6.2 - Patterns of inheritance

Question 1

what are some examples of continuous variation?

Answer 1

height
waist circumference
fur length

Question 2

what are some examples of discontinuous variation?

Answer 2

blood group
violet flower colour

Question 3

what causes genetic variation in meiosis?

Answer 3

crossing-over of alleles, independent assortment of chromosome
random fusion of gametes in fertilization

Question 4

what are inherited characteristics that are continuous usually known as?

Answer 4

polygenic - e.g skin colour

Question 5

what are inherited characteristics that are discontinuous usually known as?

Answer 5

monogenic e.g flower colour

Question 6

Define a homozygote

Answer 6

An organism that carries 2 of the same allele

Question 7

Define a heterozygote

Answer 7

An organism that carries 2 different alleles

Question 8

Define the locus

Answer 8

The fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in a pair

Question 9

what phenotypic ratio can be expected from a dihybrid cross of two heterozygous?

Answer 9

9 : 3 : 3 : 1
all dom: 1st Dom 2nd rec: 1st rec 2nd dom: all rec

Question 10

what is the phenotypic ratio for a codominant heterozygous cross?

Answer 10

1 : 2 : 1
homozygous A : heterozygous AB : homozygous B

Question 11

what is an autosome?

Answer 11

any chromosome that isn’t a sex chromosome

Question 12

why are genes on the same autosome said to be linked?

Answer 12

won’t be affected by independent assortment, only crossing over

Question 13

what are the mutagenic agents?

Answer 13

Physical (xrays uv light)
Chemical (mustard gas nitrous acid)
Biological (transposons food virus)

Question 14

what are the types of chromosme mutation?

Answer 14

• deletion (lost)
• inversion (180 flip)
• translocation (other chromosome)
• duplication
• non disjunction (down syndrome extra chromosome)

Question 15

what is aneuploidy?

Answer 15

chromosome number is not an exact multiple of the haploid (some chromosomes fail to separate during meiosis)

Question 16

what is polyploidy?

Answer 16

diploid fertilised by a haploid will result in triploid
two diploids make a tetraploid

Question 17

when does genetic variation occur?

Answer 17

prophase 1 - crossing over
Anaphase 1 + 2 - independent assortment

Question 18

how do you test for phenotypically similar individiuals?

Answer 18

do a test cross

Question 19

what is a dihybrid cross?

Answer 19

simultaneous inheritance of two characteristics

Question 20

what gene has multiple alleles?

Answer 20

human blood groups
also codominant

Question 21

what is an example of a sex linked disease?

Answer 21

colour blind
Haemophilia A

Question 22

what is the example of colour sex linkage in cats?

Answer 22

Xco and Xcb make a tortoishell which males cannot be because it is X chromosome expression

Question 23

what is autosomal linkage?

Answer 23

gene loci present on the same autosome (non-sex chromosome) that are often inherited together

Question 24

what is epistasis?

Answer 24

interaction of non-linked gene loci where one masks the expression of the other

Question 25

what are the factors affecting evolution of a species?

Answer 25

natural selection
stabilising selection - environment unchanged
directional selection - environment change
genetic drift
genetic bottleneck - reduced diversity from decrease to increase
founder effect - descends from small no. ancestors

Question 26

what are organisms adaptaitons?

Answer 26

anatomical
behavioural
physiological

Question 27

what is allopatric speciation?

Answer 27

physical barrier

Question 28

what is sympatric speciation?

Answer 28

single ancestral species in the same region, but due to chromosomal error which leads to reproductive isolation