inheritance

Question 1

what is genetics?

Answer 1

study of the mechanism by which an organism inherits characteristics from its parents

Question 2

what is monohybrid inheritance?

Answer 2

inheritance of a single characteristic controlled by one gene

Question 3

what is mendel’s first law?

Answer 3

characteristics of an organism are determined by factors which occur in pairs
only one of a pair of factors can be present in a single gamete

Question 4

what is an allele?

Answer 4

variant nucleotide sequence for a particular gene at a given locus which codes for an altered phenotype

Question 5

what is a dominant or recessive allele?

Answer 5

dominant always expressed when present
recessive only expressed when dominant allele is absent

Question 6

what is a genotype?

Answer 6

all the alleles that individuals contain

Question 7

what is a phenotype?

Answer 7

appearance of an individual

Question 8

how do you test if a dominant phenotype is heterozygous or homozygous?

Answer 8

cross it with homozygous recessive
if homozygous dominant then all offspring will have dominant phenotype
if heterozygous then half of the offspring will show recessive phenotype

Question 9

what is pure breeding?

Answer 9

variety bred for several generations with itself so all individuals are homozygous (have same phenotype as parents)

Question 10

what is co-dominance?

Answer 10

both alleles express themselves equally in heterozygote phenotype
shows phenotype intermediate

Question 11

what is dihybrid inheritance?

Answer 11

simultaneous inheritance of 2 unlinked genes
genes located on different chromosomes
each gene will have 2 alleles

Question 12

what is the general phenotypic relationship when crossing RrYy with RrYy?

Answer 12

9:3:3:1

Question 13

what is incomplete dominance?

Answer 13

heterozygote phenotype is intermediate between that of 2 homozygotes
neither allele is completely dominant

Question 14

what is mendel’s second law?

Answer 14

either one of a pair of contrasted characters may combine with either of another pair
each member of a pair of alleles may combine randomly with either of another pair on a different chromosome

Question 15

what is the dihybrid test?

Answer 15

test a genotype by crossing it with an individual that is homozygous recessive for both genes

Question 16

what are multiple alleles?

Answer 16

more than 2 varieties forms a given gene

Question 17

what is a mutation?

Answer 17

a change in DNA
spontaneous random events that provide a source of material for natural selection and evolution

Question 18

what must happen for a mutation to be inherited?

Answer 18

must effect DNA of the gametes

Question 19

what are mutagens?

Answer 19

chemicals/radiation which increases rate of mutation
e.g. ionising radiation, chemicals

Question 20

what is a carcinogen?

Answer 20

mutagen that causes cancer

Question 21

what is chromosomal mutation?

Answer 21

large changes in chromosome structure or number
affects many genes
visible under light microscope

Question 22

what is a gene mutation?

Answer 22

small changes in base sequence, only affects one gene
result of a fault in gene replication

Question 23

how can substitution mutation affect genes?

Answer 23

maybe be silent if code is degenerate
may be neutral if amino acid altered is not essential to protein structure

Question 24

what does deletion mutation cause?

Answer 24

more servere
causes ‘frame shift’

Question 25

what does insertion mutation do?

Answer 25

more likely to result in non-functional protein

Question 26

what is sickle cell anaemia?

Answer 26

single base substitution in gene for beta haemoglobin causes quaternary structure of haemoglobin to change becomes insoluble at low O2 tensions tend to stick to other haemoglobin molecules poor at binding to oxygen homozygous is fatal heterozygous O2 level reduced by 20%

Question 27

what is down syndrome caused by?

Answer 27

non-disjunction of chromosome 21 during anaphase oocytes have extra chromosome

Question 28

what is polyploidy?

Answer 28

one gamete receives both sets of chromosomes gamete is fertilised and zygote produces has 3 sets of chromosomes

Question 29

what is cancer?

Answer 29

uncontrolled division of cells produces tumor

Question 30

what happens to malignant tumors?

Answer 30

cells may break off and be carried in blood to form secondary tumors

Question 31

what can cause cancer?

Answer 31

mutation in gene which would normally control cell division

Question 32

how does a mutated gene cause cancer?

Answer 32

tumor suppressor genes mutate so lack of proteins which would halt cell division proto-oncogens mutate and produce oncogene which release excess proteins to stimulate cell division mutations lead to lack of proteins involved in normal mechanism of cell death

Question 33

what is the importance of mutations?

Answer 33

increases variation in population most mutations are recessive to normal allele so must await replication in gene pool before expressed most gene mutations occur in junk DNA so do not influence phenotype

Question 34

what is sex linkage?

Answer 34

sex linked genes have loci on X chromosome

Question 35

what is autosomal linkage?

Answer 35

dihybrid cross where both genes are located close together on the same chromosome

Question 36

what is the importance of autosomal linkage?

Answer 36

2 genes on same chromosome so likely to be more common in parental combinations (linked)

Question 37

what is epigenetics?

Answer 37

involves heritable changes in gene function without changes to base sequence of DNA changes ability of gene to be transcriped

Question 38

what happens during heritable changes to genes?

Answer 38

change occurs after replication caused by variation in environment that alters gene expression

Question 39

how can transcription be inihibited?

Answer 39

increased methylation of DNA decreased acetylation of associated histones

Question 40

what is DNA methylation?

Answer 40

enzyme can add methyl groups to DNA base sequence bases are prevented from being recognised reduces ability of gene to be expressed

Question 41

where are methyl groups added to DNA?

Answer 41

cytosine nucleotide

Question 42

what is gene silencing?

Answer 42

more methyl groups causes DNA to become more tightly wound around histones transcription is inhibited

Question 43

what is acetylation?

Answer 43

acetylation of histones leads to gene activation histones get covered in chemical 'tags' tags accumulate through life determine shapes of histones increases acetylation causes histones to coil less tightly so increase transcription

Question 44

what is epigenome (tags)?

Answer 44

reason why identical twins do not stay identical

Question 45

what are histones?

Answer 45

proteins found in eukaryotic cells package DNA and help it condense chromosomes

Question 46

how are inactive genes made?

Answer 46

can be wrapped tightly and become inaccessible epigentic silencing