ALLELE
• One of the possible versions of a gene
• Example – flower colours could be red or white
• (somewhat like the different flavours of ice-cream)
DOMINANT• A trait which is fully expressed in the offspring, even in the
heterozygous (e.g. TT, Tt would both result in tall plants)
RECESSIVE • A trait which is not expressed in the heterozygous (hybrid)
• E.g. if tt→ t is expressed as short plants
• if Tt → t is not expressed.
INCOMPLETE DOMINANCE• A pattern of inheritance where the heterozygous (hybrid) expresses a
blending of the characteristics of the two alleles present
• (e.g. Red and White alleles → pink)
• Each of the parent alleles are only partly expressed
CO-DOMINANT• A pattern of inheritance where both alleles in a heterozygous (hybrid)
are fully expressed.
SEX-LINKED GENES• A pattern of inheritance in which traits are controlled by genes found
on the sex chromosomes
• One recessive gene found on a male’s X chromosomes → e.g. colourblindness.
• One recessive gene found on a female’s X chromosome → will not be expressed.
PUNNETT SQUARE• A chart used to predict the possible outcomes of a genetic
combination
MUTATIONS• A change in the DNA sequence of a gene
GENOTYPE• Genetic makeup of the organism
• The alleles (usually two) that an organism has for a characteristic
PHENOTYPE• The appearance of an organism
HOMOZYGOUS• An organism with matching alleles e.g. (PP or pp)
Heterozygous• An organism whose alleles do not match (e.g. Pp)
• Also called a hybrid
PRACTICE
heterozygous OR homozygous?
TT _____ Bb _____ DD _____Dd _____ ff _____ Tt _____
PRACTICE
heterozygous OR homozygous?
TT Homozygous Bb HeterozygousDD Homozygous
Dd Heterozygous Tt Heterozygousff Homozygous
PHENOTYPE
Yellow body color is dominant to blue.YY ________________ Yy ________________
yy ________________
GENOTYPEPink body color (P) is dominant to yellow (p).
Pink body = _________________Yellow body = _________________
PHENOTYPEYellow body color is dominant to blue.
YY __ Yellow __ Yy __________ Yellow _ yy _____- blue__
GENOTYPE
Pink body color (P) is dominant to yellow (p).Pink body = __PP or Pp___________
Yellow body = ___pp______________
Patterns of inheritance
Dominance/recessive
Incomplete dominance
Codominant
DOMINANCE/RECESSIVE –Dominant allele is always expressed if it is present
DOMINANT/RECESSIVE – Dominant gets capital letter, recessive gets small letter
SpongeBob SquarePants met SpongeSusie Roundpants at a dance. SpongeBob is heterozygous for his square shape SpongeSusie is round (Square is dominant to round)
What are the chances of a child with a square shape? ____ out of ____ or ____%
What are the chances of a child with a round shape? ____ out of ____ or ____%
SpongeBob SquarePants met SpongeSusie Roundpants at a dance. SpongeBob is heterozygous for his square shape SpongeSusie is round (Square is dominant to round)
What are the chances of a child with a square shape? 2 out of 4 or 50 %
What are the chances of a child with a round shape? 2 out of 4 or 50 %
S s
s Ss ss
s Ss ss
SpongeBob
SpongeS
usie
Mr. Krabbs and his wife recently had a Lil’ Krabby, who has short eyeballs. Mrs. Krabbs claims that the hospital goofed and mixed up her baby with someone else’s baby.
Mr. Krabbs is homozygous for his tall eyeballs, while his wife is heterozygous for her tall eyeballs. (Tall eyeballs is dominant)
Did the hospital make a mistake? Explain your answer.
Mr. Krabbs and his wife recently had a Lil’ Krabby, who has short eyeballs. Mrs. Krabbs claims that the hospital goofed and mixed up her baby with someone else’s baby.
Mr. Krabbs is homozygous for his tall eyeballs, while his wife is heterozygous for her tall eyeballs. (Tall eyeballs is dominant)
Did the hospital make a mistake? Explain your answer. Yes, they can’t have short eyeballed children
T T
T TT TT
t Tt Tt
Mr. Krabbs
Mrs. Krabbs
Incomplete dominance – in the heterozygous, phenotype is a blend of the two alleles present
Incomplete dominance
Codominance – Both alleles are fully expressed
• In a certain fish, blue scales and red scales are codominant.
•What happens if you breed a red fish with a blue fish
R R
B RB RB
B RB Rb
Multiple alleles –When a characteristic has 3 or more alleles
Type A → AA or Ao
Type B → BB or Bo
Type AB → A and B
Type O → oo(here A & B are co-dominant)
Sex linked traits – where the gene occurs on the X but not on the Y chromosome, a male has only one copy of the gene, so a recessive trait, e.g. colour blindness, will be seen
When a male is normal and female is a carrier
MUTATIONS – CHANGE IN THE DNA OF A GENE – CAN BE DOMINANT OR RECESSIVE
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