GENETICS TERMS

GENES- SEGMENTS OF DNA WHICH CODE FOR PROTEINS

THERE ARE DIFFERENT FORMS OF GENES. EACH “FORM” OF THE SAME GENE IS CALLED AN ALLELE.

EXAMPLES:

• Gene for earlobe shape:• Allele for attached earlobes

• Allele for detached earlobes

• Gene for Hitchhiker's Thumb:

• Allele for Hitchhiker’s Thumb

• Allele for Non-Hitchhiker’s

Each organism receives 2 alleles for each gene:

1 from mom

1 from dad

COMPLETE DOMINANCE

• When a trait exhibits complete dominance, one allele is dominant over the other. The non-dominant trait is called the recessive allele.

• NOTE Dominant does NOT mean more common. Dwarfism is a dominant trait and is not more common.

• We represent dominant alleles with capital letters.

• We represent recessive alleles with lower case letters.

• Example:• E = Widow’s peak

• e = Straight hair-line

HOW MANY DOMINANT ALLELES DO YOU NEED FOR THE DOMINANT TRAIT TO BE SHOWN?

HOW MANY RECESSIVE ALLELES DO YOU NEED FOR THE RECESSIVE ALLELE TO BE SHOWN?

RULES OF INHERITANCE

• Dominant traits only need 1 dominant allele to be visible.

• EE = widow’s peak

• Ee = widow’s peak (only need 1 capital E)

• Recessive traits need 2 recessive alleles to be visible.

• ee = straight hairline

HOW WOULD YOU DEFINE HETEROZYGOUS AND HOMOZYGOUS?

TERMS TO KNOW

•Homozygous= 2 of the same allele; either 2 dominant or 2 recessive

• Also called purebred

• Examples: TT cc dd YY

•Heterozygous = 2 different alleles

• Examples: Bb Hh Ll Rr

• Also called hybrid

PUREBRED

Homozygous BB bb

HYBRID

BbFfGg

Homozygous or heterozygous?

Mom Dad

Child

Homozygous or

heterozygous?

HOW WOULD YOU DEFINE GENOTYPE & PHENOTYPE?

DEFINITIONS•Genotype = organism’s allele combinations (always 2 letters)• Examples: GG, Tt, bb

•Phenotype = organism’s physical appearance• Think PHENO = PHYSICAL• Examples: Tall, short, round peas, wrinkled peas

Phenotype or Genotype?

Green eyes Widow’s Peak

Aa Tail length

Attached earlobes GG

Ff tt

IN ONE SPECIES OF WILD CAT, BLACK FUR IS DOMINANT TO WHITE FUR.

FILL IN THE CHART IN YOUR NOTES.

GENOTYPE PHENOTYPE

BB

Bb

White fur

MENDEL’S EXPERIMENT

• Gregor Mendel crossed (bred) pea

plants to study how traits are passed to

offspring.

• Cross Terms• P – parent generation

• F1 – offspring of P generation

• F2- offspring of F1 generation

MENDEL’S LAWS

•1. The Law of Dominance: In a cross between contrasting homozygous individuals, only one form of the trait will appear in the F1 generation - this trait is the dominant trait.

•2. The Law of Segregation: during the formation of gametes, alleles responsible for a trait separate; one allele is receive from each parent (in gametes).

•3. The Law of Independent Assortment:

- alleles responsible for different traits are distributed to gametes (and thus the offspring) independently of each other

21. Lupe grows pea plants in her garden. The pea plants have flowers that can be either purple or white, with purple color being dominant to white color. The peas produced by Lupe's pea plants can also be either round or wrinkled, with round peas being dominant to wrinkled peas.

Lupe crosses two pea plants that are heterozygous for both traits. If a gamete from this cross receives a dominant allele for flower color, how does this influence the probability of the gamete receiving a dominant allele for pea shape?

(Assume that the genes for flower color and pea shape follow the law of independent assortment.)         

A.No effectB.Decreases probabilityC.Gamete can’t receive the allele D. Increases probability

Lupe crosses two pea plants that are heterozygous for both traits. If a gamete from this cross receives a dominant allele for flower color, how does this influence the probability of the gamete receiving a dominant allele for pea shape?

A. NO EFFECT!

BECAUSE THE ALLELES SORT INDEPENDENTLY INTO GAMETES, THEY DO NOT AFFECT THE RECEPTION OF THE SECOND ALLELE.

• A Punnett Square is a tool used to predict the offspring from a cross.

• Uses the laws of probability• Probability- describes how likely it

is that an event will occur

• Each outcome is equally likely to occur despite previous outcomes

• Each allele combination is equally likely to occur because the alleles sort independently

MENDELIAN RATIOS

• When crossing 2 heterozygotes with complete dominance, you get the following ratios always:

• 1:2:1 Genotypic

• 1 Homozygous dominant (25%)

• 2 Heterozygous (50%)

• 1 homozygous recessive (25%)

• 3:1 Phenotypic

• 3 dominant phenotype (75%)

• 1 recessive phenotype (25%)

B b

B BB Bb

b Bb bb

TEST CROSS

• We use a test cross when we have an organism with an unknown genotype and we cross it with a homozygous recessive organism.

- BLUE = DOMINANT- YELLOW = REC.

RESULTS FROM TESTCROSS:50% BLUE50% YELLOW

Heterozygous Homozygous

b b

B Bb Bb

B Bb Bb

b b

B Bb Bb

b bb bb

MONOHYBRID CROSSES

•Looks at only 1 characteristics/gene

•Basically, all the problems we’ve been doing

b b

B Bb Bb

b bb bb