Lecture 12: Mendelian Genetics

gene

unit of hereditary info

allele

alternative versions of genes

character

a observable, heritable feature

trait

detectable variant of a character

genotype

genetic makeup / what alleles are present

phenotype

observable physical traits

gene → ...

gene, character, hair color

allele → ...

allele, trait (character state), red hair

Who was Gregor Mendel?

Father of genetics / determined basic rules of inheritance in eukaryotes

what three quantitative methods did Gregor Mendel use in his experiments?

experimental approach, documented protocol, recorded data

true breeding

always expresses same trait after self fertilization (NO EXCEPTIONS)

blending inheritance hypothesis

gametes contain a sampling of fluids from parents' bodies that cause offspring to be an intermediate of the parents

P generation

parent generation / first two individuals to mate in genetic cross

F1 generation

first filial generation / offspring of P generation

F2 generation

second filial generation / offspring of the F1 generation.

what was Mendel's process in his pea experiments?

1. true breeding of P generation

2. mate P with opposite phenotypes (big & small)

3. mate F1 generation with eachother

particulate inheritance

hypothesis that characters are controlled by 2 factors, 1 from each parent

4 components of Mendel's model

1. Alleles

2. 2 "factors" for each character (diploidy)

3. Dominance

4. 2 principles of heredity (Mendel's laws)

dominant alleles

an allele whose trait always shows up in the organism when the allele is present (YY)

recessive alleles

an allele that has no noticeable affect on phenotype when present (yy)

what are the 2 principles of heredity

1. law of segregation

2. law of independent assortment

law segregation

Mendel's law that states that the pairs of homologous chromosomes (2 alleles for character) separate during gamete formation (meiosis) so that only one chromosome from each pair is present in each gamete

what events does the law of segregation describe?

anaphase 1 during meiosis

Homozygous

2 of the same alleles at a locus

example of homozygous

YY or yy

heterozygous

2 different alleles at a locus

example of heterozygous

Yy

Law of Independent Assortment

Mendel's second law, stating that allele pairs (chromosomes) separate from one another during gamete formation

what events does the law of independent assortment describe?

random orientation of tetrads during metaphase 1

Why is independent assortment important?

genetic variation / new combination of alleles in offpsring

genetic crosses

the possible combinations of alleles that can be represented using punnet squares

what do genetic crosses show?

1. what gametes are possible in each parent

2. what possible genotypes in the offspring

3. calculate the frequency of each possible genotype

monohybrid test cross

a cross between heterozygous alleles (one characteristic is tracked)

in true breeding...

the alleles is one homozygous dominant and one homozygous recessive (YY x yy)

punnet square

tool used to determine possible offspring and their frequencies in a genetic cross

what is the phenotype ratio in a monohybrid cross?

3:1

what is the genotype ratio in a monohybrid cross?

1:2:1

Yy is ...

heterozygous dominant