Genetics cont.

Why did Mendel experiment on peas?

• research had already been conducted

• small and easy to grow

• many varieties

• easy to do controlled experiments

Do peas self-fertilize?

peas self-fertilize if left alone because both male and female organs are encased

Mendel’s Experiment Format

1. plants are allowed to self-fertilize for multiple generations to ensure the traits being studied are being transmitted unchanged between generations: true-breeding

2. true-breeding exhibiting alternate forms of traits were crossed, including reciprocal crosses

3. hybrid offspring were allowed to self-fertilize for generations to follow the inheritance of alternative forms of a trait

P1 is the

parent gene: parents genes are pure bred for whatever trait Mendel was looking for

F1 is the

Filial generation: crossed between pure lines

F2 is a cross of

F1

1st Outcome of Mendel’s 5 Element Method

transmission of genes is not physiologically based

2nd Outcome of Mendel’s 5 Element Method

when two individuals are crossed, one copy of each gene is received

3rd Outcome of Mendel’s 5 Element Method

not all copies of the gene (alleles) are identical: some copies create one type of plant and some copies create another

4th Outcome of Mendel’s 5 Element Method

the two alleles remain discrete/unique

-ex. yellow peas give yellow color and green peas give green color but crossing gives green or yellow

5th Outcome of Mendel’s 5 Element Method

presence of the allele does not ensure trait expression (dominant vs. recessive)

2 Mendelian Principles

Law of Segregation and Law of Independent Assortment

Law of Segregation states

the movement of homologous chromosomes during meiosis 1 results in a random arrangement of homologous chromosomes in the gametes

Monohybrid definition

a cross that only considers one trait

-ex. seed shape, height, flower color, etc.

Law of Independent Assortment is shown in

dihybrid crosses: the alleles of each gene assort independently

-inheritance of different traits is separate/segregated

-assortive only if genes are on different chromosomes

4 Criteria for Mendelian Traits

1. traits must be controlled by a single gene

2. gene regulating the trait can only have two alleles

3. all genes must have an allele that shows complete dominance

4. must be no interaction with other genes or the environment

True or false: In recessive traits, heterozygous are carriers but don’t show the effect.

true

Consanguinity definition

being related by blood

Test cross definition

crossing the individual with a homologous recessive allele

-offspring genotypical ratio will show the ratio of gametes (alleles) from the unknown

Lethal allele definition

some trait that is dominant for (hairlessness) will reserved for embryonic death

-ex. cystic fibrosis and sickle cell anemia

Incomplete/partial dominance

the phenotype of heterozygous alleles will be a mixture of two other traits

Codominance

both traits are present in the offspring

Hemophilia definition

low iron content in the blood

Epistasis is

interaction between genes: alleles for one gene can mask or cover the trait for another gene

Relationship between A and B in enzymatic reactions

If A is recessive, it isn’t functional, so it doesn’t matter what B is (vice versa)

-recessive = no pigment

Mendelian Inheritance assumes

the gene is on an autosome

Sex determination may be

chromosomal

True or false: There is not the same complement of chromosomes in the sexes.

True

Environmental factors that may alter gene expression

changes in the environment: temperature, pH, and/or ions

If a gene is on the x chromosome, it can’t show

true inheritance

Dosage Compensation (Sex determination considerations)

disjunction and non-disjunction

Disjunction

during meiosis, homologous chromosomes will separate into daughter cells

Non-disjunction occurs when

chromosomes don’t separate during meiosis, and results in extra copies of the chromosome in the offspring (can lead to trisomy 21- down syndrome)

True or false: non-disjunctions of large autosomes are not viable

true

Sickle cells do not show sex determination because

they are on autosomes

Incomplete dominance in sickle cells causes

ex. reduced oxygen carrying capacity

Codominance in sickle cells occurs when

both types of cells are present

Complete dominance in sickle cells and malaria

No malaria if a complete set of sickle cells is present

Pleitropic effects in sickle cells

changes in red blood cell shape, blood flow ability, and joint swelling

If there is no malaria, what is the effect on sickle cell alleles?

Less effect of sickle cell alleles