The study of heredity

Heredity is the passing on of traits from parents to offspring

Genetics is the study of heredity and how genes work in this process.

Heredity and environment are two factors that influence the development of living things

2. Genes display dominance and recessiveness.- Since genes occur in pairs, usually only

one gene will show its trait.

Gregor Mendal's conclusions.

1.Genes occur in pairs. (Remember: genes are just regions on a chromosome that code for a trait. Chromosomes are made of DNA.)

example:If tall is dominant over short in pea plants,

then the plant with either of these two gene pairs (TT or Tt) will be tall.

Dominant gene = the gene whose trait will be expressed in an individual. Dominant genes are noted by capital letters.

example: Tt = tall plantTT = tall plant

tt = short plant (because of two recessive genes that code for short plants)

Recessive gene =- Does not show its trait if the other gene in the

pair is dominant.- This gene is overpowered by the dominant gene.- Noted by using small letters (t).

- Only if both genes in a gene pair are recessive will the recessive trait be expressed.

4. The law of independent assortment:When genes pairs separate they go to

gametes independently of other gene pairs.

example:The genes for eye color are not related to genes for hair color, or height, etc.

3. The law of segregation:When gametes are formed only one gene of a pair will be found in that gamete. (a

result of meiosis).

Combinations of genes could be:

Homozygous -Both genes the same - either dominant or recessive (TT or tt)

Heterozygous - Genes are different (Tt)

- true-breeding, purebred

- hybrid

Genes occur in pairs...

Phenotype - What an individual looks like

On homologous chromosomes

Genotype - Genes that an organism possesses

- Represented by capital and lower case letters

tT

Could be:•Dominant

•Recessive

DNA replication

TT tt

Then...

Meiosis

Gametes - with only one copy of the gene

Punnett square shows: - Results of meiosis (gametes) &

T t

T

t

TT

Tt

Tt

tt

-POSSIBLE results of fertilization

Parent 1

Parent 2

How to Solve a Genetics Problem

• Read the problem and determine the dominant trait(s)

• Make a key to describe what genes your letters represent. Ex. T = tall t = short

• Determine genotype of parents • Determine possible gametes formed

by parents

• Draw a punnett square • Place gametes of each parent on

top and along left side • Show results of fertilization by

filling in boxes • List results = Genotype &

Phenotype

In pea plants tall is dominant over short. Cross a homozygous tall plant with a heterozygous tall plant. What are the possible outcomes?

Monohybrid Cross

Freckles are dominant in humans. Cross a purebred freckled man with a woman who does not have freckles.

In chinchillas black is dominant over grey. Cross two heterozygous individuals.

Dihybrid CrossIn pea plants tall plants and yellow seeds are dominant over short plants and green seeds. Cross a heterozygous tall yellow plant with a homozygous tall green plant. What are the possible outcomes?

Key:

Parents Genotypes:

Determining Gametes

Punnett square:

Results:_______ X ________

Cross a homozygous tall, yellow plant with a short, green plant. What could the F2 generation of this cross look like?

Intermediate Inheritance

In some cases there are no dominant genes. Or equally dominant genes. As a result, a cross may result in:

- both characteristics being present

- a true blending of the characteristics

Many traits are incompletely dominant over others, which result in intermediate forms.

In guinea pigs the straight hair shape is dominant and curly hair is recessive. Wavy hair is also a phenotype. Cross a guinea pig with straight hair to a curly haired guinea pig, and list the results.

In snap dragons, red in incompletely dominant over white. Pink is also a phenotype. Cross a white flower with a pink flower and list the results.

In horses, roan color is the result of codominant genes both showing up.

Individual hairs are either one color or the other.

• alleles are shown by XN = normal and Xn = affected

Sex-linked traits

• traits whose genes are located on the X chromosome

• show up more often in males

There is no second X chromosome to contain a dominant gene.

Red green Colorblindness is a sex-linked trait. Cross a carrier female with a normal male. What are the possible results?

A person with blood type AB marries a person with blood type O. What are the possible blood types of their children?

Multiple alleles• Genes with more than 2 alleles• Most commonly used example is blood types

IA, IB, i

2. Cross a person with an AB blood type with an AO blood type and list the results.

3. A woman with type B blood is accusing a man with type A blood of being the father of a child with type O blood. Will the courts be able to prove that the man is not the father of the child? Is it possible that the man is the father of the child? Do a cross and list the results to justify your answer.