patterns of inheritance Flashcards
1
Q
What is chlorosis?
A
When the leaves of a plant look pale or yellow because the cells are not producing the normal amount of chlorophyll. • This lack of chlorophyll reduced the ability of the plant to make nutrients by photosynthesis
2
Q
Describe the plants which
show chlorosis
A
• Most have normal genes coding
for chlorophyll production
• The change in their phenotype is
the result of environmental
3
Q
Give examples of where both genetic and environmental variation play a role in determining an organism’s characteristics
A
- Chlorosis in plants
* Body mass of animals
4
Q
What environmental factors
can cause chlorosis in plants?
A
Lack of light - e.g. when a gardening tool is left on a lawn. In the absence of light, plants turn off chlorophyll production to conserve resources • Mineral deficiencies - e.g lack of iron or magnesium. Iron is needed as a cofactor by some enzymes that make chlorophyll, and magnesium is found at the heart of the chlorophyll molecule • Virus infections - when viruses infect plants, they interfere with the metabolism of cells
5
Q
How can environmental factors
affect animals’ body mass?
A
In the majority of cases, obesity and being severely underweight are a result of environmental factors • Amount and quality of food eaten • Quantity of exercise the organism gets • Presence of disease
6
Q
How can genetic factors affect
animals’ body mass?
A
Genetic mutations can cause the
pattern of fat deposition in the body
to be altered
7
Q
How is genetic variation
created?
A
• For most genes there are many different possibles alleles or variants • Combination is determined by sexual reproduction involving meiosis (formation of gametes), and the random fusion of gametes at fertilisation
8
Q
What are modifications?
A
Changes to a person’s phenotype due to the environment • Not inherited • Only mutations (changes to the DNA) in the gamete can be passed on to the offspring
9
Q
What are the 2 different types
of allele?
A
• Dominant allele - the version of the genes that will always be expressed if present in an organisms • Recessive allele - will only be expressed 2 copies of this allele are present in an organism
10
Q
What are the 2 different types
of genotype?
A
• Homozygous - they have 2 identical alleles for a characteristic. Either homozygous dominant, or homozygous recessive • Heterozygous - the have 2 different alleles fora characteristic. The allele for the dominant phenotype will be expressed
11
Q
Compare continuous and
discontinuous variation
A
12
Q
What are the steps in drawing
a genetic cross diagram?
A
1. State the phenotype of both parents 2. State the genotype of both parents. Capital letter for dominant allele, and corresponding lowercase letter for recessive allele 3. State the gametes of each parent. Common practice is to circle the letters 4. Use a Punnett square to show the results of random fusion of gametes during fertilisation 5. State the proportion of each genotype which are produced among the offspring 6. State the corresponding phenotype for each of the possible genotypes
13
Q
What is codominance?
A
Codominance occurs when two different alleles occur for a gene - both of which are equally dominant • As a result both alleles of the alleles are expressed in the phenotype of the organism if present • e.g. Red and White allele make Pink flower • CR = red, CW = white
14
Q
Give an example of a
characteristic that is
determined by a gene with
multiple alleles?
A
Blood group • The immunoglobulin gene (Gene I) coders for the production of different antigens present on the surface of red blood cells • IA = antigen A • IB = antigen B • IO = antigen O
15
Q
Describe the alleles involved in
determining blood group
A
IA and IB are codominant, whereas IO is recessive to both of the other alleles. This leads to 4 blood groups: • Blood group A = IAIA or IAIO • Blood group B = IBIB or IBIO • Blood group AB = IAIB • Blood group O = IOIO
16
Q
How is sex determined?
A
• The 23rd pair of chromosomes in humans are sex chromosomes • Female = XX • Male = XY • X-chromosome is large and contains many genes not involved in sexual development • Y-chromosomes is very small containing almost no genetic information, but does carry a genes that causes the embryo to develop as a male
17
Q
What are sex linked
characteristics?
A
Characteristics determined by genes carried on the sex chromosomes • Y-chromosomes is much smaller, so there are many genes in the Xchromosome that males have 1 copy of • Any characteristic caused by a recessive allele on the section of the X-chromosome which is missing in the Y-chromosome occurs more frequently in males
18
Q
What is haemophilia?
A
Sex-linked genetic disorder • Blood clots extremely slowly due to the absence of a protein bloodclotting factor (usually factor VIII) • If a male inherits the recessive allele that codes for haemophilia, they cannot have a corresponding dominant allele on their Y chromosome, so they develop the condition • Females who are heterozygous for the haemophilia coding gene are known as carriers
19
Q
What is dihybrid inheritance?
A
The inheritance of two genes
20
Q
What is the ratio for dihybrid
crosses with heterozygous
parents?
A
9 : 3 : 3 : 1
21
Q
What can the actual ratio differ
from the expected ratio?
A
• The fertilisation of gametes is a random process so in a small sample a few chance events can lead to a skewed ratio • The genes being studied are both on the same chromosome. These are known as linked genes. If no crossing over occurs, the alleles for the two characteristics will always be inherited together
29
Q
What is the chi-squared test
formula?
A
39
Q
What happens in stabilising
selection?
A
• The average is selected for (positive selection), and the extremes are selected against (negative selection) • Results in a reduction in the frequency of alleles at the extremes, and an increase in the frequency of average alleles • e.g. natural selection in baby weight
40
Q
What is directional selection?
A
When there is a change in the environment and the normal (most common) phenotype is no longer the most advantageous • Organisms which are less common and have more extreme phenotypes are positively selected • The allele frequency then shifts towards the extreme phenotypes and evolution occurs • e.g. peppered moths during the industrial revolution
41
Q
What is disruptive selection?
A
When the extremes are selected for and the norm is selected against • The opposite to stabilising selection when the norm is positively selected • e.g. feather colour in lazuli bunting birds
