Patterns of Inheritance

Question 1

is chlorosis genetic or environmental?

Answer 1

environmental

Question 2

factors causing chlorosis

Answer 2

• lack of light
• mineral deficiencies
• virus infections

Question 3

how does lack of light cause chlorosis?

Answer 3

plants turn off the chlorophyll production to conserve resources

Question 4

how do mineral deficiencies cause chlorosis?

Answer 4

• lack of iron or magnesium
• ion is a cofactor of the enzymes involved in chlorophyll production
• magnesium makes up the chlorophyll

Question 5

how do viral infections cause chlorosis?

Answer 5

• viruses interfere with the metabolism of cells
• infected tissues can no longer support the synthesis of chlorophyll

Question 6

chlorosis

Answer 6

condition causing leads to look pale or yellow as a result of sales not producing the normal amount of chlorophyll

Question 7

which general factors affect body mass?

Answer 7

• mainly environmental
• sometimes genetic

Question 8

genotype

Answer 8

the genetic makeup of an organism

Question 9

phenotype

Answer 9

observable characteristics of an organism

Question 10

dominant allele

Answer 10

allele that will always be expressed if present in an organism

Question 11

recessive allele

Answer 11

allele that will only be expressed of two copies of this alley or present in an organism

Question 12

steps to perform a genetic cross

Answer 12

• state phenotype of both parents
• state genotype of both parents
• state gametes of each parent (gametes should have one letter)
• draw a Punnett square
• state the ratio of each genotype
• state the corresponding phenotype for each of the possible genotypes

Question 13

ratio of heterozygous monogenetic cross

Answer 13

3:1

Question 14

codominance

Answer 14

occurs when two different areas occur for a gene - both of which are equally dominant leading to the expression of both alleles in the phenotype

Question 16

how do you represent codominant alleles?

Answer 16

• use a letter to represent the gene
• use a small letter above to represent the allele

e.g. for coloured pigments use:
- C^(R) for red pigment
- C^(W) for white pigment
- C^(P) for pink pigment

Question 17

what is the relationship between IA, IB and IO blood type alleles?

Answer 17

• IA and IB are codominant
• IO is recessive

Question 18

how many chromosomes do humans have?

Answer 18

• 23 pairs
• 46 chromosomes

Question 19

sex linkage

Answer 19

genes that are carried on sex chromosomes

Question 20

example of a sex linked disorder

Answer 20

haemophilia (slow blood clots)

Question 21

why are males more likely to have recessive sex linked genetic disorders?

Answer 21

• X chromosome is bigger than the Y
• X chromosome contains alleles for genes that the Y chromosome might not have
• male only needs to inherit one recessive value from the mother to have the disorder

Question 22

how do you represent sex linked alleles?

Answer 22

X and Y with little uppercase and lowercase alleles (only above the chromosome that carries it, usually X)

Question 23

dihybrid inheritance

Answer 23

inheritance of two genes

Question 24

steps to carry out a dihybrid cross

Answer 24

• state phenotypes of the parents
• state genotypes of parents
• state gametes from each parent (gametes should have two letters)
• draw a Punnett square
• state ratio of genotypes
• state corresponding phenotypes

Question 25

what would the gametes be for: YYRR x yyrr

Answer 25

YR YR x yr yr

Question 26

why might the actual genetic ratio be different to the expected?

Answer 26

- fertilisation of gametes is random so in a small sample a few chance events can lead to a skewed ratio - genes being studied of both on the same chromosome (linkage)

Question 27

(dihybrid) phenotypic ratio of: dom homo x rec homo YYRR x yyrr

Answer 27

4:0 (100% dominant heterozygous/YyRr)

Question 28

(dihybrid) phenotypic ratio of: dom hetero x dom hetero YyRr x YyRr

Answer 28

9:3:3:1 YYRR : YYrr : yyRr : yyrr

Question 29

what can split up autosomally linked genes?

Answer 29

crossing over in meiosis

Question 30

autosomal linkage

Answer 30

genes butter present on the same non-sex chromosome so are inherited as one unit

Question 31

recombinant offspring

Answer 31

offspring with different combinations of alleles than either parent

Question 32

what affects the chances of autosomal genes being separated during crossing over?

Answer 32

genes butter coaster together are less likely to be separated by crossing over

Question 33

recombination frequency

Answer 33

measure of the amount of crossing over that has happened in meiosis

Question 34

recombination frequency formula

Answer 34

no. of reconbinant offspring rec freq = ————————————— total no. of offspring

Question 35

what do the recombination frequency values mean?

Answer 35

- 50% indicates no linkage - less done 50% indicates gene linkage - as degree of crossing over reduces, the recombination frequency also gets smaller

Question 36

how can recombination frequency be used to estimate how close together genes are on a chromosome?

Answer 36

- recombination frequency is linked to a distance on a chromosome - e.g. 1% relates to one map unit on a chromosome

Question 37

epistasis

Answer 37

interaction of genes at different loci

Question 38

dominant epistasis

Answer 38

occurs when a dominant allele results in a gene having an effect on another gene