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

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 sex cells, such as sperm and egg cells.

What does it mean that gametes are haploid?

They contain one set of chromosomes, rather than the two sets found in most body cells.

How many alleles of each gene on its chromosomes does a gamete normally carry?

One allele.

What happens to the gametes’ chromosome sets at fertilisation?

The two gametes fuse and their chromosome sets combine, giving the offspring genetic information from both parents.

What is a chromosome made of?

A long DNA molecule associated with proteins.

Where are genes found on a chromosome?

Many genes occur at particular positions along its DNA.

In a cell with two chromosome sets, where does each chromosome in a homologous pair come from?

One is inherited from each parent.

How do homologous chromosomes compare in their genes and alleles?

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

What is a gene?

A section of DNA containing information used to make a functional product, such as a protein.

What are alleles?

Different versions of the same gene that differ in their DNA sequence.

What two aspects of protein production can inherited alleles affect?

The protein produced or the amount of it made.

How can allele effects on proteins contribute to an organism's phenotype?

Proteins influence cell structures and processes, which can contribute to the phenotype.

Do different alleles necessarily produce different observable phenotypes?

No. Different alleles do not necessarily produce different observable phenotypes.

What controls a characteristic showing single-gene inheritance?

Alleles of a single gene.

What is the difference between homozygous and heterozygous genotypes?

A homozygous genotype has two identical alleles; a heterozygous genotype has two different alleles.

When is a dominant allele expressed?

When at least one copy is present.

When is a recessive phenotype expressed in an individual with two copies of a gene?

When there are two recessive alleles and no dominant allele.

What type of inheritance does red-green colour blindness commonly show?

X-linked recessive inheritance.

Why can a person with only one X chromosome express red-green colour blindness with one recessive allele?

There is no second allele of that gene on the other sex chromosome.

What is polygenic inheritance?

Inheritance in which a characteristic is influenced by multiple genes, with alleles at those genes contributing together to the phenotype.

Why can a single-gene cross not generally represent the inheritance of most characteristics fully?

Most characteristics are influenced by multiple genes.

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

Family relationships across generations and which individuals express a characteristic.

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

• Squares: males
• Circles: females
• Shading: individuals with the characteristic shown in the key

What do the lines in a pedigree indicate?

Parental relationships and offspring.

What can the pattern of affected and unaffected relatives in a pedigree help infer?

Possible inheritance patterns and genotypes.

Can a pedigree always determine every individual's genotype uniquely?

No. Some genotypes may not be uniquely determined.

What must an inference from a genetic family tree be consistent with?

The information shown in the tree and the proposed inheritance pattern.