Ch.14 Mendel and the Gene Idea

These notes are going to be

relatively short because I believe

practicing with problems is the

best way to cover genetics.

Obviously, this is Gregor Mendel.

Mendel’s discoveries

A Blending- Hereditary material- Both parents contribute genetic material.

B Inheritable factors, genes are passed from generation to generation

Pea experiments

1.Worked with 7 traits

2.Used purebreeding plants first then crossed them.

Mendels Pea Crosses

Law of independent assortment-see random orientation in ch.16.

a homologous chromosomes move independently.

b Ex. Chromosome with A or a will go separate from chromosome with B or b.

Law of Segregation

• Homologous pairs segregate during gamete formation(meiosis) and pair again after fertilization

• Ex. If a pea is Pp then half the gametes will receive a P and half a p.

Know the vocabulary

HomozygousHeterozygous

PhenotypeGenotype

Testcross- Mating an unkown to a homozygous recessive

Monohybrid Cross- a cross between parents that are heterozygous for one trait.

Dihybrid Cross

Incomplete dominance

• Incomplete dominance leads to a blending of traits, red + white yields pink

Codominance - is not a blending but a mixing of the traits

Codominance

• Codominance - A and B are both dominant to O but not to each other, giving the AB blood type

Epistasis

• One gene has an effect on another. C leads to deposition of color while B or b leads to color BBcc would be white even though the genes code for black color.

Polygenic inheritance

• Combinations of genes can yield cumulative effects. The more dominant alleles the more color.

Environmental Effects

• Sometimes the environment can change the way a gene is expressed, like these hydrangia, and the color based on pH of the soil.

Pleiotropy

• One gene can have an effect on other parts of the body. The sickle cell gene which causes problems with blood cells has far reaching affects on the body.

Pedigree analysis- square is male,circle is female.

Achondroplasia

Amniocentesis

Cystic Fibrosis

Sickle Cell Anemia

Tay- sachs

Huntington’s Corea

Sample problems

Mendel crossed short and tall pea plants(purebred cross) TT x tt = P gen.

t t

T Tt Tt All offspring are heterozygous

T Tt Tt All are tall (Tt)

Mendel crossed round, yellow pea plants to wrinkled, green pea plants (RRYY x rryy)

The only possible gametes are RY from parent 1 and ry from parent 2 so

ry ry

RY RrYy RrYy All offspring are round

RY RrYy RrYy and yellow (RrYy)

Monohybrid Cross -two heterozygotes mated

Tt xTt

T t

T TT Tt 1TT:2Tt:1tt

t Tt tt 3 tall: 1 short

Dihybrid cross

Heterozygotes for 2 traits are crossed RrYy x RrYy

You can make the folowing gametes for each parent RY,Ry,rY,ry, this means a four by four box as in the next slide

Dihybrid Cross

Dihybrid crosses can also be done like this;

R r Y y

R RR Rr Y YY Yy

r Rr rr y Yy yy

Now calculate the chances of RRYY (1/4 x 1/4)

RRYy (1/4 x2/4) RrYY (2/4 x 1/4)

RRyy (1/4 x 1/4) RrYy ( 2/4 x 2/4)

Rryy (2/4 x 1/4) rrYY (1/4 x/1/4)

rrYy (1/4 x 2/4) rryy (1/4 x 1/4)