7

Question 1

Define genotype

Answer 1

The genetic constitution of an organism

Question 2

Define phenotype

Answer 2

The expression of the genotype and its interaction with the environment

Question 3

What are alleles and how do they arise

Answer 3

Alleles are variations of a particular gene with the same locus and they arise by mutation (change in DNA base sequence)

Question 4

What are alleles and how do they arise

Answer 4

Alleles are variations of a particular gene with the same locus and they arise by mutation (change in DNA base sequence)

Question 5

How many alleles of a gene can be found in diploid organisms?

Answer 5

2 as diploid organisms have 2 sets of chromosmes but there may be more than 2 alleles of a single gene in a population

Question 6

Describe the different types of alleles

Answer 6

Dominant allele ALways expressed and shown in phentoype
Recessive allele- Only expressed when 2 copies are present (homozygous recessive) not when heterozygous
Co dominant alleles- Both alleles expressed/contribute to phenotype

Question 7

Describe the different types of alleles

Answer 7

Dominant allele ALways expressed and shown in phentoype
Recessive allele- Only expressed when 2 copies are present (homozygous recessive) not when heterozygous
Co dominant alleles- Both alleles expressed/contribute to phenotype

Question 8

Define homozygous and heterozygous

Answer 8

Homozygous- Alleles at specific locus on each homologous chromosome are the same
Heterorzygous- Alleles at a specific locus on each homologous chromosme are different

Question 9

Define homozygous and heterozygous

Answer 9

Homozygous- Alleles at specific locus on each homologous chromosome are the same
Heterorzygous- Alleles at a specific locus on each homologous chromosme are different

Question 10

What do monohybrid and dihybrid crosses show?

Answer 10

Monohybrid cross- Inheritance of one phenotypic characteristic coded for by a single gene
Dihybrid cross- Inheritance of two phenotypic characteristics coded for by 2 different genes

Question 11

What do monohybrid and dihybrid crosses show?

Answer 11

Monohybrid cross- Inheritance of one phenotypic characteristic coded for by a single gene
Dihybrid cross- Inheritance of two phenotypic characteristics coded for by 2 different genes

Question 12

What is a sex linked gene

Answer 12

Gene with a locus on a sex chromosome
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Question 13

What is a sex linked gene

Answer 13

Gene with a locus on a sex chromosome
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Question 14

Explain why males are more likely to express a recessive x linked allele

Answer 14

This is because, men have XY chromosmes that have 1 allele and this recessive allele is always expressed. WOmen have XX chromosomes and so they can be carriers, females have to be homozygous in order to express the gene and this is less likely

Question 15

Explain why males are more likely to express a recessive x linked allele

Answer 15

This is because, men have XY chromosmes that have 1 allele and this recessive allele is always expressed. WOmen have XX chromosomes and so they can be carriers, females have to be homozygous in order to express the gene and this is less likely

Question 16

Explain how autosomal linkage affects inheritance of alleles

Answer 16

-Two genes located on the same autosome (non sex chromosome)
-Alleles on the same chromosome are inherited together as they stay togehter during independent segregation of homologous chromosomes during meiosis
-But crossing over between homologous chromosomes can create new combinations of alleles
If the genes are closer together on a autosome, they are less likely to be split by crossing over

Question 17

What is epistasis?

Answer 17

The Interaction of (products of) non-linked genes where one masks the expression of the other

Question 18

Suggest why in genetic crosse, the observed phenotypic ratios obtained in the offspring are often not the same as the observed ratio?

Answer 18

-Fertilisation of gametes is random
-Epistasis/Autosomal linkage
-Sample size not representative of whole population
-Some genotypes may be lethal

Question 19

Write the chi-squared equation

Answer 19

-

Question 20

What is a population?

Answer 20

A group of organisms of the same species in one area at one time that can interbreed

Question 21

Describe how a chi squared value can be analysed

Answer 21

• Number of degrees of freedom = number of categories - 1 (eg. 4 phenotypes = 3 degrees of freedom)
• Determine critical value at p = 0.05 (5% probability) from a table
  If X squared value is [greater / less] than critical value at p < 0.05
• Difference [is / is not] significant so [reject / accept] null hypothesis
  -So there is [less / more] than 5% probability that difference is due to chance

Question 22

What is a gene pool?

Answer 22

All the alleles of all the genes in a population at any one time

Question 23

What is allele frequency

Answer 23

Proportion of an allele of a gene in a gene pool

Question 24

What does the hardy weinberg principle state and what are the conditions under which the principle applies?

Answer 24

Allele frequency will not change from generation to generation if:
-Population is large
-No immigration/migration
-No mutations
-No selection for or against alleles
-Random mating

Question 25

What is the hardy weinberg equation?

Answer 25

p squared+ 2pq+ q squared= 1

Question 26

Explain reasons why individuals within a population of a species may show a wide variation in phenotype

Answer 26

Genetic factors
-Mutations
Crossing over between homologous chromosomes during meiosis
-Independent segregation
Random fertilization of gametes during sexual reproduction
Environmental factors

Question 27

What is evolution

Answer 27

The change in allele frequency over many generations in a population occurring through the process of natural selection.

Question 28

Describe the factors that may drive natural selection

Answer 28

Predation disease and competition for the means of survival, these result in differential survival and reproduction

Question 29

Explain how natural selection occurs in evolution of populations

Answer 29

-There are random gene mutations which result in new alleles of a gene
-Due to selection pressure, the new allele might benefit its possessor and organism has selective advantage
-Possessors are more likely to survive and have increased reproductive success
-The advantageous allele is inherited by offspring
-Over many generations, the allele increases in frequency in the gene pool

Question 30

Explain the cause and effects of stabilising selection and how it impacts the selection graph

Answer 30

Organisms with alleles coding for average variations of a trait have a selective advantage so frequency of alleles coding for average variations of a trait increase and those coding for extreme variations of a trait decrease. So standard deviation is reduced.
Graph becomes steeper

Question 31

Explain the causes and effects of directional selection and impact of selection graph

Answer 31

Organisms with alleles coding for one extreme variation of a trait have a selective advantage, so frequency of alleles coding for this extreme variation of the trait increase and those coding for the other extreme variation of the trait decrease. The graph shifts right toward extreme

Question 32

Explain the causes and effects of disruptive selection and how it affects the selection graph

Answer 32

Organisms with alleles coding for either extreme variation of a trait have a selective advantage, so frequency of alleles coding for bothe extreme variations of the trait increase and those coding for average variation of the trait decrease. This can lead to speciation . The graph has curve at both extremes

Question 33

Describe speciation (How new species arise from existing species)

Answer 33

Reproductive separation of two populations can result in accumulation of differences in their gene pool. New species arise when these genetic differences lead to an inability of members of either population to interbreed to produce fertile offspring

Question 34

Describe allopatric speciation

Answer 34

-Population is split up due to geographical isolation
-This leads to reproductive isolation separating gene pools by preventing interbreeding between populations.
Random mutations cause genetic variations within each population
Different selection pressures act on each population. So different advantageous alleles are passed on in each population
Allele frequencies within each gene pool change over many generations so eventually populations cannot interbreed to produce fertile offspring.