Biology Regents Periods 2, 4 and 7. What is Genetics? Genetics is the scientific study of heredity.
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Transcript of Biology Regents Periods 2, 4 and 7. What is Genetics? Genetics is the scientific study of heredity.
Biology RegentsPeriods 2, 4 and 7
What is Genetics?Genetics is the scientific study of heredity
What is a Trait?A trait is a specific characteristic
that varies from one individual to another.Examples: Brown hair, blue eyes, tall,
curly
What is an Allele?Alleles are the
different possibilities for a given trait.Every trait has at least
two alleles (one from the mother and one from the father)
Example: Eye color – Brown, blue, green, hazel
Examples of Alleles:A = Brown Eyesa = Blue EyesB = Green Eyesb = Hazel Eyes
What are Genes?Genes are the sequence of DNA that codes for a protein and thus determines a trait.
Gregor MendelFather of Genetics1st important studies of
heredityIdentified specific traits in the
garden pea and studied them from one generation to another
Mendel’s Conclusions
1.Law of Segregation – Two alleles for each trait separate when gametes form; Parents pass only one allele for each trait to each offspring
2.Law of Independent Assortment – Genes for different traits are inherited independently of each other
Dominant vs. RecessiveDominant - Masks the other trait; the trait
that shows if presentRepresented by a capital letter
Recessive – An organism with a recessive allele for a particular trait will only exhibit that trait when the dominant allele is not present; Will only show if both alleles are presentRepresented by a lower case letter
R
r
Dominant & Recessive Practice
TT - Represent offspring with straight hair
Tt - Represent offspring with straight hair
tt - Represents offspring with curly hair
T – straight hairt - curly hair
Genotype vs. PhenotypeGenotype – The genetic makeup of an
organism; The gene (or allele) combination an organism has. Example: Tt, ss, GG, Ww
Phenotype – The physical characteristics of an organism; The way an organism looksExample: Curly hair,
straight hair, blue eyes, tall, green
Homozygous vs. HeterozygousHomozygous – Term used
to refer to an organism that has two identical alleles for a particular trait (TT or tt)
Heterozygous - Term used to refer to an organism that has two different alleles for the same trait (Tt)
RR
Rr
rr
Punnett SquaresPunnett Square – Diagram
showing the gene combinations that might result from a genetic cross
Used to calculate the probability of inheriting a particular traitProbability – The chance
that a given event will occur
Punnett SquareParent
Parent Offspring
How to Complete a Punnett Square
Y-Yellowy-white
Genotype:1:2:1
(YY:Yy:yy)
Phenotype:3 Yellow1 White
You Try It Now!Give the genotype and phenotype for the
following cross: TT x tt (T = Tall and t = Short)
TT x ttStep One: Set Up Punnett Square (put one parent
on the top and the other along the side)
T T t t
TT x ttStep Two: Complete the Punnett Square
T T t t
Tt Tt
Tt Tt
TT x ttStep Three: Write the genotype and phenotype
T T t t
Tt Tt
Tt Tt
Genotype: 4 - Tt
Phenotype:100% Tall
Remember: Each box is 25%
You Try It Now!Give the genotype and phenotype for the
following cross: Tt x tt
Tt x ttStep One: Set Up Punnett Square (put one parent
on the top and the other along the side)
T t t t
Tt x ttStep Two: Complete the Punnett Square
T t t t
Tt tt
Tt tt
Tt x ttStep Two: Complete the Punnett Square
T t t t
Tt tt
Tt tt
Genotype: Tt - 2 (50%)tt - 2 (50%)
Phenotype:50% Tall50% Short
Remember: Each box is 25%
Some Terminology P1 – Original parents
F1 – First generation
F2 – Second generation
P1 X P1 = F1
F1 X F1 = F2
Incomplete DominanceIncomplete Dominance - Situation
in which one allele is not completely dominant over another.Example – Red and
white flowers are crossed and pink flowers are produced.
CodominanceCodominance - Situation in which
both alleles of a gene contribute to the phenotype of the organism.Example – A solid white cow is crossed
with a solid brown cow and the resulting offspring are spotted brown and white (called roan).
+
Multiple AllelesMultiple Alleles- Three or more
alleles of the same gene.Even though three or more alleles
exist for a particular trait, an individual can only have two alleles - one from the mother and one from the father.
Examples of Multiple Alleles1. Coat color in rabbits is determined
by a single gene that has at least four different alleles. Different combinations of alleles result in the four colors you see here.
Examples of Multiple Alleles2. Blood Type – 3 alleles
exist (IA, IB, and i), which results in four different possible blood types
3. Hair Color – Too many
alleles exist to countThere are over 20
different shades of hair color.
Multiple AllelesThere Are Always Multiple Alleles!
Genetic inheritance is often presented with straightforward examples involving only two alleles with clear-cut dominance. This makes inheritance patterns easy to see.
But very few traits actually only have two alleles with clear-cut dominance. As we learn more about genetics, we have found that there are often hundreds of alleles for any particular gene. We probably know this already - as we look around
at other people, we see infinite variation.
Polygenic TraitPolygenic Trait - Trait
controlled by two or more genes.Polygenic traits often show
a wide range of phenotypes. Example: The wide range of
skin color in humans comes about partly because more than four different genes probably control this trait.