19)Inheritance and variation

Question 1

Inheritance

Answer 1

Passing genetic material from one generation to another

Question 2

Allele

Answer 2

Different form of the same gene

Question 3

Chromosome

Answer 3

Thread of DNA made from genes

Question 4

Gene

Answer 4

Length of DNA, with specific gene sequence, to code for a specific length of protein

Question 5

Homozygous

Answer 5

Two identical alleles for a specific gene

Question 6

Heterozygous

Answer 6

Two different alleles for a specific gene

Question 7

Dominant allele

Answer 7

Allele that is expressed when its present in both homozygous or heterozygous

Question 8

Recessive allele

Answer 8

Allele that is expressed only in absence of dominant allele

Question 9

Genotype

Answer 9

Genetic combination of alleles on the chromosome

Question 10

Phenotype

Answer 10

Physical appearance of an organism due to genes and environmental factors

Question 11

Diploid cells

Answer 11

Cells containing 2 sets of chromosomes

Question 12

Haploid cells

Answer 12

Cells containing one set of chromosomes

Question 13

Co-Dominance

Answer 13

A pair of alleles are equally dominant , they are both expressed in phenotype, where the phenotype is intermediate of both
E.g. Blood group AB

Question 14

Sex linked inheritance

Answer 14

Characteristic/disease controlled by genes present on sex chromosome and inherited on X chromosome

Question 15

Why are colour blindness characteristics are more common in male than females

Answer 15

-They are sex linked characteristics
-It is a characteristic controlled by gene present on sex chromosome and inherited on X chromosome
-So for male to be diseased, needs to inherit one recessive allele only one X chromosome from mother and Y from father
-For females to be diseased they must inherit 2 recessive alleles on two X chromosome from each parent
-Diseased make has 0 dominant allele to mask effect of recessive

Question 16

Explain why colour blind is considered a sex linked disease

Answer 16

More common in males than females
No male carrier only females

Question 17

Test cross

Answer 17

-Test carried to find out the genotype of an individual with dominant phenotype for a particular gene
-By crossing it with a known homozygous recessive genotype for the same gene

Question 18

Limitations of test cross

Answer 18

1.Cant do it on humans
2.Need to have a large number of offsprings, as by chance none of the gametes carrying recessive allele were successful in fertilisation

Question 19

Compare between mitosis and meiosis

Answer 19

Both are nuclear division
Mitosis:
Nuclear division that give to genetically identical daughter cells
-Happens in all body cells
-Produces 2 genetically identical daughter cells
-Each nucleus has a diploid number of chromosome
Role:
1. Growth and tissue repair
2. Replacement of damaged cells
3.Asexual reproduction

Meiosis:
Reduction division in which number of chromosomes are reduced from diploid to haploid, resulting in genetically different daughter cells
-Happens in reproductive organs
-Produces 4 genetically non identical daughter cells
-Each nucleus has a haploid number of chromosomes
Role:
Formation of gametes for sexual reproduction
A)Halves number of chromosomes from diploid to haploid
B)Gives genetic variation

Question 20

Why meiosis is needed in production of gametes

Answer 20

1.Meiosis is a reduction division
-Number of chromosomes are reduced from diploid to haploid
-So upon fertilisation, diploid number of chromosomes are restored
-without doubling in each generation
-Ensuring genetic stability

2.Meiosis causes variation
3.Increases chance of recessive allele to be expressed

Question 21

Why meiosis cause variation

Answer 21

1.Divides number of chromosome from diploid to haploid
2.Producing genetically non identical cells
3.So upon fertilisation which happens randomly
4.where male and female nuclei fuse
5.Zygote receives one set of chromosomes from father and another from mother

Question 22

Stem cells

Answer 22

Unspecialised cells that divide many times by mitosis, then differentiate and specialise into specific cells by turning on certain genes

Question 23

Compare between embryonic and adult stem cells

Answer 23

Embryonic stem cells:
Have the ability to differentiate into any type of cells
uses of embryonic stem cells:
-Treatment of some diseases as diabetes
-Its ethically not accepted by some people

Adult stem cells:
Have the ability to differentiate into limited types of cells
-Found in bone marrow skin and lining of alimentary canal

Question 24

Some cells in shoot tips become leaf and others become cells in stem or flower
Explain why its important that only some of genes in cell A are expressed in these cells

Answer 24

-Plant has stem cells
-They are unspecialised cells that divide many times by mitosis and become specialised
-Where specific genes are activated
-These genes code for specific protein to give specific characteristics
-While other genes remain deactivated as their function arent needed
-Resulting in plant having different specialised cells, tissue, organs with different function

Question 25

Variation

Answer 25

Differences among members of same species

Question 26

Compare between the two types of variation

Answer 26

Discontinuous variation: -Non measurable -Affected only by genes and not by environmental factors -Limited phenotypes with no intermediate -(represented on bar chart, e.g. blood group) Continuous variation: -Measurable -Affected by genes and environmental factors -Range of phenotypes with intermediates (represented on a histogram e.g. height, body mass, IQ)

Question 27

Causes of genetic variation

Answer 27

A).Meiosis: 1. It involves the production of gametes 2. By reduction division 3. Reducing number of chromosomes from diploid to haploid 4. Producing genetically non identical cells B).Fertilisation: 1.Happens randomly 2.When female and male nuclei fuse together 3.Forming genetically different individual which result from receiving 1 set of chromosome from each parent C).Mutation: Sudden random change in genetic material due to exposure to 1.Ionisng radiation 2.Chemicals

Question 28

Types of mutation

Answer 28

1.Gene mutation Sudden random change in base sequence producing a new allele coding for a different protein 2.Chromosomal mutation Chromosomes cant divide equally (mainly in females)

Question 29

Explain how mutation in gene coding causes a change in activity of this protein (enzyme)

Answer 29

1.Mutation in gene coding for protein causing a change in base sequence 2.Resulting in a new allele 3.Producing different mRNA 4.Coding for different sequence of amino acids 5.Resulting in different protein 6.Enzyme's active site shape will shape, no longer commentary with substrate

Question 30

Natural selection process

Answer 30

1. There is variation 2. Variation is due to meiosis/ fertilisation/ mutation 3. Selection pressure 4. Those who have favourable characteristic are able to survive 5. Those who have less favourable characteristic will die 6. So survival of the fittest , those who have favorable trait will grow and reproduce 7. Pass on the mutant allele to the coming generations 8. By natural selection

Question 31

Importance of variation

Answer 31

1.Allows adaptation -Allowing selection and evolution 2.Help reduce competition -Increase survival chance and reduce extinction 3.Increase in gene pool and biodiversity

Question 32

Artificial selection by selective breeding

Answer 32

1.Decide what characteristics needed for next generation: 2.Choose parents with desired features and breed them Plant: transfer the pollen grain using brush Animal: Isolate or by artificial insemination 3.Select from offsprings those showing desired featured and breed again 4.Repeat the crossing over many generation

Question 33

Why repeat crossing and selection over many generations

Answer 33

To reduce variation Increasing homozygosity To maintain desired features To ensure the coming generations will continue to show the desired trait

Question 34

Compare between Natural selection and Artificial selection

Answer 34

Natural selection: 1.Caused by the environment 2.Species are better adapted 3.Increase fitness 4.Maintains genetic variation 5.Random mating 6.Slower 7.More biodiversity Artificial selection: 1.Man made selection 2.Less adapted 3.Doesnt increase fitness 4.Less genetic variation 5.Selective breeding 6.Fater process 7.Less biodiversity