Download Document

HEREDITY, GENES & DNA
ENDURING UNDERSTANDINGS
* Heredity is the passing of traits from parents to offspring.
* DNA is a double helix made up of nucleotides.
* A gene is a set of instructions for a specific trait.
* Meiosis is the reproduction of sex cells.
Try Human Wheel using Handout Inherited Characteristics (40)
MENDEL & HEREDITY
Heredity is the passing of traits from parents to offspring.
Gregor Mendel studied pea plants to see how traits pass from parent to offspring.
Mendel compared the offspring of true-breeding and cross-pollinated plants.
True-breeding plants are self-pollinated
and produce offspring exactly like the
parent.
Cross-pollination produces a
combination or variety of traits from the
parents.
DOMINANT VS RECESSIVE TRAITS
A dominant trait is a trait that appears in
the offspring.
A recessive trait is a trait that does not
appear in the offspring.
Mendel's Ratios compare the number of
dominant traits with the number of
recessive traits.
Probability is the mathematical chance that
an event or trait will occur.
insert B7 Quicklab (paper copy)
Genetic Variation in the Classroom
GENES, ALLELES & PUNNETT SQUARES
A gene is a set of instructions for a specific trait.
Offspring inherit 2 sets of genes, 1 from each parent. These combinations of 2 different forms of the
same gene are called alleles.
A genotype is the combination of inheritated alleles.
A phenotype is the appearance of a genotype.
HOMOZYGOUS ALLELES
Homozygous alleles have either both dominant or both recessive genes.
HETEROZYGOUS ALLELES
Heterozygous alleles have 1 dominate gene and 1 recessive gene.
Punnett Squares use parent alleles to construct a
diagram showing all possible phenotypes for a particular
trait.
Write the alleles and fill in the Punnett squares for ...
C can curl tongue, c cannot curl.
C
C
C
C
C
C
c
C
One parent has homozygous dominant
alleles, one parent has heterozygous
alleles.
Both parents have heterozygous alleles.
Problem
Consider a cross between a pea plant that is heterozygous for round seeds and a pea
plant that has wrinkled seed. The allele for round seeds is dominant (R) over that for
wrinkled seeds (r). Determine the genotypes of the offspring and indicate both the
genotypic and phenotypic ratios.
Let statements: Let R represent the dominant allele for round seeds.
Let r represent the recessive allele for wrinkled seeds.
P generation: Rr X rr
Punnett Square:
Activity
1) Monohybrid Problems 3C / Dihybrid Problem 3U
2) Breeding Pigs
Taking it one step further....
Often in genetics the question comes up whether the inheritance of one trait would affect the inheritance of
another trait?
For example if flower colour is governed by flower height?
In order to answer such a question we introduce
Di
hybrid Crosses
- is a cross between two parents that breed true for different
versions of two traits
Lets revisit the example above....
Flower colour is governed by gene P
Flower height is governed by gene T
Let P represent the dominant allele for pink colour
Let p represent the recessive allele for white colour
Let T represent the dominant allele for tall height
Let t represent the recessive allele for short height
If we crossed a homozygous pink & tall flower with a homozygous white & short flower
our punnet square would look like this.
PPTT X
Alleles assort
independently
PT
PT
PT
PT
pt
pt
pt
pt
pptt
PT
pt
pt
pt
pt
PT
PT
PT
All F1 generation have the same genotype & phenotype
PpTt (Pink & tall).
However, we are still not sure whether the alleles for colour
and height were inherited together or if they segregated
independently.
Further crossing is required. We need F2
PpTt
X
PpTt
During Meiosis Alleles
assort independently
PT
Pt
pT
pt
PT
Pt
pT
pt
P - pink
T - tall
p - white
t - short
PT
Pt
pT
PT
Pt
pT
pt
pt
Conclusion
Genes that segregate independently in meiosis do not influence each others inheritance
Practice Problems #1~3 pg. 136