Biology > 3.7.1 Inheritance > Flashcards

3.7.1 Inheritance Flashcards

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1
Q

Genotype

A

The genetic constitution of an organism (the alleles it has for a gene)

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2
Q

Phenotype

A

The expression of the genes and its interaction with the environment- a characteristic or trait

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3
Q

Homozygous

A

A pair of homologous chromosomes carrying the same allele for a single gene. Can be 2 dominant or 2 recessive.

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4
Q

Heterozygous

A

A pair of homologous chromosomes carrying two different alleles for a single gene. 1 dominant and 1 recessive

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5
Q

Recessive allele

A

An allele only expressed in the phenotype if no dominant allele is present

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6
Q

Dominant allele

A

An allele always expressed in the phenotype

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7
Q

Codominant

A

Both alleles are equally dominant and both expressed in the phenotype

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7
Q

Multiple alleles

A

More than two alleles for a single gene

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8
Q

Sex linkage

A

A gene that’s locus is on the X chromosome

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9
Q

Autosomal linkage

A

Genes that are located on the same chromosome (not the sex chromosome)

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10
Q

Epistasis

A

When one gene modifies or masks the expression of a different gene at a different locus

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11
Q

Monohybrid

A

Gene inheritance cross of a characteristic that is determined by one gene

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12
Q

Dihybrid

A

Genetic inheritance cross for a characteristic that is determined by two genes

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13
Q

What is a gene?

A

A small section of DNA (sequence of bases) that codes for a specific polypeptide

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13
Q

What does each gene determine?

A

A single characteristic of an organism

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14
Q

What is the locus?

A

The position of a gene on a chromosome

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15
Q

What are alleles?

A

Versions of the same genes. There may be many alleles for the same gene.

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16
Q

What 3 types of allele are there?

A

Dominant, recessive or codominant

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17
Q

Describe the alleles in diploid organisms?

A

The alleles in diploid organisms at a specific locus are heterozygous or homozygous.

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18
Q

What is a diploid organism?

A

When each cell contains two complete sets of chromosomes eg. In humans, 46 individual / 23 pairs

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19
Q

What is a haploid cell?

A

One which contains only one complete se of unpaired chromosomes eg. Gametes contain 23 individual/unpaired chromosomes

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20
Q

What is monohybrid inheritance?

A

Inheritance of a phenotype that is determined by a single gene with two alleles of the gene.

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21
Q

What is the law of segregation?

A

Characteristics in diploid organisms are determined by pairs of alleles. Only one allele in each pair can be present in a gamete. (so it can’t have more than one pair of alleles for the same gene.

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22
Q

What is a pedigree diagram?

A

A family tree of the inheritance of more than one gene

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23
What is evidence for a recessive condition in a pedigree diagram and why?
If 2 parents without the condition have a child with the condition. This means the parents are carriers of the recessive allele for the condition but do not show the condition. Therefore the condition must be recessive.
24
What is the evidence for a dominant condition in a pedigree diagram and why?
2 parents with the condition have a child who doesn’t have the condition. Parents must be heterozygous as they carry the recessive allele, but due to the dominant allele they have the condition themselves. Therefore the condition is dominant.
25
What is dihybrid inheritance?
When the inheritance of two genes is considered on the same genetic cross, despite them being separate characteristics and carried on different chromosomes.
26
Who, and what experiment identified dihybrid inheritance?
Mendel’s peas
27
What does f1 mean?
First generation
28
What will be the ratio in a dihybrid cross if two heterozygous parents for both genes are crossed?
9:3:3:1
29
What is codominance?
Occurs when instead of one allele being dominant and another being recessive, both alleles are equally dominant. This means both alleles of a gene are expressed in the phenotype.
30
31
How many phenotypes are there in codominance?
3- heterozygous genotype has its own phenotype
32
Why are actual offspring ratios not always the same as expected from a genetic cross?
Because the fusion of gametes is random (any sperm can fuse with any egg) Small sample size Chance in mating Linked genes Epistasis Differential mortality/ lethal genotypes
33
What is multiple alleles?
When there are more than two alleles for a gene in a population
34
What is an example of multiple alleles in humans?
Blood group
35
What are the dominant alleles for blood group?
A and B (codominant)
36
What is the recessive allele for blood type?
O
37
What antigens does each blood group have on their red blood cells?
A- A B- B AB- A and B O- none
38
What plasma antibodies does each blood group produce?
A- anti-B antibodies B- anti-A antibodies AB- none O- anti-A and anti-B
39
As an example, why dont blood group A have anti-a antibodies?
Their own red blood cells would be targeted by the immune system
40
What is sex linkage?
When the gene that codes for a characteristic is on the sex chromosome ie. Allele is carried on the sex chromosome
41
What are the sex chromosomes in humans for males/females?
Female = XX Male = XY
42
In humans what is the probability of the child being a girl OR a boy?
50 %
43
What does the gender of a child depend on?
Whether the sperm that fertilises the egg has a Y chromosome or not (random fusion of gametes)
44
When does the sex become a phenotype?
When a characteristic is sex-linked
45
Why are males more likely to express X-linked recessive traits?
Males only have one X chromosome This means the recessive alleles on the X chromosomes are always expressed
46
Name 3 sex linked traits?
Haemophilia Red-green colourblindness Coat colour in cats
47
What type of allele causes red-green colour blindness?
Recessive allele on the X chromosome
48
What type of allele causes haemophilia?
Recessive allele on the X chromosome
49
What are the rules for x-linked recessive disorders in pedigrees?
Mother without trait has son with trait (means mother must be a carrier/heterozygous) (Mother without trait and) father with trait have daughter without trait
50
What rate the rules for dominant x-linked disorders in pedigrees?
ALL females in a generation are affected if their fathers are affected If the mother is affected, both sons and daughters can be affected
51
What are the rules to show that a disorder is not x-linked?
If the condition affects males and females in equal numbers If an affected male passes on the trait to sons, it is not x linked as there would be no male to male transmission If mother who is affected has son who is unaffected (normally would pass x onto son)
52
Exam q- in fruit flies, a gene for body colour has a dominant allele for grey body and a recessive allele for black body. Explain how you would determine if the genotype of a grey fly is homozygous or heterozygous for body colour?
Cross the grey fly with a homozygous recessive fly If the offspring are black then the grey fly is heterozygous.
53
What is an autosome?
Any chromosome not considered as a sex chromsome (not involved in sex determination)
54
How many autosomes does a human cell have?
22 pairs
55
What is autosomal linkage?
When two or more genes are carried on the same autosome that show up together in the same combinations in the offspring
56
Why might genes on the same chromosome not show autosomal linkage?
When they are far apart due to crossing over
57
Why can autosomal linkage only produce certain combinations of alleles in the gametes?
Because genes are on the same chromosome so alleles are inherited together
58
What is epistasis?
When one gene influences the expression of another gene by suppressing or masking it. It involves the interaction of genes that are not alleles
59
What is the hardy Weinberg equation?
A mathematical model used to predict the allele frequencies within a population
60
Define gene pool
All of the alleles of all of the genes within a population at one time
61
Define allele frequency
The proportion of an allele within the gene pool
62
What is a population?
All of the individuals of one species in one area at one time
63
What assumptions does the hardy-Weinberg equations use?
There will be no change in the allele frequency between generations: -no migration to introduce or remove alleles from the population -no mutations to create new alleles -No selection favouring particular alleles -random mating (no inbreeding) -large population size
64
What is the problem with the hardy weinberg equation?
Pitied accuracy due to the assumptions
65
Write the hardy Weinberg equation?
P^2 + 2pq + q^2 = 1 P + q = 1
66
What does each part of the hardy Weinberg equation stand for?
P- frequency of dominant allele Q- frequency of recessive allele P^2- frequency of homozygous dominant genotype 2pq- frequency of heterozygous genotype Q^2- frequency of homozygous recessive genotype
67
What statistical test is used to compare the observed vs expected frequencies of a phenotype within a population?
Chi-square
68
Exam question- why are males more likely to inherit a recessive X-linked condition than females?
Males only have one X chromosome so only have one ALLELE for the condition. Means if they inherit the recessive allele then the condition is always expressed. Whereas females have two X chromosomes so have two ALLELES for the condition. This means they need to inherit two recessive alleles for the condition to be expressed.
69
Exam q- state 2 reasons why the observed phenotypic ratio may differ from the expected phenotypic ratio?
Random fusion/fertilisation of gametes Small sample size Linked genes (crossing over/sex linkage) Epistasis Lethal genotypes
70
Exam q- which statistical test do we use to measure the difference between observed and expected phenotypic ratios and why?
Chi squared Because the data is categorical
71
Exam q- explain how the observation of the chromosomes from an embryo cell could enable the sex to be determined.
The Y chromosome would be shorter than the X chromosome XX- female XY- male
Biology
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