genetics review m1

gene or locus

specific region of DNA that may or may not code for a polypeptide

genome

all the chromosomes within a cell

genetic amplification

making multiple copies of a molecule (DNA) from one starting template

*misconceptions about inheritance before Mendel

1. They thought the father contributed more genetically than the mother to the offspring

2. Parental traits blended together and were permanently changed. 

dispelled myth of uneven parental contribution by:

being able to perform reciprocal crosses where traits of male and female parents could be reversed

also: chose true breeding lines and only scored mutually exclusive traits

first law of segregation

there are 2 alleles for each trait that separate when the gametes are formed (1 allele in each gamete) and alleles reunite at random via fertilization (1 from each parent)

this found by crossing two true breeding lines with one trait difference (P gen)

100% of offspring showed the dominant phenotype (F1)

when F1’s are self-crossed, they produced ratio of 3:1 dominant to recessive, suggesting/proving that there are two alleles for each trait and they’re not lost, the dominant just masks the presence of the recessive phenotypically (F2)

second law of independent assortment

during gamete formation, 2 different alleles segregate independently, one does not affect the other. 

tested with dihybrid self-crossing the F1's (heterozygous at 2 loci) 

how many unique gametes can be made by an individual heterozygous at n loci?

2^n

sum rule

probability of mutually exclusive events is the sum of their individual probabilities

ex. prob of 2 girls 1 boy=

GGB (1/2×1/2×1/2)= 1/8

BGG (1/2×1/2×1/2)= 1/8

GBG (1/2×1/2×1/2)= 1/8

1/8 + 1/8 + 1/8 = 3/8

product rule

probability of individual events all occurring is the product of their individual probabilities 

ex. 2 kids, probability of 1st being a girl second being a boy = ½ * ½ = 1/4

recessive trait

2 unaffected parents producing an affected offspring

dominant trait

2 affected parents producing an unaffected offspring

some traits controlled by a single locus do not show typical mendelian ratios because of…

lethality

pleiotropy

>2 alleles

codominance

incomplete dominance

incomplete dominance

1 allele does not completely mask the presence of another

ex. snap dragons true breeding red and white produce 100% white

codominance

both alleles are expressed equally in the phenotype

ex blood type Ia and Ib sugars, ppl heterozygous can produce both sugars

>2 alleles (more than 2 alleles)

still only 2 alleles in every genome, but more than 2 alleles could be possible which can give an non-typical mendelian ratio

pleiotropy

1 locus affects more than one phenotypic trait; 1 gene= multiple traits.

ex. PKU- can’t break down phenylalanine so it accumulates, resulting in numerous symptoms  

lethality

some alleles in homozygous form are lethal

if homozygous recessive, they die in embryonic stage and ratios will vary

ex. achondroplasia dwarfism 

wild type allele

at least 1% in population (wt or +)

mutant type allele

less than 1% in population

dominance series

more than 2 alleles at a gene locus with variable dominance relative to each other

ex. the agouti, black back, and black mice

multifactorial traits

traits as a result of 2 or more loci

complimentary gene action

complimentary genes work together to give a certain phenotype.

when crossed, 1 parent provides what the other is missing

to test: cross 2 true breeding parents with the same phenotype but different lines,

if the F1s have different phenotypes, them assume more than one gene affects that trait

epistasis

allele at one locus could mask the presence of an allele at a different locus

two types: recessive and dominant epistasis

recessive epistasis

when homozygous recessive genotype at one locus masks the presence of an allele at the second locus

ex. in labs, _ _ ee is a yellow dog no matter what. 

dominant epistasis

when 1 dominant allele at first locus masks the presence of allele at second locus

ex. summer squash color will be white as long as _ _ B _

*heterogenous traits

traits controlled by many loci where mutation in only one can cause the same phenotype

heterogenous trait vs multifactorial trait

het= one mutation produces 1 outcome

multifactorial trait= 1 mutation at different areas can produce different outcomes

not all with same genotype have same phenotype, why?

1. chance

2. environmental differences

3. modifier genes

4. expressivity

5. penetrance

penetrance

% of individuals in a population with the genotype that express the phenotype

expressivity

degree to which a genotype is expressed as a phenotype

modifier genes

alter phenotypes produced by alleles at other loci

environment

any external force, can affect penetrance and expressivity (ex. tanning?)

chance

can impact expressivity and penetrance

additive gene action

genes work together to increase expressivity

aka: presence of specific alleles at a locus controlling a specific trait increase the expression of that trait

(ex. height); variability also due to additive gene action and environment

chromosomal theory of inheritance

chromosomes carry genes so they carry genetic information as well

only equal contribution from both parents is the nucleus

n

number of chromosomes in a gamete (haploids)

2n

number of chromosomes in somatic cells (diploids)

meta-centric

centromere is closer to the middle of the chromosome

acrocentric

centromere is closer to the end of a chromosome

karyotype

image of chromosomes in metaphase arranged in size order; use metaphase because they are condensed, aligned attached to the sister chromatids and spindle fibers

aneuploidy

wrong number of a specific chromosome

ex. down syndrome

happens during meiosis where they fail to split (1 daughter cell ends up with extra)

nondisjunction

when chromosomes fail to separate

resulting in one daughter cell with extra, and one with no copies of that chromosome

gametogenesis

requires mitosis and meiosis 

oogenesis- gametogenesis in females

spermatogenesis- gametogenesis in males

risk of nondisjunction

males can make sperm whenever, but females make in embryo and have them for life, they’re arrested at meiosis metaphase II until fertilization, so the longer they wait to reproduce, the more likely it is that chromosomes are stuck together

2 pieces of evidence for Sutton’s chromosomal theory of inheritance

•Sutton’s evidence:

–Every cell has 2 copies of every chromosome and (from Mendel) every cell has 2 copies of every gene

–Chromosomes (like genes) don’t change when passed from parent to offspring

–During meiosis homologous chromosomes pair and then segregate to different gametes, just like alternate alleles of each gene

–Chromosomes assort independently without regard to other chromosome pairs, just like alternate alleles of unrelated genes

–At fertilization, egg’s chromosomes unite with chromosomes from a sperm encountered at random, just like alleles from 1 parent unite with those from the other parent at random

–All cells derived from a fertilized egg have 1/2 maternal chromosomes and 1/2 paternal chromosomes

sex-linked

trait is coded for by a gene carried in a sex chromosome

sex-limited

affect structure or process found in one sex but not the other

sex-influenced

appear in both sexes but expressivity may differ based on gender

who wrote cask of amontadillo

edgar allan poe

3 people inducted in the country hall of fame/rocknroll

1. elvis

2. dolly parton

3. johnny cash