Mendel's Laws

Law of Dominance

If the two alleles at a locus differ, then the dominant allele determines the organism’s appearance while the recessive allele has no effect

Law of Segregation

The two alleles separate during gamete formation and end up in different gametes

Law of Independent Assortment

Each pair of alleles segregates independently of other pairs of alleles during gamete formation

But when does independent assortment not occur and what is it called?

Not occur: When genes on loci are close together on single chromosome

Called: Linkage

Linkage Disequilibrium

• What

• Occurs because

• Measured by

• Formula

• If D = 0

• If D ≠ 0

What: Some allele combinations are linked and passed on together more often than random

Occurs because: The loci are physically close on the chromosome

Measured by: D (difference between observed frequency and expected frequency)

Formula: D = F_AB​−(F_A​×F_B​)

• F_AB​ = Observed frequency of allele A at locus 1 and allele B at locus 2 appearing together

• F_A = Frequency of allele A

• F_B = Frequency of allele B

D = 0: No linkage disequilibrium (alleles inherited independently)

D ≠ 0: There’s linkage disequilibrium (non random association)

What occurs when loci are close together on the same chromosome?

• Crossing over?

• Alleles?

• % of parental gametes

Crossing over: Less likely to occur

Alleles: Stay together (just like in parents)

% of parental gametes: >50% (more parental/non-recombinant gametes)

What occurs when loci are far apart on the same chromosome?

• Crossing over?

• Alleles?

• % of parental gametes?

Crossing over: More likely to occur

Alleles: Switch places during crossing over creating recombinants

% of parental gametes: <50% (more recombinant gametes)

What gene converts the embryo into a male?

SRY gene making it genetically barren (without SRY gene = female)

Why do more males than females have sex linked disorders?

Because males only have one x linked locus so if recieve mutant allele from mother it will express the trait

What is pleiotropy?

When one gene influences two or more traits (multiple effects)