10.2- inheritance

Question 1

unlinked genes ——- ———- as a result of meiosis

Answer 1

segregate independently

Question 2

what is segregation?

Answer 2

the separation of the two alleles of every gene that occurs during meiosis

Question 3

what is independent assortment?

Answer 3

the alleles of one gene segregate independently of the alleles of other genes

Question 4

genes found on different chromosomes are

genes which are on the same chromosome are

the exception is

Answer 4

unlinked and segregate independently

linked and do not segregate independently

linked genes that are far apart on the chromosome (due to crossing over)

Question 5

look at how to form a punnet square for dihybrid traits

Answer 5

p446

Question 6

describe the difference between a monohybrid and a dihybrid trait

Answer 6

monohybrid cross: the cross happening in the F1 generation offspring of parents differing in one trait only, ie the inheritance of a single trait.

dihybrid cross: the cross happening in the F1 generation offspring of parents differing in two traits, the simultaneous study of the inheritance of two different traits.

Question 7

when are gene loci said to be linked?

Answer 7

if they are on the same chromosome and hence don’t independently assort (unless synapsis occurs)

Question 8

define a locus

Answer 8

a locus is a specific, fixed position on a chromosome where a particular gene or genetic marker is located.

Question 9

monohybrid inheritance =

Answer 9

linked genes = two potential gamete combinations

Question 10

dihybrid inheritance =

Answer 10

unlinked genes = 4 potential gamete combinations

Question 11

define homologous chromosomes

Answer 11

two chromosomes that have the same sequence of genes.

Question 12

why are homologous chromosomes not usually identical to each other?

Answer 12

for at least some of the genes on them, the alleles will be different

Question 13

what is the name of non-sex chromosomes?

Answer 13

autosomes- these are common to both males and females

Question 14

what are the two types of linkage?

Answer 14

autosomal gene linkage, when the genes are on the same autosome
sex linkage, when the genes are located on the X chromosome

Question 15

variation can either be

Answer 15

discrete - no in-between categories
continuous - eg height

Question 16

continuous variation

Answer 16

Monogenic traits (characteristics controlled by a single gene loci) tend to exhibit discrete variation, with individuals expressing one of a number of distinct phenotypes

Question 17

discrete variation

Answer 17

Polygenic traits (characteristics controlled by more than two gene loci) tend to exhibit continuous variation, with an individual’s phenotype existing somewhere along a continuous spectrum of potential phenotypes

Question 18

describe how the phenotypes of polygenic characteristics tend to show continuous variation

Answer 18

Increasing the number of loci responsible for a particular trait increases the number of possible phenotypes
This results in a phenotypic distribution that follows a normal distribution curve

Question 19

why do offspring with unlinked genes have an equal possibility of inheriting any potential phenotypic combination?

Answer 19

due to the random segregation of alleles via independent assortment

Question 20

Offspring with linked genes will only express the phenotypic combinations present in either parent unless

Consequently, the ‘unlinked’ recombinant phenotypes occur —– ——- than the ‘linked’ parental phenotypes

Answer 20

crossing over occurs

less frequently

Question 21

revise the use of chi-squared tests

Question 22

Null hypothesis (H0):
Alternative hypothesis (H1):

Answer 22

There is no significant difference between observed and expected frequencies (i.e. genes are unlinked)
There is a significant difference between observed and expected frequencies (i.e. genes are linked)

Question 23

Morgan’s discovery of non-Mendelian ratios in Drosophila.

Answer 23

Breeding experiments involving fruit flies clearly demonstrated that linked genes were not independently assorted
- when cross-breeding red-eyed wild types with white-eyed mutants, he discovered a clear sex bias in phenotypic distribution
- he inferred this was caused by the gene for eye colour being located on a sex chromosome (i.e. X-linked)

Morgan also observed that the amount of crossing over between linked genes differed depending on the combination of traits
- this led to the idea that crossover frequency may be a product of the distance between two genes on a chromosome – genes with a higher crossover frequency are further apart, whereas genes with a lower crossover frequency are closer together

Question 24

Polygenic traits such as human height may also be influenced by

Answer 24

environmental factors, such as nutrition, disease, activity

Question 25

How are linked genes often shown?

Answer 25

As vertical pairs

Question 26

The frequency of recombinant phenotypes within a population will typically be —– than that of non-recombinant phenotypes; why?

Answer 26

lower

crossing over is a random process and chiasmata do not form at the same locations with every meiotic division

Question 27

The relative frequency of recombinant phenotypes will be dependent on; why?

Answer 27

the distance between linked genes

• recombination frequency between two linked genes will be greater when the genes are further apart on the chromosome because there are more possible locations where a chiasma could form between the genes

Question 28

how can recombinant phenotypes be identified?

Answer 28

performing a test cross (crossing with a homozygous recessive for both traits); LOOK AT THIS