Download Genetics

Genetics
Objective: There is a genetic basis for the transfer of
biological characteristics from one generation to the
next through reproductive processes.
Welcome Back for your spring semester!
Please take a moment to reflect on your
grade for the fall semester using the goal
sheet as a guide.
Set a new goal for our genetics unit that we
begin today.
http://www.cnn.com/video/#/video/us/2011/01/03/lklv.lavend
era.birds.cnn?iref=allsearch
¼ Genetics and Chromosomal
Mutations
• O. All living organisms have genetic
material that carries hereditary
information.
• J. I can explain how DNA codes for
proteins which are expressed as the
heritable characteristics of an organism
(explain transcription and translation, at
least 5 sentences.)
Terms
Characteristic: heritable feature (plant height)
Trait: variant of a characteristic (tall and short)
Gene: section of DNA that codes for a trait, they make up the
chromosome
Allele: different forms of a gene ex. tall, short
Dominant allele: if it is present it will be expressed
Recessive allele: will not be expressed in the presence of the
dominant allele
Homozygous: carrying two of the same alleles (TT, tt)
Heterozygous: carrying two different alleles (Tt)
Terms continued
Genotype: the actual genes an individual carries ex. Tt
Phenotype: the expression of those genes, tall
Parent generation (P) – the first cross
Filial (F1)– first son or offspring from the parent cross
(F2) – offspring from the F1 generation
One-factor cross(monohybrid cross) – cross involving 1 character
Two-factor cross(dihybrid cross) – cross involving two characters
O. I should be able to perform a
monohybrid cross by the end of the
hour without any trouble.
J. Cross two heterozygous axial flowers
and predict the genotypic and
phenotypic ratios.
O. I will understand how the Law of
Independent Assortment relates to the
dihybrid cross. I will be able to perform
a dihybrid cross.
Take out Punnett Sq. packet, we will go
over those problems.
Gregor Mendel
• Father of Genetics
• Monitored 7 characteristics in pea plants for
many generations and picked up on patterns
in the inheritance of these characteristics.
• Developed three laws that still hold true
today
1. Law of Dominance
2. Law of Segregation
3. Law of Independent Assortment
Pea plants naturally self-pollinate. This means there were all
true-breeding plants.
Mendel caused the plants to cross-pollinate in his experiments.
He created hybrids.
Punnett Square
The method used to predict the outcome of the offspring from
two organisms.
Basic steps in using the Punnett Square:
1. Pick the letters for the alleles
dominant allele – capital letter
recessive allele - lowercase letter
2. Determine the Parents (P generation) genotype
note: each individual has two alleles/trait
3. Complete the Punnett Square
4. Determine the genotypic ratio and phenotypic ratio
Practice: Cross a homozygous dominant tall plant with a
homozygous recessive short plant. Determine the genotypic and
phenotypic ratios in the offspring.
Tall - ______
Short - _____
Parent cross: ______ x _______
F1 cross:
Cross the offspring of the last cross together and predict the
genotypic and phenotypic ratios for the F2 generation.
Application
You are using the Law of Dominance when you predict the
phenotype of an individual with a genotype of Tt.
You are representing the Law of Segregation when you separate the
alleles in the formation of gametes in the Punnett square.
You are moving through the same steps that Mendel took in his
discoveries. (a shortened version)
The Punnett square also represents what is going on in meiosis.
Let’s tie it all together….
Meiosis review…
• One cell makes _______ daughter cells
• Daughter cells are identical or nonidentical
• Meiosis forms gametes which are ____ and
•
•
•
•
________
There are ____ divisions in meiosis
If a diploid cell with 24 chromosomes divides four
haploid cells with ____ chromosomes are made
Tetrads form in ____________
Crossing-over occurs in ____________
Meiosis, segregation, gamete formation, fertilization – What else
could you ask for in a Punnett square?
1/8 Genetics
• O. All living organisms have genetic
material that carries hereditary
information.
• J. If it is known that brown is dominant
to gray coat color in mice, what do you
know about the genotype of a mouse
with gray coat color? Why?
Law of Independent Assortment
Mendel proved that chromosomes sort
independently of one another.
We can show this using the Punnett square and a
two-factor cross.
I can also show you using chromosomes.
• What happens if there is more than one
gene?
• Does inheriting a certain gene for seed
color affect the inheritance of another
trait like plant height?
2 Factor Crosses
• Mendel performed experiment to follow
two different genes as they passed
from one generation to the next.
• These experiments are known as two
factor (Dihybrid) crosses.
• Mendel crossed plants that were truebreeding for two different traits.
– Round, yellow peas
• Genotype RRYY
– Wrinkled green peas
• Genotype rryy
Which traits are dominant?
Which traits are recessive?
RRYY X rryy
Why are there so many boxes?
•Each parent can
produce 4 different
kinds of sex cells
(gametes)
•Each gamete has an
equal chance of
combining with each
of the other parents 4
types of gametes.
F2: Dihybrid Cross
• Each of the offspring in the example are
hybrids for BOTH traits - Dihybrids
• Mendel crossed these offspring to
produce another generation of plants
(F2)
• If the genotype of each parent is RrYy,
What kinds of gametes will each parent
produce?
Gametes
• Parent 1: RrYy
– _____ _____ _____ _____
• Parent 2: RrYy
– ______ ______ _____ _____
RrYy x RrYy
Results
• The results of the F2 cross showed that
the alleles for the two different traits
segregated independently into the
gametes.
• The offspring from this cross showed a
9:3:3:1 ratio of the different
phenotypes.
Summary of Mendel’s Principles
• Inherited traits are determined by genes.
Genes are passed from parents to offspring
• Some forms of the gene may be dominant
and others may be recessive
• The genes segregate during meiosis so only
one copy of a gene goes into the gamete
• Alleles for different genes usually segregate
independently of one another.