7.1 Inheritance Flashcards
genotype?
the genetic constitution of an organism - the alleles an organism (or cell) has.
Phenotype
the expression of the genetic constitution - the characteristics an organism has.
allele?
a version of a gene
How many alleles does a diploid organism carry?
2
Dominant allele?
An allele with a characteristic that appears in the phenotype even if there’s only one copy present.
Recessive allele?
An allele with a characteristic that only appears in the phenotype if no dominant allele is present, so there must be two copies.
heterozygous?
one allele is dominant; one is recessive.
homozygous?
both alleles are dominant or both recessive.
Monohybrid inheritance?
where the inheritance of a characteristic is controlled by a single gene
What are the resulting genotypes of a monohybrid cross of two parents with heterozygous genotypes
(alleles (G and g)
b) what % will express the characteristic determined by allele g?
3 combinations with a dominant allele. One combination with two recessive alleles.
b)25% - only one combination results in the expression of the recessive allele.
What are the resulting genotypes of a monohybrid cross between a homozygous dominant parent and a homozygous recessive parent?
(alleles G and g)
All heterozygous offspring.
Draw an example of a genetic diagram, listing each of the columns.
For brown eyes and blue eyes where blue is expressed by the recessive allele.
What are pedigree diagrams used for?
to trace the pattern of inheritance
How can you determine whether a trait is dominant or recessive.
If a trait is dominant, one of the parents must have the trait. Dominant traits will not skip a generation. If the trait is recessive, neither parent is required to have the trait since they can both be heterozygous.
How can you determine whether the chart shows an autosomal or sex linked trait?
e.g. in X linked recessive traits, alleles are much more commonly affected than females.
In autosomal traits, both males and females are equally likely to be affected (usually in equal proportions).
Use the diagram to deduce and explain:
the type of allele that causes albinism.
Albinism is caused by a recessive allele.
Person number 9 is an affected individual despite parents 6 and 7 being unaffected.
6 and 7 must be carriers of the of the recessive allele and 9 has inherited one recessive allele from each parent.
Use the diagram to deduce and explain:
the genotype of individuals 9 and 7.
The genotype of person 9 must be homozygous recessive (aa) and the genotype of 7 must be heterozygous (Aa).
Person 9 is an affected individual with albinism: as this is determined by the recessive allele they must have two copies of the albinism allele.
Person 7 must be heterozygous as he does not have albinism but has passed o the recessive allele to person 9.
Use the diagram to deduce and explain:
The possible genotypes of 10 and 11.
The possible genotypes of 10 and 11 are heterozygous (Aa) or homozygous dominant (AA).
They are both unaffected individuals so must posses at least one dominant allele (A), however, it is possible that they each might have inherited a recessive allele (a) from one parent (both parents must have a copy of the recessive allele in order for person 9 to have albinism).
Define dihybrid inheritance
Where two phenotypic characteristics are determined by two different genes present on two different chromosomes at the same time.
Draw a Punnett square to show a dihybrid cross with parental genotypes of RrGg and RrGg.
b) How many of these offspring should have the same phenotype as there parents.
To get the possible alleles:
Put the first letter next to each allele of the second.
Do the same for the second allele of the first letter.
(Qu. on pic is wrong - both RrGg)
In fruit flies, the allele for a grey body, G, is dominant to the allele for an ebony body, g, and the allele for normal wings, N is dominant to the allele for vestigial wings, n. Vestigial winged flies, heterozygous for body colour, were crossed with ebony bodied flies heterozygous for normal wings.
What are the possible phenotypes of the offspring.
What are the possible phenotypes of a dihybrid cross between two lizards with the genotypes:
FdDd and ffdd
forked tounge - F
not forked - f
dark spots - D
light spots - d
Find the phenotypes and genotypes of the offspring of a cross between red and white flowers where the alleles for the red flowers and the alleles white flowers are codominant.
The colour gene, C, has two alleles
C^R = red allele
C^W = white allele
b) Find the phenotypes and genotypes of the second generation.
What do you need to remember about multiple alleles?
When a gene (e.g. gene I) has multiple alleles (I^A, I^B and I^O) different combinations of the alleles can be inherited and can result in the same phenotype (e.g. blood group: A,B,AB,O)
What are the phenotypes (blood groups) of the offspring of parents with the blood groups: A and B
Alleles:
Group A: I^AI^O
Group B: I^BI^O
a) Looking at the table, what evidence is there that:
a) I^O allele is recessive
b) I^A and I^B alleles are codominant
a) I^O is only present twice in one gene 25% of the time.
b) The phenotype expressed for one combination is a blend of groups A and B (group AB).
What are the typical phenotypic ratios for the F1 and F2 generations of a cross between these two codominant alleles:
Draw a punnet square to show a sex-linked cross with parental genotypes of X^HXh and X^HY.
b) Describe the four possible phenotypes of these offspring.
Normal female
Carrier female
normal male
affected male
Draw a punnet square to show how multiple alleles cross with parental genotypes of I^AI^O and I^BI^O.
If I^A and I^B are codominant and I^O is recessive, which alleles could the offspring express.
AB, A, B or O
Draw a punnett square to show an epistasis cross with parental genotypes AABB and aabb.
Genotypes BB or Bb allow expression gene A, while genotype bb masks gene A. With this in mind , what % of the offspring will have gene A masked?
25%
