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Biology > Inheritance - M6 > Flashcards

Inheritance - M6 Flashcards

1
Q

Gene

A

A length of DNA that codes for the production of a polypeptide

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2
Q

Allele

A

A variant form of a particular gene

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3
Q

Locus

A

The position of a gene on a chromosome

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4
Q

Dominant

A

Represented with an upper case letter.
Has the same effect on the phenotype whether one or two alleles are present

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5
Q

Recessive

A

Represented with a lower case letter.
Only affects the phenotype if its homozygous

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6
Q

Codominant

A

Both alleles of one gene are dominant

Both alleles affect the phenotype in a heterozygous individual

Eg: white and red dominate allele = pink phenotype

As a result, both alleles are expressed in the phenotype of the organism if present.​

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7
Q

Heterozygous

A

A genotype where the two alleles are different. E. G: Aa

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8
Q

Homozygous

A

A genotype where the two alleles are the same. E.g: AA or aa

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9
Q

Heterogametic

A

Possession of two different sex chromosomes. E.g: XY in human males

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10
Q

Homogametic

A

Possession of the same sex chromosomes.

XX in human females

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11
Q

Genotype

A

The genotype of an organism refers to the alleles of a gene possessed by that individual.

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12
Q

Phenotype

A

The expression of the alleles, giving the individuals observable characteristic

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13
Q

Monohybrid cross

A

A genetic cross involving one gene

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14
Q

Dihybrid cross

A

A genetic cross involving two GENES (on different chromosomes)

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15
Q

Linkage

A

Two genes on the same chromosome are said to be linked

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16
Q

Sex linkage

A

characteristic is sex linked if the genes that code for it are Genes with a locus on one of the sex chromosomes. In humans normally on the X

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17
Q

Haemophilia A

A

A sex linked disease that stops blood clotting.
The gene is found on the X chromosome

caused by a recessive allele of a gene that codes for a faulty version of the protein factor VIII

X^H = normal allele
X^h = haemophillia allele

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18
Q

Sickle cell anaemia

A

An example of a disease caused by codominant alleles. The red blood cells change shape and can cause clots

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19
Q

Epistasis

A

when two genes on different chromosomes affect the same feature

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20
Q

F1 generation

A

When a homozygous dominant individual is crossed with a homozygous recessive individual the offspring

All of the F1 generation are heterozygous

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21
Q

F2 generation

A

The offspring produced when two of the F1 generation are crossed

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22
Q

Chi-squared

A

A statistical test to test the significance of the difference between observed and expected results

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23
Q

Genome

A

The sum total of genes in an Organism

24
Q

Expected ratio of F1 generation of heterozygous dihybrid cross (YyRr x YyRr)

A

9:3:3:1

25
Q

Expected ratio of recessive epistasis

A

9:3:4

26
Q

Dominant epistasis expected ratio

A

12:3:1

27
Q

Recessive epistatic alleles ​

A

If one GENE is recessive, it will mask the other GENE

e.g: (E.g. Flower pigment is controlled by two genes. Gene 1 codes for a yellow pigment (Y) and gene 2 codes for an enzyme that turns the yellow pigment orange (R)​

If a plant is homozygous recessive for the epistatic gene (yy) (yellow allele isn’t expressed) then it will be colourless, masking the colour of the orange gene (R))

28
Q

Dominant epistatic alleles​

A

When the epistatic allele is dominant, then having at least one copy will mask the expression of the other gene. ​

(E.g. Squash colour is controlled by two genes – the colour epistatic gene (W/w) and the yellow gene (Y/y)​)

If Ww or WW then squash will be colourless

if ww, Yy or YY = yellow, yy = green

29
Q

Autosome

A

not a sex chromosome

30
Q

autosomal linkage

A

Genes that are on the same autosome (not a sex chromosome)

genes on same autosome are said to be linked - they’ll stay together during independent assortment meiosis 1

Won’t happen if crossing over splits them up

-closer the genes are on the chromosome, the more linked they are

31
Q

most X linked conditions are found in ______

A

males

32
Q

chi squared test is used to

A

test if your results fit the pattern you expected

33
Q

Null hypothesis for chi squared

A

THere is no significant difference between the observed + expected results

34
Q

chi squared how to calculate degrees of freedom

A

The degrees of freedom can be worked out from the results. It is calculated by subtracting one from the number of classes

n-1

35
Q

example of Multiple Alleles for one gene

A

Blood type.

I^A , I^B , I^O

where A and B are codominant and O is recessive to both

36
Q

Blood type Genotype

I^A , I^B

gives phenotype :

A

Type AB

“Universal receivers as immune system sees both antigens as A and B (type o codes for no antigen)

37
Q

Why are Males more likely to be affected by sex linked diseases

A

Males have XY chromosome

More easily affected by alleles on X
(X chromosome is larger than Y)

therefore no alleles on Y to “counteract” it

38
Q

Why are females less likely to be affected by sex linked diseases

A

Females have XX chromosomes

have a different allele on other X chromosome which does not code for disease :. would counteract it

39
Q

How many possible phenotypes arise from Codominance

A

3

e.g: white, red and pink (Codominant bc red + white)

40
Q

How to represent alleles in codominance

why?

A

superscripted

e.g: I^W , I^R
for white and red petal colours

RW would represent two different genes (epistasis)

41
Q

what leads to genetic variation in sexual reproduction

A
  • Crossing over of non-sister chromatids during prophase I of meiosis
  • Independent assortment of homologous chromosomes during metaphase I of meiosis
  • Random fusion of gametes during fertilisation
42
Q

what leads to Unexpected ratios in inheritance

A

-Random fertilisation -> can’t predict which gametes are successful

-Autosomal linkage (genes which are inherited as a package due to closeness to each other on chromosome) + no crossing over to separate these genes (crossing over to separate genes is less likely if they are closer together on chromosome because they would be swapped together if swapped )

-epistasis

43
Q

To test if there is linkage or epistasis
(causing unexpected ratios), you must …

A

Chi squared test. - find significant difference between expected + observed ratios of offspring

44
Q

When is a Chi squared calculated value Significant

A

If the chi squared value is GREATER than the critical value (0.05)

X^2 > 0.05

(opposite to in maths)

45
Q

a particular gene that is found only on the X chromosome has two alleles G and g. The genotype of a heterozygous female would be written as …….. . A males dom genotype would be written as …….

A

X^GX^g

X^GY

46
Q

Phenotypic variation is

A

the difference in phenotypes between organisms of the same species

47
Q

Different environments around the globe experience very different conditions in terms of the:
5

(for plants)

A

-Length of sunlight hours (which may be seasonal)
-Supply of nutrients (food)
-Availability of water
-Temperature range
-Oxygen levels

48
Q

Some questions in the exam may ask you to explain why the variation in phenotype due to genetics is inherited but the variation in phenotype due to environmental factors is not. This is because

A

genetic variation directly affects the DNA of the gametes but variation in phenotype caused by the environment does not.

49
Q

The small differences in DNA base sequences between individual organisms within a species is called

A

genetic variation

50
Q

To work out the number of different possible chromosome combinations the formula ……. is used where n =

A

2^n can be used, where n corresponds to the number of chromosomes in a haploid cell

For humans this is 2^23 which calculates as 8 324 608 different combinat

51
Q

mechanism of independent assortment of homologous chromosomes during metaphase 1

A

random allignemnet of chromosomes results in random different combinations of chromosomes and different allele combinations in each gamete

= genetic variation between gametes produced by an individual

52
Q

Mechanism of crossing over of non-sister chromatids during PROPHASE 1

A

Exchange of genetic material between non-sister chromatids leads to new combinations of alleles on chromosomes. Can also break linkage between genes

53
Q

what are recombinant offspring

A

offspring that ahave a different combination of characteristics to their parents

54
Q

what are parental type offspring

A

offspring that have the same combination of characteristics to their parents

55
Q

f a large number of genes have a combined effect on the phenotype they are known as

A

polygenes

56
Q

Discontinuous variation:
At the genetic level:
Different genes have ………….. effects on the phenotype
Different alleles at a single gene locus have a ……… effect on the phenotype

A

different

large

57
Q

Continuous variation:
At the genetic level:
Different alleles at a single locus have a …….. effect on the phenotype
Different genes can have the same effect on the phenotype and these add together to have an ………. effect

A

small
additive

Biology (45 decks)

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