Heredity and Genetics

Heredity and Genetics

What makes you, you?

Learned vs. Inherited

Learned behaviors

• Table manners• How to throw a ball

Inherited

• Eye color• Curly hair• Height

Heredity

• The passing of traits from parents to offspring.

Characteristics vs. Traits

• Characteristic- a feature that has different forms in a population– Such as hair color (general)

• Trait- different forms of the characteristics– Such as black hair (specific)

History of Genetics

• Gregor Mendel- the father of modern genetics

– Studied pea plants• Why?

– Fast growing– Able to cross pollinate and self-pollinate

Vocabulary Cross pollination: pollen from one plant fertilizes another plant.

Self-pollination: pollen from flower fertilizes itself

True-breeding plant: a plant, that when it self pollinates, its offspring will have the same traits. “Pure”

Hybrid: an offspring of two different parents

Mendel’s First Experiment

• Mendel crossed (cross pollinated) true-breeding purple flowered pea plant with a true-breeding white pea plant. The offspring are called first generation (F1).

• All of the pea plants in the first generation had purple flowers.

Mendel got similar results each time, one trait was always present in the first generation and the other trait seemed to disappear.Mendel called the trait that appeared the Dominate Trait. (shown as a capital letter)The trait that does not express itself is called the Recessive Trait. (shown as a lower case letter)

Mendel’s Second Experiment

• Mendel then allowed the F1 generation plants to self-pollinate, producing an F2 generation.

• Some of the F2 generation plants were white.

• Mendel noticed that the ratio of dominant (purple) plants to recessive (white) plants was 3:1

• His results could only be explained if each plant had 2 sets of instructions, one from each parent.

Each parent gives a set of instructions called alleles.

Two alleles make up a genotype (gene).

Alleles are shown with either a capital letter (dominant) or a lower case letter (recessive).

Example

B b Bb

allele allele genotype

Vocabulary

• Genotype: both inherited alleles (Hh, AA, ff).• Homozygous: gene with two dominant or two

recessive alleles (BB, dd). True-breeding.• Heterozygous: gene with one dominant and

one recessive allele (Gg, pP). Hybrid.• Phenotype: the outward expression of the

genotype. What the genotype would look like, example: red hair.

Punnett Squares

• a diagram that is used to predict the probability that a given trait will be expressed.

Mendel’s ExperimentP=purple p=white

pPPxpp

P=purplep=white

pPpxPp

What needs to happen for a recessive trait to appear?

• The genotype has to be homozygous recessive.– Two lower case letters

Incomplete Dominance

• Both alleles are expressed, resulting in a combined phenotype

• Example: R = red W = whiteRR x WW

Incomplete Dominance

Sex Chromosomes

• Males– XY

• Females– XX