Mendelian Genetics: Genetic Segregation

Question 1

locus

Answer 1

gene location on chromosome

Question 2

allele

Answer 2

alternate forms of a gene

Question 3

dominant

Answer 3

allele/phenotypic trait that’s expressed in heterozygotes

Question 4

recessive

Answer 4

allele/phenotypic trait that’s expressed only in homozygotes

Question 5

phenotype

Answer 5

appearance; expressed form of gene(s)

Question 6

genotype

Answer 6

genetic constitution

Question 7

heterozygote/heterozygous

Answer 7

inherited different alleles at one of more loci
relates to individuals
ex: Diploid Aa
Tetraploid AAaa

Question 8

homozygote/homozygous

Answer 8

inherited identical alleles at one or more loci
relates to individuals
ex: diploid AA
tetraploid AAAA

Question 9

heterogenous

Answer 9

population of individuals with different genotypes
relates to groups/populations
ex: AA, Aa, aa

Question 10

homogenous

Answer 10

population of individuals with same genotype
relates to groups/populations
ex: Pop.1= AA, AA,AA
Pop. 2= Aa, Aa, Aa

Question 11

somatic cells

Answer 11

any cell of a living organism other than the reproductive cells
chromosomes in the nuclei of somatic cells usually occur in pairs

Question 12

Gregor Mendel

Answer 12

examined inheritance of clear-cut alternative traits

Question 13

Homologous chromosomes

Answer 13

chromosome pairs, one from each parent, that are similar in length, gene position, and centromere location
The position of the genes on each homologous chromosome is the same, however the genes may contain different alleles

Question 14

true breeding

Answer 14

progeny showed no genetic segregation

Question 15

Mendel’s Proposed Principles

Answer 15

• Theory of Particulate Inheritance
• Dominance/Recessiveness
• Law of Segregation
• Law of Independent Assortment

Question 16

Theory of Particulate Inheritance

Answer 16

• Observable traits determined by discrete units of inheritance and different units make up a trait
• 2 particles of heredity (alleles) for each trait (diploid)

Question 17

Dominance/Recessiveness

Answer 17

When 2 different, but homozygous individuals are crossed their F1 progeny will be uniform
F1: expressed trait= dominant
trait not expressed= recessive allele

Question 18

Law of Segregation

Answer 18

• during gamete formation, paired alleles of a gene segregate randomly so each gamete receives one allele or another with equal probabilities
• relates directly to what happens in meiosis
• see segregation take place in F2:
  
  • > individual contains pair of identical alleles= all gametes receive same allele
  • > individual contains pair of unlike alleles= each gamete has 50% chance of receiving one vs. the other)

Question 19

Law of Independent Assortment

Answer 19

Random separation of chromosomes; during gamete formation, segregation of alleles at one locus is independent of segregation of alleles at another locus (exception: linked genes)

• relates directly to what happens in meiosis
• dihybrid cross

Question 20

gametes

Answer 20

a mature haploid male or female reproductive cell that is able to unite with another of the opposite sex in sexual reproduction to form a zygote

Question 21

Testcross

Answer 21

cross an individual expressing a dominant phenotype and with one expressing a recessive phenotype
-used to determine genotype of dominant plant (homozygous or heterozygous)

Question 22

determine the number of possible gametes

Answer 22

2^n = # of gametes produced

where n is the number of heterozygous genes

Question 23

product/multiplication law

Answer 23

taking into account a possibility in different events
probability of 2+ events occurring simultaneously is equal to the product of their individual probabilities; events are mutually exclusive if the outcome of one does not affect the outcome of other events

Question 24

sum law

Answer 24

different possibilities, same event

probability of independent events being accomplished in more than one-way

Question 25

Binomial distribution

Answer 25

(p+q)^n 
where n= sample size or # of progeny
utilizes both the multiplication and sum rule
exponents of p decrease from n to 0
exponents of q increase from 0 to n
coefficients given by Pascal’s triangle

can calculate frequency of families with certain proportion of individuals showing a certain genotype

steps:
(1) assign initial probabilities to each outcome p=# & q=#
(2) locate appropriate term based on n
(3) plug in #s p and q and calculate

Question 26

monohybrid cross

Answer 26

one trait – occur in fourths
F1 generation→ dominant phenotype for one trait
Each trait can be treated independently
Looking for a 1/4th distribution
(One trait but multiple phenotypic categories → epistasis!)

Question 27

dihybrid cross

Answer 27

two traits – occur in sixteenths
independent assortment
F1 generation→ dominant phenotype for each trait
4 combinations of an F2 generation for a dihybrid cross 9:3:3:1 phenotypic ratio

(Determined 1/16th but not 9:3:3:1 → epistasis)
2^n= # of gametes (n= number of heterozygous genes)

Question 28

Chi-squared test

Answer 28

Evaluation of the fitness of observed results to theoretical expectation

(o-e)^2/e

Reject null hypothesis: deviation from the expected ratio is due to more than chance alone
Fail to reject: deviation can be attributed to chance, therefore observed values fit the expected ratio

Use p=0.05 to determine reject (p 0.05) null hypothesis

Question 29

multihybrid cross

Answer 29

each trait can be treated independently because of independent assortment
3:1 ratio in the F2
use branch diagram/forked line
multiplication rule to determine proportions of trait combos