Unit 10: Mendelian Genetics

Law of Dominance

when an organism has a pair of contrasting alleles for a trait,

• dominant allele is expressed

• recessive allele is hidden

Law of Segregation

homologous chromosomes carrying genes for the same traits are separated during meiosis & recombined through fertilization

Punnett squares tell you the likelihood of

fertilization between gametes

F₁ (family 1) generation is the result of

the P₁ cross

5 types of genetic crosses

1. simple dominance

2. incomplete & codominance

3. sex-linked

4. multiple alleles

5. dihybrid

Simple dominance is a cross between 2 individuals that involves

• a pair of contrasting alleles

• one allele is dominant & can hide the presence of the other in a heterozygous genotype

Incomplete dominance/codominance

• combination of 2 contrasting alleles, resulting in an intermediate phenotype

• neither allele is completely dominant over the other

• incomplete dominance: genotypes - blend of alleles

• codominance: genotypes - alternation of alleles

Sex-linked is genes for certain traits that are linked to the X sex chromosome with

no corresponding gene on the Y chromosome

when c is a mutated variant of x, X^cX would be

a carrier female

when c is a mutated variant of x, X^cX^c would be

a colorblind female

when c is a mutated variant of x, X^cY would be

a colorblind male

Multiple alleles

inheritance of some traits are determined by more than 2 types of alleles

Dihybrid cross

inheritance of 2 different traits/pairs of alleles at the same time

First, create a chart listing the

observed and expected outcomes of the experiment including totals

Calculate the Chi-Square value (# of terms in equation are = to

the # of outcomes in experiment))

Degrees of freedom

df=n-1 (n=number of outcomes)

The probability that the results are due to pure chance and not bias are between

___ and ___ %; therefore the results are accepted/not accepted.

Results equal or greater than .05 (5%) are

accepted

Pedigree

genetic representation of a family tree that diagrams the inheritance of a trait/disease through several generations

Normal male & female

Affected male & female

*Impossible to be a carrier as a male

(either has it/doesn’t)

Sex-linked inheritance

more males with disorder but no carrier males

Autosomal recessive inheritance

• normal is dominant allele

• male & female carriers

• generally = amount of males & females showing disorders

Autosomal dominant inheritance

• abnormal is dominant allele

• no m/f carriers

• lots of abnormal m/f