10.2

Question 1

What is a monohybrid cross

Answer 1

examines one trait at a time whilst using punnet squares to check for dominance and sex-linkage

Question 2

What is a dihybrid cross

Answer 2

follows the inheritance of two traits, and a dihybrid Punnett square which would give the expected ratio of phenotypes in the offspring If the traits are independently assorted

Question 3

What do the outside and adjacent edges of the grid show in dihybrid punnet squares

Answer 3

show the possible alleles found in the egg on the outside edge and the possible alleles found in the sperm along the adjacent edge

two different letters are used

Question 4

What do the internal boxes show

Answer 4

the allele combinations that can be produced by fusion of the gametes

two Paris of alleles, two copies each of two different letters

Question 5

What does each square in the punnet grid represent

Answer 5

the possible genotype of the diploid offspring

Question 6

if both parents are heterozygous what is the ratio usually in the F2 generation

Answer 6

9 : 3 : 3 : 1

Question 7

what is epistasis

Answer 7

the effect of one gene depending on the presence of another gene

Question 8

What type of genes show independent assortment

Answer 8

genes found on different chromosomes

Question 9

What are linked genes

Answer 9

genes found on the same chromosome, they are physically connected since they occur along he same DNA molecule, but they can often give the same results as unlinked genes in genetic crosses

the closer the loci of two linked genes, the less frequently they are separated by crossing over

Question 10

What is a linkage group

Answer 10

several genes on the same chromosome that do not show independent assortment

Question 11

How are new allele combinations created

Answer 11

by crossing over

Question 12

What did Thomas Morgan demonstrate with the help of fruit flies

Answer 12

that genes are found on chromosomes and that they do not always follow mendelian ratios

Question 13

What types of methods did Morgan use

Answer 13

radiation - to cause heritable mutations with visible effects on phenotypes

Question 14

What was the first clear exception to the Mendelian inheritance

Answer 14

found in Drosophila and was the inheritance of white eyes, fruit flies usually have red eyes

Question 15

What did Morgan establish

Answer 15

sex linked trans and suggested that some traits can be located on the sex chromosomes

Question 16

What is the most common allele of any trait notated in Morgans method

Answer 16

with a +

Question 17

What happens when two genes are very close together

Answer 17

it becomes very rare that a chiasma will form between them, thus, they are almost always inherited together

Question 18

How do you show that genes are linked

Answer 18

a special notation is used, a capital letter is used for dominance and two horizontal lines represent the homologue chromosomes with one allele for each gene.

Question 19

What are the two distinct possibilities for the genotype of a heterozygous parent (using t and b)

Answer 19

TB// tb or Tb// tB

Question 20

What is the easiest way to test for a linkage between two genes

Answer 20

to use a test cross where a heterozygous parent is crossed with a homozygous recessive parent

Question 21

What does it mean when something is a recombinant

Answer 21

an organism that contains a different combination of alleles to either of its parents

Question 22

What do you use for a test cross

Answer 22

homozygous recessive parent

Question 23

What does it mean if non-Mendelian ratios are obtained in a dihybrid cross

Answer 23

the genes are likely to be linked

Question 24

what is a non-median ratio

Answer 24

an unusual ratio of phenotypes such as

3: 5
5: 3
6: 2
2: 6

Question 25

what does it mean the lower the recombinant frequency...

Answer 25

the closer the linked genes are on the chromosome

Question 26

What factors can influence phenotype

Answer 26

- more than one gene may affect a single trait - a single gene may affect traits - a gene may impact the expression of another gene - some alleles are not expressed in all individuals - some alleles are expressed with varying intensity - some genetically influenced traits also have important environmental influences

Question 27

What is an example of a polygenic trait

Answer 27

when more than one gene may affect a single trait for example, the human eye color is polygenic because it is determined lately by two genes with some additional influence from genes on at least a dozen loci

Question 28

What is an example of a pleiotropic gene

Answer 28

when a single gene may affect multiple traits of example, the CFTR gene codes for a transmembrane protein with effects in multiple organs when the cystic fibrosis allele is homozygous, the functions of the lungs, intestines and pancreas are all affected

Question 29

How may a gene impact the expression of another gene

Answer 29

for example the TYR gene produces a polypeptide that is a necessary first step in creating the melanin that gives skin, hair and eyes their many possible colors. When the TYR gene is not functional, the individual will exhibit albinism (lack of pigment) no matter which alleles are present

Question 30

Example of alleles that ae nto expressed in all individuals

Answer 30

BRCA1 alleles have incomplete penetrance because even though they greatly increase the risk of breast cancer, some women with the allele never develop it

Question 31

examples of how some alleles are expressed with varying intensity

Answer 31

the polydactyl allele in cats (causes extra toes) has varied expressivity because some cats only gave one or two extra toes while others have four extra toes per paw

Question 32

name an example of genetically influenced traits that have impotent environmental influences

Answer 32

MC1R gene cause freckling when the skin is exposed to the sun. The development of freckles has both genetic components and environmental aspects related to the amount and intensity of sunlight the individual experiences.

Question 33

What is discrete variation

Answer 33

a trait with phenotypes that can be grouped into distinct categories usually coded by a single gene

Question 34

What is an example of discrete variation in genes

Answer 34

ABO blood group

Question 35

What is continuous variation

Answer 35

traits that display an unbroken range of phenotypes in the population

Question 36

What did Morgan do in his experiment with fruit flies

Answer 36

He breezed a white eyes male mutantt with ed eyed female flies: - the 1st generation offspring all had red eyes - consistent with mendelian they concerning dominant and recessive traits - the 2nd generation contained a small number (roughly 25% of flies) with white eyes - again consistent with mendelian theory - however all the white eyed flies were male - this is inconsistent with mendelian theory and suggested that the two traits are linked

Question 37

What characteristics tend to show continuous variation

Answer 37

polygenic chacteristics

Question 38

What do traits with continuous variation show

Answer 38

an unbroken range of phenotypes in the population they are often polygenic traits

Question 39

What is the distribution of when gaphsed of continuous variation

Answer 39

normal (bell shaped) distribution

Question 40

What is an example of polygenic inheritance

Answer 40

height in humans

Question 41

What type of variation is heigh in humans

Answer 41

continuous aviation

Question 42

What is involved usually in the orientation of homologous Pais during meiosis and the pairing of gametes in fertilization

Answer 42

a random element

Question 43

What does a chi squared test do

Answer 43

it assess the edge of difference between observed results and expected results

Question 44

What would the expected ratio in a monohybrid cross between two pea plants heterozygous for pea colour be

Answer 44

3: 1

Question 45

What can the chi-squared tell you about your results?

Answer 45

how well the observed results compare with the expected results

Question 46

What is the equation for the chi-squared test

Answer 46

(obtained - expected)^2 / expected

Question 47

What was the conclusion of Morgan’s discovery about the inheritance of eye colour and shape in Drosophila?

Answer 47

the two genes do not ascot independently they are linked

Question 48

How would you explain a test cross involving dihybrid flies in which parental-type offspring and small numbers of new combinations of parental phenotypes are produced?

Answer 48

The two genes are linked on the same chromosome and crossing over has occurred.

Question 49

If three genes control one characteristic, what is the number of possible genotypes produced?

Answer 49

27 3^3 = 27

Question 50

Not rejecting the null hypothesis in a chi-squared test calculated in a dihybrid cross indicates that:

Answer 50

the predicted ratio of the phenotypes follows the mendelian law

Question 51

In a chi-squared test, the null hypothesis is that two genes are unlinked. The value produced by the chi-squared test was much higher than the critical chi-squared value. What does this indicate?

Answer 51

the genes are likely to be linked

Question 52

A heterozygous dihybrid cross resulted in three possible genotypes. What can be concluded?

Answer 52

The genes are linked but crossing over did not take place. Since there are only three resulting genotypes, this means that recombinants are not included. This indicates that the genes are found on the same chromosome (linked) but crossing over did not take place. That is why recombinants were ignored. If recombinants are to be included, the number of outcomes produced should be 16 (4 x 4), with 9 possible genotypes.

Question 53

How would you explain a test cross involving dihybrid flies in which parental-type offspring and small numbers of new combinations of parental phenotypes are produced?

Answer 53

The two genes are linked on the same chromosome and crossing over has occurred.