StemUp: AQA A level Biology 3.7.1 Inheritance

What is meant by the term 'genotype'? (1)

The genetic constitution of an organism e.g. Bb‎‏‏‎ ‎

What is meant by the term 'phenotype'? (1)

The expression of a genetic constitution and its interaction with the environment e.g.‎‏‏‎ blue eyes

What is meant by 'alleles'? (1)

Different versions of the same gene

What are the different types of alleles? (3)

- Dominant

- Recessive

- Co-dominant

What are dominant alleles? (2)

- The allele that is always expressed in a phenotype when present in the genotype

- Always denoted in capital letters

What are recessive alleles? (2)

- The allele is only expressed when the genotype is homozygous recessive

- Always denoted in lowercase

What is co-dominance? (2)

- Where both alleles are expressed in the phenotype (i.e. they are both dominant)

- E.g. pink flowers are expressed by a C_W​ C_R genotype

In a diploid organism, what are the possible states of the alleles at a specific locus?

- Homozygous

- Heterozygous

What is a homozygous genotype? (2)

- Where both alleles in the genotype are the same

- E.g. BB (homozygous dominant) or bb (homozygous recessive)

What is a heterozygous genotype? (2)

- Where both alleles in the genotype are different to each other

- E.g. Bb

What are the two sex chromosomes? (2)

- X

- Y

What is the sex chromosome genotype of all females? (1)

XX

What is the sex chromosome genotype of all males? (1)

XY

Describe what is meant by 'sex-linked' genes (2)

- Where the gene is carried on only one type of sex chromosome

- Usually the X‏‏‎ chromosome

What is a common example of sex-linked genes? (1)

- Colour blindness

- Which is caused by a recessive allele that is carried on the X ‎‏‏‎chromosome

Why are sex linked conditions more common in males than females? (3)

- Males only contain one X chromosomes

- Females contain two X chromosomes

- X-linked disorders are always expressed in males (as they only have one X-chromosome)

Describe what is meant by 'multiple alleles' (3)

- Where there are more than two alleles of a particular gene

- However, only two alleles can be present in a genotype

- E.g. There are 3 different alleles for the blood group gene (I^A , I^B and I^O)

Mendel studied the inheritance of height in pea plants. He crossed pure breeding (homozygous) tall and dwarf plants.

Show this result on a genetic diagram with the F1 ratio

Assail is a florist with a beautiful botanical garden. He decides to cross two pink flower plants.

Show this in a genetic diagram with the F1 ratios

Ali, a genetic counsellor is investigating the cross between heterozygous blood group A and heterozygous blood group B parents.

Show the results in a genetic diagram with the F1 ratios

Emily is a carrier of the allele for haemophilia, a recessive condition that is carried on the X chromosome. She would like to see the genetic cross before she decides to have children with her 'normal' partner

Show the results of her cross in a genetic diagram with the F1 ratios

A farmer decided to cross two plants who's both produce round and yellow seeds (heterozygous) . The allele for round seeds, R is dominant to the allele for wrinkled seeds, r and the allele for yellow seeds, Y is dominant to the allele for green seeds, y.

Show the genetic cross between these two plants as well as their F1 ratios

Where are autosomal linked genes located? (2)

- Present on the same chromosome at different loci

- Rather than on separate chromosomes (as previously considered in dihybrid inheritance)

How many potential gamete combinations result from autosomal linked genes? (2)

- Result in two potential gamete combinations

- Rather than four (as previously considered in dihybrid inheritance)

What type of cross pattern should be used for autosomal linked genes? (1)

Monohybrid pattern rather than a dihybrid pattern

(What this means is that when approaching questions related to autosomal linked genes, you should treat the question as if you were asked about a monohybrid pattern (4 box punnet square) rather than a dihybrid inheritance (16 box punnet square)

What is an example of gamete production with autosomal linked genes? (3)

- If genes A and B, and a and b are linked

- The gametes each parent produces are AB and ab (linked together)

- Rather than AB, Ab, aB, and ab (not linked).

What is epistasis? (2)

- Occurs when two or more genes interact

- To contribute to a phenotype

Where does epistasis often occur? (3)

- In metabolic pathways

- That are controlled by enzymes

- Coded for by different genes

How does enzyme dependency affect metabolic pathways in the context of epistasis? (2)

- Each enzyme is dependent on the previous enzyme for its substrate

- If any one of these enzymes is non-functional, the pathway comes to a halt

Draw a table that shows the most common exam questions that related to pedigree diagrams (8)

How would you carry out a chi-squared test? (4)

Why do we use the chi squared test? (2)

- To compare the 'goodness of fit' of observed phenotypic ratios with expected ratios

- It is used to determine if there is a statistical difference between the expected and observed ratios from the results of a genetic cross ‎