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A Level Biology: Topic 8 (Edexcel) > Genetic Information > Flashcards

Genetic Information Flashcards

1
Q

What are the three sources of genetic variation?

A

Meiosis
Mutation
Random fertalisation

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2
Q

What stages of meosis can cause genetic variation?

A

Independent assortment

Crossing over

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3
Q

How can independent assortment during meiosis cause genetic variation?

A

The genes from mother and father are distributed randomly

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4
Q

How can crossing over during meiosis cause genetic variation?

A

Enzymes cut and join different bits of chromasomes together

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5
Q

How can mutations be a cause of genetic variation?

A

There are slight changes in the DNA of the organism

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6
Q

How can random fertalisation cause genetic variation?

A

Each sperm carries a different combination of alleles and the process determining which sperm fertalises he egg is completely random.

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7
Q

What is a phenotype?

A

The physical and chemical characeristics that make up the appearance of an organism.
Result of genetics and environment

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8
Q

How many chromasomes do humans have?

A

46 (28 pairs)

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9
Q

What is an allele?

A

A different variation of the same gene

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10
Q

What is a homozygote?

A

A person where their two alleles code for the same characteristic
eg: both coding for blue eyes

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11
Q

What is a heterozygote?

A

A person where their two alleles code for different characteristics
eg: one allele is brown eyes and the other is green

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12
Q

What is a dominant allele?

A

The allele is expressed, even when it’s heterozygus

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13
Q

What is a recessive allele?

A

Both alleles must be the same in order for it to be expressed (homozygus recessive)

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14
Q

What are polygenic traits?

A

Traits determined by a number of alleles

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15
Q

Why are the ratios seen in punnet squares never the same as a real-life experiment?

A

It happens at random so there is still the element of chance
Some offspring may die before they are sampled
Insufficent techniques like an organism escaping

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16
Q

What is Mendell’s law of segregation?

A

The idea that one allele is inherited from each parent to give a total fo 2 alleles for that trait. Some alleles are dominant over others

17
Q

What does it mean when a trait has multiple alleles?

A

There are more than two possible variants of the trait but two of them are still inherited.

18
Q

What does it mean when an allele is codominant?

A

Both alleles are dominant and expressed, acting independantly of each other and not mixing.
eg: AB blood group

19
Q

What does the chi squared test do?

A

Compare the differences between two sets of data and evaluate if they differ from each other significantly

20
Q

What affects how closely two genes are linked?

A

How close together they are on a chromasome

21
Q

What is a crossover value?

A

Shows how closely linked genes are. More closely linked genes will give smaller values

22
Q

What is a recombintant phenotype?

A

Where the offspring have different phenotypes to the parents due to recombination of the chromasomes during sexual reproduction

23
Q

How do you work out the crossover value?

A

total number of offspring

24
Q

What sex chromasomes are there in female mammals?

A

XX

25
Q

What chromasomes are there in male mammals?

A

XY

26
Q

How do we know when a trait is sex-linked?

A

When the trait is located on the X chromasomes

27
Q

Why will mutations on the X chromasome be more likely to affect males?

A

They don’t have a second X chromasome from their other parent to take over if the gene is ineffective

28
Q

What is a heterogametic person?

A

Someone with two different types of sex chromasomes (males)

29
Q

What is a homogametic person?

A

Someone with only one type of sex chromasome

30
Q

What are pedigree diagrams used for?

A

To help us see genetic illnesses and identify if they are sex-linked

31
Q

What does it mean if a person on a pedigree diagram is shaded in?

A

They’re affected by the condition

32
Q

What does it mean if a person on a pedigree diagram is half shaded in?

A

They’re a carrier

33
Q

What does it mean if a person on a pedigree diagram is represented by a circle?

A

They’re female

34
Q

What does it mean if a person on a pedigree diagram is represented by a square?

A

They’re male

A Level Biology: Topic 8 (Edexcel) (2 decks)

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