Genetics

Question 1

Genes

Answer 1

units of DNA coding for a particular piece of information

Question 2

Chromosomes

Answer 2

segments of DNA which also contain proteins

Question 3

Cell cycle

Answer 3

• contains interphase and division

Question 4

Interphase

Answer 4

• G1: cell makes components that allows the cell to divide to make two identical cells
• S: DNA is synthesised as each cell has to have its own copy of genetic material
• G2: cell continues to grow

Question 5

Prophase

Answer 5

• chromosomes condense

- each chromosome made from 2 chromatids joined at a region called the centromere

Question 6

Telomere

Answer 6

• region at the end of a chromosome

- protects chromosome from damage

Question 7

Metaphase

Answer 7

• chromosomes line up along the metaphase plate of the cell as a spindle has formed
• fibres extend down from opposite poles to the middle of the cell and grab hold of the centromere
• spindle fibres attach to the kinetochore

Question 8

Kinetochore

Answer 8

• complex of proteins surrounding the centromere

- where spindle fibres attach to

Question 9

Spindle fibres

Answer 9

• forms of proteins called microtubules

- initiated from opposite poles of the cell

Question 10

Anaphase

Answer 10

• once spindle fibres attach to kinetochore, microtubules contract and pulls them apart to opposite sides

Question 11

Telophase

Answer 11

• 2 nuclei are produced

- 2 daughter cells are formed

Question 12

Meiosis

Answer 12

Meiosis I

• each chromosome is replicated so sister chromatids are formed
• homologous chromosomes form bivelant with each other
• spindles form, attach to centromeres, pull chromosomes apart

Meiosis II
- starts with 2 products which have one copy of each chromosome
- spindle fibres form and attach to centromere
fibres shorten and pull apart chromatids
- 4 haploid products are formed

Question 13

Diplotene

Answer 13

• stage during Prophase I
• there are regions within bivelants where sister chromatids interact
• parts of sister chromatids break and rejoin by crossing over
• forms chiasma

Question 14

Independent assortment

Answer 14

• allows different products to be formed from different combinations of chromosomes
• bivelants assort independently

Question 15

Wild-type

Answer 15

common form of a character (normal)

Question 16

Mutant

Answer 16

rare form of a character (affected)

Question 17

Homozygous

Answer 17

2 identical alleles

Question 18

Heterozygous

Answer 18

2 different alleles

Question 19

Phenotype

Answer 19

the appearance controlled by combination of alleles

Question 20

Dominant inheritance

Answer 20

if an affected individual has an affected parent

Question 21

Test cross

Answer 21

used to determine genotype of an individual who is showing the dominant feature phenotype

Question 22

Pleitropy

Answer 22

a single gene mutation influences multiple phenotypes and characteristics

Question 23

Expressivity

Answer 23

variation in degree to which the phenotype is shown

Question 24

Penetrance

Answer 24

individual in one generation can have the mutant genotype, but do not express the phenotype

Question 25

Incomplete dominance

Answer 25

- form of inheritance where one allele for a specific trait is not completely expressed over its paired allele - results in third phenotype which physical trait is a combination of both

Question 26

Complete dominance

Answer 26

- form of dominance in heterozygotes | - allele regarded as dominant completely overrides effect of allele that is recessive

Question 27

Sex linked chromosomes

Answer 27

genes on the X chromosome are said to be sex linked

Question 28

Epistasis

Answer 28

interaction of phenotypes controlled by different genes, but affect the same character

Question 29

Complementation test

Answer 29

- genetic experiment that indicates whether two mutations affect one gene or two different genes - one gene = no complementation - two genes = complementation

Question 30

Pseudo-autosomal region

Answer 30

- regions at each end of the Y chromosome, which allow it to align with the X chromosome

Question 31

SRY gene

Answer 31

- determines male development

Question 32

Aneuploidy

Answer 32

- when there is an abnormal number of chromosomes - eg. down syndrome has 47 chromosomes as there are 3 copies of chromosome 21 1 copy - monosomy 2 copies - disomy 3 copies - trisomy 4 copies - tetrasomy

Question 33

Trisomy

Answer 33

- results in death in other chromosomes apart from 13, 18 and 21 - occurs through problem in meiosis - non-dysjunction is failure to separate either homologous chromosomes or sister chromatids

Question 34

Barr bodies

Answer 34

dark staining region representing inactive x chromosome

Question 35

X chromosome inactivation

Answer 35

- known as dosage compensation - prevents females having too much of same gene expressed - one copy of each gene is switched off in either chromosome

Question 36

Polyploids

Answer 36

- organisms with extra copy of chromosomes - fatal in humans, acceptable in plants - results in larger appearance

Question 37

Mutations

Answer 37

occur when DNA sequence is changed

Question 38

Epigenetics

Answer 38

study of change in activity of genes that do not result from changes in DNA sequence

Question 39

Genomic imprinting

Answer 39

- expression of different genes is determines by with parent it is inherited from - imprint is erased in germline cells - imprint is maintained in somatic cells

Question 40

Epigenetic mark

Answer 40

mechanism that switches off X chromosome

Question 41

Cell autonomous phenotype

Answer 41

- determined by the genotype of the cell it has formed from | - only cells with mutant genotype show mutant phenotype

Question 42

Cell non-autonomous phenotype

Answer 42

- cells can show mutant phenotype regardless of their genotype

Question 43

Hardy Weinberg equilibrium

Answer 43

- no change in allele frequency from one generation to another p2 + 2pq + q2 = 1

Question 44

Hardy Weinberg true if:

Answer 44

``` - there is random mating there is no selection - there is no migration - there is no mutation - population is large ```

Question 45

Anisogamy

Answer 45

gametes differ in size

Question 46

Hermaphroditism

Answer 46

- organism has both male and female gametes | - favoured if mate searching efficiency is low