrow stalk of the
carpel in a flower
Ovary-a flower structure that
contains one or more ovules
from which the female
gametes are made
Ovule-female gamete
Vascular Tissue in Plants
 Xylem-vascular tissue that carries water
from the roots to the rest of the plant
 Phloem-vascular tissue that transports
nutrients and carbohydrates made by
photosynthesis
 Vascular Bundles-a plant stem structure
that contains xylem and phloem tissue
Plant Life Cycle
Plant Fertilization
 http://www.youtube.com/watch?v=L
dlxUJhoyx4
Plant Fertilization
Learning Targets
 I can describe the basic mechanisms
of plant processes, especially
movement of materials and plant
reproduction.
 I can explain the functions of unique
plant structures.
Learning Targets
 I can identify and explain Mendel’s
laws of segregation and independent
assortment
 I can construct and interpret Punnett
squares (calculating and predicting
phenotypic and genotypic ratios of
offspring)
Mendel’s Procedure
1. Remove immature stamen from plant
2. Took brush and removed pollen from
one plant
3. Then brushed pollen onto ova of
another plant
4. Allowed plant to seed and then
planted the seeds
Mendel’s Peas
 Studied over 30,000 plants in 10 years
 Usually followed his plants for 3 generations
 Studied flower color, seed color, seed shape,
height
 Always started with true breeders
 Covered plants to keep pollinators away
Mendel’s Peas
Began by crossing tall & short plants
Expected an intermediate height plant
Instead all plants were tall
Let these plants self pollinate and got
3:1 ratio
 Three tall plants to every short plant
 He decided that each trait had at least
two factors for each trait; called these
alleles




Probability and Punnett Squares
 The principles of probability can be
used to predict the outcomes of
genetic crosses.
 Flipping a coin
 50/50 chance of getting a head every
time
Punnett Squares
 A diagram used to predict genetic
probabilities
 Can compare genetic variations that
will result from a specific cross
Monohybrid Crosses
 A monohybrid cross occurs between
two parents that breed true for
different versions of a single trait
 Allows tracking of one trait only
Monohybrid Cross
P Generation
T
t
t
T
Tt
Tt
Tt
Tt
All were tall
Monohybrid Cross
F1 Cross
T
T
t
TT
Tt
Phenotype: 3:1
Genotype: 1:2:1
t
Tt
tt
Rule of Dominance
 To be dominant, an organism must
possess either two dominant alleles
or at least one dominant allele
 To be recessive, the organism must
receive two recessive alleles; one
from each parent
Principle of Segregation
 Pairs of alleles separate during
gamete formation in meiosis.
 The fusion of gametes pairs the
alleles again at fertilization
Principle of Independent
Assortment
 Each pair of alleles separates
independently of each other during
gamete formation
Incomplete Dominance
R
Snap Dragons
r
Red crossed with
White
Expected 3:1 ratio
Red to White
r
R
Rr
Rr
Rr
Rr
Got all PINK!
Codominance
 The expression of two different alleles
in a heterozygote
 Many genes have different alleles;
but usually only two or less are
expressed in the individual
 Blood is expressed in different alleles:
A, B, AB or O
 A and B are dominant; O recessive
 AB is codominant
Dihybrid Crosses
 A cross where two traits are
examined
 Predicts two different traits
 Parents will have four possible
gametes displaying the various
combinations of the two traits
 Mendel used seed shape and seed
color for one of his dihybrid crosses
Dihybrid Cross
 RRYY




R = round
Y = Yellow
r = wrinkled
y=green
x
rryy
Dihybrid Parent Cross
RY
RY
RY
RY
ry
RrYy
RrYy
RrYy
RrYy
ry
RrYy
RrYy
RrYy
RrYy
ry
RrYy
RrYy
RrYy
RrYy
ry
RrYy
RrYy
RrYy
RrYy
Dihybrid Cross
 Crossing pure breeding homozygous
dominant with pure breeding
homozygous recessive
 RRYY X rryy
 All offspring are heterozygous for the
trait
 RrYy
Dihybrid F1 Cross
RY
rY
Ry
ry
RY
RRYY
RrYY
RRYy
RrYy
rY
RrYY
rrYY
RrYy
rrYy
Ry
RRYy
RrYy
RRyy
Rryy
ry
RrYy
rrYy
Rryy
rryy
F1 Generation Dihybrid Cross
 Allowing F1 to cross pollinate results
in a 9:3:3:1 ratio
 9 will be round, yellow
 3 will be round, green
 3 will be wrinkled, yellow
 1 will be wrinkled, green
Learning Targets
 I can identify and explain Mendel’s
laws of segregation and independent
assortment
 I can construct and interpret Punnett
squares (calculating and predicting
phenotypic and genotypic ratios of
offspring)