2.15 patterns of inheritance & sex linkage

Question 1

locus

Answer 1

a specific location of a gene on a chromosome

Question 2

alleles

Answer 2

different versions of a gene at the same gene locus

Question 3

phenotype

Answer 3

the physical traits, including biochemical characteristics, expressed as a result of the interactions of the genotype with the environment

Question 4

genotype

Answer 4

the genetic make-up of an organism with respect to a particular feature

Question 5

homologous pairs

Answer 5

matching pairs of chromosomes in an individual which both carry the same genes, although they may have different alleles

Question 6

homozygote

Answer 6

an individual where both alleles coding for a particular characteristic are identical

Question 7

heterozygote

Answer 7

an individual where the two alleles coding for a particular characteristic are different

Question 8

dominant

Answer 8

a characteristic which is expressed in the phenotype whether the individual is homozygous of heterozygous for that allele

Question 9

recessive

Answer 9

a characteristic which is only expressed when both alleles code for it; the individual is homozygous for that recessive trait

Question 10

true breeding

Answer 10

a homozygous organism which will always produce the same offspring when crossed with another true-breeding organism for the same characteristic

Question 11

monohybrid cross

Answer 11

a genetic cross where only one gene for one characteristic is considered

Question 12

codominance

Answer 12

in heterozygots, where both alleles at a gene locus are fully expressed in the phenotype
eg blood type A + B = AB

Question 13

sex-linked traits

Answer 13

characteristics which are inherited on sex chromosomes

Question 14

homologous chromosome

Answer 14

chromosomes with the same suze & structure, has the same genes at the same loci

Question 15

why do sampling errors occur?

Answer 15

1. reproduction is a result of chance, combination of alleles in each gamete is completely random
2. some offspring die before they can be sampled
3. insufficient sampling techniques

Question 16

test cross

Answer 16

it reveals the parental genotype. the individual is crossed with a homozygous recessive individual.

Question 17

why do breeders have to test cross?

Answer 17

they need to know itf the stock will breed true

Question 18

what are properties or organisms that are good for a genetic experiment?

Answer 18

1. relatively cheap and easy to grow to minimise experimental costs
2. have a short life cycle so results of crosses/ mutations can be seen quickly
3. produce large numbers of offspring so that the results are statistically relevant
4. have clear, easily distinguishable characteristics

Question 19

why can’t we carry out genetic experiments on humans?5

Answer 19

because it is unethical

Question 20

autosomes

Answer 20

chromosomes which carry information about the body but do not determine the sex of an individual

Question 21

homogametic

Answer 21

an individual who produces gametes that contain only one type of sex chromosome: the female

Question 22

heterogametic

Answer 22

an individual who produces two of gamete each containing different types of sex chromosome: the male

Question 23

epigenetics

Answer 23

the study of changes in gene expression (active vs inactive genes) that does not involve changes to the underlying DNA sequence but affects how cells read genes

Question 24

sex- linked diseases

Answer 24

genetic diseases that result from a mutated gene carried on the sex chromosomes (x chromosome)

Question 25

red-green color blindness

Answer 25

a sex-linked genetic condition which affects the ability to distinguish tones of red and green

Question 26

completely unlinked genes

Answer 26

two genes found on separate chromosomes and approx equal numbers of gametes are formed which contain either the parental combinations of alleles or a different combination of alleles

Question 27

linked genes

Answer 27

inherited as if they were a single gene

Question 28

what happens with linked genes during meiosis?

Answer 28

closely linked genes will rarely get separated so they will be inherited as a single unit
linked genes that are positioned further apart are more likely to undergo crossing over, so recombinant gametes are produced

Question 29

x chromosome

Answer 29

• larger than y chromosome
• carries many genes in the non-homologous region which aren’t present on Y
• those genes code for traits eg clotting factors in blood & ability to distinguish between certain colors

Question 30

hemophilia

Answer 30

recessive x-linked mutation in haemophiliacs lead to to one of the clotting factors not being produced. therefore, the clotting response to injury does not work and the patient can bleed to death

Question 31

how can haemophilia be treated?

Answer 31

blood transfusions with clotting factor VIII extracted from donated blood/ genetic engineering the clotting factor

Question 32

how is gene transfer used to treat haemophilia

Answer 32

1. the gene for healthy human clotting factors is found
2. the gene for clotting factor is inserted into bacterial plasmid to produce large quantities of pure factor VIII
3. it is extracted and purified to produce injections for patients