Explaining Inheritance

Explaining Inheritance:

Plants and animals produce gametes (sex cells) The male produce sperm cells in animals and pollen grains in plants. The female gametes are egg cells in plants AND animals. Gametes have only one copy of each chromosome.

Gametes have only one allele for each gene. In sexual reproduction the gametes fuse together, so the new organism formed contains two alleles for each gene. (one from each parent).

If the offspring receives two alleles for flower colour from it's parents. (one being white and one purple) only the allele for purple flowers would have an effect because it's said to be dominant. The white flower allele has no effect and is described as recessive.

A recessive characteristic is only seen if both alleles are recessive, this can be shown in a genetic cross diagram. This shows possible combinations of alleles when two organisms breed.

Dominant alleles are shown by a capital letter and recessive the same letter but in lower case. The alleles in an organism are it's Genotype. What the organism looks like it it's Phenotype.

Homozygous are if both alleles for a characteristic are the same.
Heterozygous are if both alleles for a characteristic are different.

Possible genotypes produced can be shown in a Punnet Square. 
It's a diagram used to predict different characteristics that will be present in the offspring of two organisms with known combinations of alleles. Using the square you can work out the probability that the offspring will inherit a certain feature.


Key Words:

Gametes
Sperm Cells
Pollen Grains
Egg Cells
Dominant
Recessive
Genetic cross diagram
Genotype
Phenotype
Homozygous
Heterozygous
Punnet Square
Probability


Questions:

1. How many chromosomes are in a normal human sperm cell?
2. When will a recessive allele affect a phenotype?
3. The pea plant gene for height has two alleles T (dominant, causing tall plants) and t (recessive, causing short plants) Draw a punnet square showing this.
4. What's the percentage probability of getting a tall phenotype plant?


What you should've learnt:

The meaning of, and use appropriately, the terms: dominant, recessive, homozygous, heterozygous, phenotype and genotype.

How to analyse and interpret patterns of monohybrid inheritance using a genetic diagram and Punnet squares.

How to calculate and analyse outcomes (using probabilities, ratios and percentages) for monohybrid crosses.