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AQA A-level Biology > topic 7:inheritance > Flashcards

topic 7:inheritance Flashcards

1
Q

what are homologous chromosomes?

A

sperm and egg both contribute a set of chromosomes to offspring
known as homologous pairs because they carry the same genes
but are genetically different because of different alleles

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2
Q

total number of chromosomes

A

46(2n)
diploid

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3
Q

number of gametes in sperm and egg cells

A

haploid (n)
23

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4
Q

genotype

A

the genetic constitution of an organism

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5
Q

pheontype

A

the expression of the genetic constitution and its interaction with the environment

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6
Q

allele

A

a different form of the same gene
codes for a different version of the same characteristic
arise due to random mutations

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7
Q

dominant allele

A

always expressed in the phenotype

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8
Q

recessive allel

A

expressed in the phenotype only in the presence of another identical allele

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9
Q

homozygous

A

if an organism carries 2 identical copies of the same gene
e.g. AA,aa

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10
Q

heterozygous

A

if an individiual possess 2 different copies of the same gene
e.g. Aa

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11
Q

how are alleles represented?

A

using letters
capital letters represent dominant alleles
recessive for the same gene represented by lower case of same letter

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12
Q

what is monohybrid inheritance?

A

the inheritance of a single characteristic (gene) controlled by different alleles

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13
Q

ratio of phenotypes in monohybrid inheritance?

A

3:1 if heterozygotes are crossed

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14
Q

what is a Punnett square?

A

square grid to present results of genetic crosses by showing genotype of offspring
always draw circles round gametes

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15
Q

what is dihybrid inheritance?

A

inheritance of 2 characteristics(genes) controlled by different alleles located on different chromosomes

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16
Q

what are dihybrid crosses used for?

A

to investigate the simultaneous inheritance of 2 different characteristics

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17
Q

there is a pattern of offspring produced in dihybrid crosses, as there is in monohybrid inheritance. who first discovered these patterns?

A

Gregor Mendel in the 19th century
he was a monk famous for carrying out thousands of genetic crosses on pea plants

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18
Q

how do you write out the parental gametes in dihybrid inheritance?

A

one allele from each pair in each gamete
in organisms there are 2 copies of every gene, but the gametes will have one of the copies for every single gene

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19
Q

the ration of the F2 generation in any dihybrid cross

A

9:3:3:1
dominant:gene 1 d, gene 2 r: gene 1 r,gene 2 ;recessive

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20
Q

what is a test cross?

A

a method used to work out the unknown genotypes of individual organisms

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21
Q

when is a test cross carried out?

A

between an individual of unknown genotype showing a dominant phenotype and individual of recessive phenotype

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22
Q

what is codominance?

A

occurs when neither allele for a characteristic is recessive so they are Both expressed

23
Q

what is incomplete or partial codominance?

A

an intermediate phenotype can be produced in some circumstances when the offspring is heterozygous for both dominant alleles
both are expressed

24
Q

what does it mean to have multiple alleles?

A

different versions of the same gene on the same locus
more different alleles means more different phenotypes

25
Q

what is sex-linked inheritance?

A

alleles for sex linked characteristics are located on the sex chromosomes
there are 23 pairs of chromosomes,22 are autosomes and the last 2 are the sex chromosomes
there are several characteristics coded for by alleles on these
the pattern of how these are inherited is sex-linked inheritacne

26
Q

what gametes do females produced

A

all gametes will have x chromosome

27
Q

what gametes do males produce

A

one X and one Y
half gametes with each

28
Q

why are males more likely than females to show recessive phenotypes for sex linked genes?

A

males only have one X chromosome so often only have one allele for sex-linked genes
because they only have one copy, they express the characteristic of this allele even if its recessive

29
Q

what are X linked conditions?

A

genetic diseases and conditions caused by faulty alleles located on the X chromosome
includes colourblindness and Haemophilia

30
Q

why cant males be carriers of recessive conditions?

A

they only have one X chromosome so they either have it or don’t

31
Q

when will a female be affected by a recessive condition?

A

if father is a recessive allele, and mother is a carrier of has it herself
if mother is affected, all sons will have it and daughters all be carriers

32
Q

what is a pedigree chart?

A

an alternative method for presenting information about inheritance
genetic pedigree diagrams show how an inherited trait runs in a group of related individuals

33
Q

what does a pedigree chart show?

A

genotypes and phenotypes in different generations
gives information on how allele are inherited

34
Q

how do you answer a question including a pedigree chart?

A
  • think of it like a puzzle
  • work out genotypes you are sure of and write them down next to the individual
    -this helps to identify patterns between parent and offspring
35
Q

how are females represented in pedigree charts?

A

circles

36
Q

how are males represented in pedigree charts?

A

squared

37
Q

how are carriers/heterozygotes represented in pedigree charts?

A

shape will be half one colour, half other

38
Q

how does a pedigree diagram show a recessive allele

A

if unaffected parents give rise to an affected individiual

39
Q

what is autosomal linkage

A

if 2 or more genes are carried on the same autosome
autosomes are the remaining 22 chromosomes that arent sex linked

40
Q

what are unlinked genes?

A

genes located on different chromosomes

41
Q

linkage groups

A

a set of genes on different loci on the same gene that tend to be inherited together
except for crossing over

42
Q

what happens to linked genes in meiosis?

A

assuming no crossing overall linked genes stay together during meiosis so pass into the gametes and offspring together and don’t segregate

43
Q

what happens to genes on different chromosomes?

A

independent segregation can occur as genes are carried on different pairs of homologous chromosomes

44
Q

what happens if crossing over occurs

A

variety of gametes increase

45
Q

when is it easier for crossing over to occur?

A

when genes are far apart on a chromosome

46
Q

when is it harder for crossing over to occur?

A

when different genes are close to each other

47
Q

what does it mean if chromosomes are recombinant?

A

any point the genes have switched and have exchanges genetic material

48
Q

why is the chi-squared test used?

A

to look at the differences between categorical variables in populations
basically, what you expect vs what you see

49
Q

what is the null hypothesis?

A

the opposite of what you expect the experiment to show
it is rejected or accepted

50
Q

conclusion from the result of the chi-squared test if it is LESS than the critical value

A

the chi-squared is less than the critical value which means there is a greater than 5% probability that the results occurred by chance
we can accept the null hypothesis
there is no significant difference between observed and expected
w

51
Q

conclusion from the result of chi squared if it is GREATER than the critical value?

A

if it is greater than the critical value it means there is a less than 5% probability that results occurred by chance
reject null hypothesis
there is a significant difference between observed and expected

52
Q

define epistasis

A

the influence of one gene on the expression of another

53
Q

what does epistasis result in

A

a combination of genotypes in a hierarchy with each allele more dominant than another
leads to a variety of different phenotypes

AQA A-level Biology (32 decks)

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