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Biology > 20 - Patterns of inheritance and variation > Flashcards

20 - Patterns of inheritance and variation Flashcards

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1
Q

What is chlorosis?

A

When cells are not producing the normal
amount of chlorophyll (a green pigment
essential for photosynthesis), plants with this condition look pale or yellow. The plants ability to photosynthesis is reduced

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2
Q

What are 3 examples of environmental factors that cause chlorosis?

A

lack of light
Mineral deficiencies
Virus infections

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3
Q

Why does a lack of light cause chlorosis?

A

when plants are in an absence of light thy turn of chlorophyll production, to conserve
resources.

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4
Q

why does mineral deficiencies cause chlorosis?

A

A plant will be unable to produce chlorophyll if there are mineral deficiencies. For example iron is needed as a cofactor by some enzymes that make chlorophyll, magnesium forms the core of the chlorophyll molecule

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5
Q

Why does a virus infection cause chlorosis?

A

when a plant is infected by a virus it interferes with the metabolism of cells

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6
Q

How does animal body mass vary?

A

it is determined by both genetic and
environmental factors. The amount and quantity of food eaten and quantity of exercise can affect body mass.

mutations can also affect body mass

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7
Q

What influences the characteristics an organism displays?

A

the individual mixture of alleles an organism inherits

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8
Q

How is the mixture of alleles an organism
inherits determined?

A

the random fusion of gametes and sexual
reproduction

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9
Q

What is genotype?

A

The genetic make-up of an organism, or the
particular alleles that an organism possesses

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10
Q

What is phenotype?

A

Observable characteristics of an organism

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11
Q

What are modifications?

A

Changes the environment makes on a persons phenotype

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12
Q

What is a dominant allele?

A

an allele that is always expressed present in an organism’s genome

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13
Q

what is a recessive allele?

A

an allele that is only expressed if 2 copies are present in an organism’s genome

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14
Q

What is continuous variation, give an example, how is it caused and what is its genetic control?

A

a characteristic that can take any value within a range

it is caused by genetics and environment

Polygenes - controlled by a number of genes

Leaf surface area, animal mass, skin colour

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15
Q

What is discontinuous variation, give an
example, how is it caused and what is its genetic control?

A

characteristic that can only appear in specific, discrete, values.

it is caused by mostly genetics

one or two genes

blood group, albinism, round or wrinkled pea shape

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16
Q

Steps for performing a genetic cross?

A

Step 1: State the phenotype of both
parents.
Step 2: State the genotype of both parents.
Step 3: State the possible gametes that can
come from each parent. It is good practice
to circle the letters of the gametes.
Step 4: Perform the genetic cross (either
via a genetic diagram or Punnett square)
to determine the potential genotypes of
the offspring.
Step 5: State the proportion of each
genotype produced.
Step 6: State the corresponding phenotype of each possible genotype

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17
Q

What is co-dominance?

A

Both alleles are expressed in the phenotype, neither are recessive

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18
Q

How do you represent co-dominant alleles?

A

a letter is chosen to represent the gene, and a second letter is used as a superscript to represent the different versions.

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19
Q

What is different between the X and Y
chromosome?

A

The Y chromosome is smaller than the X
chromosome. It codes for fewer genes.

This means that most genes on sex
chromosomes are only carried on the X
chromosome. and that is contains many
genes not involved in sexual development

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20
Q

why are some genetic conditions more likely to be expressed by males than females?

A

Males only have one copy of the X chromosome. This means that they will express this allele, even if it is recessive, because it’s the only copy they have.

21
Q

A female carrier of colour blindness is crossed with an unaffected male. Why do none of the offspring have colour blindness?

A

they will always inherit a healthy copy of the X gene from their unaffected father.

22
Q

What is a dihybrid cross?

A

We use a dihybrid cross to see how two different genes are inherited at the same time.

23
Q

What does autosomal linkage cause?

A

When the phenotypic ratios differ significantly from what is expected

24
Q

What is autosomal linkage?

A

When the genes that are linked are found on one of the other pairs of chromosome. Genes are located in the same chromosome.

25
Q

Why are linked genes inherited as one unit?

A

There is no independent assortment during
meiosis unless the alleles are separated by
chiasmata.

26
Q

What are recombinant offspring?

A

Crossing over can cause the separation of linked genes. The offspring produced are recombinant, they have different allele combination of alleles than either

27
Q

What does it mean if genes are close together on the chromosome?

A

The are less likely to be separated during
crossing over, leading to fewer recombinant offspring

28
Q

equation for recombinant frequency

A

Number of total recombinant offspring/total number of offspring

29
Q

What is epistasis? Give an example.

A

The interaction of genes at different loci
Gene regulation, where regulatory genes control the activity of structural genes (Lac operon)

30
Q

What is an epistatic and hypostatic gene?

A

-affects / blocks the expression of another
gene.
-The gene that is affected by an epistatic
gene is known as a hypostatic gene.

31
Q

What is recessive epistasis?

A

-two copies of a recessive epistatic allele
blocks the expression of another gene.
-For example – a recessive allele may mean
an enzyme is not made.

32
Q

What s dominant epistasis?

A

the presence of the dominant allele blocks
the expression of another gene.

33
Q

Two situations of dominant epistasis?

A

->The gene could code for a repressor
protein – This would produce a protein
which represses the expression of the gene
even if it is dominant. E.g. someone has
the dominant gene for brown eyes but has
blue eyes because the repressor protein
blocks the brown eye gene from
producing melanin.
->The gene could code for an enzyme – If
the enzyme modifies a substrate in a
biochemical pathway it will not be able to
move onto the next step in the pathway.

34
Q

An example of recessive epistasis?

A

a recessive allele may mean an enzyme is
not made.

35
Q

What is a population?

A

A group of organisms of the same species living in a particular area

36
Q

What is a gene pool?

A

The complete range of alleles present in a
population

37
Q

What is allele frequency?

A

The relative frequency of a particular allele in a population

38
Q

What is evolution?

A

The change in the frequency of different alleles within a population over time. This results in changes to inherited characteristics.

39
Q

Steps of natural selection

A

-New alleles are generated by random,
spontaneous mutation in genes.
-Individuals within a population vary
because of the different alleles present.
-‘Selection pressures’ are anything that
affects an organism’s chances of survival
and reproduction e.g. competition,
disease, predation. This creates a struggle
for survival. (think of selection pressures
as a ‘force’ pushing evolution in a
particular direction)
-Due to variation some individuals are
better adapted to cope with the selection
pressure than others.
-Individuals with advantageous alleles are
more likely to survive, reproduce and
pass alleles on to offspring.
-A greater proportion of the next
generation inherit the alleles and are
more likely to survive and reproduce.
-The frequency of advantageous alleles
increase from generation to generation.

40
Q

5 factors affecting evolution

A

mutation- formation of new alleles
sexual selection
gene flow- the movement of alleles
between populations
Genetic drift- a change in allele frequency
due to the random mature of mutation
Natural selection leads to increase in the
number of individuals that have characteristics that improve their chances

41
Q

What is essential for the process of natural
selections?

A

genetic diversity which leads to variation

42
Q

What is stabilising selection? What does it lead to?

A

The norm/average is selected for and the
extremes are selected against.
A reduction in the frequency off alleles at the extremes, and an increase in the frequency of average alleles

43
Q

What is directional selection? What does it lead to?

A

Occurs when there is a change in the
environment ad the normal phenotype is no longer the most advantageous. Organisms which have more extreme phenotypes are positively selected. The allele frequency shifts towards the extreme phenotypes and evolution.

44
Q

What is disruptive selection?

A

The extremes are selected for and the norms are selected against

45
Q

Genetic drift and population size

A

-it has a greater effect in smaller populations where chance has a greater
influence
-Tends to cause genetic diversity to
decrease in small populations
-This can make them less adaptable to
future environmental change and at
greater risk of extinction

46
Q

What is genetic bottleneck?

A

-An event such as a natural disaster causes
a large reduction in population size,
leading to a reduction in gene pool., and
therefore genetic diversity
-Evolution by genetic drift has a greater
effect if there’s a genetic bottleneck

47
Q

What is the founder effect?

A

-When just a few organisms from a
population start a new population, with
only a small number of alleles in the initial
gene pool and less genetic variation.
-Without further gene flow the new
population will grow with reduced genetic
diversity.
-Any previously rare alleles will now be
present at a much higher proportion and
will have a much bigger impact during
natural selection

48
Q

How does a stable environment affect selection?

A

It makes it more likely that individuals with
alleles and characteristics of the range will
survive and reproduce. This reduces the range of possible phenotypes

49
Q

what is p and q in P+q=1

A

p= dominant q: recessive

Biology (24 decks)

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