Genetic Crosses

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Slide 1

Genetic Crosses

Show possible outcomes of genes the new generation will have

We use:

Gene diagrams

Punnett Squares

Slide 2

Terminology

Genotype Phenotype Parent Gamete Offspring

dominant recessive allele

Slide 3

Gene control of characteristics

All characteristics are controlled by a minimum of 2 genes.

These genes give the characteristic a different of presenting itself.

Different genes that control the same feature are called ALLELES

Slide 4

Eye Colour

Possible alleles – blue , brown, green, hazel etc (each colour needs its own gene)

It is possible to have pairs of different alleles, alleles are usually given a letter

Slide 5

Genotype and phenotype

Genotype is the letter or term used to describe the allele of an individual gene or pair of genes

Phenotype – is how the gene (or pair) shows itself, how it appears.

Slide 6

Dominance and recessiveness

Some alleles for a feature are able to mask the influence of other (weaker) gene when they are paired

Stronger gene is DOMINANT and is represented by a capital letter e.g. H

The masked gene is RESSESIVE shown as lower case of the same letter e.g. h

Slide 7

Gene diagram – Flower colour

Genotype of alleles- R = red flower r = yellow flower

All genes occur in pairs – so 2 alleles affect a characteristic – possible combinations are;

genotype RR Rr rr

Phenotype RED RED YELLOW

Slide 8

Gene diagram – Flower colour

Male female

RR

rr

parent

gamete

R R r r

Offspring genotype

Rr

Rr

Rr

Rr

Phenotype

All red

Slide 9

Gene diagram – Flower colour

Male female

Rr

Rr

parent

gamete

R r R r

Offspring genotype

RR

Rr

Rr

rr

Phenotype

Red yellow red red

3 red : 1 yellow

Slide 10

Gene diagram – Flower colour

Male female

Rr

rr

parent

gamete

R r r r

Offspring genotype

Rr

Rr

rr

rr

Phenotype

Red yellow yellow red