Year 10 Biological Sciences

NOTES

LEARNING OUTCOME 3

GENETIC CHARACTERISTICS – TRAITS

ACTIVITY TIME

INHERITENCE OF TRAITS

INHERITENCE OF TRAITS

MEIOSIS

FERTILISATION

FERTILISATION

22 + X chromosomes from mum

22 + X chromosomes from

dad

22 + Y chromosomes from

dad

Genotypic characteristics represented in forms of alleles.

GENOTYPE

Phenotypic traits expressed that can be observed.

PHENOTYPE

Genes can be expressed as different forms.

ALLELE

Different forms of the same gene.

ALLELE

Alleles for the same gene are located on the same position on a pair of chromosomes.

ALLELE

ALLELE

Some alleles are more dominant than the other.

ALLELE

Brown eyes are dominant over blue eyes.

DOMINANT/RECESSIVE ALLELES

• Dominant alleles

stand out in their phenotypic features.

represented in capital letters

• Recessive alleles

repressed/masked/supressed by dominant alleles

represented in small letters

WHY?

Why are my eyes brown in colour when a brown allele

and a blue allele are placed together?

Phenotypes being expressed

A combination of two alleles is the genotype that will code for the phenotypic characteristic.

Remember that homologous chromosomes are paired up!

HOMOZYGOUS DOMINANT

Homozygous dominant

two similar dominant alleles are present.

HOMOZYGOUS RECESSIVE

Homozygous recessive

two similar recessive alleles are present.

HETEROZYGOUS

Heterozygous

two different recessive alleles are present.

HETEROZYGOUS

The dominant allele is repressing/suppressing/masking the recessive allele.

PLANTS HAVE SIMILAR TRAITS TOO!

Characteristics for alleles in plants are similar in function to human beings.

The diagrams show the allele controlling a trait susceptible to plants.

SCHEMATIC GENETIC DIAGRAM

Year 10 Biological Sciences