4.3 inheritance Flashcards by Ellie Thomas

define homozygous dominant
define homozygous recessive

genotype contains 2 copies of the dominant allele
genotype contains 2 copies of the recessive allele

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what is a back cross?

crossing the organism with another that is homozygous recessive for the trait

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what does a back cross determine?

whether an organism is homozygous or heterozygous

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how would you know if the parent is heterozygous from doing a back cross?

if any of the offspring show the homozygous recessive trait in the phenotype

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what is mendels 1st law of genetics?
define it

the law of segregation
the characteristics of an organism are determined by factors (genes) which occur in pair. only 1 member of a pair of factors can be represented in a single gamete

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define monohybrid inheritance

the inheritance of a single pair of contrasting characters

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define co-dominance

2 alleles which are both expressed in the phenotype

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what is incomplete dominance?

phenotype of heterozygote is intermediate between the 2 parental phenotypes

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define incomplete dominance in a simpler way
give an example

both alleles contribute to a blended phenotype
a red flower crossed with a white flower will make a pink flower

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what does each allele code for in incomplete dominance?

one codes for an enzyme which catlyses something
the other codes for an enzyme without catalytic properties

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define dihybrid inheritance

the inheritance of 2 separate genes which are unlinked

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what is mendels 2nd law of genetics?
define it

the law of dominance
an organism with alternate forms of a gene will express the form that is dominant

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what is mendels 3rd law of genetics?
define it

law of independent assortment
genes for different traits are sorted seperately from one another so that the inheritance of one trait is not dependent on the inheritance of another

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what is the ratio for a heterozygous/dihybrid?

9:3:3:1

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what are recombinants?

a new combination of alleles is produced from combining one allele from 1 chromo with 1 allele from another chromo

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define sex linked inheritance

the inheritance of genes found on the sex chromosomes

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what are non sex chromosomes called?
how many pairs do we have?

autosomes
we have 22 pairs

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what are the 2 case studies for sex linked inheritance?

haemophilia
duchenne muscular distrophy (DMD)

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what does haemophilia do?
who are the carriers?

impairs the body’s ability to control blood clotting
females

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who is more likely to get haemophilia and why?

males as it’s an X chromosome disorder
males have XY so lack a ‘back up’ copy for the gene (another X)

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what is DMD caused by and what does this do?

caused by a lack of dystrophin protein which is a component of the glycoprotein stabilising the cell membrane of muscle fibres
(causes the muscle fibres to break down)

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what does DMD lead to?

a loss of muscle mass and weakness

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define a mutation

a change in the amount, arrangement or structure of the DNA in an organism

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what are the 2 types of mutations?

gene mutations
chromosome mutations

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what are the 2 ways that can increase the rate of mutation?

- ionising radiation - mutagenic chemicals e.g carcinogens cause cancer

what do mutations do to a population?

increase variation

what 2 things can increase the rate of mutation?

ionising radiation mutagenic chemicals e.g carcinogens cause cancer

what are the 4 ways in which a mutation can occur?

1. gene/point mutation 2. chromosome mutation 3. aneuploidy 4. polyploidy

what are the 4 ways in which a mutation can occur?

1. gene/point mutation 2. chromosome mutation 3. aneuploidy 4. polyploidy

define gene/point mutation

changes in the base sequence occurs if DNA is not sopied correctly in S phase (synthesis phase - DNA replicates) before cell division

define a gene/point mutation

changes in base sequence occurs if DNA is not copied correctly in S phase (synthesis phase - DNA replicates) before cell division

what can also happen in a gene/point mutation?

duplication - same base twice inversion - DNA bases exchange positions

what are the other 2 things that it can happen? what happens during them? | gene/point mutation

duplication - same base twice inversion - DNA bases exchange positions

what is a silent mutation?

change in base doesn't change the amino acid it codes for

define a silent mutation

change in a base doesn't change the amino acid it codes for

what can the deletion of a base cause? what is this?

a 'frame shift' - loss of single nucleotide

what can the deletion of bases cause? what is this?

'frame shift' - loss of a single nucleotide

what kind of mutations may cause cancer?

somatic

what kind of mutations may cause cancer?

somatic

what are the only mutations that can be inherited and what are they called?

only those that occur in the formation of gametes - germ cell mutation

define germ cell mutation

only those mutations which occur in the formation of gametes can be inherited

what are germ cell mutations the basis of and why?

discontinuous variation as they cause sudden and distinct differences

what are they the basis of? | germ cell mutation

discontinuous variation

what is an oncogene?

a gene that, when mutated or expressed at high levels, can turn a normal cell into a tumour cell

what are proto-oncogenes?

genes that if they mutate can become oncogenes

what do they increase the rate of? | oncogenes

cell division

what are tumour suppressor genes?

protective genes that control cell growth by suppressing cell division

what is a proto-oncogene?

genes that if they mutate can become oncogenes

what do oncogenes increase?

the rate of cell division

what are tumour supressor genes?

protective genes that control cell growth by suppressing cell division

what happens? | sickle cell

red blood cells deform and block capillaries when oxygen levels are low

what can mutations to tumour suppressor genes and oncogenes cause?

cancer

what is an example of a point mutation?

sickle cell

what gene is on what chromosome? | sickle cell

HBB gene on chromosome 11

what does the mutation involve? what does this change? | sickle cell

a substitution of an A for a T changes 1 amino acid

what is the allele for normal haemoglobin? what is the allele for mutant haemoglobin? | sickle cell

HbA HbS

what is the co dominant allele which reduces the ability of RBC to carry oxygen? what can this lead to? | sickle cell

HbSHbS lead to death

what is the heterozygous co dominant allele? if someone has this, what does it mean? | sickle cell

HbAHbS they have at least 50% haemoglobin with trait less severe symptoms

what is a chromosome mutation?

change in chromosome numbers

what is this usually the result of? what stage does it happen at? | chromo mutation

errors occuring during meiosis happens at anaphase 1 or 2 when homologous chromos or chromatids fail to seperste correctly

what autosome is down syndrome?

trisomy 21

define aneuploidy what does it result in?

the loss or gain of a single chromo results in the formation of gametes with either one too many or one too few chromos

define polyploidy

changes in the number of whole sets of chromosomes

what 3 things can polyploidy be caused by?

- a defect at the spindle (anaphase - too many chromatids move to a pole) - 2 diploid gametes fuse (tetraploid) - cytokinesis doesn’t happen - endomitosis

define epigenetics

the control of gene expression by factors other than changes in the DNA base sequence

DNA can be modified post - replication. explain this

this doesn't change the DNA base sequence but changes the ability of a gene to be transcribed during protein synthesis

what is DNA methylation?

the addition of methyl groups to bases prevents those bases from being recognised and reduces the ability of that gene to be expressed

what are used to organise the DNA in a chromosome?

histone proteins

how can histone proteins be modified? (hint: coiling)

if the histone coils more tightly it can prevent gene expression or if it coils more loosely it can increase gene expression

what is the chi2 test used for?

determining the validity of results of experiments by comparing observed and expected data

during the chi2 test, how do you determine whether you accept or reject the null hypothesis?

if value is less than critical value (0.05) - accept as there's no significant difference if value is more than critical value - reject as there is significant difference and the probability is lower of it being due to chance