4.3. Inheritance

Question 1

gene??

Answer 1

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

Question 2

genotype??

Answer 2

the genetic constitution of an organism

Question 3

phenotype??

Answer 3

the expression of an organism’s genetic constitution, combined w/ its interaction w/ the environment

Question 4

locus??

Answer 4

the fixed position on a DNA molecule occupied by a gene

Question 5

allele??

Answer 5

diff forms of a particular gene, found at the same locus on a chromosome, a single gene could have many alleles

Question 6

homozygous??

Answer 6

having 2 identical alleles of a gene e.g. FF or ff

Question 7

heterozygous??

Answer 7

having 2 diff alleles of a gene e.g. Ff

Question 8

dominant allele??

Answer 8

an allele that is always expressed, represented w/ a captial letter

Question 9

recessive allele??

Answer 9

an allele that is only expressed if 2 copies are present, represented w/ a small letter

Question 10

codominant alleles??

Answer 10

2 dominant alleles that both contribute to the phenotype, either showing a blend of both characteristics or the characteristics appearing together

Question 11

autosome??

Answer 11

a chromosome that is not an X or Y chromosome

Question 12

sex chromosome??

Answer 12

a chromosome that determines the sex of an organism e.g. X & Y chromosomes in humans & other mammals

Question 13

F1 generation??

Answer 13

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

Question 14

F2 generation??

Answer 14

the second gen of offspring resulting from the cross of 2 individuals in the F1 gen

Question 15

monohybrid inheritance??

Answer 15

where one phenotypic characteristic is controlled by a single gene

Question 16

Mendel’s first law of inheritance??

Answer 16

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

Question 17

Mendel’s second law of inheritance??

Answer 17

-law of independent assortment
-the alleles of genes assort independently of other genes during gamete formation

Question 18

purpose of a test cross??

Answer 18

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

Question 19

describe how a test cross is carried out??

Answer 19

-an individual of unknown genotype is bred w/ a homozygous recessive individual
-offspring phenotypes observed to determine the genotype of the unknown individual

Question 20

dihybrid inheritance??

Answer 20

the determination of a trait by the inheritance of two genes

Question 21

What does Mendelian inheritance assume??

Answer 21

it assumes that the genes involved are not linked

Question 22

sex-linkage??

Answer 22

-an allele is located on one of the sex chromosomes
-its expression depends on the sex of the individual

Question 23

example of a phenotype which shows sex-linkage

Answer 23

-haemophilia
- Duchenne muscular dystrophy

Question 24

haemophilia??

Answer 24

• X-linked recessive condition
  -results in excessive bleeding & blood that is slow to clot

Question 25

Duchenne muscular dystrophy??

Answer 25

-X-linked recessive condition
-characterised by muscle degeneration & weakness

Question 26

why are haemophilia & Duchenne muscular dystrophy more common in males??

Answer 26

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

Question 27

linkage??

Answer 27

-2 or more genes positioned on the same autosome
-unlikely to be separated by crossing over during meiosis so often inherited together

Question 28

chi-squared test??

Answer 28

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

Question 29

how is the chi-square test performed??

Answer 29

-make a null hyp
-use median ratios to calc the expected numbers
-calc chi-squared value using chi-squared eqn
-calc degrees of freedom
-select approp sig level
-find crit val
-compare the chi-squared val w/ crit val
-accept or reject null hyp

Question 30

how is degrees of freedon calc??

Answer 30

the number of categories minus 1

Question 30

is chi-squared val is GREATER than or equal to the cirt val is null hyp accepted or rejected??

Answer 30

REJECTED

Question 31

what does it mean if null hyp is rejected??

Answer 31

there is a significant diff bet the observed & expected results

Question 32

if the chi-squared val is LESS than the crit val is the null hyp accepted or rejected??

Answer 32

ACCEPTED

Question 33

what does it mean if the null hyp is accepted??

Answer 33

the diff bet te observes & expected results is not significant the results occured due to chance

Question 34

mutation??

Answer 34

-an alteration to the vol arrangment or structure of DNA
-may affect a single gene or a whole chromosome

Question 35

when do most mutations occur??

Answer 35

-crossing over in prophase I
-non-disjunction in anaphase I & II

Question 36

gene mutation??

Answer 36

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

Question 37

an example of condition caused by a gene mutation??

Answer 37

sickle cell anaemia

Question 38

describe sickle cell anaemia??

Answer 38

recessive genetic disorder caused by a substitution mutation on chromosome 11
results in abnormal haemoglobin which distorts rbcs

Question 39

chromosome mutation??

Answer 39

a change in structure or number of chromosomes affecting many genes

Question 40

example of a condition caused by chromosome mutation??

Answer 40

Down’s syndrome

Question 41

describe Down’s Syndrome??

Answer 41

• genetic disorder characterised by delayed development & learning disabilities
  -due to non-disjunction an affected individual possesses three copies of chromosome 21

Question 42

chromosome nondisjunction??

Answer 42

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

Question 43

mutagen??

Answer 43

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

Question 44

examples of mutagens??

Answer 44

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

Question 45

what is a carcinogen??

Answer 45

a type of mutagen that causes cancer

Question 46

oncogene??

Answer 46

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

Question 47

epigenetics??

Answer 47

the study of changes in gene expression that are not due to alterations in the nucleotide base sequence of DNA

Question 48

how can histone modification affect gene expression??

Answer 48

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

Question 49

how can DNA methylation affect gene expression??

Answer 49

-addition of methyl (CH3) grp to cytosine bases
-prevents recognition of the bases, reducing gene expression