Genetic Diversity - A10

Question 1

What does it mean if body cells have the diploid no. of chromosomes?

Answer 1

They contain two of each chromosome (a pair) -> 1 from the mother and 1 from the father

Question 2

True or false: each pair of chromosomes are the same size and contain the same genes

Answer 2

True -> could have different versions pf the same alleles

Question 3

What are pairs of matching chromosomes called?

Answer 3

homolagous pairs

Question 4

How many homologous pairs do humans have?

Answer 4

-23 homologous pairs
-46 is the diploid number in humans

Question 5

What are the gametes and males and females respectively?

Answer 5

males - sperm
females - egg

Question 6

Are gametes haploid or diploid?

Answer 6

haploid - contain one copy of each chromosome in a homologous pair

Question 7

What is the human haploid number?

Answer 7

23

Question 8

What happens to the gametes during fertilisation?

Answer 8

The two gametes’ nuclei fuse during fertilisation, forming a zygote

Question 9

What happens to the zygote during fertilisation?

Answer 9

it divides by mitosis to make an embryo

Question 10

Is the zygote haploid or diploid?

Answer 10

diploid zygote made from haploid gametes

Question 11

How is fertilisation random?

Answer 11

Any sperm can fertilise any egg - fertilisation is random/random fusion of gametes -> genetic diversity increases by producing new allele combinations

produces zygotes with different combinations of chromosomes to both parents

Question 12

What are the stages of meiosis 1(the first division)

Answer 12

prophase 1 :
-DNA condenses and becomes visible
-(DNA replication occurs in interphase) so chromosomes consist of two sister chromatids joined by a centromere
-crossing over occurs
-spindle forms
-nuclear envelope breaks down
metaphase 1:
-homologous chromosome pairs/bivalents line up along the equator
anaphase 1 :
-homologous chromosome pairs/bivalents are pulled apart to opposite sides of the cell by spindle fibres
telophase 1:
-nuclear envelopes form around the two groups of chromosomes
cytokinesis:
-division of cytoplasm
-produces 2 haploid cells

Question 13

What happens to the chromosome in meiosis 1?

Answer 13

The chromosome number is halved

Question 14

What are the stages of meiosis 2?

Answer 14

No interphase
prophase 2:
-nuclear envelope breaks down
-chromosomes condense and become visible
metaphase 2:
-chromosomes line up in single file along the equator
anaphase 2:
-sister chromatids are separated by spindle fibres to opposite poles
telophase 2:
-nuclear membranes form around each group of chromosomes
cytokinesis:
-cytoplasm divides creating 4 haploid gametes

Question 15

What are the condensed mark points for meiosis?

Answer 15

-produces 4 genetically different haploid gametes
-DNA replication occurs
-homologous chromosomes pair up and are separated
-1st division occurs
-sister chromatids are separated
-2nd division occurs

Question 16

What is meiosis used for?

Answer 16

cell division to produce gametes in the reproductive organs of multicellular, eukaryotic organisms

Question 17

What are the 4 ways of creating genetic variation in gametes, and which occur in meiosis?

Answer 17

1)mutation
2)random fertilisation
in meiosis:
3)crossing over of chromatids
4)independent segregation pf chromosomes

Question 18

How does crossing over of chromatids create genetic variation?

Answer 18

-during meiosis 1(between prophase 1 and metaphase 1)
-homologous pairs of chromosomes associate/formed a bivalent
-non-sister chromatids twist together forming chiasmata
-equal lengths of non-sister chromatids and therefore alleles are exchanged
-producing new combinations of alleles

Question 19

Define homologous pairs.

Answer 19

two chromosomes that carry the same gene

Question 20

How does independent segregation cause genetic variation?

Answer 20

-in metaphase 1
-each homologous pair of chromosomes is made of one maternal chromosome and one paternal chromosome
-when homologous pairs are separated in meiosis 1, it’s random which chromosomes from each pair ends up in which daughter cell
-the 4 cells produced by meiosis end up with different combinations of those maternal and paternal chromosomes -> maternal and paternal are reshuffled in different combinations

Question 21

What do the number changes mean in life cycles?

Answer 21

-need to be able to spot where meiosis is occurring in a life cycle you haven’t seen before
-stays the same :mitosis
-halves: meiosis
-doubles: fertilisation

Question 22

What is a mutation?

Answer 22

change in the base sequence of DNA

Question 23

What can cause mutations?

Answer 23

errors during DNA replication

Question 24

What can increase the rate of mutations?

Answer 24

mutagenic agents

Question 25

What are the 6 types of mutation?

Answer 25

substitution, addition, deletion, duplication, inversion, translocation

Question 26

What is a duplication mutation?

Answer 26

one or more bases are repeated

Question 27

What is an inversion mutation?

Answer 27

the sequence of bases is reversed e.g. GCC becomes CCG

Question 28

What is a translocation mutation?

Answer 28

A sequence of bases is moved from one location in the genome to another. This could be movement within the same chromosome or movement to a different chromosome

Question 29

What is the effect of mutations?

Answer 29

Change in DNA base sequence causes a change in the amino acid sequence of a polypeptide may change the final tertiary structure of the protein by changing the hydrogen/ionic/disulphide bonds formed, altering it's function

Question 30

Why do not all mutations effect the order of amino acids in the protein?

Answer 30

The degenerate nature of the genetic code means that some amino acids are coded for by more than one DNA triplet

Question 31

What happens if the number of bases in the DNA code has changed?

Answer 31

-additions, duplications, and deletions within a gene will almost always change the amino acid sequence of a polypeptide -these mutations all change the no. of bases in the DNA code -causes a frameshift in the base triplets that are downstream

Question 32

What are mutagenic agents?

Answer 32

-mutations occur spontaneously(DNA replication) -mutagenic agents increase the rate of a mutation -e.g. UV radiation, ionisation radiation, some chemicals, some viruses

Question 33

What happens when meiosis goes wrong? (chromosome mutations)

Answer 33

-meiosis can go wrong - cells produced have variations in the numbers of hole chromosomes or part chromosomes -e.g. one cell might end up with two chromosome 6s and the having none

Question 34

What can chromosome mutations caused by errors in meiosis lead to?

Answer 34

- lead to inherited conditions because the errors are present in the gametes -example -> chromosome non-disjunction - a failure of the chromosomes to separate properly -another example is Down's Syndrome

Question 35

What is natural selection?

Answer 35

Mutation Variation Adventageous allele ->characteristic Out compete(differential reproductive success) Survive Reproduce Inherit advantageous allele Many generations Allele frequency changes (increase/decrease)

Question 36

What happens if the advantageous allele is useful?

Answer 36

if allele is useful the allele will code for a protein and therefore a characteristic which is advantageous for survival

Question 37

What are the different types of adaptation?

Answer 37

-Behavioural -> acts in a certain way to increase the chance of survival -physiological -> process inside the organism's body that increase it's chances of survival -anatomical -> structural features of an organism's body which increase it's chances of survival

Question 38

What is stabilising selection?

Answer 38

-individuals with alleles for characteristics towards like middle of the range are more likely to survive and reproduce(passing on favourable alleles) -selection pressures at both ends of the distribution -ultimately reduces the range of possible phenotypes by eliminating the extreme alleles and therefore extreme phenotypes -occurs when the environment isn't changing

Question 39

What is directional selection?

Answer 39

-individuals with alleles for a single extreme phenotype are more likely to survive and reproduce(passing on favourable allele) -could be in response to an environmental change -so the frequency of that allele will increase in the population

Question 40

Define genetic diversity.

Answer 40

The number of different alleles of genes in a species or population

Question 41

If there is a large number of alleles, is there a small or large genetic diversity?

Answer 41

large genetic diversity

Question 42

Whys is genetic diversity important?

Answer 42

low genetic diversity = population at risk of being wiped out by a change in environment/new selection pressures(e.g. disease)

Question 43

How is genetic diversity increased?

Answer 43

-mutations in DNA forms new alleles - some can be advantageous and some can be harmful -different alleles being introduced into a population through migration - gene flow -genetic diversity allows natural selection to occur because some characteristics are more advantageous then others

Question 44

What is a genetic bottleneck?

Answer 44

-an event causes a bug reduction in a population -reduces the number of different alleles in the gene pool and reduces allele frequency and therefore genetic diversity -survivors reproduce and a larger population is created from a few individuals ->meaning less similar alleles->less able to adapt to changes in the environment in the future

Question 45

What is the founder effect?

Answer 45

-a few organisms from a population start a new colony(often due to migration, causing a geographical isolation) and there are only a small number of different alleles in the initial gene pool -the allele frequency in the new population may be very different to allele frequency in the original population e.g. an allele that was quite rare in the original population may be more common in the new colony -sometimes lead to higher incidence of genetic disease