topic 7 biology

Gene definition

A sequence of bases on a DNA molecule that codes for a particular protein resulting in a characteristic

Allele definition

Variant of a gene for example black or brown. Written in letters Aa. Each allele codes for a different protein. 1 from mum and 1 from dad so 2 alleles for each gene

Loci definition

The fixed position where the allele of each gene is found

Genotype defintion

Genetic constitution of an organism/ combination of alleles an organism has

Phenotype definition

Expression of the genetic constitution and its interaction with the environment

Dominant alleles definition

The Dominant allele is always expressed in the phenotype when in the genotype

Recessive alleles definition

Only show in the phenotype when both recessive alleles are in the genotype

Homozygous definition

Two of the same alleles for a gene

Heterozygous definition

Two different alleles for a gene

What s the usual phenotypic ratio of a mono hybrid cross of two heterozygous parents

3:1

What is codominance

Where both alleles are expressed in the phenotype

What does it mean if a characteristic is sex linked

That the alleles that code for that characteristic are located on a sex chromosome

Why are males more likely to express sex linked characteristics then women

• most genes on the sex chromosomes are carried on the X chromosome

• For women the recessive allele is often masked by a dominant normal allele on the other X chromosome but would be a carrier

• As males have one X chromosome they only have one allele for sex linked Genes so as they only have one copy they will express the characteristic of this alele event when it is recessive

• This is called X-linked

In a diagram how can you tell if something is sex linked

Affected female with an affected father and it will be located on the X chromosome