Biology 101 Fall, 2007 Week 4 – Genetics Inherited traits Week 4 – Genetics Inherited traits.
the transfer of characteristics (traits) from one generation to another your inherited...
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Transcript of the transfer of characteristics (traits) from one generation to another your inherited...
the transfer of characteristics (traits) from one generation to another
your inherited characteristics (traits) are determined by the genes located on your chromosomes
Inheritance - Mendel
chromosomes are found in pairs in humans, there are 46 chromosomes,
made up of 23 pairs of homologous chromosomes
a pair of chromosomes consists of two homologous chromosomes which look alike and carry genes for the same traits
you receive one homologous chromosome of the pair from each parent, therefore you receive 2 genes for each trait
Homologous chromosomes:
This term is used to describe the physical or visible appearance of an individual as determined by the gene combination you inherit from your parents.
Example: in the case of eye colour, having brown eyes is the phenotype and is dominant
Phenotype
the gene combination that produces the trait
these genes may be the same or different
genotypes are represented by upper and/or lower case letters e.g. Bb
there are three possibilities for genotypes for a single trait.
e.g. BB or Bb or bb
Genotype
alternate forms of a gene same location on a each chromosome of
pair affects the same trait but differently alleles are different forms of a gene that
carry different instructions eg. Brown eyes or blue eyes
Allele
Characteristic that is always expressed its gene is present
only one dominant allele needs to be present for the dominant trait to be expressed
an upper case letter designates a dominant allele
eg. Tall is dominant. It is represented with
a “T”
Dominant Trait/Allele
Characteristic that is only expressed when two genes for that trait are present
two recessive alleles need to be present for a recessive trait to be expressed
if a dominant allele is present it “masks” the recessive allele
eg: Short is recessive. It is represented with a
“t”
Recessive Trait/Allele
“homo” means the “same” the condition where both alleles for a trait
are the same there are two conditions for homozygous
genotype: homozygous recessive genotype “aa” homozygous dominant genotype “AA”
Homozygous Genotype
“hetero” means “different” the condition where both alleles for a trait
are different the genetic information inherited for a trait
from both parents is different example: heterozygous genotype “Aa”
Heterozygous Genotype
Summary (example eye colour)
Genotype Condition PhenotypeBB Homozygous
dominantBrown eyes
Bb Heterozygous Brown eyesbb Homozygous
recessiveBlue eyes
Introduction to Variability Worksheet Compile your own personal profile, and then
combine it with the other members in the group.
Ratio for group Ratio for class
Activity
Dominant Trait
Description
# of students with Dominant
# of students with Recessive Ratio of
Dominant to
Recessive
Percentage with
Recessive traitsClass Class
Eye colour
Hair colour
Hairline
Freckles
Earlobe
Hair texture
Eyesight
Fingers
Ear rim
Thumb joint
Folded hands
Tongue rolling
Chin dimple
Crossed two purebred parents (One tall and one short)
All offspring were tall!!
Mendel concluded that some traits were ___________ and some traits were ___________.
Mendel’s Experiment
When individuals with contrasting traits are crossed, the offspring (F1 generation) will express only the dominant trait.
Parents: Tall x ShortF1 (Offspring): Tall Tall Tall Tall
Principal of dominance
Mendel crossed F1 generation.
F1: Tall plants x Tall plants F2 (Offspring of F1): Tall Tall Tall
Short F2 generation = 3:1 ratio
What happened next??
Each F1 parent starts with two hereditary factors (alleles); one is dominant and one is recessive
Each parent contributes only one factor (allele) Each offspring inherits one factor (allele) from
each parent If the dominant factor (allele) is present it will
be expressed. If the recessive factor (allele) is present it will
only be expressed if only recessive factors are present.
Law of Segregation
Mendel crossed two purebred plants TT – tall plant Tt – short plant
Monohybrid cross – only one trait is being tested
Monohybrid Cross
Punnett Square Is a grid system resembling a checkerboard,
used in computing possible results of various genetic combinations
Simply stated, it is a way of representing the possible combinations of genes when an egg and sperm unite in fertilization
Punnett Squares
Characteristic hair texture – ◦ Dominant allele (gene) is curly hair - C. ◦ Recessive allele (gene) is straight hair - c
Mother ◦ Phenotype – straight hair◦ Genotype- homozygous recessive - cc
Father ◦ Phenotype – curly hair ◦ Genotype – homozygous dominant – CC
Predicting genotype and phenotype possibilities using Punnett Squares
Egg
Sperm
c c
C Cc Cc
C Cc Cc
Punnett SquareAll of their children will have curly hair. They all have a different genotype from their parents.
Homework…. Bikini Bottom Genetics – Monohybrid
Crosses Due tomorrow (Wednesday) – Will be
marked and recorded.
RY RY
ry
ry
What happened when Mendel crossed two pea plants that different in TWO traits?
In his second experiment Mendel crossed a pea plant with round/yellow (RRYY) seeds with a pea plant with wrinkled/greed seed (rryy).
What genotypes resulted?
What phenotypes resulted?
RY RY
ry RrYy RrYy
ry RrYy RrYy
Genotype: RrYy F1 - GenerationRatio 100%Phenotype: Round/YellowRatio 100%
RY Ry rY ry
RY
Ry
rY
ry
Crossing F1(RrYy) x F1(RrYy)
RY Ry rY ry
RY RRYY RRYy RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
What genotypes resulted?
What phenotypes resulted?
Genotype: RRYY RRYy Rryy RrYY RrYy rrYY rrYyrryy
Ratio: 1 2 2 2 4 1 2 1Phenotype: Round/Yellow Round/Green Wrinkled/Yellow Wrinkled/GreenRatio: 9 3 3 1
F2 - Generation