Chapter 20- Inheritance. A Level Biology
OCR
Explain genetic drift? - ANS-Individuals in a population have variation in their genotypes, and by
chance one genotype is passed on more often to the offspring. This continues until the allele is
more common overall in the population
\Give 2 examples of faulty alleles on sex chromosomes? - ANS-Colour blindness and
haemophilia
\Give an example of a gene in humans which is co-dominant? - ANS-Sickle cell anaemia gene
\Give an example of a genetic factor which contributes to phenotypic variation? - ANS-Sexual
reproduction to produce offspring as chromatids continuing different alleles cross over
\Give an example of an epistatic gene in humans? - ANS-The gene for baldness overrides the
gene for a widow's peak. So if you have the gene for baldness and a widows peak, only
baldness will be expressed
\Give an example of a genetic bottleneck? - ANS-a natural disaster
\Give an example of how the environment affects the phenotypic ratio in plants and animals? -
ANS-Chlorosis in plants, caused by lack of magnesium
Diet in animals
\How do you know how many degrees of freedom there are? - ANS-You minus 1 from the
number of phenotypes
\How does sexual reproduction lead to genetic variation? - ANS-Meiosis makes gametes with a
random assortment of alleles due to crossing over and assortment of chromosomes
\How does the founder effect occur, give an example? - ANS-By migration of a species, e.g. the
amish
\How many alleles are there for blood type? - ANS-3
\If genes are closer to each other on a chromosome, then what is the effect on recombinant
offspring? - ANS-Fewer recombinant offspring due to decreased crossing over effect
\If someone has the genotype IaIb, what is their blood type and why? - ANS-Blood type AB,
because the alleles are co-dominant
\What 2 factors contribute to phenotypic variation? - ANS-Environmental and genetic
\What are p and q equal to in the Hardy Weinberg equation? - ANS-P is the frequency of the
dominant allele and q is the frequency of the recessive allele
\What are the 3 alleles for blood type? - ANS-Io, Ia, Ib
\What are the 3 ways in which reproductive isolation occurs? - ANS-Seasonal changes (e.g.
members in a species being sexually active at different times)
Mechanical changes (changes in genitalia)
Behavioural changes (e.g. courtship rituals developing)
\What are the disadvantage of artificial selection? - ANS-Gene pool reduced, so monoculture
may develop.
Potentially useful alleles are lost.
Less variation in species, natural evolution cannot occur
OCR
Explain genetic drift? - ANS-Individuals in a population have variation in their genotypes, and by
chance one genotype is passed on more often to the offspring. This continues until the allele is
more common overall in the population
\Give 2 examples of faulty alleles on sex chromosomes? - ANS-Colour blindness and
haemophilia
\Give an example of a gene in humans which is co-dominant? - ANS-Sickle cell anaemia gene
\Give an example of a genetic factor which contributes to phenotypic variation? - ANS-Sexual
reproduction to produce offspring as chromatids continuing different alleles cross over
\Give an example of an epistatic gene in humans? - ANS-The gene for baldness overrides the
gene for a widow's peak. So if you have the gene for baldness and a widows peak, only
baldness will be expressed
\Give an example of a genetic bottleneck? - ANS-a natural disaster
\Give an example of how the environment affects the phenotypic ratio in plants and animals? -
ANS-Chlorosis in plants, caused by lack of magnesium
Diet in animals
\How do you know how many degrees of freedom there are? - ANS-You minus 1 from the
number of phenotypes
\How does sexual reproduction lead to genetic variation? - ANS-Meiosis makes gametes with a
random assortment of alleles due to crossing over and assortment of chromosomes
\How does the founder effect occur, give an example? - ANS-By migration of a species, e.g. the
amish
\How many alleles are there for blood type? - ANS-3
\If genes are closer to each other on a chromosome, then what is the effect on recombinant
offspring? - ANS-Fewer recombinant offspring due to decreased crossing over effect
\If someone has the genotype IaIb, what is their blood type and why? - ANS-Blood type AB,
because the alleles are co-dominant
\What 2 factors contribute to phenotypic variation? - ANS-Environmental and genetic
\What are p and q equal to in the Hardy Weinberg equation? - ANS-P is the frequency of the
dominant allele and q is the frequency of the recessive allele
\What are the 3 alleles for blood type? - ANS-Io, Ia, Ib
\What are the 3 ways in which reproductive isolation occurs? - ANS-Seasonal changes (e.g.
members in a species being sexually active at different times)
Mechanical changes (changes in genitalia)
Behavioural changes (e.g. courtship rituals developing)
\What are the disadvantage of artificial selection? - ANS-Gene pool reduced, so monoculture
may develop.
Potentially useful alleles are lost.
Less variation in species, natural evolution cannot occur
