2.5 - inheritance

Question 1

what’s a gene

Answer 1

length of DNA on a chromosome that codes for the production of one or more polypeptide chains + functional RNA

Question 2

define genotype

Answer 2

genetic constitution of an organism

Question 3

define phenotype

Answer 3

expression of an organisms genetic constitution, combined with/ its interaction within the environment

Question 4

what’s a locus

Answer 4

fixed position on a DNA molecules occupied by a gene

Question 5

what’s an allele

Answer 5

different forms of particular gene, found at same locus on chromosome
single gene can have many alleles

Question 6

define homozygous

Answer 6

having two identical alleles of a gene
e.g: FF or ff

Question 7

define heterozygous

Answer 7

faving two different alleles of a gene
e.g: Ff

Question 8

what’s a dominant allele

Answer 8

• allele always expressed
• represented w/ capital letter, e.g: F

Question 9

what’s a recessive allele

Answer 9

• allele only expressed in absence of dominant allele, only expressed if 2 copies present
• represented w/ small letter, e.g f

Question 10

what’s meant by codominant alleles

Answer 10

2 dominant alleles that both contribute to phenotype, either by showing blend on both characteristics, or characteristics appearing together

Question 11

what’s an autosome

Answer 11

chromosome not an X or Y chromosome

Question 12

what’s a sex chromosome

Answer 12

chromosome determining sex of an organisms
e.g: X + Y chromosomes in humans + other mammals

Question 13

what’s the F1 generation

Answer 13

first generation of offspring resulting from cross of 2 individuals in parental generation

Question 14

what’s the F2 generation

Answer 14

second generation of offspring resulting from cross of 2 individuals in F1 generation

Question 15

define monohybrid inheritance

Answer 15

where one phenotype characteristic is controlled by a single gene

Question 16

what’s mendels first law of inheritance

Answer 16

• law of segregation
• alleles separate randomly into gametes
• each parent passes one allele to their offspring

Question 17

what’s mendels second law of inheritance

Answer 17

• law of independent assortment
• alleles of genes assortment independently of other genes during gamete formation

Question 18

PKU is a recessive condition
two heterozygous parents have offspring
predict proportion of offspring that will have PKU

Answer 18

75% chance of normal phenotype
25% chance of PKU phenotype

Question 19

what’s the purpose of a test cross

Answer 19

used to determine whether an individual w/ dominant trait is heterozygous or homozygous domiannt

Question 20

describe how a test cross is carried out

Answer 20

• individual of unknown genotype bred w/ homozygous recessive individual
• offspring phenotypes observed to determine genotype of unknown individual

Question 21

define dihybrid inheritance

Answer 21

determination of trait by inheritance of 2 genes

Question 22

what does mendelian inheritance assume

Answer 22

genes involved aren’t linked

Question 23

what’s meant by sex-linkage

Answer 23

• allele located on one of the sex chromosomes
• expression depends on sex of individual

Question 24

give example of phenotype which shows sex-linkage

Answer 24

• haemophilia
• DMD

Question 25

describe haemophilia

Answer 25

• X-liked recessive condition
• results in excessive bleeding + blood too slow to clot

Question 26

describe DMD

Answer 26

• X-linked recessive condition
• characterised by muscle degeneration + weakness

Question 27

why are haemophilia + DMD more common in males

Answer 27

they’re X-linked recessive conditions
males only inherit one X chromosome so are more likely to express the gene in their phenotype

Question 28

what’s linkage

Answer 28

• two or more genes positioned on same autosome
• unlikely to be separated by crossing over during meiosis so often inherited together

Question 29

what’s the chi squared test

Answer 29

statistical test used to determine whether difference between observed + expected data is due to chance or real effect
can be used to compare expected phenotypic ratios w/ observed ratios

Question 30

hows a chi squared test performed

Answer 30

1. make null hypothesis
2. used mendelian ratios to calculate expected numbers
3. calculate chi squared value using chi squared equation
4. calculate degrees of freedom
5. select appropriate significant level (usually 0.05)
6. find critical value
7. compare chi squared value w/ critical value
8. accept or reject null hypothesis

Question 31

how are degrees of freedom calculated

Answer 31

number of categories minus 1

Question 32

if chi squared value is greater than or equal to critical value, is null hypothesis accepted or rejected

Answer 32

rejected

Question 33

what is meant if null hypothesis is rejected

Answer 33

theres a significant difference between the observed + expected results

Question 34

if chi squared value is less than critical value, is null hypothesis accepted or rejected

Answer 34

accepted

Question 35

what is meant if null hypothesis is accepted

Answer 35

no significant difference between observed + expected results
results occurred due to chance

Question 36

what’s a mutation

Answer 36

• alteration to volume, arrangement, or structure of DNA
• may affect single gene or whole chromosome

Question 37

when do most mutations occur

Answer 37

• crossing over in prophase I
• non-disjunction in anaphase I + II

Question 38

what’s a gene mutation

Answer 38

• change to at least one nucleotide base in DNA or arrangement of bases
• may occur spontaneously during DNA replication + can be beneficial, damaging, or neutral

Question 39

give an example of condition caused by gene mutation

Answer 39

sickle cell anaemia

Question 40

describe sickle cell anaemia

Answer 40

• recessive genetic disorder caused by substitution mutation on chromosome 11
• results in abnormal haemoglobin which distorts red blood cells

Question 41

what’s a chromosome mutation

Answer 41

change in structure or number of chromosomes, affecting many genes

Question 42

give an example of condition caused by a chromosome mutation

Answer 42

down syndrome

Question 43

describe down syndrome

Answer 43

• genetic disorder characterised by delayed development + learning disabilities
• due to non-disjunction, affected individual possesses 3 copies of chromosome 21

Question 44

what’s chromosome nondisjunction

Answer 44

failure of homologous chromosomes to separate in meiosis I or sister chromatids to separate in meiosis II
results in gametes w/ one extra or less chromosome than normal

Question 45

what’s a mutagen

Answer 45

chemical, biological, or physical agent that increases rate of gene mutations above normal level

Question 46

give examples of mutagens

Answer 46

• ionising radiation (gamma radiation, UV, X-rays)
• chemicals (e.g: polycyclic hydrocarbons)

Question 47

what’s a carcinogen

Answer 47

type of mutagen that causes cancer

Question 48

what’s an oncogene

Answer 48

mutations of proto-oncogenes that are activated continuously, resulting in uncontrolled cell division

Question 49

define epigenetics

Answer 49

study of changes in gene expression that aren’t due to alterations in nucleotide base sequence of DNA

Question 50

how can histone modification affect gene expression

Answer 50

• alteration of histones by addition of methyl, acetyl, or phosphate groups
• increases or decreases gene expression by causing histone to coil more tightly or loosely

Question 51

how can DNA methylation affect gene expression

Answer 51

• addition of methyl (CH3) group to cytosine bases
• prevents recognition of bases, reducing gene expression