Mendel and His Gene- ius Idea… - Willis' Science · Big Idea 3: Living systems store, retrieve, transmit, and respond to info essential to life processes. Mendel and His Gene-ius

Big Idea 3: Living systems store,

retrieve, transmit, and respond to

info essential to life processes.

Mendel and His Gene-ius Idea…

Essential Knowledge

• 3A3: The chromosomal basis of

inheritance provides an understanding

of the pattern of passage of genes

from parent to offspring.

•… “particulate”

hypothesis is the idea

that parents pass on

discrete heritable units

(genes)…

Gregor Mendel

1822-1884

Mendel’s

Peas…

Planned

experiments

using characters

(flower color) and

traits

(purple/white)

Purple =

dominant

White =

recessive

3:1 Ratio

Mendel’s heritable factor = gene

Alternate versions =alleles

IA Video

Law of Segregation and I.A. apply to genes

on diff. chromosomes.

• Genes near

each other

on same

chromosome

tend to move

as a unit

• Probability of

segregation

is a fxn of

the distance

b/t them.

Dominant vs Recessive

• Use Punnett Squares

to predict heredity

outcomes.

• Dominant alleles:

Use upper case. Ex: R

• Recessive alleles:

Use lower case. Ex: r

• Homozygous:

alleles for trait are

same. Ex: TT

(purebred)

• Heterozygous:

alleles for trait are

different. Ex: Tt

Use probability to analyze passage of

single gene traits from parent to offspring

Punnett

Squares

!!

One Factor Punnett

Square

• Monohybrid cross.

• Ex: Cross a tall

dominant

homozygous pea

plant (TT) w/ short

recessive

homozygous pea

plant (tt).

TT is a parent

who is Tall

tt is a parent

who is Short

Both are

homozygous

that make

heterozygous

offspring.

Monohybrid Cross

Ratios to Know

TT x tt = 100% Dominant, but heterozygous

Tt x Tt = 75% Dominant, 25% Recessive, 3:1

Two factor Punnett

Square

• Cross 2 traits =

dihybrid cross.

• Example: Cross a

dominant green,

smooth pea plant

(GGSS) with a

recessive yellow,

wrinkled pea plant

(ggss)

Ratios to Know

SsTt x SsTt = 9:3:3:1

9 dominant in both traits

3 dominant in one trait or the other trait

1 recessive for both traits

Human Genetic Disorders

• Can be received by inheriting a single gene trait or

specific chromosomal change

• Ex: Tay-Sachs Disease: Mutation on Chrom. 15

causing deterioration of nerve cells.

What’s This??

Punnett Square Sample Probs