allele - weebly · allele •one of the possible versions of a gene ... incomplete dominance –in...

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