Chapter 20 Patterns of Inheritance & Variation

Question 1

What is ‘chlorosis’?

Answer 1

A condition plants suffer from…
- leaves = pale/ yellow

• cells not producing normal amount of chlorophyll pigment
• reduces ability to make food by photosynthesis

Question 2

What factors cause chlorosis? (3)

Answer 2

ENVIRONMENTAL factors

(1) Lack of light
- absence of light - plants turn off chlorophyll production - conserving resources
- only occurs where plant doesn’t get light

(2) Mineral deficiencies
- minerals (iron / magnesium) needed for production of chlorophyll

(3) Virus infections
- virus interferes w/ the metabolism of cells

• yellowing = cannot support synthesis of chlorophyll

Question 3

What is genetic variation caused by?

Answer 3

versions of genes you inherit

• combination of alleles determined by sexual reproduction
  (meiosis) - forming gametes
  (random fusion of gametes)

Question 4

Define ‘genotype’.

Answer 4

combination of alleles an organism inherits - genetic make-up

Question 5

What is a dominant allele?

Answer 5

version of the gene which will always be expressed if present in an organism

• (showing) individual can have 1 OR 2, you can’t tell from phenotype

Question 5

What is a recessive allele?

Answer 5

only expressed if 2 copies of allele are present

• you know their genotype - they must have 2 is they are presenting

Question 5

Define ‘phenotype’.

Answer 5

observable characteristics of an organism

Question 6

What is homozygous?

Answer 6

2 identical alleles for a characteristic

• can be homozygous recessive (rr)
• can be homozygous dominant (RR)

Question 7

What is heterozygous?

Answer 7

2 different alleles for a characteristic

• always DOMINANT is expressed

Question 8

Variation divided into 2 groups??

Answer 8

CONTINUOUS
- extremes and everything between (can take any value)
- many genes involved (poly)

DISCONTINUOUS
- distinct groups
- one/ two genes involved

Question 9

What is monogenetic inheritance?

Answer 9

the inheritance of 1 gene

• genetic cross diagram

Question 10

What is codominance?

Answer 10

occurs when 2 diff alleles occur for a gene

• both equally dominant!!
• both expressed in phenotype

Question 11

Sex-linkage??

Answer 11

X chromosome - large - have many genes (not involved in sexual development)

• sex linked = genes (found on sex chromosomes) which determine characteristics

Question 12

What is dihybrid inheritance?

Answer 12

the inheritance of 2 genes (can be on diff homologous chromosomes - m/f)

• dihybrid cross 9:3:3:1

Question 13

What is autosomal linkage?

Answer 13

when genes which are linked are found on 1 of the other pairs of chromosomes.

(NOT sex-linkage)

Question 14

Linked genes??

Answer 14

Inherited as 1 unit

• no independent assortment - during meiosis
• unless allele serrated by chiasmata

Question 15

What are recombinant offspring?

Answer 15

have diff combo of alleles than either parent

Question 16

Chi squared

Answer 16

statistical test
- measures size of diff
- between expected and observed results

• helps determine whether the diff is significant
• by comparing size of diff and no. of observations
• used to test the null hypothesis

Question 17

What is the null hypothesis in Chi squared tests?

Answer 17

• there is no significant diff between expected and observed
• any diff is due to chance

Question 18

What do Chi squared test values tell us?

Answer 18

used to find the probability of the diff being due to chance alone

Question 19

What is epistasis?

Answer 19

interactions of genes at diff loci

Question 20

What is dominant epistasis?

Answer 20

When the dominant allele is results in a gene having an effect on another gene.

Question 21

What factors affect evolution?? (5)

Answer 21

(1) mutation
- new alleles produced - genetic variation

(2) sexual selection
- leads to allele coding for characteristics

(3) gene flow
- movement of alleles between populations

(4) genetic drift
- occurs in small populations
- mutation

(5) natural selection

Question 22

What do population genetics investigate?

Answer 22

allele frequencies within populations - how they change over time

Question 23

Example of selection pressures?

Answer 23

• changes in environment
• presence of new diseases
• prey
• competitors
• human influence/ interference

Question 24

What are the 2 types of limiting factors?

Answer 24

(1) density-dependent factors
- dependent on pop size
- competition, predation, prey, communicable disease

(2) density-independent factors
- affect all pop of any size
- climate change, natural disasters, seasonal change, human activities

Question 25

What is the founder effect?

Answer 25

small pop arise due to establishment of new colonies by a few isolated individuals

• leads to founder effect (extreme example of genetic drift)

Question 26

Types of selection (3)??

Answer 26

(1) Stabilising selection

(2) Directional selection

(3) Disruptive selection - diversifying

Question 27

Types of speciation?

Answer 27

(1) allopatric
- separation due to physical barrier
- geographically isolated

(2) sympatric
- 2 organisms of diff species interbreed = fertile offspring
- more likely to happen in plants
- hybrid formed
- diff no of chromosomes
- reproductively isolates hybrid organism