Inheritance

Question 1

Gene

Answer 1

length of DNA that codes for a particular polypeptide

Question 2

Allele

Answer 2

a different version of a gene
there may be many alleles of a single gene (e.g. blood)
Alleles may be dominant, recessive or codominant

Question 3

Homozygous

Answer 3

when organism has 2 of the same alleles for a gene

Question 4

Heterozygous

Answer 4

when organism has 2 different alleles for a gene

Question 5

Phenotype

Answer 5

the expression of the genetic constitution and its

interaction with the environment

Question 6

Genotype

Answer 6

the genetic constitution of an organism

Question 7

Genome

Answer 7

all of the DNA in an organism

Question 8

Recessive

Answer 8

an allele that’s only expressed when 2 copies are present

Question 9

Dominant

Answer 9

an allele expressed when only when copy is present

Question 10

codominance

Answer 10

when two alleles both contribute to phenotype

e.g. AB blood type

Question 11

what is monohybrid inheritance ?

Answer 11

• inheritance of a single gene

Question 12

what is the basic law of genetics (aka the law of segregation) ?

Answer 12

• in diploid organisms, characteristics are determined by alleles that occur in pairs
• only one of each pair of alleles can be present in a single gamete

Question 13

what’s a ratio?

Answer 13

a measure of the relative size of 2 groups expressed as a proportion

Question 14

why are actual results of genetic crosses different from predicted results

Answer 14

discrepancies due to statistical error

Question 15

what is dihybrid inheritance ?

Answer 15

how 2 characters, determined by two different genes located on different chromosomes, are inherited

Question 16

what’s a carrier?

Answer 16

• a person carrying an allele which isn’t expressed in the phenotype but can be passed on to offspring

Question 17

What does diploid mean?

Answer 17

having paired sets of chromosomes in a cell

Question 18

What does haploid mean?

Answer 18

having a single set of unpaired chromosomes

Question 19

What kind of organisms are humans?

Answer 19

diploid (we have 2 sets of chromosomes) so we have 2 alleles for each gene

Question 20

What are gametes?

Answer 20

• sex cells
• contain half the genetic material of the organism
• contain one allele for each gene

Question 21

What happens when two gametes (from two parents) fuse together?

Answer 21

alleles they contain form genotype of offspring produced

Question 22

what do monohybrid crosses show?

Answer 22

the likelihood of the different alleles of that gene (so different versions of the characteristic) being inherited by offspring of certain parents

Question 23

First set of offspring referred to as what?

Answer 23

F1 generation

the second called F2 generation

Question 24

How to do dihybrid crosses

Answer 24

e.g. seed colour (yellow or green) and seed shape (wrinkled or round)
1 work out parental genotypes 
2 write out parental gametes 
3 work out offspring genotypes (4 by 4 punnet square.... four possible outcomes:
round and yellow 
round and green
wrinkled and yellow 
wrinkled and green) 
4 calculate ratio

Question 25

why can any four types of gametes (in dihybrid crosses) of one plant combine with any of the four types from another plant ?

Answer 25

because fertilization is random

Question 26

what is codominance?

Answer 26

both alleles expressed in the phenotype

Question 27

what are multiple alleles?

Answer 27

where there are more than 2 alleles, of which only 2 may be present at the loci of an individual’s homologous chromsomes)

Question 28

In a dihybrid F1 generation cross, the phenotypic ratio for the F2 generation is always what ?

Answer 28

9:3:3:1

Question 29

when does autosomal linkage occur?

Answer 29

if 2 or more genes are located on the same autosome (non-sex chromosome)
- two genes less likely to be separated during crossing over, resulting in the alleles of the linked gene being inherited together

Question 30

when does sex linkage occur?

Answer 30

• when there is a gene on the X chromosome, not present on the Y chromosome
  (meaning males are more likely to exhibit recessive disorders like haemophilia)

Question 31

What is epistasis?

Answer 31

the interaction between two non-linked genes which causes one gene to mask the expression of other in the phenotype

Question 32

How do epistatic genes work?

Answer 32

• antagonistically (against each other) or in a complementary fashion

Question 33

which is the epistatic gene?

Answer 33

• the gene suppressing another gene

Question 34

what is the hypostatic gene?

Answer 34

• the gene being suppressed

Question 35

Antagonistic epistasis can be what?

Answer 35

• either recessive or dominant

Question 36

Describe dominant antagonistic epistatsis

Answer 36

• expression of dominant allele (epistatic gene) prevents expression of hypostatic gene

Question 37

What is recessive epistasis?

Answer 37

• it occurs when presence of two copies of the recessive allele at the first locus prevents expression of another allele at a second locus

Question 38

give an example of complementary epistasis?

Answer 38

• two genes work together

for example, they may encode two enzymes that work in succession

Question 39

sex chromosomes of males and females

Answer 39

females - XX chromosomes

males - XY chromsomes

Question 40

what makes a gene sex-linked?

Answer 40

• if it is carried on the X or Y chromsome

Question 41

why are recessive alleles found in females more likely to expressed in their male offsprings?

Answer 41

• X chromosome is much longer than Y, meaning most of the X chromosome doesn’t have an equivalent portion on Y chromosome
• meaning recessive alleles found on this portion of the X chromosome will be
  more likely to be expressed
  THEREFORE:
  recessive phenotypes are more likely to be present in men e.g. haemophilia