Topic 5.1 Inheritance OCR (A) Biology GCSE

What is a gamete?

A gamete are sex cells (sperm or eggs)

What is a chromosome?

Tightly packaged DNA around histone proteins

What is a gene?

A section of DNA that can (but not always) code for a protein

What is an allele?

Different versions of the same gene

What is a dominant allele?

A version of a gene where only one copy is needed for it to be expressed

What is a recessive allele?

A version of a gene where two copies are needed for it to be expressed

What does it mean when an organism is homozygous?

When an organism has two copies of the same allele (two recessive or two dominant)

What does it mean when an organism is heterozygous?

When an organism has two different versions of the same gene (one dominant and one recessive)

What is the genotype?

The genes present for a trait

What is the phenotype?

The visible characteristic

What is the genome?

All of the genes present in an organism

What is discontinuous variation?

Variation that produces distinct categories (e.g. eye colour or blood groups)

What is continuous variation?

Variation that cannot be placed into distinct categories and instead produces a spectrum (e.g. height, weight)

What causes variation?

Mutations in the genetic code

How can a mutation in a coding DNA sequence be detrimental?

It may change the sequence of amino acids in the protein which will change its structure, affecting proteins like enzymes and antibodies.

What may happen if there is a mutation in non-coding DNA?

It may stop transcription and alter the expression of genes.

What is one advantage of sexual reproduction?

It introduces variation.

What is one disadvantage of sexual reproduction?

It is slower and produces a limited amount of offspring.

What is one advantage of asexual reproduction?

It produces lots of offspring quickly.

What is one disadvantage of asexual reproduction?

It does not introduce variation and all offspring are susceptible to the same environmental pressures as the parents.

What is the difference between diploid and haploid cells?

Haploid cells have half the amount of genetic information as diploid cells; haploid cells are germ cells, while diploid cells are body cells.

What type of cell does meiosis produce?

Haploid germ cells (sperm and egg cells).

How are dominant alleles represented in a Punnett square?

They are represented using uppercase letters.

How are recessive alleles represented in a Punnett square?

They use the lowercase version of the same letter as the dominant allele.

What are three important findings of Gregor Mendel?

1. Organisms inherit hereditary units from their parents. 2. Offspring receive units from both parents and so share traits with both parents. 3. Traits can be passed on but not visible.

What discovery led to people accepting Mendel's ideas?

The discovery of the gene.