Ocr A2 Biology - Inheritance (Part 1)

Front 1

Define the term 'gene'.

Back 1

• A sequence of bases on a DNA molecule that codes of a proteins (polypeptide), which results in a characteristics e.g. a gene for eye colour.

Front 2

Define the term 'allele'.

Back 2

• A different version of a gene.
• Most plants and animals, including humans, have two alleles of each gene, one from each parent.
• The order of bases in each allele is slightly different - they code for different versions of the same characteristic.
• They are represented using letters, e.g. the allele for brown eyes (B) and the allele for blue eyes (b).

Front 3

Define the term 'genotype'.

Back 3

The alleles for an organism e.g. BB or bb for eye colour.

Front 4

Define the term 'phenotype'.

Back 4

The characteristics the alleles produce e.g. blue eyes.

Front 5

Define the term 'dominant'.

Back 5

• The allele whose characteristics appears in the phenotype even when there's only one copy.
  
• Dominant alleles are shown by a capital letter e.g. BB or Bb would mean they would have brown eyes (B = brown eyes).

Front 6

Define the term 'recessive'.

Back 6

• An allele whose characteristics only appear in the phenotype if two copies are present.
• Recessive alleles are shown by a lowercase letter e.g. b codes for blue eyes. If a person's genotype is bb, they will have blue eyes.

Front 7

Define the term 'codominant'.

Back 7

Alleles that are both expressed in the phenotype - neither one is recessive e.g. the alleles for haemoglobin.

Front 8

Define the term 'locus'.

Back 8

The fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosomes in a pair.

Front 9

Define the term 'homozygotes'.

Back 9

An organism that carries two copies of the same allele e.g. BB or bb.

Front 10

Define the term 'heterozygotes'.

Back 10

An organism that carries two different alleles e.g. Bb.

Front 11

Define the term 'carrier'.

Back 11

A person carrying an allele which is not expressed in the phenotype but that can be passed on to offspring.

Front 12

The body cells of individuals have ....... alleles for each gene.

Back 12

two

Front 13

How many alleles do gametes (sex cells) have for each gene?

Back 13

One for each gene.

Front 14

When gametes from two parents fuse together, the alleles they contain form the ......... of the .......... produced.

Back 14

1. genotype

2. offspring

Front 15

Genetic diagrams can be used to...

Back 15

...predict the genotype and phenotypes of the offspring produced if two parents are crossed (bred).

Front 16

Draw a genetic diagram of these parents.

Back 16

Front 17

What is the F1 and F2 generations?

Back 17

• F1 is the first generation of offspring.
• F2 is the second generation of offspring.

Front 18

Draw a Punnett square for the following alleles. Do this for the F1 and F2 generation.

Back 18

Front 19

Draw a genetic diagram for sickle-cell anaemia. Explain what the alleles show.

Back 19

• These alleles show codominance.
• HN is normal haemoglobin whereas HS is sickle haemoglobin.

Front 20

Draw a Punnett square for these alleles. IA, IB are codominant (people with genotype IAIB will have blood type AB) and IO is recessive. Calculate the odds of each blood type.

Back 20

25% chance of each blood type.

Front 21

What is dihybrid inheritance?

Back 21

The inheritance of two characteristics which are controlled by different genes.

Front 22

Define the term phenotypic ratio.

Back 22

The ratio of different phenotypes in offspring.

Front 23

Draw a dihybrid cross for the following genotypes. State the phenotypic ratio.

Back 23

Front 24

State the phenotypical ratios for these three scenarios.

Back 24