BIO_SCI 2200 Mizzou John David Exam 3

9:3:3:1 ratio

-Two heterozygous parents at the same two independent loci in which the wild type allele at both is dominant

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3:1 ratio

Two heterozygous parents and wild type is dominant

1:3 ratio

Two heterozygous parents and mutant is dominant

1:3:3:9 ratio

Two parents heterozygous at the same two independent loci and the mutant allele at both is dominant

1:1 ratio

One parent heterozygous and the second homozygous recessive

1:1:1:1 ratio

One parent heterozygous and the second homozygous recessive at the same independent loci

Advantages of genetic variation

brings neutral, already beneficial, and deleterious genes/alleles for new combinations and removal; also harder for parasites to adapt to

Compare and contrast Binary fission, parthenogenesis, hermaphrodites, and sexual reproduction

Sexual reproduction is the most predominant, but all others are quicker forms of reproduction

Specialization of sexual function

assures sex chromosomes segregate and prevents intermingling

X and Y chromosomes

-number of active genes on Y chromosome has went down dramatically

-X has 2000-3000 "normal genes"; Y has 20-30 genes that determine male characteristics (SRY triggers testes formation)

-both pair in meiosis to segregate and do not cross over in regions containing sex-determining genes

X chromosme

-Male gives his X to all daughters

-female gives her Xs to her sons and daughters

X- linked recessive

-in a male will always be expressed

-in a female may be masked by a wild type allele

- ex: Duchenne Muscular Dystrophy (satellite cells possible solution)

- loss of function

-more common in males (color blindness)

X-linked dominant

-more common in females than males

- x- linked dominant mutant allele will always be expressed

-2 Xs in females

Y- linked traits

- only expressed in males

- passed from father to son to grandson

-cannot skip a generation

- dominant and recessive have no meaning

Sex-limited traits

-autosomal

-expressed in one sex or the other (never both)

-ex: milk production in cattle, facial hair in humans

Sex-influenced traits

-autosomal

-expressed in both sexes but with different frequency

-ex: male pattern baldness

Autosomal recessive

-not specific to gender

-any gene not located on a sex chromosome Aa x Aa cross AA, Aa, Aa, aa (disease)

- not seen in every generation of an affected family

-two copies of the mutation are needed to cause the disease (each parent)

-ex: Sickle cell

Autosomal dominant

-not specific to gender

-from generation to generation

-a single copy of the disease-associated mutation is enough to cause disease

-ex: Huntingtons Disease, Marfan syndrome

x^cx

carrier

x^cy

disease

How many alleles at a single locus in diploid individuals; in a diploid population

2; many

Codominance

-When which the phenotypes of both alleles are exhibited in the heterozygote

-F2 genotypic and phenotypic ratios are 1:2:1

-IA/IA x IB/IB--> IA/IB--> IA/IA, IB/IB/ IA/IB (1:2:1)

-ex: blood groups

1:2:1 ratio

-both parents are heterozygous at one locus and the alleles are either codominant or incompletely dominant

Incomplete dominance

-can't mask it completely, not completely dominant

Pleiotrophy

a defect in a single gene that causes multiple phenotypic effects

-ex: Marfan syndrome and Porphyria Variegata (autosomal dominant)

Gene Product interaction

- produces a new phenotype (from 2 or more loci)

- ex: comb shape; Rose (p/p R/R) x Pea (P/P r/r)--> walnut shaped (P/p R/r) (9P/_ R/_:3P/_ r/r:3 p/p R/_:1 p/p r/r)

- multiple loci can influence the same phenotype

Difference between codominance and incomplete dominance, with a 1:2:1 ratio

- whether one or two gene products are made from alleles at a single locus

Multiple allelic series

-one gene can't have multiple gene products (alternative processing)

-one locus, two alleles with complete dominance/recessiveness, but some may be codominant and others incompletely dominant

Complementary Gene Action

-9:7 ratio

-the products from two non-allelic genes are required to product the final phenotype

- white x white--> purple

white x purple--> 9 purple, 7 white

- ex: albanism

Duplicative Gene Action

- 15:1 ratio

- triangular x ovoid--> 15:1 15 comes from 9:3:3

- gene product involved

- A/_ B/_, A/_ b/b, a/a B/_, a/a b/b

Recessive epistasis

- 9:3:4 ratio

-the absence of a product at one locus (c/c) masks the presence of the product of a second locus (Y/_)

Epistasis

-the interaction of non-allelic gene products in which the product of one gene influences/masks the presence of the product of another gene

-caused by a color control gene

-ex: color of rats tail

Difference between epistasis and dominance

gene products from one locus (dominance) vs two loci (epistasis)

Dominant epistasis

- the presence of one locus (A/_) masks the presence of the product of a second locus (B/_)

Penetrance

- the frequency with which a dominant gene or a homozygous recessive gene is expressed in the phenotype of a population of individuals

-"all or nothing", but can be complete or incomplete

- function of gene and environment

- ex: retinoblastoma of the eye (autosomal dominant, 80% penetrant); mugwumps

Expressivity

-the degree to which a penetrant gene or genotype is phenotypically expressed

- at a single locus can be mild, intermediate, or strong

- function of gene and environment

- ex: osteogenesis imperfecta (autosomal dominant with 100% penetrance); also an example of Pleiotropy

Continuous traits

- quantitative traits

-determined by multiple genes (polygenic)

-many phenotypes that do not fall into a few easily separated categories but are present in a relatively continuous distribution

- ex: birth weight, adult height, blood pressure, ear length in corn

Discontinuous traits

- determined by a single genetic locus

- a few alternative phenotypes are distinct and easily separated

-ex: ABO blood types, albinism, flowers either purple or white, presence or absence of single digits

number of loci, alleles, and phenotypes

as the number of genetic loci (gene products) in a polygenic series increases, the number of discrete phenotypes increases by a factor of 2n+1

-the frequency of the most common phenotype decreases

- the range of phenotype values increases

Trait vs number of genes involved

-skin color in humans: 4-6

-fruit weight in tomatoes: 7-11

-ear length in corn: 16

-oil content in corn: >17

Internal and external environmental effects

No environmental effect: T/T

Small environmental effect: T/t

Large environmental effect: t/t

Multifactorial traits

- environmental effects overlay the genetic component

-ex: schizophrenia, autism spectrum disorder, diabetes type 2, human height

Pure bread

homozygous (aa or AA)

Test cross

between a homozygous recessive individual and a corresponding suspected heterozygote to determine the genotype of the latter