BIOL 239 Midterm 1

Natural Selection

individuals with certain traits are more likely to survive and reproduce in a given environment

Artificial selection

humans choose which individual plants/animals produce

What happened to dogs?

wolves were domesticated, created lots of genetic variation and led to diverse changes in gene

Fox domestication experiment

foxes were selected for tameness

domestication syndrome

having floppy ears, variation in coat colour, shorter muzzle, smaller teeth, prolonged juvenile behaviour, hormonal changes, etc.

Who is Mendel?

Established principles of inheritance with experiments with garden peas

phenotype

An individuals observable traits

What did the mating of true-breeding parents with antagonistic traits show?

appearance of an antagonistic trait, one is dominant and one is recessive

What did people believe before mendel’s theories?

one parent contributes to offspring’s inherited features

parental traits become mixed and changed in the offspring

What is a genotype?

genetic makeup, description of genetic information, from DNA sequence

Gene

discrete units of inheritance

alleles

alternative forms of a single gene

What is an individual who has two alleles of the same gene

homozygous

what is an individual who has two alleles of a different gene?

heterozygous

genes/alleles are always designated by…

italics

In every population, there will always be different allele of every gene, why?

gene has several alleles occurring in a population

this is polymorphic

Diploid individuals

can only have 2 alleles for 1 gene

monomorphic

genes with only 1 allele present in a population

mendel’s law of segregation

2 alleles for each trait separate during gamete formation then unite at random, one from each parent during fertilization.

what is the expected ratio from a monohybrid cross?

Genotypic ratio: 1:1

Phenotypic ratio: 1:1

how does genotype influence phenotype?

different alleles differ in nucleotide sequence

in protein coding genes, this causes amino acid sequence and resulting protein

how does seed texture get influenced by genotype

enzyme (SBE1) influences phenotype due to genetic mutations (inactive/mutated = wrinkled)

How does genotype of mendel’s pea shape gene affect phenotype?

Dominant RR, Rr has normal SBE1 function, recessive rr has none

What if someone gives you a yellow pea to determine its genotype?

1. self fertilize and see what colour peas it produces, compare homozygous vs. heterozygous outcomes

2. perform test cross

Test cross

cross the individual with unknown genotype against homozygous recessive phenotype for the trait in question

dihybrid crosses

crossing individuals with 2 genes and the alleles have dominant/recessive traits with NEW phenotypic combinations

In dihybrid crosses, the two traits act…

independently

Law of independent assortment

how different alleles of different genes behave

What phenotypic ratio is observed in dihybrid crosses?

9:3:3:1

The number of gametes is calculated by:

2^n where n=# of genes/traits

The law of product

the probability of two or more independent events occurring together = the product of the probabilities that each event will occur by itself.

the chance of cross between heterozygotes producing homozygous recessive offspring is an example of:

law of product

the chance of flipping heads twice in a row in a coin toss = probability of a head AND a head

law of product

the law of sum is

the probability of either of two mutually exclusive events occurring is the sum of their individual probabilities

the chance of rolling an even number on a 6-sided = probability of 2 or 4 or 6 added together

the law of sum

chance of cross between heterozygotes producing a dominant orange offspring

the law of sum

multihybrid crosses are matings between individuals that differ…

in three or more traits

many traits exhibit phenotypic patterns that don’t appear to follow mendel’s rules. this is because:

• no definitively dominant/recessive allele

• more than 2 alleles exist

• multiple genes involved

• gene-environment interactions

incomplete dominance is

the heterozygote has an intermediate phenotype (red + white snap dragons produce all pink offspring)

How is incomplete/codominance represented

with alleles represented by upper case letters, different alleles defined by superscripts

incomplete dominance has the same genotypic & phenotypic ratio of

1:2:1

what is the reason for incomplete dominance in snapdragon flower colour

needs 2 normal alleles producing functional enzyme to express a red colour, resulting in pink flower (1 normal allele)

what is codominance

contribution from both alleles are visible in the phenotype of 1 offspring

F1 of codominance

alternative traits are both visible

F1 of incomplete dominance

offspring resembles neither purebred parent (mix of phenotype)

genotypic and phenotypic ratio in codominance is

1:2:1

dominance relations between alleles do not affect

transmission of alleles

type of dominance depends on

type of proteins encoded and the biochemical functions

multiple alleles

there can be more than two alleles for any gene

multiple alleles of a gene can

segregate in populations

diploid individuals can only carry

2 alleles

wild type allele

the most common phenotype in a population

mutant type

rare alleles in a population

wild type alleles are designated with

a superscript +

reciprocal crosses are conducted

between pure-breeding lines of each phenotype to establish dominance relationships with all types of alleles

blood type in humans are

polymorphic genes with 3 alleles

blood type in humans is determined by

gene encoding enzyme that adds terminal sugar on polymer chain

pleiotropy is

one gene that influences multiple traits

sickle cell disease is destruction of RBCs that lead to

multiple phenotypic effects (anemia, heart disease)

lethal alleles

some dominant and recessive alleles that can kill the organism

mendelian ratios rely on all phenotypes

being equally viable

Agouti gene

recessive for lethality, controls coat colour

Manx cats are

dominant for tailessness, recessive for lethality

dominance for lethality is not possible because

the offspring would die before the allele is passed on

Additive genes

2 or more genes influence one trait in a cumulative manner

what is the ratio in F2 progeny of additive genes

9:3:3:1

Epistasis

one gene hides the effect of another gene

epistatic gene

the gene that masks the other

hypostatic

the gene that gets masked

recessive epistasis

epistatic allele must be homozygous for it to mask the hypostatic gene

dominant epistasis

one allele is enough for hypostatic gene to be masked

eumelanin in Labradors

deposits black or chocolate colour using protein E

no eumelanin results in no colour because of

no protein E

pheomelanin

results in yellow labradors

dominant epistasis has a phenotypic ratio of

12:3:1

recessive epistasis has a phenotypic ratio of

9:3:4

complementary gene action

2 or more genes work together in the same pathway to produce a particular trait

For a heterogenous trait

a mutation in any one of a number of genes can create the desired phenotype

complementary gene action for heterogenous trai has a phenotypic ratio of

9:7

complementation tests

observation of complementation in offspring of two affected individuals shows the mutation is present in different genes

complex traits/multifactorial inheritance

trait is determined by many genes OR interaction between gene and environment

penetrance

percentage of population with a particular genotype (how many are affected)

expressivity

degree/intensity the genotype is expressed in a phenotype (how dark)

sex linked traits

controlled by genes on X or Y chromosome

sex limited traits

affect only one sex

sex influenced traits

in both sexes but expression differs between sexes

environmental influence: conditional lethality

allele is lethal under certain conditions

permissive conditions

conditions where individual survives

restrictive conditions

condition where individual dies

what is pedigree analysis used for

human inheritance, family genetic features, matings and genetic conditions

autosomal dominant trait

affected children have at least 1 affected parent, vertical pattern of inheritance, 2 affected heterozygote parents can produce unaffected children

autosomal recessive trait

affected individuals can be children of unaffected carriers, all children of 2 affected parents should be affected, horizontal pattern of inheritance

x linked recessive

trait never passes from male to male, female offspring of affected males are carriers, ½ of male offspring of female carriers will inherit the trait

x-linked dominant

trait seen in every generation, never passes from a male to male offspring, affected males produce 100% affected female offspring

y-linked

only affects males, no carriers

cystic fibrosis is a recessive trait that

encodes abnormal CTFR protein that regulates Cl ions through membrane, heterozygotes have enough CTFR for normal function

Huntington disease is a dominant trait that

damages nerve cells even if normal protein is present