Lecture 1.4 Mendelian Inheritance

More than — (out of — ) genes have variants known to cause distinct health conditions

8000; ~23,000

How do single gene diseases differ from other types of illness?

we can predict the probability of a person to inherit it, we can test for disease causing mutations, frequency can vary by population and they may be “fixable”

Gregor Mendel

“father of genetics” conducted experiments in 1857-1863

Mendelian trait

controlled by a single locus in an inheritance pattern. In such cases, a mutation in a single gene can cause a disease that is inherited according to mendel’s laws

Mendel studied — traits in pea plants. What are these traits (indicate dominant and recessive)?

7; Round(R) or wrinkled(r), yellow (Y) or green(y), inflated pod(V) or restricted pod(v), green pod(G) or yellow pod(g), axial stem(F) or terminal stem(f), gray seed(A) or white seed(a), tall(T) or short(t).

P1

parental generation

F1

first filial generation

F2

second filial generation

Mendel deduced that consistent — in the offspring indicated that plants transmitted —

ratios of traits; distinct units

Monohybrid cross

follows one trait. Breeding experiment between P generation organisms that differ in a single given trait

True breeding (pure breed)

a kind of breeding in which parents will produce offspring of the same phenotype

When a pure breeding tall plant and a pure breeding short plant were crossed what was the resulting F1 generation? What about the F2 generation produced by self-crossing?

in F1 there is 100% tall plants that are heterozygous and in F2 there is a 3:1 tall plant to short plant phenotypic ratio and a 1:2:1 homozygous dominant to heterozygous to homozygous recessive genotypic ratio

Elementen

term coined by mendel for hereditary material aka gene

Law of segregation

Mendel's first law. States that during gamete formation, the allele for each gene segregate from each other so that each gamete carries only one allele for each gene

How to distinguish a pure bred from a hybrid

if you cross a pure bred with another pure bred you only get the pure bred phenotype where as a hybrid would have the 3

Test cross

crossing the recessive homozygous specimen with an unknown specimen to test whether the unknown is heterozygous or homozygous dominant

Law of dominance and uniformity

third law of mendel. Some alles are dominant while others are recessive. Recessive alleles will always be masked by dominant alleles.

Wild type

most common phenotype (may be recessive or dominant)

Mutant phenotype

variant of a gene’s expression that arises when the gene undergoes mutation

Autosomal dominant inheritance

a trait that affects individuals who have the dominant allele (either heterozygous or homozygous dominant)

Autosomal recessive traits

a trait that affects individuals with who have two recessive alleles

Criteria for autosomal recessive traits

affects both males and females, may skip generations, parents of an affected individual must be heterozygotes or homozygous recessive (has the trait). May be transmitted unless it causes death before reproductive age. More common in consanguinous families.

Compare autosomal dominant and recessive inheritance

both affect males and females with equal frequency. Autodom cannot skip generation while recessive can. Affected individuals of an autodom trait must have an affected parent (unless de novo mutation) while auto recessive may have a carrier parent/s.

Recessive traits are usually due to — of function

loss

t/f recessive disorders tend to be more severe and produce symptoms earlier than dominant disorders

true

Dominant traits usually arise form — of function

gain

Dihybrid cross

cross which analyzes two different traits

Law of independent assortment

Mendel's second law. Genes of different traits can segregate independently during formation of gametes. Consider two genes on different chromosomes. They may not assort independently if they are close together on the same chromosome.

Probability

the likelihood that an event will occur

Product rule

probability of simultaneous independent events are the product of their individual probabilities

Pedigree

symbolic representations of family relationships and the transmission of inherited traits

Autosomal dominant trait on a pedigree

does not skip generations and affects both sexes.

Autosomal recessive trait on a pedigree

may skip generations. Parents are inferred to be heterozygotes . example

Steps to solve a genetic problem

list all genotype and phenotypes for the trait, determine parents genotypes, derive possible alleles in gametes, unite gametes in all combinations to reveal possible genotypes, and repeat for successive generations