Patterns of inheritance and variation

Question 1

What is phenotypic variation?

Answer 1

Variation shown in the characteristic of an organism (phenotype)

Question 2

Give an example of phenotypic variation

Answer 2

human blood group

Question 3

What is polygenic variation?

Answer 3

Variation influenced by many genes

Question 4

Give an example of polygenic variation

Answer 4

Human skin colour

Question 5

What is monogenic variation?

Answer 5

Variation influenced by only one or a small number of genes

Question 6

Give an example of monogenic variation

Answer 6

Violet flowers, either coloured or white

Question 7

How can variation be categorised?

Answer 7

continuous and discontinuous

Question 8

What are alleles?

Answer 8

different versions of genes within the same species

Question 9

What is etiolation?

Answer 9

plants don’t get enough light so grow spindly and long

Question 10

What is chlorosis?

Answer 10

plants don’t get enough magnesium so don’t produce enough chlorophyll and turn yellow

Question 11

What two factors can affect variation?

Answer 11

genetic and environmental

Question 12

Give two examples where genetic and environmental factors affect phenotype variation

Answer 12

• body mass in humans
• dwarf and tall pea plants

Question 13

How is genetic variation achieved during meiosis?

Answer 13

• crossing over of non-sister chromatids (prophase 1)
• independent assortment of homologous chromosomes (metaphase 1)
• independent assortment of chromatids (metaphase 2)
• independent segregation of chromatids (anaphase 2)

Question 14

What is monogenic inheritance?

Answer 14

the inheritance of a single gene

Question 15

Is cystic fibrosis caused by a dominant or a recessive allele?

Answer 15

recessive

Question 16

What did Gregor Mendel do?

Answer 16

Mendel experimented genetic crosses using pea plants. He used true breeding plants to breed together and studied the outcome.

Question 17

What are true breeding plants?

Answer 17

plants that were homozygous for traits

Question 18

What were the offspring of true breeding crosses called?

Answer 18

F1 generation

Question 19

In homozygous crosses, what are the offspring?

Answer 19

They are all heterozygous

Question 20

What is a heterozygous cross?

Answer 20

where 2 of the F1 offspring are taken and crossed

Question 21

What are the offspring of heterozygous crosses called?

Answer 21

F2 generation

Question 22

What is the result of a heterozygous cross?

Answer 22

3 offspring with dominant trait to 1 offspring with the recessive characteristic

Question 23

What is codominance?

Answer 23

when 2 different alleles are equally dominant so both alleles are expressed in the phenotype

Question 24

Give and describe an example of codominance

Answer 24

Snapdragons:
Allele for red flowers: codes for enzyme that catalyses the production of red pigment from a colourless precursor
Allele for white flowers: codes for an altered enzyme that doesn’t code for a pigment

Question 25

Give an example of a trait that has more than two different alleles

Answer 25

blood groups

Question 26

What are blood groups determined by?

Answer 26

the immunoglobulin gene (gene I) coding for antigens present on the surface of blood cells

Question 27

What does I A produce?

Answer 27

antigen A (spherical shape)

Question 28

What does I B produce?

Answer 28

antigen B (triangle shape)

Question 29

What does I O produce?

Answer 29

no antigen

Question 30

Which two alleles for blood groups are codominant?

Answer 30

I A and I B

Question 31

Which allele for blood groups is recessive to the other two alleles?

Answer 31

I O

Question 32

What two genotypes express blood group A?

Answer 32

I A I A and I A I O

Question 33

What two genotypes express blood group B?

Answer 33

I B I B and I B I O

Question 34

What genotype expresses blood group AB?

Answer 34

I A I B

Question 35

What genotype expresses blood group O?

Answer 35

I O I O

Question 36

How many chromosomes are there in a human body cell?

Answer 36

46

Question 37

What are the two chromosomes found in males?

Answer 37

XY

Question 38

What are the two chromosomes found in females?

Answer 38

XX

Question 39

Give an example of a characteristic determined by a gene linked to X and Y chromosomes

Answer 39

Haemophilia

Question 40

What is haemophilia?

Answer 40

slow blood clotting due to absence of clotting factor

Question 41

What does XH represent?

Answer 41

the dominant 'healthy' allele on the X chromosome

Question 42

What does Xh represent?

Answer 42

the recessive allele coding for haemophilia on the X chromosome

Question 43

What does Y represent?

Answer 43

the Y chromosome which has no allele attached to it

Question 44

What is dihybrid inheritance?

Answer 44

the inheritance of 2 genes

Question 45

What is the expected phenotypic ratio of the F2 generation of a dihybrid cross test?

Answer 45

9:3:3:1

Question 46

Why might the phenotypic dihybrid cross-ratio differ in reality?

Answer 46

- fertilisation is random - sometimes the genes may be linked so always inherited together

Question 47

What is autosomal linkage?

Answer 47

It is the inheritance of linked genes on the chromosomes other than those that determine sex (XX & XY)

Question 48

How are linked genes inherited together?

Answer 48

They don't usually undergo independent assortment but they may sometimes be separated by crossing over.

Question 49

If alleles are linked, what does this produce?

Answer 49

more gametes containing that combination of linked alleles

Question 50

What are recombinant allele combinations?

Answer 50

Allele combinations that are only produced occasionally during crossing over

Question 51

What is x^2/ chi-squared for?

Answer 51

statistical test to measure if there is a significant difference between the observed and expected results in a genetic cross

Question 52

What is the null hypothesis of genetic crosses?

Answer 52

There is no significant difference between the observed and expected and any difference is due to chance alone.

Question 53

What is the equation for chi-squared?

Answer 53

x^2 = the sum of (O - E)^2 / E

Question 54

How do you work out the critical value?

Answer 54

Usually use 0.05 and the degrees of freedom is the number of possible outcomes - 1

Question 55

Do we accept or reject the null hypothesis when x^2 is less than the critical value?

Answer 55

accept and we say there is no significant difference between the observed and expected, any difference must be due to chance

Question 56

Do we accept or reject the null hypothesis when x^2 is more than the critical value?

Answer 56

reject and we say that there is a statistically significant difference between the observed and expected so there must be a reason for this

Question 57

Which type of graph can be used to present continuous data?

Answer 57

line graph

Question 58

Which type of graph can be used to present discontinuous data?

Answer 58

bar chart