Chapter 5Basic Genetics

GCA General BiologyMr. Cobb

Mendel’s Genetics

Monk

Worked with pea plants

7 traits

Mendel’s Concepts

Unit Characteristics

Dominant and Recessive

Law of segregation

Unit Characteristics

Traits are caused by factors that occur in pairs.

He represented these with letters.

T = tall

t = short

Dominant & Recessive

Dominant gene hides a recessive gene.

TT = Tall plant

Tt = Tall plant

tt = short plant

SegregationWhat does Segregate mean?

When a cell forms gametes genes separate.

Only 1 factor for each trait will be in each gamete.

He had figured out Meiosis, but did not know why or how.

TerminologyPhenotype = physical appearance

Genotype = the specific genes

allele = an alternate form of a gene (purple flower allele or white flower allele)

Homozygous = both alleles are the same

Heterozygous = alleles for a trait are different.

Punnett SquaresUse to determine the probability of an outcome.

25% both heads

50% heterozygous

25% both tails

Punnett Square

Free earlobes = F

Attached = f

What is phenotype and genotype?

Punnett SquareResults are expressed in ratios pg. 116

homozygous dominant: heterozygous: recessive.

Cross two heterozygous for trait P, what is the genotypic ratio.

P is for purple and p is for yellow, what is the phenotypic ratio?

Test CrossIf you corn that shows the dominant purple kernels (P), then what is the genotype?

PP or Pp, it could be either.

Do a test cross and mate with corn that is yellow recessive because that genotype is pp.

If any of the offspring show the recessive trait, then the unknown was heterozygous.

Variations of MendelIncomplete dominance = one trait is not completely dominant over the other, so they “blend”. Red flower + White flower = pink

Variation (continued)codominance = both alleles are expressed, but there is no blending.

Variation (continued)Multiple alleles = More than two alleles in the population. Blood type

Blood TypeA and B Blood Types are both Dominant and notated by IA and IB.

The recessive is not having the antigens and it is notated as i.

A person with A blood type could be IAIA or IAi

AB Blood type is IAIB.

Read the box on top of page 121. Did a mixup happen?

Dihybrid Crosses

Same as Punnett Square, but now we are looking at the probability of two traits together

Our example is pod color and is the pod constricted (skinny) or inflated (fatter).

Dihybrid Cross

When would this be useful in society?

Independent Assortment

The separation of one allele does not affect the other alleles.

For example, the pod color does not affect the pod shape or flower color.

These alleles are sorted independently of each other.

Independent Assortment

The “G” Chromosome is independent from the “I” chromosome.

Polygenic Inheritance

2 or more genes working together result in a single trait.

Human traits like hair color, skin color, eye color, height.

The example in the book is the comb of chickens.

PleiotrophyJust FYI

Pleiotrophy is one gene controls many characterisitics.

Example is sickle cell anemia and affects 1 in 12 black people in the U.S.

Sickle cell anemia causes the red blood cell to sickle in high elevation and in activity.

Sickle Cell Anemia

Ryan Clark of Pittsburgh can not play in Denver due to sickle Cell Anemia.

Sickle Cell Anemia Red Blood Cells

Sex ChromosomesChromosomes that determine the sex of an individual.

The autosomes are the other 22 chromosomes.

XX is a female

XY is a male

Sex Chromosomes

The male donates the Y chromosome. So the male determines the sex of the offspring.

Sex Chromosomes

There are traits on the chromosomes and these are called sex-linked traits.

Hemophilia - blood does not clot correctly

baldness

color blindness

Sex Chromosomes

Males usually exhibit the traits. Why?

Males only have 1 X chromosome and females have 2 X chromosomes.

Males will exhibit the recessive trait.

Color Blind Test

Color Blind Test

Color Blind Test

Pedigree

A chart used to track a genetic trait through a generations.

This is a pedigree of hemophilia in the British Royal Family.