Slide set 8 - Mendelian Genetics

4 types of genetics

Transmission genetics (patterns of inheritance), Genomics (study of all genetic content of an organism), Molecular Genetics (physical sequences of DNA and RNA), Population Genetics (selection of traits and gene pool)

what is genetics

the study of heredity and gene transmission

Two original ideas of heredity

Blending: genetic info inside of cells gets blended, passed to children

Particulate: small particles which physically carry genetic information diffuse into offspring cells

Alleles

different versions of a gene which could lead to different phenotypes

genotype

the alleles carried by an individual

phenotype

physical characteristics associated with genotype

homozygous

an individual carries two of the same alleles for a certain gene

heterozygous

an individual carries two different alleles for the same gene

dominant allele

if the allele is present, the phenotype is always expressed

recessive alleles

need two copies (homozygous) to express the phenotype

true breeding

when two individuals are crossed, their offspring are all heterozygotes, which indicates that one parent was homozygous dominant, and one was homozygous recessive

P1

parental generation

F1-Fn

F indicates offspring, number indicates the generation, with 1 being the first generation of offspring

Mendels pea experiments

P1: RR x Rr

P2: Rr, Rr, Rr, Rr

P3: RR, Rr, rR, rr

1:2:1 genotypic ratio, 3:1 phenotypic ratio

finding the probability of two events occurring

multiply the probability fraction of each event

finding the probability of either of two events occurring

add the two individual probabilities together

autosomal

equal inheritance between males and females

sex-linked

more likely to be inherited by one sex (ie X-linked)

purpose of mendel’s dihybrid cross

determine if genes are linked to each other (passed down together) or independent

dihybrid cross

cross of two individuals who are both heterozygous for two traits

Mendel’s Laws

1. law of dominance (dominant alleles will be expressed over recessive ones)

2. law of independent assortment (traits pass down independent of one another)

Pedigree symbols

square: male, circle: female, filled: expressing trait

dominant patterns of inheritance

if an offspring displays trait, at least one parent must also display trait

recessive patterns of inheritance

can be inherited by offspring if neither parent expresses it (parents are both carriers)

pedigree assumption

all individuals introduced are assumed to not carry conditions unless progeny indicates otherwise

3 questions when assessing pedigrees

1. autosomal or sex linked?

2. dominant or recessive?

3. what is the target genotype?

X-linked recessive

one-allele males will show it because heterozygous mothers could be unaffected

X-linked dominant

two-allele females will show it because they have double the chance of inheriting an allele