Heredity/Genetics

Heredity – passing of traits from parents to offspring

Genes – section of DNA that contain a trait.

- each gamete contains one gene for a trait.

Alleles – different forms of a gene

Egg – gene for white flower (r )

Sperm – gene for red flower (R )

Genetics – study of how traits are inherited through the action of alleles.

Gregor Mendel

Austrian monk

Worked with pea plants to predict offspring

Father of Genetics

Mendel’s experiment

Two purebred tall pea plants

both alleles – T T

All offspring – tall

Two purebred short pea plants

All offspring – short tt

Purebred plant/ animal – both alleles are the same for the trait

TT tt

Tall short

1. Pollinated plants by putting male gametes on female gametes of 1 TT plant onto 1 tt plant.

Result: 4 tall plants but are NOT purebred. They have an allele for shortness. Tt

2. Took two hybrid pea plants (Tt) and pollinated them.

Result: 3 tall plants 1 short plantTT Tt Tt tt

Hybrid – organism that contains alleles of opposite traits.

Homozygous – trait with two alleles that are alike TT tt

Heterozygous – trait with two different alleles Tt

Dominant trait – trait that overpowers its opposite trait.

Recessive trait – trait that is being overpowered Ttexcept if homozygous tt

Genotype – the genetic make up of a trait RR Rr rr Phenotype – the physical appearance of a trait. Red pink white

Copy in notebook

Write a genotype for every phenotype listed.

NOTE: use S for spherical

Y for yellow

P for color

I for inflated

G for green

Complete this punnett square

1. Homozygous tall with homozygous short

2. Homozygous tall with heterozygous tall

3. Heterozygous tall with heterozygous tall

4. Heterozygous tall with homozygous short

Incomplete DominanceMendel’s experiement with peas does not work for all kinds of plants.With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that shows a blending of the parental traits. 

The trick is to recognize when you are dealing with a question involving incomplete dominance.  There are two steps to this: 1) Notice that the offspring is showing a 3rd phenotype.  The parents each have one, and the offspring are different from the parents. 2) Notice that the trait in the offspring is a blend (mixing) of the parental traits.

Questions: 1. A cross between a blue blahblah bird & a white blahblah bird produces offspring that are silver.  The color of blahblah birds is determined by just two alleles. a) What are the genotypes of the parent blahblah birds in the original cross?

b) What is/are the genotype(s) of the silver offspring?c) What would be the phenotypic ratios of offspring produced by two silver blahblah birds?2.  The color of fruit for plant "X" is determined by two alleles.  When two plants with orange fruits are crossed the following phenotypic ratios are present in the offspring: 25% red fruit, 50% orange fruit, 25% yellow fruit.  What are the genotypes of the parent orange-fruited plants?

Multiple genesShades of colors of eyes – produced by a combination of many genesPolygenic inheritance – group of gene pairs act together to produce a single traitProduces a wide variety of phenotypes

Skin color, height, weight, shape of eyes, ears and ear lobes, hair color – result of polygenic inheritance.