Mendelian Genetics (Principles & Probability)

Question 0

Alleles

Answer 0

Alternative forms of genes

ex) gene for seed colour has alleles that code for yellow (Y) or green (y) seeds

Question 1

Genes

Answer 1

the determinants of traits

ex) seed colour, hair colour

Question 2

Phenotype

Answer 2

trait you can measure

ex) appearance, biochemistry, behaviour

Question 3

Genotype

Answer 3

genetic constitution of an organism, determines the phenotype, determined by the combination of alleles
diploid organisms have 2 alleles for each gene

Question 4

Homozygous

Answer 4

both alleles code for the same phenotype (YY,yy)

Question 5

Heterozygous

Answer 5

each allele codes for a different phenotype (Yy)

Question 6

Dominant allele

Answer 6

alleles that masks other alleles

ex) heterozygotes for seed colour (Yy) have yellow seeds

Question 7

Recessive Allele

Answer 7

allele that is masked by other alleles (y) phenotype is only seen in homozygotes (yy)

Question 8

Principle of Segregation

Answer 8

the 2 alleles of same gene - separate from one another during the formation of gametes

Question 9

Principle of Independent Assortment

Answer 9

genes on different xsomes assort independently in gamete production

Question 10

Binomial Expansion equation

Answer 10

(p+q)^n

Question 11

Binomial Equation

Answer 11

P(x)=N!/X!(N-X)! *(p^x)(q^N-x)

Question 12

Probability

Answer 12

proportion of times a particular outcome is expected to occur

Question 13

Independence

Answer 13

Probability of an outcome does not depend on previous outcomes

Question 14

Product Rule

Answer 14

Probability that 2 independent outcomes will both both occur= product of the individual probabilities

Question 15

Sum Rule

Answer 15

probability that either one or the other of the two independent events will occur=sum of individual probabilities

Question 16

Two types of xsomes:

Answer 16

Autosomes- equally present in both sexes

Sex xsomes- differently represented in the sexes

Question 17

Sex-linked Clues

Answer 17

• female and male have different phenotypic ratios in F1 or F2
• reciprocal crosses may have different results
• criss cross inheritance: allele for father=>daughters=>grandsons

Question 18

X-linked recessive

Answer 18

affected father(normal mother): all daughters carriers, normal sons

Question 19

X-linked dominant

Answer 19

affected father(normal mother): daughters affected, normal sons

Question 20

Y-linked Traits

Answer 20

affected father(normal mother): normal daughters, all sons affected

Question 21

Sex-limited traits

Answer 21

-influenced by autosomal genes that are only expressed in one sex
ex) horns in some deer and sheep: only males express
milk production: female mammals only

Question 22

Sex-Influenced Traits

Answer 22

Autosomal genes in which the relationship between genotype & phenotype differs between males & females
ex) pattern baldness: het. male bald, het. female full hair

Question 23

Rules of thumb for pedigrees

Answer 23

1. Dominant vs recessive: recessive-skips generation or family; dominant-does not skip generation
2. Autosomal vs. sex linked: autosomal evenly distributed b/w sexes
   - X-linked recessive more common in males
   - X-linked dominant more common in females (2X= 2 chances); affected males=>all daughters
   - Ylinked only in males; affected father=>all sons

Question 24

Autosomal Recessive

Answer 24

• most affected individuals have normal (heterozygous) parents
• trait often skips generations (or families) AaxAa=>3A_:1aa
• if two affected individuals mate, all progeny will be affected
• mating b/w relatives is more likely to lead to affected individuals

Question 25

Autosomal Dominant

Answer 25

• affected individuals are usually heterozygotes
• most mating of affected individuals is w/ normal individual (homozygotes)
• half the progeny will be affected
• doesn’t usually skip generations

Question 26

X-linked recessive

Answer 26

• more males than females affected
• an affected female will pass the trait to all her sons
• a carrier female will pass the trait to half of her sons, and the allele to half of her daughters
• an affected male will pass the allele to all of his daughters & no sons
• father to son inheritance is very rare

Question 27

X-linked dominant

Answer 27

• more females affected than males
• an affected female is usually heterozygous & will pass the trait to half her offspring
• skipped generations are unlikely
• an affected male & normal female will pass the allele to all daughters & no sons

Question 28

Y-linked

Answer 28

Only affects males

all sons of an affected male will be affected

Question 29

Sex Xsome Aneuploids

Answer 29

In humans: OY is lethal

In Drasophila: XXX and OY

Question 30

Mammalian Sex Determination

Answer 30

Y Present: gonads=>testes

Y Absent: gonads=> ovaries

Question 31

Diversity in Sex Determination-Drasophila

Answer 31

Drasophila: Xxsomes/Autosomes

>1lethal; X:A=1 female; 0.5<1 intersex; X:A=0.5 male; X:A=0 lethal

Question 32

Diversity in Sex Determination - C. Elegans

Answer 32

XX - hermaphrodite, normally self fertilize

XO - “super sperm” outcompetes hermaphrodite sperm

Question 33

Diversity in Sex Determination - ZW system

Answer 33

female- heterogametic sex - ZW
male- homogametic sex - ZZ
z-linked genes behave like x-linked genes

Question 34

Environmental Sex Determination

Answer 34

some turtles: egg temperature sex determination

clown fish: gender changes with body size

Question 35

Barr Body

Answer 35

formation early in development (500-1000 cells)
one X deactivated/cell
deactivated X is random
ex) tortoise shell & calico cats, anhidrotic ectodermal dysplasia (lack of sweat glands), colourblindess

Question 36

ways to get equal gene product in male and female

Answer 36

• shut transcription down in one female X (turning it into a Barr Body)
• decrease rate of transcription in female (homogametic sex) (C.elegan)
• increase rate of transcription in male (heterogametic sex) (Drasophila)