Genetic inheritance Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Biology — Foundation

What does a monohybrid cross predict, and how?

It predicts inheritance of one characteristic by combining the alleles each parent can pass on to find possible offspring genotypes.

How does a Punnett square show possible offspring genotypes?

Possible parental alleles are placed along the edges; each cell shows a possible offspring genotype.

How are offspring genotypes used to find a phenotypic ratio?

Use the genotypes to predict the offspring phenotypes, then calculate their ratio.

With one dominant and one recessive allele, what phenotypic ratio is predicted from crossing two heterozygous parents?

3:1 dominant to recessive.

With one dominant and one recessive allele, what phenotypic ratio is predicted from crossing a heterozygous parent with a homozygous recessive parent?

1:1 dominant to recessive.

What is inheritance?

The transmission of genetic information from one generation to the next.

What does an organism inherit from its parents?

Alleles of genes.

What is an organism’s genotype?

Its genetic make-up, including the alleles it has.

What is an organism’s phenotype?

Its observable features.

What are gametes?

Reproductive cells that carry genetic information from a parent to offspring.

What are the two types of gamete?

Sperm cells and egg cells.

How many sets of chromosomes does a gamete normally contain?

One set.

How many alleles of a gene does a gamete normally carry on a chromosome it contains?

One allele.

What happens to gametes at fertilisation?

Two gametes fuse, bringing together chromosomes and alleles from the two parents.

What is a chromosome?

A long DNA molecule associated with proteins and carrying many genes.

How are chromosome pairs in body cells inherited?

Generally, one chromosome of each pair is inherited from each parent.

How do the genes and alleles on corresponding chromosomes compare?

They carry the same genes at corresponding positions, but may carry different alleles.

How many chromosomes from each pair do gametes normally contain?

One chromosome from each pair.

What is a gene?

A section of DNA that provides information for a functional product, often a protein.

What is an allele?

A version of a gene with a distinct DNA base sequence.

In what two ways can alleles affect a protein?

They can affect the protein produced or how much of it is made.

How do proteins link an organism’s alleles to its phenotype?

Alleles can affect proteins, which act in cells and influence how characteristics develop.

Do different alleles always produce an observable difference?

No. Different alleles do not necessarily produce an observable difference.

For a gene with two copies, what is the difference between homozygous and heterozygous?

Homozygous: the two alleles are the same. Heterozygous: they are different.

When is a dominant allele expressed in the phenotype?

When at least one copy is present, including in a heterozygote.

In a two-copy model, when is a recessive allele expressed in the phenotype?

When both alleles are recessive.

What does dominance describe about alleles?

Their relationship in their effect on a characteristic.

Does dominance mean that an allele is more common?

No. Dominance does not indicate how common an allele is.

Does a dominant allele remove a recessive allele?

No. A dominant allele does not remove the recessive allele.

How does single-gene inheritance differ from polygenic inheritance?

Single-gene inheritance involves alleles of one gene; polygenic inheritance involves the combined effects of alleles at several genes.

Why does a single-gene cross not represent the whole pattern of polygenic inheritance?

Because alleles at several genes contribute to the phenotype.

What inheritance pattern can red-green colour blindness show?

It can be a single-gene, X-linked recessive characteristic.

Under what condition can a male express X-linked recessive red-green colour blindness?

When he has one affected allele on his X chromosome.

What does a genetic family tree, or pedigree, represent?

Family relationships and which individuals have a characteristic.

What do squares, circles, shading and connecting lines represent in a pedigree?

• Squares: males
• Circles: females
• Shading: individuals with the characteristic
• Lines: partnerships and offspring across generations

For a simple recessive characteristic, what does an affected child with two unaffected parents indicate about the parents?

Both parents carry a recessive allele.

What limitation should be kept in mind when inferring genotypes or inheritance patterns from a pedigree?

More than one genotype or inheritance pattern may fit the evidence.