lecture 3

Question 1

what are chromosomes

Answer 1

coloured stainable bodies

Question 2

describe chromosome theory of inheritance - chromosomes

Answer 2

Chromosomes like mendels elements, (chromosomes describe elements)
come in matched homologous pairs in an organism

Question 3

describe chromosome theory of inheritance - members of a pair

Answer 3

members of homologous pair separate during meiosis, so each sperm or egg receives just one member

Question 4

describe chromosome theory of inheritance - sorting

Answer 4

members of diff chromosome pairs are sorted into gametes independently of one another in meiosis
just like alleles of diff genes in mendel’s
chromosomes segregate differently

Question 5

describe what thomas hunt morgan thought

Answer 5

skeptical about chromosome theory of inheritance - responsible for heredity
Thought we were overlooking other possibilities that may equally give 2 kinds of germ cells that mendelian explanation calls for

Question 6

describe the flies - what thomas hunt morgan thought

Answer 6

wild type flies have red eyes = traditional functional gene
morgan studied organism
showed what mendel describe
eye colour trait made the point
why white = did mendels experiment and tested hypothesis

Question 7

describe morgans experiment 1

Answer 7

red female x white male = red male and red female F1
red dominant over white
trait is about phenotype
white flies have mutations in the gene that transports precursors of red pigment to the eye
follows mendels law

Question 8

what was the prediction of flies experiment based on mendels law

Answer 8

red male WW x red male WW F1 = 1/4 red WW, 1/4 red wW. 1/4 red Ww and 1/4 white w/w

Question 9

what was actual result of flies experiment

Answer 9

red female x red male = 1/2 red female, 1/4 white male, 1/4 red male
white only in males = bias for sex

Question 10

describe morgans experiment 2

Answer 10

white female x red male = F1 1/2 red female, 1/2 white male
contradicts mendels law

Question 11

describe drosophila chromosomes in females and males

Answer 11

the pattern of W inheritance resembles how X chromosomes are sorted during meiosis
fit how x are sorted, but result explains if heredity carried out by chromosome, white gene on x chromosome

Question 12

explain why morgans experiment 1 got the results it got

Answer 12

Xred Xred female cross Xwhite Y male
F1 = 1/2 red female, 1/2 red male, since 2 Xred female chromosomes equivalent, males get y from dad and x from mom and that x is always red
F2 = females heterozygous and males all red, so can get white female x and male y = 1/4 red female, 1/4 red female, 1/4 red male, 1/4 white male * depends on which x chrom inherited from mother

Question 13

explain why morgans experiment 2 got the results it got

Answer 13

white female x red male = 1/2 red female, 1/2 white male, since red x = on male, so males can only inherit one chrom from dad = y chrom, so always get white from mom, since mom white, females always red since inherit x chrom from dad = always red

Question 14

what were the reasons why mendels experiement worked

Answer 14

traits affected by only one gene - many traits, like height, are affected by multiple genes
pure genetic background and ability to cross or self pollinate = must be able to control cross or mating
ability to obtain a large number of progeny - tested large number of F2s - cannot do with humans

Question 15

how does mendel’s work apply to humans

Answer 15

pedigrees

Question 16

what can pedigree tell us

Answer 16

tell us about a trait/phenotype/disease

Question 17

how to determine if dom or recessive in pedigree

Answer 17

if have unaffected parents but child is affected = recessive
dominant = many affected

Question 18

how to determine if autosomal or sex linked in pedigree

Answer 18

if male and female affected = not y linked
could have mutated copy of x in mom, if recessive = must have both mutated copies for mom

Question 19

how to determine if common or rare trait in pedigree

Answer 19

most people who enter fam are carriers = common trait

Question 20

how to do probability for a pedigree

Answer 20

all diff independent events
do punnets/determine genotype of parents
then chances of being affected
ex 4 children 1/2 x 1/2 x 1/2 x 1/2 = 1/16 chance

Question 21

how to calculate the risk - probablity

Answer 21

find out genotype of parents and then those ratios time the chance of getting disease = for each side of fam and then multiply those together times the chance child is affected, if recessive (1/4 mendelian result)

Question 22

Why is the prevalence of CF in Canada around 1/3600 when 1/30 is a carrier?

Answer 22

1/30 x 1/30 x 1/4 (1/4 based on mendels law) = 1/3600

Question 23

why do flies have white eyes

Answer 23

white flies have mutations in the gene that transports precursors of red pigment to eye
loss of function mutation = cannot transfer red precursor to eye
haplosufficient, so red dom over white as long as single copy of wild type red gene

Question 24

why do flowers have white petals

Answer 24

mutation that prevented purple pigment, also haplosufficient = one trait dom over other

Question 25

explain morgans experiment 2 and drosophila

Answer 25

white gene inheritance pattern does not seem to follow mendels law = can be explained by inheritance pattern of the x chrom
set of traits determined by x chrom - inheritance pattern, all follow segregation of x chrom, many traits on x chrom since drosophila does not have many chromsomes
nobel prize 1933